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ANNEX 2. IDENTIFY THE ENVIRONMENTAL CONSEQUENCES OF
FARMING SYSTEMS OVER THE PAST 50 YEARS AND THEIR LONGTERM SUSTAINABILITY
In this report we begin by summarising the broad impacts of agriculture on the wider
environment. We then provide more detail on the priority areas: greenhouse gas
(GHG) emissions, air and water quality, water resources and soil degradation, all of
which need to be assessed when evaluating the sustainability of agricultural systems.
We also summarize the interaction between agriculture and land use change (LUC),
including ecosystem services and biodiversity. Finally we summarize the main
environmental impacts of the farming systems identified in Task 1.
Summary of findings
The environmental impacts of farming systems over the past 50 years and their longterm sustainability have been evaluated with respect primarily to their impact on a
range of environmental factors.
All farming systems may have adverse impacts on the environment; while it might be
assumed that intensive systems have the greatest adverse environmental impact this is
not always the case. Intensive production tends to emit less GHG per t of produce.
This is mainly because intensive systems may use inputs more efficiently but also
because intensive systems are not usually encroaching upon natural ecosystems and
do not lead to indirect emissions from LUC. Intensive farming is also less likely to
lead to land degradation since greater crop yields return more organic matter to land,
hence better maintaining soil organic matter (SOM) and soil structure. Inputs of
manures and fertilizers maintain soil fertility. However, intensive farming has greater
impacts on local water and air quality and also makes greater use of water resources,
principally via the need for irrigation water and also, to a much lesser extent, as a
consequence of draining wetlands. The adverse impacts on air and water quality tend
to result from intensive agriculture emissions being concentrated and causing point
source pollution.
The key concerns for each farming system are:
Intensive arable
The major environmental impacts of intensive arable farming are a reduction in water
quality and emissions of N2O arising from applications of fertilizer-N. However, in
many EU countries inputs of fertilizer-N, the major source of emissions of N2O and
NO3, have stabilised while yields of the major arable crops have continued to
increase.
Intensive dairy farming
Intensive dairy production is a significant source of GHG but productivity can
increase without corresponding increases in emissions. Large herd sizes and
concentrations of livestock within small areas pose serious concerns for their impacts
on water and air quality. In addition, indirect LUC may be stimulated by demand for
ingredients such as soya or cassava for concentrated feeds.
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Intensive livestock farming
Intensive livestock farming poses similar problems to those of dairy farming.
Intensive horticulture.
As horticulture, particularly vegetable production, becomes more specialised and
intensive the large fertilizer applications required and intensive cultivation are likely
to increase local water pollution.
Extensive beef and sheep grazing
Extensive livestock production is a significant source of the GHG CH4 and a driver to
LUC. In addition, soil nutrient supplies can be depleted leading to a cycle of further
extensification and demand for LUC to create new pastures.
Wetland rice cultivation
Irrigated rice cultivation is a major source of CH4 but changes to production methods
are forecast to lead to no net increase in CH4 emissions to 2030 despite forecasts of
substantial increases in production. However, rice cultivation is likely to continue to
be a major source of N2O and NH3.
Irrigated
Without significant improvements in water use efficiency it will be difficult to greatly
increase production from this farming system. In some regions maintaining current
production may be difficult.
Smallholder rain-fed humid
Climate change is forecast to reduce rainfall in several of the regions which depend
upon rain-fed smallholder production. Substantial areas are also prone to land
degradation. Unless inputs can be made available to improve productivity and
management to avoid degradation, there will be pressure for LUC.
Smallholder rain-fed highland
This farming type is particularly vulnerable to soil erosion. Dixon et al. (2001)
suggest that this system has great potential for intensification, by using soil restoration
methods and improved water management techniques. However, this may
compromise the sustainability of the system itself.
Smallholder dry and cold
These systems often have low productivity due to environmental constraints including
nutrient poor soils, low temperatures and lack of rainfall. This low input of
precipitation explains the need for additional water abstraction in these areas, leading
to water stress.
Dualistic mixed
Heavy demand for water in some areas is diminishing water resources while a
combination of increased agrochemical inputs and decreased water flows is reducing
water quality. In some areas soil reserves of P and K are not being maintained.
Fisheries
The loss of mangrove swamps to shrimp farming has had major adverse effects on
coastal environments. The majority of sea fisheries are over-exploited and it may
prove difficult to maintain current production.
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1.
Impacts of agriculture on the environment
Agriculture has changed the environment since the first farmers modified the existing
habitat to cultivate crops and suppress competition from other plants and grazing by
animals. As human populations have increased so has the replacement of natural
ecosystems by agriculture. Of the world’s fourteen biomes, more than half have had
20-50% of their surface converted to croplands (Olson et al. 2001). Tropical dry
broadleaf forest, temperate grasslands and flooded grasslands and savannas have had
the greatest conversion to agriculture over the past 50 years. More than 50% of the
global wetlands and 60% of major world rivers have been transformed or modified by
humans over the past 100 years (Millennium Ecosystem Assessment 2005), reducing
biodiversity through habitat flooding, disruption of flow patterns, and fragmentation
of animal populations and travel corridors. Water abstraction from rivers in many
regions of the world has significantly reduced flows and, in some cases, left some
major rivers nearly dry.
As well as reducing biodiversity and modifying water supplies, the removal of
plant cover and tillage of soil break down soil organic matter (SOM) and lead to
substantial emissions of the GHG carbon dioxide (CO2). Breakdown of SOM, and
release of CO2, may continue for decades after initial LUC and the process also
releases nitrate (NO3) which can pollute watercourses. In recent years agricultural
production has increased primarily through increased production per ha, reducing the
pressure for LUC and consequent emissions of CO2 from soil. However, this has not
eliminated the impact of increased agricultural production on GHG emissions.
Increased production of arable and forage crops in many parts of the world has been
made possible by increased use of mineral fertilizers, in particular N, and in the soil a
proportion of that N is converted to the GHG nitrous oxide (N2O). The growing
demand for livestock products has led to increases in emissions of the GHG methane
(CH4) which arises primarily from enteric fermentation.
As agriculture intensifies soil quality can be reduced, in some cases leading to
erosion, and further contamination of watercourses, and in extreme cases degradation
such that the land can no longer be farmed. The input of agrochemicals and mineral
fertilizers, especially nitrogen (N) can lead to further reductions in water quality due
to increased NO3 leaching, phosphate (P2O5) enrichment and pesticides. Emissions to
air may also be increased not only as N2O but also as ammonia (NH3). To be able to
improve the sustainability of global production systems, it is necessary to first identify
the environmental impacts of the systems.
1.1
Greenhouse gases
Table 1 below presents current estimates of CH4 emissions expressed per litre (L) of
milk produced in different world regions. There are very large differences among
regions and that greater productivity tends to emit less CH4 per L.
Table 1. Default CH4 in different regions, per L of milk yield, from IPCC 2006
table 10.11, dairy cattle
NAFTA
EU
CIT
Oceania
Latin America
Enteric CH4 kg head-1 yr-1
121
109
89
81
63
3
Milk L head-1 yr-1
8400
6000
2550
2200
800
g CH4 L-1
14.4
18.2
34.9
36.8
78.8
N Africa, mid-East
S Asia
E and SE Asia
SS Africa
40
47
61
40
475
900
1650
475
84.2
52.2
37.0
84.2
The above picture is not quite so straightforward as it appears. The output is per
lactating dairy cow. The greater yielding cows tend to have a shorter lifetime, going
through fewer lactations within that lifetime, and hence the ratio of replacement
animals (followers) per dairy cow is greater. Since these followers produce CH4 as
they mature (but before they start producing milk) they will indirectly contribute to
the GHG burden of milk production. In addition, the move toward breeds suitable
only for milk production lessens the opportunity for unwanted male dairy calves to be
sold to beef producers for fattening, hence indirectly increasing the GHG emissions of
beef production (Webb et al., 2009). Nevertheless, when the contribution of followers
is taken into account the ranking of the above regions is unlikely to change
significantly; production in the NAFTA and EU regions will emit less GHG per L
milk produced than production in other regions. But the difference will not be as great
as that produced by the simple estimate above.
Table 2 below presents default emissions for beef production in different
regions.
Table 2. Default CH4 emissions from beef production in different regions, from IPCC
2006, beef cattle
NAFTA
EU
CIT
Oceania
Latin America
N Africa, mid-East
S Asia
E and SE Asia
SS Africa
Enteric kg CH4 head-1 yr-1
*53
57
58
60
56
31
27
47
31
**meat kg head-1 yr-1
65 - 69
65 - 69
45 - 67
20 - 23
13 - 19
13 - 19
15 - 22
15 - 22
13 - 19
kg CH4 kg-1 meat
0.8
0.9
1.3
3.0
4.3
2.4
1.8
3.1
2.4
*Includes beef cows, bulls, calves, growing steers/heifers, and feedlot cattle.
**Estimated from Bouwman et al. (2006)
These data also indicate that increased production of livestock products does not
inevitably come at the price of increased emissions, albeit there is a general trend in
that direction.
Table 3 presents average estimated N excretion for the main types of livestock
in each region of the world. Emissions of N2O from manure management and
following application of manures to land will be broadly in proportion to these
estimates of daily N excretion. There is less variation in these estimates, which is
partly due to their being expressed per day, and thus not taking account of the longer
time to maturity in some regions. Such differences are found mainly with
extensively-raised ruminants. Hence emissions of N2O per kg extensively-raised beef
or lamb will be greater for produce raised in Africa, the Middle East and Latin
America.
Table 3. Default N excretion, kg N (1000 kg animal)-1 mass day-1, from IPCC 2006
NAFTA
EU
Dairy
0.44
0.48
Beef
0.31
0.33
Finishing pigs
0.42
0.51
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Sheep
0.42
0.85
Buffalo
0.32
0.32
Horses
0.30
0.26
Layers
0.83
0.96
Broilers
1.10
1.10
CIT
Oceania
Latin America
N Africa, mid-East
Sub-saharan Africa
S Asia
E and SE Asia
0.35
0.44
0.48
0.70
0.60
0.47
0.47
0.35
0.50
0.36
0.79
0.63
0.47
0.47
0.55
0.53
1.57
1.57
1.57
0.42
0.42
0.90
1.13
1.17
1.17
1.17
1.17
1.17
0.32
0.32
0.32
0.32
0.32
0.32
0.32
0.30
0.30
0.46
0.46
0.46
0.46
0.46
0.82
0.82
0.82
0.82
0.82
0.82
0.82
1.10
1.10
1.10
1.10
1.10
1.10
1.10
The other major source of GHG emissions from agriculture is N2O arising following
application of mineral-N fertilizers. The current IPCC default emission factor (EF) is
1.0% of applied N. Although there is evidence of emissions being more or less than
this default depending upon soils and subsequent weather conditions, several factors
control N2O emissions and these will broadly correlate with applications of N
fertilizer. Hence productions systems such as the high-input systems used in the EU,
and increasingly China and parts of India, will emit much more than extensive
systems in other regions. However, since yields in regions such as NW Europe are
larger than in many other areas N2O emissions per kg of output will not be in
proportion to overall N2O emissions.
As indicated above, GHG emissions, primarily in the form of CO2, arise when
land is converted to agriculture. While soils under well-managed agricultural
grassland may contain amounts of carbon similar to some natural ecosystems, soils
under tillage will contain less (Guo and Gifford, 2002). However, when evaluating
fluxes of CO2 to the atmosphere, it needs to be remembered that only considering
changes to soil carbon takes no account of changes in above ground carbon stocks
which may be greatly reduced by land use change. The current estimate of total
carbon storage, both SOC and above ground, is c. 360 t/ha for Brazilian rainforest
(IPCC, 2006) and hence conversion to either grassland or arable will lead to
significant emissions of CO2.
1.2. Water and Air Quality
With respect to broader environmental impacts of N, in particular NO3 leaching and
NH3 volatilization, Bouwman et al. (2006) report some differences among regions in
the efficiency with which applied N is used, as reflected in the recovery of N as a %
of inputs (nitrogen use efficiency: NUE). For most regions NUE for 1995 was
reported as c. 50%, but only c. 40% for E Asia and 78 and 108% respectively for SE
Asia and SS-Africa. Forecasts for 2030 were between c. 60 and 70%, but are rather
less for E Asia (42%) and more for CIT (83%), SE Asia (90%) and SS-Africa (131%).
The latter figure is a cause for concern. While a relatively large NUE indicates that
losses of N to the environment are relatively small, some losses, especially of NO3
leaching and denitrification in humid areas, are unavoidable and even in a sustainably
fertilized system NUE would be expected to be < 100%. If N removal in crops is
exceeding inputs it means there is a net loss of N from the soil-crop system potentially
leading to a reduction in soil fertility. The forecast increase in NUE suggests these
problem of nutrient depletion will increase. In turn declining soil fertility is likely to
increase pressure for clearance of forests and savannahs for agricultural production.
