Download Fertile soils: friend or foe of a clean environment? -the

Fertile soils: friend or foe of a clean
environment?
-the role of soil analysis([email protected])
Content
 Perceptions of soil fertility
 Relationships between fertilizer use and losses
 Handles to reduce losses
 Limiting nutrients: Von Liebig at work
 Is SMN analysis informative?
 Are P recommendations too blunt?
 Is extensification prudent?
 Conclusions
Many perceptions of a fertile soil....

‘Not any richer than what should be tolerated from a water quality point of
view’,
Many perceptions of a fertile soil....

‘Not any richer than what should be tolerated from a water quality point of
view’,

‘Providing all ecosystem services, crop production being (just) one of them’,
Many perceptions of a fertile soil....

‘Not any richer than what should be tolerated from a water quality point of
view’,

‘Providing all ecosystem services, crop production being (just) one of them’,

‘Balanced availability of all nutrients required by crops in most years’,
Many perceptions of a fertile soil....

‘Not any richer than what should be tolerated from a water quality point of
view’,

‘Providing all ecosystem services, crop production being (just) one of them’,

‘Balanced availability of all nutrients required by crops in most years’,

‘Ample availability of all nutrients, also under exceptional weather conditions’,
Many perceptions of a fertile soil....

‘Not any richer than what should be tolerated from a water quality point of
view’,

‘Providing all ecosystem services, crop production being (just) one of them’,

‘Balanced availability of all nutrients required by crops in most years’,

‘Ample availability of all nutrients, also under exceptional weather conditions’,

‘Maintenance of status quo, regardless crop requirements’,
Many perceptions of a fertile soil....

‘Not any richer than what should be tolerated from a water quality point of
view’,

‘Providing all ecosystem services, crop production being (just) one of them’,

‘Balanced availability of all nutrients required by crops in most years’,

‘Ample availability of all nutrients, also under exceptional weather conditions’,

‘Maintenance of status quo, regardless crop requirements’,

‘Excess application of some nutrients (e.g. P) should be OK, if that happens to
be the inevitable consequence of the N source that I like to use’.
Generic relationship between fertilizer use and losses
Handles to reduce losses to the environment
Justus Von Liebig’s Law of the Minimum: the shortest
stave determines the utilization of all other resources
P is needed to utilize N
N is needed to utilize P
Environmental regulations complicate the quest

Find!: the
combination of
manure and
mineral fertilizer
N that complies
with 50 mg
nitrate per litre
target (solid
line), with a
balanced P input
(dashed line),
and with both
(solid dot)
(Schröder et al.,
2007)
Which nutrient is most limiting?

Global crop production by definition limited by N due to inevitable losses from
soils (N2, N2O, NO3, NH3, NH4) and ‘downstream losses’ (livestock housing,
industries, private households, waste treatment plants)
N/P2O5 ratios in crops and manures*
(Schröder & Sörensen, 2011)
Grassland
3.7
Silage maize
3.3
Wheat grain
2.6
Cattle slurry
1.2-2.3
Cattle FYM
1.0-1.5
Pig slurry
0.8-1.4
*including residual N effects of manures

Does that justify a focus on analyzing soils for N?

Is the presence of other nutrients to be taken for granted?
Limiting nutrients
 Is the presence of other nutrients to be taken for granted?
● ‘new’ inputs from atmospheric deposition, weathering,
and flooding compensate insufficiently for ∑(exports,
leaching, acidification, fixation), so: NO!
● Demands of K, Mg, Ca, CO32-, S!, P and micronutrients:
● Justify the use of organic fertilizers
● Make it impossible to rely on just NPK fertilizers
● Justify regular soil analysis
 And what about soil analysis of SMN?
Are SMN analyses informative?
 Soil mineral N (SMN) in late winter or early spring?:
● little variation unless manured in preceding period,
● too early, not indicative of potential mineralization
Are SMN analyses informative?
 Soil mineral N (SMN) in late winter or early spring?:
● little variation unless manured in preceding period,
● too early, not indicative of potential mineralization
 Late spring (post-emergence) SMN, facilitating conditional inseason N application(s)?:
● not always feasible or effective
Are SMN analyses informative?
 Soil mineral N (SMN) in late winter or early spring?:
● little variation unless manured in preceding period,
● too early, not indicative of potential mineralization
 Late spring (post-emergence) SMN, facilitating conditional inseason N application(s)?:
● not always feasible or effective
 Still under study: soil organic N%, hot water extractable N?:
● better than nothing but as yet not very reliable
Are SMN analyses informative?
 Soil mineral N (SMN) in late winter or early spring?:
● little variation unless manured in preceding period,
● too early, not indicative of potential mineralization
 Late spring (post-emergence) SMN, facilitating conditional inseason N application(s)?:
● not always feasible or effective
 Still under study: soil organic N%, hot water extractable N?:
● better than nothing but as yet not very reliable
 Alternative guesstimate: field records of manuring history
(number of years, manure type, rates)
Fate of one application of 100 kg organic N per ha: 25% mineralizing in 1st year,
13% in 2nd year, 8% in 3rd year 6% in 6th year, 3% thereafter (Schröder et al.,
2013)
Experiments lasting one year reflect nothing more
than just the 1st year contribution, and so do
recommendations based on them
Fate of two consecutive applications
Fate of three consecutive applications
Fate of four consecutive applications
Fate of five consecutive applications
Fate of fifty consecutive applications
In summary:
 SMN analysis does not acknowledge residual N effects
 Reliable alternative soil tests are not available
 Most field experiments do not reveal residual N effects of
organic inputs
 Recommendations to farmers are generally inspired by
numbers from these short-term experiments only
 So, re-thinking of residual contributions is urgently
needed
Are present P recommendation too blunt?

Many crops are only in
need of excessive P
supplies during the
juvenile stage and in a
specific part of the soil
profile

We yet apply the
required P as if it is
needed every day of
the season in every
cubic centimetre of
soil.....

P placement saves
fertilizer and
reduces loss risks!
Schröder et al. (2015) Eur. J. Agron. 64, 29-36.
Extensification: tempting but not always prudent
Typical response of grain yield to N in intensified and
Attending N surplus (input – output) per unit area
extensified systems
and per unit yield and land consumption
Intensive Extensive
kg N surplus per ha 16.6
15.0
kg N surplus per ton grain1.9
2.0
ha per ton grain
0.11
0.13

no gains in terms of total N loss to water or wilderness
conservation, if the same volume of grain is to be produced

admitted: extensification may be considered for the benefit of infarm biodiversity
Conclusions
 Soil fertility: a balanced availability of all nutrients required by
crops in most years
 Nutrient losses can be limited, not avoided
 N is a blessing for yields, a burden for water
 Utilization of N can, ironically, hardly be supported by soil
analyses of N itself, but the more so by checking the sufficient
presence of the other growth factors
 Room for improvement:
● Better account of residual N effects
● More refined recommendations for P
 ‘Sustainable’ intensification to be preferred over extensification
Thank you for your attention