The small NUE for E Asia is due to the prevalence of paddy rice cultivation
from which emissions of N are particularly large. Emissions of NH3 being increased
by the high pH of these systems while waterlogging leads to intense denitrification,
albeit the predominant loss is as molecular N (N2) which does not harm the
environment. Emissions of NH3 are particularly large in China, and some CIT due to
the use of the fertilizer ammonium bicarbonate (AB) (Cai et al., 1998). In their
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projections of fertilizer-N use to 2030, Bouwman et al. (2005) assumed 90% of the
AB used in China would be substituted by urea, hence greatly reducing, but by no
means eliminating, emissions of NH3.
1.3. Water resources
Views have been put forward that current patterns of water extraction are close to
what can be sustained, or may be exceeding it. Some major rivers no longer reach the
sea including the Indus, Rio Grande, Colorado, Murray-Darling and Yellow rivers.
This is at least partly due to extraction for cereal production.
Freshwater fish populations are in decline. According to the World Wide Fund
for Nature (WWF, 2003), fish stocks in lakes and rivers have fallen roughly 30%
since 1970. This is a bigger population decline than that suffered by most forms of
wildlife. Half the world’s wetlands, in one estimate, were drained, damaged or
destroyed in the 20th century, mainly because, as the volume of fresh water in rivers
falls, salt water invades the delta, changing the balance between fresh and salt water.
On this evidence, there may be systemic water problems, as well as local disruptions.
1.4. Soil degradation
A UNEP survey (cited in Smeets et al., 2004) on soil degradation reported that the
rate of soil erosion is 10 to 20 times the renewal rate in temperate regions and 20 to 40
times the same rate in the tropics. This results in an annual worldwide loss of cropland
of between 5 and 12 million ha per year. Deforestation is thought to be responsible for
43% of the total erosion and overgrazing and mismanagement for 29% and 24%
respectively (Smeets et al., 2004).
Despite this, in many parts of the world such as northwest Europe, soils have
been cultivated for over two millennia and are more productive than ever. This
production is largely dependent on inputs of mineral fertilizers and other
agrochemicals, but the production of high yielding crops may lead to substantial
returns of organic matter to soils, helping to maintain soil structure. This has led to
the view being put forward that regions such as Europe, with fertile and stable soils,
equitable climate and in consequence large yield potentials, have a duty to optimize
food production to reduce the burden on pristine ecosystems and less resilient soils in
other parts of the world.
1.5. Land use change, ecosystem services and biodiversity
Ecosystem services (ES) may be defined as 'the benefits of nature to households,
communities, and economies.' (Boyd and Banzhaf, 2006). Clearly the continued
provision of ES requires the natural ecosystem to remain intact, and hence changes in
land use from natural ecosystems to agriculture reduces the provision of ES. It is
presumed that increased food production is better achieved by increased production
on existing agricultural land than by converting natural systems. The Millennium
Ecosystem Assessment has categorised ecosystem services into the four general areas
of support, regulation, provision, and cultural services, shown in Table 4 below. Each
general area is sub-divided into increasingly detailed roles that support human society.
Table 4. Categories of ecosystem services (Millennium Ecosystem Assessment)
Support
Nutrient Cycling
Soil Formation
Primary Production
Provision
Food
Fresh Water
Wood and Fibre
Fuel
Regulation
Climate Regulation
Flood Regulation
Disease Regulation
Water Purification
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Cultural
Aesthetic
Spiritual
Educational
Recreational
These ecosystem services depend on all of the component ecosystem species within:
plants provide primary production and food for herbivores, soil invertebrates aerate
the soils and recycle nutrients, bacteria and fungi decompose plant and animal litter,
birds distribute seeds of plants and so on. All of these roles are interlinked among the
thousands or millions of species that inhabit an ecosystem.
There is increasing evidence that high levels of biodiversity may act as
“insurance” that buffer ecosystem services from environmental change. Therefore
maintenance of species composition and abundance is essential to maintaining the
ecosystem services upon which humans depend. Loss of biodiversity is directly
associated with habitat change, climate change, invasive alien species,
overexploitation and pollution (MEA 2005). The effects of this loss are particularly
pronounced in areas that have been deforested or where wetlands have been drained.
Key impacts here include loss of ecosystem services that act as natural breaks on
flooding and erosion, as well as release of carbon stored in soils. Some of these
changes are irreversible, particularly deforestation in areas that are vulnerable to
desertification. These are crucial differences to the impact of deforestation in
temperate and tropical regions. Unlike the deciduous forests of temperate regions,
tropical rain forests are not easy to regenerate once lost.
2.
Identification of environmental impacts of production systems and their
long-term sustainability
In our assessment of the potential environmental impacts of providing food security
by 2030 we will focus on the evaluation of the necessary changes to farming practice
with respect to their impacts on:
GHG emissions;
air and water quality;
water resources;
soil sustainability;
LUC, including biodiversity.
The impacts outlined in this report range from those which are local, which is usually
the case for soil erosion and water pollution, those which are transboundary, such as
emissions to air, and global impacts such as emissions of GHGs. We also make a
distinction between direct and indirect LUC. Direct LUC arises when a farming
system expands into land that had not previously been used for agriculture, for
example, cultivating savannah to grow sugar cane. Indirect LUC arises when a
change in one farming system, which arises without increasing the farmed area of that
system, promotes indirect LUC by increasing demand for inputs sourced from
elsewhere. An example of this is the impact, on Amazonian rainforests, of increased
demand from Asia for soybeans to feed livestock (World Development Report, 2008).
It is important to remember the global footprint of a system, taking into account
production, distribution and consumption of goods, and not just the direct impacts felt
in the immediate environment.
This study intends to evaluate production systems in light of the following criteria:
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1.
Can production be maintained into the future without causing irreparable
damage to the means of production? For example, is the rate of soil loss or
salinisation likely to lead to degradation?
2.
Can production be maintained into the future without reliance on inputs which
will not be available in the foreseeable future? For example, the use of fossil water
from aquifers which are being depleted faster than the rate of replenishment.
3.
Can production be maintained within the existing cultivated area without the
need for continual encroachment on uncultivated land?
4.
Can production be maintained into the future without having a negative impact
on the income generation capacity of the farmers?
The sustainability of the production systems outlined in Task 1 was assessed
according to the extent to which they comply with the above criteria.
We summarize below, for each region in turn, the main environmental impacts that
have been identified from each farming system. In addition, we draw upon projections
made by the Intergovernmental Panel on Climate Change (IPCC) in its 4th Assessment
Report (IPCC, 2007) in order to consider how each production system might be
affected by a changing climate.
2.1
NAFTA and EU
These regions are reported together as their farming has much in common particularly
with respect to the impacts on the environment.
2.1.1 Intensive arable
Production of
carbohydrate and
protein kg/ha/year
Rain-fed or
irrigated
Emissions to water
(nitrate, phosphate,
biological oxygen
demand)
Environmental impacts
Cereal yields (2005)
In the United States – 6.45 t/ha
In Canada - 3.03 t/ha
In UK – 7.23 t/ha
Italy – 5.43 t/ha
Netherlands – 8.15 t/ha
In these regions the great majority of production is rain fed.
In some countries fertilizer application has been applied in excess, outstripping
the soil’s capacity to hold nutrients and make these available to crops. NO3 and
P2O5 can be leached to ground and surface waters (Breeuwsma and Silva,
1992). To give an idea of potential run-off to water, the following figures from
WRI (2009) show fertilizer consumption in selected countries where intensive
arable farming is a major farming system:
Fertilizer use is very high in the US where 25.278 * 10^6 t of nutrient were
used in 2005 (WRI, 2009). This equates to 109 kg/ha (WRI, 2009) (This also
applies to the intensive livestock and arable farming in NAFTA.)
Canada used 17.870 * 10^5 t of nutrient fertilizer in 2005 (WRI, 2009), with an
intensity of 53.7 kg/ha.
In the UK in 2005, 1,502 kg * 10^6 of fertilizer was used. This is a high level
of fertilizer in line with Canada (WRI, 2009). The intensity of use in 2005 was
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287.5 kg/ha
This represents an intensive production system.
Nitrate concentrations exceed the guide level of 25 mg/l in 85% of farmland in
the EU. However, a combination of reduced prices for produce, increases in
prices of fertilizers, and measures such as the EU Nitrates Directive have
reduced such losses in recent years. Nevertheless, the application of fertilizers
to maintain current yields will inevitably lead to some leaching.
Extensive use of pesticides can initiate a negative feedback loop – as herbicides
remain in the soil where crop rotations and fallow periods are short, crop yields
can be reduced. This also lowers the ability of soil to remove pollutants thereby
inhibiting the migration of pollutants to nearby water bodies (Zaldis et al.,
2002).
Emissions to air
(GHGs, NH3, NOx,
non-methane
VOCs)
Soil erosion, soil
degradation or
desertification
ADAS (2002) suggest that using less pesticide can increase arable crop yields
when compared with high input production. A recent study by Young et al
(2001) found that for yields of 66 crops grown in low input production systems,
average gross margin was 2%, equivalent to £12 per hectare, greater than gross
margins for the high input system. However, where herbicide inputs were
reduced, weed burden increased in some cases. Conversely, cutting N fertilizer
application by 50% reduced gross margins by 9%, equivalent to £64 per
hectare, emphasizing the importance of N and a more strategic approach to
cutting its use. The success of this low input system will vary depending on
soil and crop types.
The main issues are N2O and NH3 from N fertilizer and CO2 from cultivation;
emissions of the latter are few from long-term arable soils but there will still be
net emission from former grassland soils.
Agriculture has become more intensive with widespread use of heavy
machinery, fertilizers, pesticides, and large-scale irrigation. As a result of
changing agricultural practice, crop choice and higher water consumption, land
desertification is occurring along with soil salinisation and salt water intrusion
in countries around the Mediterranean Basin including western Greece, Tunisia
and Lebanon (Zalidis et al., 2002).
Biological degradation of soils can be attributed to many agricultural practices.
Particularly in Mediterranean countries, soils are low in organic matter which
leads to reduced soil fertility and damaged structure due to reduced root
penetration, soil moisture content and permeability. In turn, erosion increases
along with the rate of runoff, thus lowering biological activity (EEA, 1995).
Microorganisms assist in maintaining the water content of soils, promoting
good soil structure and thereby reducing erosion. Many features of the intensive
arable farming system cause disruption to microbes, including lower plant
diversity above ground caused by tillage and extensive grazing of livestock
(Christensen, 1989 and Boddy et al., 1988 in Zalidis et al., 2002).
Biodiversity
In NAFTA, particularly the mid-west United States, significant damage to soils
has occurred as a result of intensive cereal production. The nutrients provided
by soil organic matter have been used by the cereal crops, making the soil less
fertile and stable. As a result of this and the arid, windy environment, soil
erosion has been significant.
Farms in the mid-west can be thousands of acres in size, which can dwarf farms
in some EU Member States. Wheat is grown widely and there are no annual
rotations so inputs remain the same. This means the soils do not have a chance
to recover and organic matter cannot be replenished. No livestock farming
takes place, so there is no organic matter/manure to import to improve the soils.
Declining abundance of farmland plants and animals is a feature of intensive
arable agriculture. For example, in arable areas in the UK, there is a lack of
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nesting sites available for lapwings and skylarks (Donald et al., 2001).
However, the presence of over-winter stubbles is believed to attract skylarks
back. Initial negative trends showed recovery of the birds with 10–20 ha of
stubble per 1 km square. Thus, it is believed that agri-environment schemes
which promote over-winter stubbles can help attract birds, thus helping to
reverse current population declines (Gillings et al., 2004).
Forestry/LUC/
agro forestry
Climate change
impacts for this
system
Biotic and abiotic soil processes are affected by extensive pesticide use. This
influences the role of soil as a service provider: as a habitat for soil and other
biota, reducing resilience, converting nutrients and toxicants and protecting
surface and groundwater from pollutants (Zaldis et al., 2002)
In NAFTA and EU countries deforestation for agriculture is now uncommon
and some countries are increasing native wooded areas through planting.
The effects of climate change and increased CO2 in the atmosphere are
projected to result in increases in crop productivity in some parts of Europe,
with wheat yields increasing from 37 % under the B2 scenario to 101% under
the A1 scenario by 2050 (IPCC, 2007). It is suggested that crops currently
grown largely in southern Europe such as maize, sunflower and soybeans will
become viable for growing further north or at higher-altitude southern areas
(Audsley et al., 2006). However, some productive lands are at risk of
inundation by rising sea levels and yields in some of the most productive areas
may be reduced by increased temperatures and drought stress. In contrast many
of the areas of Europe in which crop yields have potential for increase are
dominated by sandy soils of only moderate yield potential and are unlikely to
be able to fully make up any shortfall in production.
Yield increases are expected to occur largely in northern Europe. , For example,
wheat yields are forecast to increase by between 2% and 9% by 2020, +8 to
+25% by 2050 and +10 to +30% by 2080 (IPCC, 2007) while sugar beet yields
are expected to rise by between 14% and 20% during the next forty years in
England and Wales (IPCC, 2007).
The greatest yield reductions in all crops are expected in the Mediterranean, the
southwest Balkans and in the south of European Russia (Olesen and Bindi,
2002; Alcamo et al., 2005; Maracchi et al., 2005). In southern Europe, general
decreases in yield (e.g., legumes, range: -30 to + 5%; sunflower, range: -12 to
+3% and tuber crops, range: -14 to +7% by 2050 and increases in water
demand (e.g., for maize +2 to +4% and potato +6 to +10% by 2050) are
expected for spring sown crops (IPCC, 2007).
In North America, rain-fed agricultural yields are set to increase early in the
21st century. However, coastal vulnerability in North America may increase
with disruption to transport and infrastructure on the Atlantic Coast as sea level
rises and tidal surges increase.
Current water stresses in Australasia are likely to be compounded from the
2020s onwards.
Key points
The major environmental impacts of intensive arable farming are a reduction in water
quality and emissions of N2O arising from applications of fertilizer-N. However, in
many EU countries inputs of fertilizer-N, the major source of emissions of N2O and
NO3, have stabilised while yields of the major arable crops have continued to
increase. Hence in regions where soil and water are not limited it is possible that crop
yields can continue to increase without commensurate increases in emissions.
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2.1.2 Intensive dairy farming
Production of
carbohydrate and
protein
kg/ha/year and
productivity
Emissions to
water (nitrate,
phosphate,
biological
oxygen demand)
Environmental impacts
In NAFTA and EU 27, highly productive commercialized dairy sector feeding
high quality forage and grain. Average milk production:
NAFTA - 8,400 kg head-1 yr-1;
EU - 6,000 kg head-1 yr-1
Countries in transition - commercialised dairy sector feeding mostly forages,
2,550 kg head-1 yr-1.
Oceania - commercialised dairy sector based on grazing, 2,200 kg head -1 yr-1
In New Zealand, dairy cattle numbers increased to 5.6 million in 2008, up 6 %
from the previous year (New Zealand Government, 2009).
In addition to groundwater pollution by NO 3 and P2O5 as a results of application
of mineral fertilizers and livestock manures, surface water often becomes directly
polluted when manures are applied to wet soils and run-off occurs. The true
problem of surface and groundwater pollution from farming (dairy and other) has
not been thoroughly investigated in all EU countries (EC, 2000).
Similar to arable farming, the following figures from WRI (2009) give an
indication of fertilizer use in countries with heavy involvement in dairy farming.
Fertilizer use is very high in the US where 25.278 * 10^6 t of nutrient were used
in 2005 (WRI, 2009). The intensity of use in 2005 was 287.5 kg/ha,
UK: 1.502 * 10^6 t which is a high level of fertilizer use. This equates to an
intensity of 287.5 kg/ha (2005) (WRI, 2009).
Emissions to air
(GHGs, NH3,
NOx, nonmethane VOCs)
Defra (2009) give the following figures for fertilizer use on grasslands (kg/ha) in
the UK:
Total N – 65
Total P – 14
Total K2O – 18
Nitrous oxide – emissions arise from manure fertilizer application to pasture;
deposition of manure and urine by animals (greater in intensive systems than
extensive systems) and from the storage of manure in stall-feeding systems such
as the feedlot system.
Perhaps the main problem is that of NH3 which is produced at all stages of
manure management. This is an increasing cause of concern in the US and
Canada has led to the introduction of the EU National Emissions Ceilings
Directive and. Ammonia emissions are highest in intensive systems from manure
storage and application to arable land.
Dairy production has an indirect impact on CO2 and N2O emissions due to the
energy consumed to produce feed concentrates and forage as well as that used in
housing systems (EC, 2000).
Soil erosion/soil
degradation/
desertification
The majority of CH4 is produced by enteric fermentation. A projected shift
towards in-house feeding in grazing systems is likely to increase storage of
manure in a liquid or waterlogged form, and this is the main source of CH4
emissions from manure.
Soils under grass are generally protected from soil erosion while the addition of
organic matter in manure and excreta improves soil quality.
The major concern is that some feed concentrates contain phytotoxic heavy
metals including copper, zinc and cadmium which can all build up in soils.
Biodiversity
High stocking rates can lead to greater soil compaction around gateways and
water troughs as cattle trample the land, thus reducing infiltration and increasing
runoff and erosion from these areas (EC, 2000)
Pastures maintained and cut for silage or grazed intensively are less biodiverse
than traditional hay meadows.
11
Succession of meadows by scrub and woodland, decline in open grassland and
field boundaries, degradation of hydro geological systems.
Vet medicines may persist in dung, affecting its fauna and potentially populations
of birds which feed on these invertebrates.
Invasive species and decline in species diversity as a result of increased fertilizer
use (N&K), silage, less grazing.
Forestry/LUC/
agro forestry
Climate change
impacts for this
system
Changing intensity of production in traditional farms may lead to lower
complexity and stability of food webs, especially in river-based and mixed
Mediterranean systems (EC, 2000)
Deforestation for agricultural cultivation is now uncommon and some countries
are increasing their wooded areas. Indirect LUC may be stimulated by demand
for ingredients such as soya or cassava for concentrated feeds.
Rising frequency and intensity of heat waves in Europe may threaten the health
and wellbeing of livestock reared indoors and outdoors. This may lower forage
crop productivity to the extent that they are not suitable for livestock at current
stocking rates without irrigation (IPCC, 2007);
Coastal vulnerability in North America, disruption to transport and infrastructure
on the Atlantic Coast as sea level rises and tidal surges increase;
Current water stresses in Australasia are likely to be compounded from the 2020s
onwards.
In North America, rain-fed agricultural yields are set to increase early in the 21 st
century. Having been exposed to extreme weather events during the past decade,
this system, along with intensive arable and livestock, is well adapted to cope
with a changing climate. For instance, diversification of crops and business has
taken place, as well as improved soil and water conservation. This highlights the
resilience of the system to moderate potential damage from climate change
(IPCC, 2007).
Key points
Forecasts indicate that intensive dairy production can be more productive without
emissions of GHGs increasing in proportion. Effective measures to reduce emissions
of NH3 have been developed and are being implemented in some countries. However,
continued increases of herd sizes and concentrations of livestock within small areas
pose serious concerns for the impacts on water and air quality.
2.1.3 Intensive livestock farming
Production of
carbohydrate and
protein
kg/ha/year and
productivity
Environmental impacts
In New Zealand, beef cattle numbers fell to 4.1 million in 2008, down 6% on the
previous year (New Zealand Government, 2009).
NAFTA: separate beef cow herd, primarily grazing with feed supplements
seasonally. Fast-growing beef steers/heifers finished in feedlots on grain.
To calculate meat production per carcass – total meat production/total number of
animals. Figures are for total cattle stocks – may include dairy but can’t get
separate figures. All figures from WRI (2009).
Canada: 4.493*109 t/14.830*106 heads = 303 kg/carcass
EU 27: dairy cows also used for beef calf production. Very small dedicated beef
cow herd. Minor amount of feedlot feeding with grains.
12
France: 5.206*109 t /19.418*106 = 268 kg/carcass
Countries in transition: separate beef cow herd, primarily grazing. Minor amount
of feedlot feeding with grains. Separate beef cow herd, primarily grazing
rangelands of widely varying quality. Growing amount of feedlot feeding with
grains.
Romania: 1.003*109 t /2.862*106 = 350.5 kg/carcass
Croatia: 120.499*109 t /483*106 = 249.4 kg/carcass
Pigs and poultry livestock convert plant protein to animal protein much more
efficiently than ruminants.
In Australia in 2003-2004, there were 2.553*106 pigs. Average slaughter weight
was 72.7 kg/head, representing a 0.5% share of the world total for pig meat
production (Australian Government, 2009)
Irrigated or rain
fed
Emissions to
water (nitrate,
phosphate,
biological
oxygen demand)
In the United States in 2007, there were 8.9 billion birds at a value of $43 billion
(USDA, 2009)
Largely rain fed.
The intensive raising of livestock may give rise to disposal problems for manure.
Where the ratio of land available to livestock manure is small there are likely to
be considerable problems with water quality, nitrate pollution, eutrophication and
direct contamination by run-off. Examples of areas affected include the Flemish
region of Belgium, much of the Netherlands and the Po valley in Italy. These
problems are not simply related to the size of the enterprises. In densely
populated areas where relatively few livestock are raised by farming families the
overall burden of manure per ha may still exceed the amount that can be re-cycled
effectively.
In addition to groundwater pollution by NO3 and P2O5 as a result of application of
mineral fertilizers and livestock manures, surface water often becomes directly
polluted when manures are applied to wet soils and run-off occurs. The true
problem of surface and groundwater pollution from farming (dairy and other) has
not been thoroughly investigated in all EU countries (EC, 2000).
Feedlots are very intense sources of NH3, but tend to be less polluting to water.
In NAFTA, water pollution concerns largely relate to the use of N and P in
ground and surface waters. In much of the United States, the emphasis is on
effects of P on water quality, however, arid areas of the western United States are
more concerned about soil salinity. Many regions of the world have greater
restriction of N than P with respect to water quality (Powers and Angel, 2008).
Emissions to air
(GHGs, NH3,
NOx, nonmethane VOCs)
In the South China Sea region, livestock are reported to be a major inland source
of phosphorous and nitrogen contamination, thereby leading to biodiversity loss
in marine ecosystems (FAO, 2006).
When emissions from land use and land use change are included, the livestock
sector accounts for 9% of CO2 deriving from human-related activities, but
produces a much larger share of even more potent GHGs. It generates 65% of
human-related N2O, which has 298 times the Global Warming Potential (GWP)
of CO2. Most of this comes from fertilizer-N and manure applications to land and
from excreta deposited directly to pastures during grazing. Livestock production
accounts for 37% of all human-induced CH4 (25 times as warming as CO2),
which is largely produced by the digestive system of ruminants, and 64% of NH3,
which contributes significantly to acid rain.
Some estimates indicate that the livestock sector generates more GHG emissions
13
as measured in CO2 equivalent – 18% – than transport.
Per kg of N excreted emissions of NH3 (ammonia) are much greater from
livestock raised entirely indoors than from livestock which spend much, or all of
the year outdoors (Webb et al., 2005).
Nitrous oxides emissions arise from manure fertilizer application to pasture,
deposition of manure and urine by animals (higher in intensive systems than
extensive systems) and from the storage of manure in stall-feeding systems such
as the feedlot system.
Stall-feeding is a very intense source of methane. A projected shift towards stallfeeding in grazing systems is likely to increase storage of manure in a liquid or
waterlogged form, and this is the main source of methane emissions from manure.
Soil erosion/soil
degradation/
desertification
Biodiversity
In NAFTA, concerns over air and water quality have largely been related to N
and P. Air emission concerns include N and sulfur. Lately, states are addressing
emissions of volatile organic compounds (Powers and Angel, 2008).
Herds cause wide-scale land degradation, with about 20% of pastures considered
as degraded through overgrazing, compaction and erosion. This figure is even
higher in the drylands of US and Australia where inappropriate policies and
inadequate livestock management contribute to advancing desertification (FAO,
2006).
Declining livestock density in the English, Welsh and Scottish uplands, caused as
a result of CAP reform, is affecting biodiversity of these grazing areas and
environmental support schemes are being used to reduce further destocking.
The intensive farming of livestock produces concentrated waste which, if near
populous (e.g. urban) areas can lead to the spread of disease including avian
influenza and tuberculosis (WDR, 2008).
Pastures managed and cut for silage or grazed intensively are less biodiverse than
traditional hay meadows.
Succession of meadows by scrub and woodland, decline in open grassland and
field boundaries; degradation of hydro geological systems.
Vet medicines may persist in dung, affecting its fauna and potentially bird
populations who use this.
Invasive species and decline in species diversity as a result of increased fertilizer
use (N&K), silage, less grazing.
Changing intensity of production in traditional farms lead to lower complexity
and stability of food webs, especially in river-based and mixed Mediterranean
systems (EC, 2000).
Forestry/LUC/
agro forestry
Climate change
impacts for this
system
Moderate intensity of grazing in the Great Hungarian Plain stimulates growth of
vegetation (Horvath et al., 2009).
Livestock now use 30% of the earth’s entire land surface, mostly permanent
pasture but also including 33% of the global arable land used to producing feed
for livestock.
A recent study (Morton et al., (2006) reported annual destruction of the Amazon
rainforest to be positively correlated with the market price for soya, which is a
major ingredient of pig and poultry feeds.
As a result of the increasing frequency of heatwaves, heat stress in Britain is
expected to increase the risk of mortality of pigs and broiler chickens produced in
intensive livestock systems (Turnpenny et al., 2001). The rate of livestock
diseases, such as bluetongue, may also rise.
14
Increased frequency of drought along the Atlantic coast for instance in Ireland,
may lower forage crop productivity to the extent that they are not suitable for
livestock at current stocking rates without irrigation (Holden and Brereton, 2003,
FAO, 2003a).
Coastal vulnerability in North America, disruption to transport and infrastructure
on Atlantic Coast as sea level rises and tidal surges increase;
Current water stresses in Australasia are likely to be compounded by 2020s and
2050s;
In North America, rain-fed agricultural yields are set to increase early in the 21 st
century
Key points
Forecasts indicate that intensive livestock production can become more productive
without corresponding increases in GHG emissions. Effective measures to reduce
emissions of NH3 have been developed and are being implemented in some countries.
However, continued increases in herd sizes and concentrations of livestock within
small areas may pose serious threats to water and air quality. Indirect LUC may be
stimulated by demand for ingredients such as soya or cassava for concentrated feeds.
2.1.4 Intensive horticulture – all world
Horticulture means the production of vegetables and of top (orchard) and protected
fruit. Vegetable production generally requires cultivation and fertilizer inputs while
fruit, much of which are perennial crops, requiring little cultivation and less fertilizer.
However, some annual fruit crops may be grown under protection, such as in
glasshouses or polytunnels.
Production of
carbohydrate and
protein kg/ha/year
and productivity
Environmental impacts
Agricultural production of roots and tubers ranges from 13.983 t/ha in Romania
to 41.692 t/ha in the US in 2005 (WRI, 2009).
In the UK in 2007, total area planted with vegetables was 116,311 ha. Total
area planted with fruit was 27,580 ha.
Total orchard fruit (apples, pears, plums) in 2007 - 18,016 ha planted;
Total soft fruit - 9,418 ha planted (Defra, 2009).
Irrigated or rainfed
Emissions to water
(nitrate, phosphate,
biological oxygen
demand)
In Indonesia, 2007, shallot production was 802,810 tonnes; cabbages 1 288 738
tonnes; potatoes 1 003 732 tonnes (Statistics Indonesia, 2009).
Horticulture is predominantly rainfed, but often supplemented by irrigation and
for some crops in some countries may depend on irrigation
Water pollution from intensive vegetable production can be greater than from
intensive arable crops. For example, while applications of N to cereals will not
usually exceed 200 kg/ha/year, annual applications to brassicae can be > 300
kg/ha/yr. In addition, N recovery by vegetables is often much less than by
cereals and some other major arable crops and much larger N residues are left
in the soil after harvest. High fertilizer inputs combined with large-scale
irrigation promotes nitrate leaching to surface and groundwater (EEA, 1995).
However, the situation is very variable and some vegetable crops have fairly
modest fertilizer requirements. Nevertheless, vegetable production requires
more cultivation than that of combinable crops and N cycling is less efficient.
The requirement for cultivation, and tendency to site vegetable production on
light sandy soils, prone to erosion, may lead to direct pollution of watercourses
from run-off.
15
Emissions to air
(GHGs, NH3, NOx,
non-methane
VOCs)
Soil erosion/soil
degradation
/desertification
Biodiversity
Forestry/LUC/
agro forestry
Climate change
impacts for this
system
As a result of harvesting, poor application of nitrogen fertilizers and lack of soil
drainage, base cations in soils are removed thus causing acidification
particularly in Mediterranean soils. At the micro level, this leads to a reduction
in soil fertility and the potential for aluminum movement (Zaladis et al., 2002).
The production of Mediterranean fruits and vegetables in heated greenhouses in
the temperate zones may lead to very large GHG emissions per t of produce,
with total GHG emissions being much greater than from imported produce
despite large distances often involved (e.g. Williams et al., 2008).
Can be considerable and locally significant under intensive vegetable
production.
The greater variety of crops grown, compared with arable production, and the
perennial nature of some crops, offers greater potential for biodiversity.
However, due to the needs for more intensive cultivation for vegetables, and
greater pesticide inputs for all crops, this biodiversity potential may not be
realised.
Production of tropical fruits can lead to rainforest destruction
The Mediterranean region can expect the greatest reductions of all crops, as
well as the south-west Balkans and in the south of Russia (Alcamo et al., 2007;
Maracchi et al., 2005). However in Germany, there may be an advance in the
beginning of growing season for fruit trees (IPCC, 2007);
Australian temperate fruits and nuts are projected to be negatively impacted by
warmer temperatures since they need to be exposed to colder temperatures in
winter. In addition, crops which require irrigation may become more vulnerable
as water stresses increase in the 2020s and 2050s.
A pest species, the Queensland fruit fly Bactrocera tryoni, could become a
growing threat to southern Australia if temperatures warm by 0.5°C – 2.0°C,
thus impacting apple, orange and pear growers.
In North America, rain-fed agricultural yields are set to increase early in the
21st century
Key points
As horticulture, particularly vegetable production, becomes more specialised and
intensive substantial fertilizer applications to some crops and intensive cultivation are
likely to increase local water pollution.
2.1.5 Extensive beef and sheep grazing – all world
Production of
carbohydrate and
protein
kg/ha/year and
productivity
Environmental impacts
Latin America: Commercialised dairy sector based on grazing. Separate beef cow
herd grazing pastures and rangelands. Minor amount of feedlot feeding with
grains. Growing non-dairy cattle comprise a large portion of the population.
Average milk yield 800 kg hd-1 yr-1.
Africa and Middle East: Commercialised dairy sector based on grazing with low
production per cow. Most cattle are multi-purpose, providing draft power and
some milk within farming regions. Some cattle graze over very large areas. Cattle
are smaller than those found in most other regions. Average milk yield 475 kg hd 1
yr-1.
E and SE Asia: Small commercialised dairy sector. Most cattle are multi-purpose,
providing draft power and some milk within farming regions. Small grazing
population. Cattle of all types are smaller than those found in most other regions
Average milk yield 1650 kg hd-1 yr-1.
16
Irrigated or rainfed
Emissions to
water (nitrate,
phosphate,
biological
oxygen demand)
Emissions to air
(GHGs, NH3,
NOx, nonmethane VOCs)
Thailand produces over 500 million tonnes of poultry worldwide in 2003.
Implementing a zoning and tax system has controlled the spread of disease and
helped reduced the intensity of poultry holdings in urban areas (WDR, 2008).
This system tends to be rain fed (Hamilton et al., 1996).
While emissions to water can still be significant, the intensity will be less than
from intensive production due to the smaller inputs of fertilizer and reduced
stocking density. Pesticide leachate to water tends to be minimal except where
treatment for parasites is required.
Excessive leakage of nutrients creates problems for water quality in this system.
Grazing animals produce faeces and urine which are lost through leaching. The
higher the dietary crude protein and rumen solubility in feed, the greater the urine
nitrogen losses (Hamilton et al., 1996)..
Increasing intensification in Asia is leading to water pollution by nitrogen,
phosphorous, cadmium, copper and zinc. Indeed, environmental concerns have
largely been in relation to emissions from manure storage and application to
water.
Emissions of NH3 from livestock decrease considerably as the ratio of time spent
grazing to time spent within buildings increases (Webb et al., 2005). However,
emissions of N2O will not be decreased as much as those of NH3, while emissions
of CH4 a tend to be greater, since diets with greater proportions of forage tend to
be less digestible, leading to greater emissions of CH4.
For sheep grazed land in New Zealand, 3.7 ± 2.2 kg N2O-N per hectare per year
and 32.0 g N2O-N per hectare per day for pastures grazed by dairy cows (Saggar
et al., 2007).
Soil erosion/soil
degradation/
desertification
Grazing land acts as a sink for methane - 0.64 ± 0.19 kg CH4-C per hectare,
higher in summer and lower in winter. In order to cut anaerobic N2O emissions,
greater CH4 oxidation at the soil surface will be favoured (Saggar et al., 2007).
Grazing animals are known to speed up the nutrient recycling process and to
redistribute nutrients. The nutrients input into this system tend to be controlled by
the animal feeds used, thus the more feeds used, the greater the nutrient output
(Hamilton et al., 1996).
In livestock, grassland, humid and temperature zones, manure is not a significant
issue due to the low concentration of livestock on grazing land (Hamilton et al.,
1996).
Biodiversity
Forestry/LUC/
agro forestry
Climate change
As woody vegetation is removed, incoming light increases, there is less
interception of rainfall and reduced release of soil nutrients. As a result,
understory forage production increases.
The density of livestock herds increases the likelihood of animal disease such as
avian flu being spread, and poses a threat where they come into contact with
human populations, particularly in east Asia (WDR, 2008).
Herds cause wide-scale land degradation, with about 20% of pastures considered
as degraded through overgrazing, compaction and erosion. This figure is even
higher in drylands where inappropriate policies and inadequate livestock
management contribute to advancing desertification (FAO, 2006).
Trend is a shift away from extensive grazing to more intensive grazing in most
developing countries. This is likely to lead to a return to forest cover and there is
potential to increase grassland cover in China and parts of South America (FAO,
chapter 12).
In developing countries, including much of Asia, livestock farming is growing in
intensity, with a shift from dispersed production systems in rural areas to
intensive, specialist production in urban areas (WDR, 2008).
Increasing frequency and intensity of drought and heat waves in summer in
17
impacts for this
system
Europe and Oceania may increasingly affect the health of livestock, as it does
already in Australia. This is likely to reduce production and productivity (IPCC,
2007).
Conversely, there are likely to be fewer deaths of young lambs and calves as a
result of milder winters in Australia and New Zealand, and possibly Europe too.
The range of the cattle tick (Boophilus microplus) is likely to move extend
southwards on thus affecting a greater proportion of the Australian beef industry
(IPCC, 2007).
Current water stresses in Australasia are likely to be compounded by 2020s and
2050s.
In North America, rain-fed agricultural yields are set to increase early in the 21st
century.
Key points
Extensive livestock production is a significant source of the GHG CH4 and a driver of
LUC. In addition, soil nutrient supplies can be depleted leading to a cycle of further
extensification and demand for further LUC.
2.2
Developing countries
2.2.1. Wetland rice cultivation
Production of
carbohydrate and
protein
kg/ha/year and
productivity
Irrigated or rainfed
Emissions to
water (nitrate,
phosphate,
biological
oxygen demand)
Emissions to air
(GHGs, NH3,
NOx, nonmethane VOCs)
Soil erosion/soil
degradation/
desertification
Biodiversity
Environmental impacts
In 1999-2000, rice yields in India were 1.99 t/ha (Ministry of Agriculture, 2000).
The average wheat production in India is in the region of 2.60 t/ha (Indian News,
2008).
In China during the 1990s, rice yields were estimated at 5.95 t/ha, an increase of
almost 100% since the 1960s (FAO, 2000a). In 2005, total grain yields in China
were 426.613*103 t, or 5.17 t/ha. The average farm produces 3.39 t rice based on
an area of 0.30 ha (IIASA, 2005).
Multiple rice crop systems are only found where rainfall is greater than 200 mm
per month for at least 6 months per year.
Extensive use of nitrogen fertilizer and pesticides has led to nitrates being found
in water and food at levels which exceed the tolerable level, particularly in the
Punjab region of India (WDR, 2008).
According to WRI (2009), fertilizer consumption in India was 19.258 *10 6 t
of nutrient.
Global rice production from wetland paddies contributes 6% of total global
atmospheric CH4 emissions (Bouwman and McCarl, 2006). It is suggested that
global rice production releases 0.13–0.89 t C per hectare per year (Ramsar, 1999).
Over 90% of worldwide rice cultivation occurs in developing countries: it is
predicted that global rice production will double between 1990 and 2050,
therefore an increase in CH4 emissions can be expected if emissions are related to
biomass (FAO, 2003b).
Rice-wheat systems in South Asia cover 12 m ha in the Indo-Gangetic Plain of
India and Pakistan. Monoculture of rice in summer and wheat in winter has
contributed to soil and water degradation, including soil salinisation, soil nutrient
depletion and reduced organic matter (WDR, 2008). Main areas affected by
salinisation include North East Thailand and the North China Plain and the
unterraced slopes of China and southeast Asia are affected by erosion (Dixon et
al., 2001).
In Asia, algal blooms and eutrophication are a result of fertilizer run off, thus
destroying wetland habitats (WDR, 2008)
Forestry/LUC/
agro forestry
18
Climate change
impacts for this
system
The IPCC suggest that South East Asia is likely to see an increasing grain harvest
under a changing climate. However, regional variations in the response of wheat,
maize and rice yields to climate change projections could be significant (Parry et
al., 2007).
The HadCM2 climate model projects that crop yields could increase by up to 20%
in East and South-East Asia but could decrease up to 30% in Central and South
Asia, taking into account any positive feedback from having extra CO 2 in the
atmosphere (IPCC, 2007).
Increased frequency and magnitude of forest fires in northern Asia as
temperatures rise and drought increases;
Key points
Irrigated rice cultivation is a major source of CH4 but changes to production methods
are forecast to lead to no net increase in CH4 emissions to 2030 despite forecasts of
substantial increases in production. However, rice cultivation is likely to continue to
be a major source of N2O and NH3.
2.2.2 Irrigated
Production of
carbohydrate and
protein
kg/ha/year and
productivity
Irrigated or rainfed
Environmental impacts
Based on the countries falling into the irrigated farming system, including Peru,
Chile and Iraq, yields of cereal are presented based on WRI (2009) datasets.
Peru: 3.54 t/ha
Chile: 5.81 t/ha
Jordan: 1.33 t/ha
Irrigated by definition.
Less than 4% of renewable water resources in Africa are used for farming;
Barriers include a lack of finance and labour force to construct irrigation and the
infrastructure needed. Also lack of agricultural technology, and access to markets
(Hanjra et al., 2009)
Emissions to
water (nitrate,
phosphate,
biological
oxygen demand)
Countries with the largest areas of irrigated land include (WRI, 2009)
China – 54,596,000 ha
India – 55,808,000 ha
Pakistan - 18,230,000 ha
Smallholder irrigated farming systems require large-scale irrigation schemes in
comparison to the scale of the farming. Rising frequency of drought in arid
regions, as a result of climate change, is a further stress factor to this farming
system.
In Latin America, lower rainfall will cause serious water shortages, e.g. in
Argentina, Chile and Brazil between 7 million and 77 million people could be
affected by the 2020s (Parry et al., 2007).
Lake Chapala in central Mexico and Lake Chad in western Africa are both
receding as a result of unsustainable irrigation (WDR, 2008).
In Sub-Saharan Africa, major investment in irrigation is required (Dixon et al.,
2001).
Hydrological impacts include a 30m drop in water table level in the coastal
aquifer Hermosillo, Mexico, as a result of water abstraction at a rate 3-4 times
greater than recharge level. This leads to intrusion of saltwater, leading to
relocation of farms.
Around 40% of irrigated land in arid Asia is affected by salinisation including
19
Emissions to air
(GHGs, NH3,
NOx, nonmethane VOCs)
Soil erosion/soil
degradation/
desertification
Biodiversity
Forestry/LUC/
agro forestry
Climate change
impacts for this
system
Pakistan and the Aral Sea basin (WDR, 2008). The result of this is loss of
productivity and land that can support agriculture.
Greenhouse gases from irrigation schemes will contribute to a high level of
emissions.
In rice production, emerging trends involve lower consumption of irrigated water.
Diversification of crops and intensification of the system by using water more
efficiently under high yield levels mean the GHG budget is changing. Methane
emissions are lower. However Nitrous oxide emissions are greater. Soil organic
carbon and therefore CO2 emissions make this system less sustainable
(Wassmann et al., 2006).
Under this production system and each of the sub-systems (including maize
mixed farming system, the cereal-root crop farming system and the highland
temperate farming system) soil fertility is decreasing. As a result of increasing
fertilizer costs, the application of fertilizers to maize and wheat has dropped. As
such, those regions previously producing smallholder maize have had to grow
local varieties without fertilizer application (Dixon et al., 2001).
In north Africa, the Nile Delta is affected by salinisation as a result of the reduced
flow of the Nile since the completion of the Aswan High Dam, and southeast
Nigeria and the Sahel are affected by erosion (Dixon et al., 2001).
Stress is exerted on river basins and their ecology and can lead to nutrient
depletion and soil erosion, as well as loss of fish and other aquatic species. As a
result, this threatens the nutritional value of this system’s outputs
Africa is projected to experience an increase of 5 to 8% of arid and semi-arid land
by the 2080s leading to reduced agricultural yields, increased desertification and
drought;
Rise in number of people at risk of hunger in Latin America, from 5, 26 and 85
million in 2020s, 2050s and 2080s respectively;
Increased frequency and magnitude of forest fires in northern Asia as
temperatures rise and drought increases;
This system is likely to be put under pressure from water shortages in coming
years. For instance, gross per capita water availability in India will drop from
around 1820 m3/yr in 2001 to as low as around 1140 m3/yr in 2050 (IPCC, 2007).
Key points
Without significant improvements in water use efficiency it will be difficult to greatly
increase production from this farm type. In some regions maintaining current
production may be difficult.
2.2.3 Smallholder rain-fed humid
Production of
carbohydrate and
protein
kg/ha/year and
productivity
Environmental impacts
In East Africa, cassava yields range from 6600 kg per head per year to 12700 kg
per head per year. Maize yields range from 700 kg to 1400 kg per head per year
(Fermont et al., 2008).
These yields are very small, given the large area of land which Sub Saharan
Africa covers at 2,429,569 ha (WRI, 2009).
Yields of cereal in countries under this farming system range from:
Ethiopia: 1.24 t/ha
Uganda: 1.70 t/ha
20
Kenya: 1.32 t/ha
Irrigated or rainfed
Emissions to
water (nitrate,
phosphate,
biological
oxygen demand)
Emissions to air
(GHGs, NH3,
NOx, nonmethane VOCs)
Soil erosion/soil
degradation/
desertification
Biodiversity
Forestry/LUC/
agro forestry
Climate change
impacts for this
system
Based on WRI (2009)
At present little irrigation is required as climates have abundant rainfall.
However, under a changing climate, yields in rainfed farming systems could
decline, threatening the achievement of the Millennium Development Goals of
ending poverty and hunger, as well as achieving environmental
sustainability.(Millennium Development Goals, 2005).
Smallholder farmers are at most risk from the impacts of climate change, which
include increased risk of crop failure; greater livestock disease and therefore
lower prices for produce; rising dependency on aid and a decline in human
development indicators including health and education (Ifid, 2008).
Losses of 17.3 kg N per hectare per year, 5.3 kg P /ha per year and 7.1 kg /ha per
year have been seen for cereals, supporting the low yields of Ethiopian production
systems.
Leaching losses of K and N were greatest under permanent crop production, at a
rate of 41.1 and 21.3 kg /ha per year.
Greenhouse gas emissions are likely to be low since irrigation use is low,
fertilizer use is low, e.g. In Venezuela, fertilizer use was 372.6 kg * 10^6 in 2006.
This represents a low level (127.2 kg/ha)of fertilizer use. (WRI, 2009)
Much of Sub-Saharan Africa is covered by this farming system (FAO, 2003b).
Here, the WDR (2008) estimate that productivity losses are in the region of 1% or
less each year; in areas of extensive production including Kenya, Ethiopia and
Uganda, this is higher. One estimate puts land degradation in the Nyando River
Basin in Kenya at 56%.
Pressure on land is low with an average of 2.5 persons per cultivated hectare.
However, land degradation is high due to wind and water erosion, particularly in
the Sahel Desert and Sub-Saharan Africa which are covered largely by the
smallholder rain fed humid system. Here overgrazing of pastoral lands is also
high (WDR, 2008).
Kaihura and Stocking (2003) published a book on the agricultural biodiversity of
smallholder farms in East Africa. They found that agricultural uniformity is
increasing, however, many farmers are promoting patchwork land use including
annual cropping, orchards, forest, fallow, home garden, and hedges)
In Yunnan, China, for example, some farmers are expanding home gardens on to
former rice paddy terraces to produce vegetables, medicinal plants, and fruits for
sale. Maize fields are being replanted with native tree species as forestry.
In western Africa, the Amazon and southeast Asia, deforestation is occurring
rapidly in tropical areas (WDR, 2008). There is little forest cover left in West
Africa and population is growing (Dixon et al., 2001).
Ifad (2008) suggest that the smaller, poorer farmers could be affected worst by
climate change. If emissions do not change and a ‘business as usual scenario’
exists, agricultural productivity may drop by 10 to 25% by 2080. For some
countries, yields in rainfed agriculture could decrease by up to 50%.
Sea level rise and coastal inundation by end of 21 st Century in Africa;
It is projected that in Latin America, lower rainfall will cause serious water
shortages, e.g. in Argentina, Chile and Brazil between 7 million and 77 million
people could be affected by the 2020s;
Rise in number of people at risk of hunger in Latin America, from 5, 26 and 85
million in 2020s, 2050s and 2080s respectively
Current water stresses in Africa are likely to be compounded by 2020s and 2050s.
21
Key points
Climate change is forecast to reduce rainfall in several of the regions which depend
upon rain-fed smallholder production. Substantial areas are also prone to land
degradation. Unless inputs can be made available to improve productivity and
management to avoid degradation, there will be pressure for LUC.
2.2.4 Smallholder rain-fed highland
Production of
carbohydrate and
protein
kg/ha/year and
productivity
Irrigated or rainfed
Emissions to
water (nitrate,
phosphate,
biological
oxygen demand)
Emissions to air
(GHGs, NH3,
NOx, nonmethane VOCs)
Biodiversity
Soil erosion/soil
degradation/
desertification
Biodiversity
Forestry/LUC/
agro forestry
Climate change
impacts for this
system
Environmental impacts
Winter wheat has a seeding rate of 171 kg/ha.
In the Gansu Province of China, farmers tend to have an average of 1.7 pigs per
household. Donkeys are used for transportation of produce and labour purposes,
and sheep, goats and cattle are also kept.
Irrigation is limited to 0.6 million ha; main crops produced are subsistence winter
wheat in areas of higher rainfall, and subsistence spring wheat in lower rainfall
areas.
Water pollution receives much attention in developing countries than in the EU
and NAFTA. However, fertilizer use in this system is low due to the extensive
nature of this farming system, its poorly developed infrastructure and lack of
machinery for application. Therefore emissions to water will are also likely to be
low.
Emissions are similar to those in smallholder rainfed humid production systems.
Inputs are limited in terms of fertilizers, irrigation and energy, therefore emissions
are likely to be low.
There is substantial soil erosion on the Loess Plateau, China. Due to soil type,
slope and rainfall, soil erosion here is greatest in China and in the world at 3720 t
km-2 year-1, (Liu, 1999).
Uplands are more prone to water erosion where cultivated slopes are steeper than
10 to 30%, where soil conservation measures are absent and precipitation rates
are high. Estimates of how much of this type of land is currently cropped cannot
be made. Land pressure in South East Asia is caused by increasing population and
has encouraged greater use of steep hill slopes for maize production, although in
countries such as Bhutan and Nepal where there is little flat land left to cultivate,
there is little choice over where cultivation can take place. Erosion occurs at a
rate of 20,000 to 50,000 kg per hectare per annum in fields and 200,000 kg per
hectare per annum in highly degraded watersheds (Dixon et al., 2001).
In many upland areas, forest cover has been reduced as cultivation expands across
the slopes. Combined with thin and infertile soils, there is not much to support a
wide range of biodiversity.
Dixon et al (2001) suggest that this system has great potential for intensification,
by using soil restoration methods and improved water management techniques.
However this may compromise the sustainability of the system itself.
Again, smallholder farmers are likely to be negatively impacted by climate
change as they are least able to afford to adapt to the consequences.
As glaciers melt at an increased rate, glacial floods will increase in frequency,
slopes will become less stable and river flows are likely to decrease.
It is thought that agricultural productivity in Asia will decline as a result of
rising temperatures, increasing severity of drought, flooding and soil degradation;
Landslides are expected to become more frequent and the
ecology of mountain and highland systems in Asia is predicted to be altered
(IPCC, 2007).
22
Key points
This farming type is particularly vulnerable to soil erosion.
2.2.5 Smallholder dry and cold
Production of
carbohydrate and
protein
kg/ha/year and
productivity
Irrigated or rain
fed
Emissions to
water (nitrate,
phosphate,
biological
oxygen demand)
Emissions to air
(GHGs, NH3,
NOx, nonmethane VOCs)
Soil erosion/soil
degradation/
desertification
Biodiversity
Environmental impacts
Crop farming is subsistence based; surplus yields are sold if it is likely that the
following harvest will be good (Ncube et al., 2009). In semi-arid Zimbabwe,
yields range from 820 kg pearl millet, 150 kg sorghum and 30 kg maize per farm
per annum on a better resourced farm, to 320 kg pearl millet, 40 kg sorghum and
10 kg groundnut on a poorly resourced farm (Ncube et al., 2009).
Irrigation is used widely; for example, in Pakistan, 18,230 thousand ha of land are
irrigated. In Kazakhstan, 3,556 thousand ha of land is irrigated (WRI, 2009).
Lack of rainfall means groundwater irrigation is used heavily in the Middle East
and South Asia, areas dominated by this farming system. Groundwater use is high
compared to the land under cultivation (WDR, 2008). In future, food needs must
be met through improved water efficiency (WDR, 2008). Almost 20 million
hectares of land requiring irrigation are located in Kazakhstan, Kyrgiz Republic,
Tajikistan and Uzbekistan (Dixon et al., 2001).
Areas experiencing water stress in major river basins have been identified in
recent research (Smakhtin et al., 2004 in WDR, 2008). Overexploited areas
include areas which are covered largely by smallholder dry and cold farming
systems. This supports the fact that such systems often have low productivity due
to environmental constraints including nutrient poor soils, low temperatures and
lack of rainfall, for instance in North Africa, parts of South Asia (India) and
Central Asia (Fermont et al., 2008; Tittonell et al., 2008; Ncube et al., 2009).
This low precipitation explains the need for additional water abstraction in these
areas, leading to water stress.
Where there are negative nitrogen balances caused by low fertilizer input, which
is common in sub-Saharan Africa, leaching into water tends not to be problematic
(FAO, 2003b). In semi-arid Zimbabwe, better-resourced farms use 2000-5000 kg
manure per season and medium resourced farms use less manure (1000 kg to 0
kg) (Ncube et al., 2009). China, however, is the world’s largest consumer of
nitrogen fertilizer with applications of around 600 kg/ha (Lin, 2009).
Part of this large input of N is due to the type of fertilizer used, predominantly
ammonium bicarbonate (NH4HCO3). This fertilizer dissolves to produce a high
pH solution in which much of the N is in the form of NH 3 and is readily lost (up
to 50%) as gaseous NH3 (Cai et al., 1998). The authorities are aware of this
problem; however, the manufacture of NH4HCO3 is a significant industry, at one
time employing c. 500,000 people, and hence the replacement of these plants with
the manufacture of alternatives will be a long-term process.
Overgrazing and land degradation is high in the Middle East and Central Asia.
Figures for soil degradation tend to be rare and where they do exist, cause debate
(WDR, 2008). In the regions of Indus, Tigris and the Euphrates river basins in
South and west Asia, salinisation is a major problem. The foothills of the
Himalayas are affected by erosion.
Soil erosion is the main cause of soil nutrient depletion, which can be
compounded by limited fertilizer application or a lack of organic manure or
fertiliser being applied. For instance in Ethiopia, nutrient depletion occurs at the
rates of 122 kg N ha yr-1, 13 kg P ha-1 yr-1 and 82 kg K ha-1 yr-1 (Haileslassie et
al., 2004). This system tends to have a very high population pressure on natural
resources, particularly around Turkey and Central Asia (Dixon et al., 2001).
As a result of stress on river basins and increasing salinisation, there has been a
rise in disease carrying pathogens in eastern Africa, in countries including
Ethiopia, Somalia, Kenya.
Forestry/LUC/
agro forestry
23
Climate change
impacts for this
system
Sea level rise and coastal inundation is projected by the end of the 21 st Century in
Africa.
It is projected that an annual increase of 25% in peak discharge could be
experienced in Bangladesh, thus aiding the productivity of the farming systems
(Parry et al., 2007).
Current water stresses in Africa are likely to be compounded by 2020s and 2050s.
Africa is projected to experience an increase of 5 to 8% of arid and semi-arid land
by the 2080s leading to reduced agricultural yields, increased desertification and
drought.
Increased frequency and magnitude of forest fires in northern Asia as
temperatures rise and drought increases.
Key points
These systems often have low productivity due to environmental constraints including
nutrient poor soils, low temperatures and lack of rainfall; for instance, in North
Africa, parts of South Asia (India) and Central Asia. This low precipitation explains
the need for additional water abstraction in these areas, leading to water stress.
2.2.6 Dualistic mixed
Production of
carbohydrate and
protein
kg/ha/year and
productivity
Irrigated or rainfed
Emissions to
water (nitrate,
phosphate,
biological
oxygen demand)
Emissions to air
(GHGs, NH3,
NOx, nonmethane VOCs)
Biodiversity
Soil erosion/soil
degradation/
desertification
Environmental impacts
A study by Pretty et al., (2006) suggests that within the dualistic mixed farming
system, 537,311 farmers have adopted agricultural sustainable technologies. This
equates to 26,846,750 hectares under sustainable agriculture, and has resulted in a
76.5 % increase in yields.
In Haryana, India, there is inadequate irrigation as a result of declining water
tables and poor discharge from tubewells. Water supply from canals is also not
sufficient and ground water is of poor quality (Indian Council of Agricultural
Research, 1998).
Nitrates are exceeding ambient levels in waters (Singh, 2000).
Pretty et al (2006) suggest that the dualistic mixed production system has the
potential to sequester 0.32 t C per hectare per annum. This is a total of 8.03 Mt C
per year, the largest figure of all production systems.
It is suggested that decomposition in drained peatlands in southeast Asia emits
between 355 and 874 Mt/y CO2 per year (Hooijer et al., 2006). This problem has
arisen because of palm oil production, an important crop in the dualistic mixed
production system in parts of Brazil, Ecuador and the Ivory Coast, as well as in
the smallholder rainfed humid production system.
In Indonesia the rapid expansion of palm oil production (Elaeis guineesis) has led
to intense international concern about its wide-scale environmental impacts.
Indonesia is experiencing unprecedented rates of deforestation, with associated
loss of biodiversity and damage to ecosystem services. Palm oil plantations
currently occupy about 6 * 106 ha in Indonesia.
The impact of grazing on soil organic carbon in the Cerrado is less than on forest.
Maquere et al. (2008) reported that total C stocks to 1 m depth under pastures that
had been established for 20 and 80 years were numerically greater than, albeit not
significantly different to, total SOC to 1 m of native Cerrado. The total SOC
estimated, at 84 t/ha, was greater than the default value of 66 t/ha for Brazilian
savannah cited by IPCC (2006).
24
Forestry/LUC/
agro forestry
Climate change
impacts for this
system
In 1980, soil phosphorous content was declining on a more widespread basis. The
area of soil with a low N content only increased from 89 to 91%. Soils with high
K content have dropped from 91% in 1980 to 61% in 1995. The wheat–rice
rotation disrupts soil nutrient balance causing soil infertility and a lack of zinc and
copper (Singh, 2000).
Deforestation is a major problem associated with cattle ranching in Latin
American countries including Guyana, Venezuela and Ecuador, where it is
projected that by 2012, more than 80% of land will be used for pasture. Tree
species including large leaved mahogany are also threatened (FAO, 2002)
In Latin America, lower rainfall will cause serious water shortages, e.g. in
Argentina, Chile and Brazil between 7 million and 77 million people could be
affected by the 2020s;
Current water stresses in Africa are likely to be compounded by 2020s and 2050s;
Rise in number of people at risk of hunger in Latin America, from 5, 26 and 85
million in 2020s, 2050s and 2080s respectively
Key points
Heavy demand for water in some areas is diminishing water resources while a
combination of increased agrochemical inputs and decreased water flows is reducing
water quality. In some areas soil reserves of P and K are not being maintained.
2.3
Fishing and aquaculture, including coastal artisanal
Production of
carbohydrate and
protein
kg/ha/year and
productivity
Environmental impacts
The Asia-Pacific region produces most of the world’s share of fish, both from
aquaculture and fisheries (91 and 48% of total world production, respectively).
This totalled 46.9 million tonnes from aquaculture and 44.7 million tonnes from
capture fisheries in 2002.
Small fish species, damaged catch and young fish targeted are often referred to as
'trash fish'. They have a low market value. Increasingly, this 'trash fish' is used as
fish meal in aquaculture and also as livestock feed, thus increasing demand and
placing greater pressure on fish stocks (FAO, 2005). Nitrogen is reported to be
the main limiting nutrient for primary production in coastal areas (Wu, 1995).
Emissions to
water (nitrate,
phosphate,
biological
oxygen demand)
During the 1990s, between 28 and 33 million tonnes of fish were used each year
for the production of fishmeal and oil and these fish were mainly landed by
marine capture fisheries. The capture of pelagic fish off the west coast of South
America contracted as a result of the
El Niño phenomenon, as did the production of fishmeal in the world; in 1998
only 23.9 million tonnes of fish were reduced to fishmeal and oil. By 1999 this
figure increased again to 30 million tonnes or almost 24 % of total world catch of
fish, representing a return to a more normal level as a result of the recovery of
fishing in South America (Dixon et al., 2001)
European salmonid farms which use artificial feed can expect to lose 52-95% of
N and 82% of P to the environment through excretion of ammonical-N and urea,
food wastage and faecal production. Most food is wasted by open sea cage culture
which use trash fish as feed, followed by pond culture using moist feed and lastly
raceways which use dry feed (Wu, 1995).
In previous years, tributyltin (TBT) was used to control fouling of fishing vessels.
However, due to its toxicity, the use of TBT has been banned in most countries.
Marine fish farming tends not to lead to eutrophication.
In the water surrounding fish farms, dissolved oxygen levels are lower and
biological oxygen demand and P, organic and inorganic N and total C are higher
(Wu, 1995). Indeed, fish farming raises sediment oxygen demand by between 2
25
Emissions to air
(GHGs, NH3,
NOx, nonmethane VOCs)
Biodiversity
and 5 times of sediments in non-fish farming areas.
European salmonid farms which use artificial feed can expect to lose between 80
and 84% of C through wastage of feed and respiration by fish (Wu, 1995).
Deep sea fishing can threaten other vulnerable marine species including delicate
cold water corals and sponges, sea-bottom seep and vent habitats that contain
unique species, and features like underwater seamounts which support sensitive
species (FAO, 2008a).
As a result of conversion for fish and shrimp farming, mangrove habitats have
suffered. Asia has lost more than 1.9 million ha as a result of land use conversion
whilst north and central America and Africa have lost in the region of 690 000
and 510 000 ha respectively in the past 25 years. Indonesia, Mexico, Pakistan,
Papua New Guinea and Panama experienced the largest losses of mangroves
during the 1980s, with. Around one million hectares were being lost in total in
these five countries. Vietnam, Malaysia and Madagascar, which all support
coastal artisanal production systems, suffered major area losses in the 1990s and
between 2000 and 2005 (FAO, 2008b).
A global assessment by the FAO found that 3.6 million hectares of mangrove
forests have been lost since 1980. It was suggested that Asia had suffered the
greatest loss, with a total of 1.9 million hectares being destroyed because of land
use change. However, it is believed that the rate of loss is slowing down from a
loss of 187,000 hectares in the 1980s to 102,000 hectares in the early 2000s
(BBC, 2008).
Mangrove loss is a serious social., environmental and economic concern for many
developing countries. Mangroves play a key role in protecting coastlines and
moderating monsoonal tidal floods and tsunamis. The United Nations suggest that
mangroves can absorb between 70 and 90 % of the energy of a normal wave
(FAO, 2008c). In addition, they are host to a wide variety of wildlife and
estuarine and near-shore fisheries. As a result, the degradation of this vital
ecosystem service will mean terrestrial and aquatic production is reduced, and
wildlife habitats are lost. Furthermore, the environmental equilibrium of coastal
forests which protect inland agricultural crops and villages will be upset.
Shrimp trawling tends to have a negative impact on other marine biodiversity.
The capture of young valuable fish before they have the chance to reproduce
threatens the sustainability of fish populations; extensive removal of non-targeted
species such as sea turtles threatens marine ecosystem biodiversity and can
thereby impacting on the fishery’s productivity (FAO, 2006b).
However, fish species can be used as bioindicators to detect signs of pollution in
coastal waters (Wu, 1995).
Climate change
impacts for this
system
At risk species include white abalone, barn door skate and large coral reef fishes.
As a result of intensive fishing, genetic diversity is lost and the adaptability of
species is reduced. Key threats include habitat destruction, pollution and climate
change (Dixon et al., 2001).
The north-east Atlantic marine ecoregion is suggested to be highly vulnerable to
climate change, particularly for marine fish and shellfish species (Baker, 2005).
Rising temperatures impact the productivity of fisheries in the North Atlantic.
Species distribution patterns will change, with greater production in northern
waters and a decreases in southern waters (IPCC, 2007);
As a result of rising atmospheric temperatures, primary productivity could reduce
in the tropical oceans. These oceans are particularly vulnerable since East Asia
and South-East Asia provide one quarter of the world’s total tuna population,
particularly the skipjack tuna (IPCC, 2007).
26
In China, marine fishery is threatened by overfishing, pollution, eutrophication
and red tides. Ribbon fish and large and small yellow croakers could be impacted
by climate change.
Key points
The loss of mangrove swamps to shrimp farming has had major adverse effects on
coastal environments. The majority of sea fisheries are over-exploited and it may
prove difficult to maintain current production.
3.
Case studies
3.1
Environmental impacts of beef production in Brazil
In Brazil, there has been widespread degradation of the main pasture type, the
Cerrado (Cezar et al., 2001). Barcelos (1996) estimated that about 80% of pastures in
central Brazil were in some state of degradation. One feature of this is depletion of P
reserves in the soil, which are historically low in much of Brazil (Butterworth, 1985).
There is also a need to replace the native flora with more productive forages. Cezar et
al. (2001) described how some native pastures used to support stocking rates of 0.5
animal units/ha (450 kg liveweight/ha) but now support only 0.2. Plans have been
made to improve large areas of pasture, although it is not clear how far and how
quickly this has progressed. Pasture restoration implies cultivation, reseeding with
more productive species and fertilizing with P and K. One limit to this restoration is
cost, which may be beyond the capacity of small farmers. Costs are relatively high
because large areas typically need cultivating, but still only support relatively few
animals. Brazil is not alone in facing such a problem of pasture degradation. In parts
of northern Australia, some pastures are estimated to have only about 20 years more
productive life left (Evans pers. comm., 2008). Nitrogen fertilizer does not seem to be
needed because N fixation should occur through legumes and free-living soil bacteria.
However, this type of degradation, depletion of nutrients, can be reversed by
the addition of mineral fertilizer. Moreover, the addition of P and K may initiate a
beneficial cycle in which forage productivity, including that of forage legumes is
increased, increasing stocking rates and hence returns of N, P and K to the soil in
excreta.
Winter feeding is restricted mainly to urea and mineral supplements rather
than the forage and concentrates that are used in Europe. This means stock gain
weight in the wet season (summer) and may lose weight in the dry season.
The comparison of beef production in Brazil with beef production in the UK
reported by Williams et al. (2009) highlights the large differences between the
relatively extensive low-input pasture based system in Brazil and the generally more
intensive systems in the EU and NAFTA countries. Emissions of GHGs at c. 32 t
CO2-eqv. per t of meat at the farm gate are greater from the Brazilian systems than
from UK production (c. 24 t CO2-eqv. per t of meat). The difference arises mainly
because of greater emissions of enteric CH4, reflecting the relatively slow growth and
reproductive rates of Brazilian cattle. To reach slaughter weight of c. 450 kg takes
around 36 months in Brazil compared with 18-22 months for the UK. The Nellore
breed that dominates in Brazil is, however, generally long lived and resilient. In both
the EU and Brazil enteric fermentation is the largest source of GHGs from pre farm
gate production. However, in the EU, substantial emissions also arise from the
production of feed and the maintenance of grazed pastures, primarily from the
manufacture of fertilizers and from subsequent emissions of N2O.
27
3.2
Meat production and the impact on rainforest and other natural ecosystems
Soya meal can be a significant component of poultry diets; Ferguson et al. (1998a;
1998b) examined diets containing c. 25-44% soya as a proportion of feed intake. In
many feeds protein quality is low, in that the proteins have less than required
concentrations of essential amino acids (EEA), and in order to supply the required
amounts of these EEA more protein has to be supplied than the animal requires. A
major reason for the inclusion of soya in the feeds of pigs and poultry is that, as well
as having a high concentration of crude protein (CP; c. 35% of dry matter) soya also
has high proportions of the EAAs needed by non-ruminants, in particular lysine.
The greatest reported association between meat production and rainforest loss
is the indirect impact of the cultivation of soya to feed to livestock. The
intensification and expansion of soya production comes at the expense of important
regions of biological diversity. Soybean production has been identified as one of the
leading causes of deforestation in Brazil’s forests, particularly the Mato Grosso
seasonal forest ecoregion (Grau et al., 2005; Casson, 2003; Morton et al., 2006).
Links have been between increases in the area under soybean cultivation and
decreases in uncultivated land and biodiversity in the Cerrado and (more recently)
rainforest. Evidence of these changes was obtained from statistical data from the
Brazilian Government and FAO (USDA, 2005). The USDA has provided an analysis
of historical soybean production in Brazil, which links soybean expansion firmly to
the price commanded for soybean on the international market and increased
profitability for Brazilian farmers (USDA, 2005). Some soybean producers clear
forests themselves. Others buy the land from small producers, often colonists, who
have already cleared it. These same small producers then move further into the
frontier and clear more land. In addition to direct habitat conversion, soybean
production in pristine areas also requires the construction of massive transportation
and other infrastructure projects. Moreover, the infrastructure developments for soya
production unleash a number of indirect consequences associated with opening up
large, previously isolated environments to population migration and to other land
uses. This infrastructure contributes directly and indirectly to habitat conversion.
Casson (2003) also reports the displacement of smallholders by soybean plantations,
causing them to migrate into the Amazon region where they clear forest for
agriculture or cattle ranching (for domestic consumption).
Soya production in the Cerrado is estimated to lead to average soil losses of 8
tonnes/hectare/year (Fritsche et al., 2006); loss of SOC is a serious problem in the
soya-producing areas of Brazil due to the warm climate and dry winters.
Nevertheless, it must be recognised that the expansion of soya production is mainly
due to demand from Europe and elsewhere for animal feed. Moreover, since poultry
raised in the EU are fed amounts of soya similar to those fed to poultry in Brazil, and
much of the soya imported into the EU originates in Brazil, there is little or no reason
to suppose that poultry production in Brazil is any greater driver of soya cultivation
than poultry raised in the EU. The key driver here is not the country of origin of
poultry and other meat products but the growing global demand for meat.
3.3
The environmental impacts of palm oil production
Palm oil is the most produced and traded of all vegetable oils. The oil palm (Elaeis
guineensis) is grown in regions of high rainfall within 10o of the equator. It is grown
for its oil, which has been used as an ingredient for cooking in Africa for hundreds of
28
years. A different type of oil can also be obtained from the kernel of the palm fruit,
which is used as a basis for soap and oleochemicals, and is the traditional export to
the European market. Finally, the residues from processing (around 70% of the
harvested matter) can be used; the empty fruit branches are used as mulch for soil and
the fibrous expeller burnt to produce heat (and power) for the oil extraction process.
The nutshells, which are rich in silica, can also be used for road surfaces.
Table 11. Summary of oil palm properties. The table below is mainly focussed on
large-scale plantations in Asia. However, oil palms are also grown in Africa, where
small and medium scale planting is common.
Palm oil
Rainfall requirements
(mm/y)
Growth conditions
Economic life
Yields (tons/ha/y)
Both palm oil and palm kernel oil are produced. The former is used as
cooking oil; the latter as a feedstock for oleochemicals.
Usually grown in areas of high rainfall. There are records of irrigation in
Africa.
High demand for nutrients. On most soils fertilizer is required to obtain
reasonable yields. Nutrient demand is less in Africa than in South East Asia.
Pesticides seldom used. According to Fairhurst and Mutert (1999) ‘wellmanaged palm oils sequester more carbon per unit area than tropical rain
forest. About 25% of the harvested biomass may be returned to the field as a
nutrient rich mulch’.
Perennial
12.24 t/ha (fruit) 3-4 t/ha (palm oil) and 0.5 t palm kernel oil/ha, but higher
yields are thought to be obtainable.
Advantages
Co-product
Co-products include the empty fruit branches which can be used as fodder or
fibre for paper and particle board; the shells, used as road cover and the palm
kernel expeller, used as a fuel or fertilizer.
Areas where palm oil Grows within regions 10o from the equator. Malaysia, Indonesia, Nigeria,
is grown.
Thailand, Colombia, Cote D’Ivoire, Ecuador.
Issues
Deforestation to establish palm oil plantations. Soil erosion and degradation
from traditional planting methods (best practice can reduce these problems).
Effluents from processing (which can be treated). Animal-human conflict,
particularly elephants and orang-utan. Soil conservation required on hilly
areas.
Fairhurst and Mutert 1999; Wahid et al., 2004
Processing results in considerable quantities of high organic strength effluent. At large
scale it is cost effective to treat this through a combination of anaerobic and aerobic
digestion to produce a treated effluent that can be discharged to local watercourses.
However, at smaller scales this is not feasible. According to the FAO (undated)
‘environmental awareness of the operators in this industrial area is low. Traditional
processors simply return liquids to the surrounding bushes. In intermediate
technology mills sludge from the clarifying tanks are carried in buckets or
rudimentary gutters to sludge pits dug in nearby bushes. When the sludge pit begins to
give off a bad odour, the pit is filled in and another one dug for the purpose. Charcoal
from cooking fires is dumped into the pits to absorb some of the odour.’
Table 12. Key factors and impacts of palm oil production
Key
Indicator
Key factor
Impact
Key indicator and score
Land use
change
Deforestation
Clearance of jungle (Ardiansyah,
2006).
Illegal logging occurs in 37 of the 41
national parks in Indonesia (UNEP
2007).
Certification scheme such as RSPO are
setting out principles for development
including no deforestation.
There are general moves to ensure
protection of high conservation value
forests and national parks.
29
Sustainability certification schemes
generally suggest use of degraded land
rather than forests.
Support for the international “Forest Law
enforcement and Governance” (see UNEP
2007.) Strengthen international programmes
of law enforcement against illegal logging,
including support from Interpol.
Strengthen surveillance and intelligence
units (UNEP 2007)
No
deforestation
Biodiversity
management
Deforestation
Agricultural
practice
Use of pesticides and herbicides in
combination with monocultures
restricts biodiversity further.
Decrease of biodiversity due to
monocultures.
Drainage of
wet lands
Flooding down stream of drained and
degraded peat lands in Indonesia,
resulting from drainage and
compaction of peat lands and loss of
forest (ref: note 2 below).
In dry periods drained peat lands result
in low water flow and lower water
table, and may result in fires.
Salt water intrusion as a result of
drainage of peat lands.
Water use
Water
pollution
from run off
Water
Pollution
from
processing.
There are national moves in Indonesia
to ensure that current concessions are
properly planted and that sustainable
practices are adopted.
Decreases in biodiversity due to
clearance of forest (WWF 2003).
Fragmentation of high conservation
value forests. Specific species
mentioned: Orang-utans; Sumatran
elephant; Sumatran tiger and rhinos,
due to conflict with humans1.
Uncontrolled fires due to deforestation
contribute to the elimination of species
rich habitat (WWF 2003).
Drainage of peatlands results in habitat
and biodiversity loss.
Oil palm is only grown in areas of high
rainfall. Generally the impact on water
use is not high.
Leaching of pesticides and
agrochemicals can be significant.
Large scale
High organic strength effluents (palm
oil mill effluent, POME) can be treated
by anaerobic and aerobic treatment at
large-scale. There is evidence in
Indonesia that the effluent is not
treated and results in water pollution
1
Expansion and infrastructure support for
“ranger quick response units” to patrol
sensitive habitats (UNEP 2007).
Creation of buffer zones for wildlife.
Use of “flying squads” to drive elephants
away from plantations.
Training manuals for small farmers.
(Ardiansyah 2006).
Ban practice of slash and burn for forests.
Policies to conserve peat lands and stop
peat land draining and burning.
Sustainability policies in countries that form
major markets for palm oil.
Good agricultural management to decrease
use of pesticides and herbicides.
Use of buffer zones to increase habitat for
wildlife.
Land management, integrated pest
management, waste management
Improved water management in peatland
plantations, embedded in water
management master plans for peatland
areas.
Forest conservation and drainage avoidance
in remaining peat swamp forests.
Restoration of degraded peatland
hydrological systems and peat swamp
forests (Hooijer et al., 2006).
International recognition of the problem and
an internationally recognised peat land
conservation and management system.
Monitor status of surface and ground water.
Good agricultural management to decrease
use of pesticides and herbicides.
Ensure that better water treatment practices
are introduced and water pollution law are
enforced. Use of POME as animal protein
(Wahid et al 2004).
UN report (2007) The Last Stand of the Orang-utan: State of Emergency: illegal logging, fire and palm
oil in Indonesia’s national parks. This report found that forests in Indonesia and Malaysia are being
felled so quickly that 98% could be gone by 2022. See: www.unep.org/grasp/docs/2007Jan-LastStandof-Orangutan-report.pdf ) 700,000 ha of tropical forest in Malaysia have been cleared for palm oil
production and around 2 Mha of palm oil plantations in Indonesia have been planted on forest land
(0317). The lowlands of Sumatra and Kalimantan are considered to be among the most species rich on
earth. There are also potential impacts in parts of Africa, Papua New Guinea, Columbia and Ecuador
where palm oil plantations are under consideration. Lowland forest clearance in Indonesia is thought to
result in loss of 80% of species (WWF 2003).
30
Small and
medium scale
Soil health
Deforestation
or drainage of
peat land
Development
on degraded
land
Erosion
Effects on
food crops
and fish kill.
In Africa large-scale Government
plantations are being split up into
smaller units, where funds for efficient
processing are not available.
Smaller and medium scale producers
do not have the means to treat
effluents, which results in local water
pollution.
Development of acid sulphate soils in
coastal areas as a result of drainage of
peat lands.
Loss of soil organic carbon as a result
of deforestation.
Planting oil palm on degraded or
abandoned land should increase
organic matter in soil and improve soil
health, once the crop is established.
Plantations planted down slope on hills
have been shown to encourage erosion.
Once plantations are established soil
erosion potential decreases.
Currently the expansion of palm oil in
the Far East appears to be at the
expense of tropical forest or peatlands
rather than the displacement of food
production. However, there has been
little work on the displacement of
indigenous populations from these
regions and whether or not their food
supply has been affected.
Palm oil is an important food in Africa
and Asia. There are ambitious plans to
use palm oil for biodiesel, which
generally involve expanding
plantations and improving efficiency
of processing rather than switching
from food to fuel.
Forest and land fires to clear jungle,
cause “hazes” in South East Asia
(Ardiansyah 2006)
Air emissions
where forest
fires occur
Forest fires
GHG
emissions
From forest
and other
habitat
clearance.
Drainage and burning of peat land to
create new land for palm oil plantation
releases CO2 to the atmosphere
(Wetlands International). Figure:
600M t/year C released. “Production of
1 tonne of palm oil causes a CO2
emission between 10 and 30 tonnes
through peat oxidation (assuming
production of 3 to 6 tonnes of palm oil
per hectare, under fully drained
conditions, and excluding fire
emissions)."( Hooijer et al., 2006).)
Fires generate an estimated 1,400M t
of CO2 /year.
GHG
Emissions
Use of coproducts
The Palm oil processing industry can
be very efficient at the use of coproducts: empty branches can be used
as mulch; secondary oil is used for
soap; fibrous expeller is used as a fuel
for the processing plant (and is also
exported to the UK for use in cofiring) and the palm nut shell is used in
roads for the plantations. Co-products
are also used as an animal feed. This
31
Develop better practice for small and
medium-scale producers.
Forest conservation and drainage avoidance
in remaining peat swamp forests.
Restoration of degraded peatland
hydrological systems and peat swamp
forests.
Ensure oil palms are only planted on
suitable aspect. The impact of erosion from
plantation roads needs to be addressed.
There is little analysis on the potential for
biodiesel production from palm oil to
displace food production, as the production
of biodiesel is still quite low. However,
palm oil is an important food crop in the Far
East. The use of OSR for biodiesel in the
EU is causing increased demand for palm
oil for food in the EU. The impact of this
should be monitored.
Zero burning policies.
Prosecute deliberate starting of forest fires.
Zero burning practices add to land-clearing
costs by US$50-150 per ha (WWF 2003).
Policies to prevent the use of vulnerable and
high conservation value habitats and the
fragmentation of such habitats.
Overall
policies
use improves the GHG balance from
biofuels production from palm oil. If
there is no carbon emissions from land
use change then emissions savings of
about 35% can be realised.
Many of the more sustainable policies
and practices are too expensive or
difficult for small-scale producers.
Develop and share sustainable palm oil
practices, with big companies sharing
information with smallholders and funding
of initiatives by co-operatives of
smallholders.
3.3.1 Growth in production and consumption.
FAO (2003b) data indicates ‘growth in oil crops, vegetable oils and products has been
the fastest growth of all sub-sectors of global agriculture in recent times. Food
demand in the developing countries accounted for half the increases in world output
of the last two decades, with output measured in oil content equivalent. China, India
and a few other countries represented the bulk of this increase. Strong demand for
protein products for animal feed was also a major supporting factor in the buoyancy
of the oil crops sector. The rapid growth of this sector reflects the synergy of the two
fastest rising components of the demand for food: food demand for oils, favouring the
oil palm and for livestock products favouring soybeans.’ The oil palm produces large
yields of oil/ha compared with other crops and the seeds can be stored for a relatively
long time. As a result they can be transported long distances and pressed elsewhere.
In addition palm oil has good properties for both the food and oleochemical sectors.
These factors, together with its relatively cheap cost are responsible for the increase in
popularity of this crop.
Growth in oil palm production (in million tonnes of oil equivalent) rose from
2.1 Mt in 1964/66 to 21.6 Mt in 1997/99 and continues to rise (37.6 Mt in 2006/7).
The main countries in which oil palm is grown are: Malaysia (51%); Indonesia (34%);
Thailand (3.2%) Nigeria (2.6%) and Colombia (2.5%). African production tends to
be at a small or medium scale, with relatively inefficient processing; production in
Asia is at all scales including large plantations scale, with much more efficient
processing.
It is estimated that 11 Mha of oil palm is planted world wide, approximately 6
Mha in Indonesia. There have been rapid increases over the past 25 years and more
increases are planned. It is expected that Indonesia’s oil palm plantations will double
in the next 20 years (Casson, 2003; Ardiansyah, 2006). In Indonesia production is
planned in Kalimantan (up to 4 Mha) and Sumatra (Raiu, Jambi, Aceh, West Sumatra
and Kalimantan).
The four main palm oil importers are China (imports total 5.6 Mt, 21% of total
imports, up 0.6 Mt from 2005/06), the EU-25 (4.5 Mt, 17%, 4.1 Mt), India (3.8 Mt,
14%, 2.8 Mt) and Pakistan (1.8 Mt, 6%, 1.8 Mt). Palm oil is the world's most widely
used oil, contributing to 32% of global vegetable oil consumption, and, of this, 74%
of palm oil is used for food purposes. Currently some 24% of palm oil is used for
industrial purposes. This includes uses in the chemical industry, washing and
cleaning liquids, cosmetics and body lotions (Glastra et al., 2002). In recent years
there has been an expansion in the proportion of palm oil used for industrial purposes,
with only 16% being used in this sector a decade ago.
3.3.2 Biodiesel production
The use of palm oil for biodiesel production is relatively recent, and represents only
1% of biodiesel production at global level in 2006 (Thoenes, 2006). Most biodiesel is
made from rapeseed oil (OSR) (84%), followed by sunflower oil (13%) and then
32
soybean and other oils (2%). However, the use of OSR has a secondary effect on
other oils. Because the EU is using so much OSR for biodiesel it has increased its
imports of other oils (including sunflower and palm oil). Thoenes (2006) indicated
that EU palm oil imports doubled during the 2000-2006 period, mostly to substitute
for rapeseed oil diverted from food to fuel uses. The additional amount of oil that has
been sourced for Europe’s food market is some 2.5 million tonnes/year, with a
gradual increase since 2000. From 2000-2006 Europe’s palm oil imports doubled, as
indicated above. This has had an impact on global plant oil prices. Thoenes (2006)
estimates that imports of oils will increase by a further 1 and 1.5 million tonnes in the
periods to 2010 and 2015 respectively.
There are indications that European producers may increase their use of palm
oil if the recent high prices of OSR continue, as it is the cheapest suitable plant oil
(although the price of palm oil has recently increased as well). Some analysts also
point out that changes in US practices due to biofuels (planting maize rather than soy)
has lead to decreased soy availability and increased demand for palm oil as a
substitute (Times, 2008). This follows a long term decline in the palm oil price to
2005 (Thoenes 2006). In addition the Malaysian and Indonesian governments have
announced plans to allocate 6 Mt of palm oil to biodiesel each year. This represents
half their nation’s outputs (see below).
In addition to the European production of biofuels, the UK Home Grown
Cereals Authority (HGCA) states that ‘in Malaysia and Indonesia, the biodiesel sector
is growing rapidly, driven by the low cost of the palm oil feedstock. This was part of
the reason why, in mid-July, the two governments agreed a deal that limited annual
palm oil usage in biodiesel to 12 Mt. Concerns have been raised that supplies of palm
oil for food uses could be limited and that the destruction of large plantations of palm
trees could reverse the carbon savings made from using biodiesel rather than
conventional diesel. However, despite the new legislation, production of biodiesel in
Malaysia and Indonesia is forecast at up to 0.13 Mt in 2006/07, with further increases
expected in the next couple of seasons’. In addition, in 2003, Thailand launched an
ambitious oil palm expansion (to cultivate an additional 800,000 ha over the next four
years) in order to produce palm oil for biofuel production (FAO, 2003b).
There is some debate over what is causing the increase in deforestation of
tropical rain forest in lowland Indonesia, which according to the FAO represents 17%
of the global loss of rainforest between 2000 and 2005. There is no doubt that loss of
rainforest can be correlated with the increase in oil palm plantations since the 1970s
(see, for example, Brown and Jacobsen 2005, Greenpeace 2007, Nellerman et al.
2007). However, illegal logging and forest fires, which may or may not be a precursor
to oil palm plantations are also blamed for deforestation. The Roundtable on
Sustainable Palm Oil may ensure that palm oil is produced more sustainably in the
future. This, however, will do nothing to prevent logging, illegal or otherwise. It is
also difficult to provide statistics that clearly indicate whether illegal logging is
directly or indirectly related to displacement of land use for palm oil production.
The above-soil carbon held in a mature oil palm plantation is only a small
fraction of what old growth forests store. Primary forests in Indonesia have been
found to hold 306 tonnes of carbon per hectare (t C/ha), whereas mature oil palm
plantations hold 63 t C/ha (Boswell et al., 2007).
3.4
GHG emissions from LUC in Latin America
Land use changes and the effects on SOC have been studied in Brazil, especially in
the Brazilian Amazon (e.g. Cerri et al., 2003, 2004, 2007 cite over 50 papers). Cerri
33
et al. (2003, 2004, 2007) studied conversion of forest to pasture for cattle ranching
using simulation models, including RothC and Century, and experimental
measurements. They showed how conversion to pasture led to initial falls in SOC
stocks in the top 20cm soil layers, but in the majority of cases this was followed by a
slow rise to levels exceeding those under native forest. One exception to this pattern
was a degraded pasture. They conclude overall that well-managed pastures can be
useful in increasing SOC stocks after deforestation. In one study (Cerri et al., 2004)
reported how pasture SOC recovered, after about 10 years decline, to the original
SOC concentration in the top 0-20 cm layer, although loss of forest SOC continued, it
was exceeded by the accumulation of pasture SOC. It cannot, however, be assumed
that all conversion will be as well managed. It also needs to be remembered that these
measurements of SOC take no account of the loss of C sequestered in forest
vegetation, which is much greater than in the soil.
Calegari et al. (2008) reported how SOC in a once-forested part of Paranà,
decreased for about 10 years when cultivated for arable crops. This was followed by
increases in SOC at differing rates according to the management practices used over a
19-year period, particularly at different depths of soil. No tillage (NT) cultivation
sequestered more SOC in the upper soil layer than conventional plough-based tillage
(CT). Winter cover crops grown under no tillage cultivation was the most successful
method of increasing SOC storage and was the only method that approached the
original SOC content of forest soil and increased C storage at a rate of abut 1.2 t C ha1
year-1. Again, the possibility of restoring some lost SOC was demonstrated, but not
all management practices necessarily operate as effectively. The potential for
sequestration also varies with soil types, as some are more capable of protecting SOC
from degradation than others. Moreover, such estimates of the impact of NT on SOC
fail to recognise that increases in SOC concentrations take place only near the soil
surface and that the SOC content of lower horizons may decrease (Gál et al., 2007)
The impact of grazing on SOC in the Cerrado is less than on forest. Maquere
et al. (2008) reported that total C stocks to 1 m depth under pastures that had been
established for 20 and 80 years were numerically greater than, albeit not significantly
different to, total SOC to 1 m of native Cerrado. The total SOC estimated, at 84 t/ha,
was greater than the default value of 66 t/ha for Brazilian savannah cited by IPCC
(2006). This finding was consistent with the results of earlier studies cited in the
paper. However, when evaluating fluxes of CO2 to the atmosphere, it needs to be
remembered that only considering changes to SOC takes no account of changes in
above-ground carbon stocks which may be greatly reduced by land use change. The
current estimate of total carbon storage, both SOC and above-ground, is c. 360 t/ha
for Brazilian rainforest (IPCC, 2006).
It is clear that land use changes contribute to the loss of stored C, either from
soils or from wood that may be burned during deforestation. There is also the
potential for some recovery from the use of pasture or better arable cropping
practices. It is worth observing that UK soils generally lost SOC following the great
increase in arable cultivation both during and after the Second World War. These
changes should be approaching a new equilibrium about now, although the asymptote
may take another 100 years or so to be reached.
34
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