Download 2.3 Improving water-use efficiency in dryland cropping

2. Improving the Productivity and EffIciency of
Food Crop and Forestry Systems
2.3 Improving water-use efficiency in
dryland cropping
Background
Key strategies
‘Dryland cropping’ refers to those rainfed
agricultural areas where the average water
supply to the crop limits potential yield to less
than 40% of full (water-unlimited) potential.
On this basis, 25% of the world’s cereal
production is dryland. Some techniques aim
to increase water supply per crop by
improving the efficiency of water storage
in fallow periods, reducing run-off during
the crop, or increasing root zone water
extraction. Often, however, production is
actually constrained by poor plant stand, low
fertility, disease, poor timing, waterlogging,
weeds etc. Nevertheless, water supply does
pose an upper limit on yield.
Improved cultivars bred for resistance to
dryland stresses can combine with other
approaches to improving dryland
productivity, including adequate soil fertility,
proper crop establishment and good weed
control. Under dryland conditions, planting
time and management of soil fertility become
more critical. Maintaining adequate soil
fertility can improve sustainability as well
as productivity, but reducing rainfall run-off
by maintaining a cover of plant material
on the soil surface, often known as
conservation tillage, best exemplifies a win–
win technology. Water supply to the crop
is increased and water erosion reduced.
Conservation tillage carries several
drawbacks, these being the need to invest
in new tillage and seeding machinery, the
need to forego the removal of the residue of
crops and pastures for forage, and the need
to resort to herbicides for weed control. There
is also often cultural resistance to reducing
tillage. However, the benefits are potentially
so large that research on ways around the
obstacles is high priority.
In the developing world, dryland farming
areas tend to be characterised by high
poverty, as well as serious soil degradation
from overgrazing and erosion. Because of
the predominance of dryland farming and
the integration of cropping and livestock
activities on most farms in temperate as
well as subtropical regions, Australia has
always had a good comparative advantage in
dryland farming research. Research, however,
is grappling with the main factors affecting
the sustainability of dryland cropping in
developing countries, such as structural
decline and erosion of soil, soil acidification,
dryland salinity, limited crop diversity, and
herbicide resistance.
The damage caused to root systems by
soil diseases and nematodes may be worst
under dryland conditions, especially with
continuous cereal monoculture. The other key
approach to reduction in losses is the use
of non-host crops in rotation with cereals
(e.g. mustard or canola). This complex change,
difficult for farmers to adopt, has been
strikingly successful in southern Australia, and
similar crop rotation research is very relevant
in developing countries.
2.3 Improving water-use efficiency in
dryland cropping
Improving the Productivity and EffIciency of Food Crop and Forestry Systems
In developing countries, ruminants are usually
part of dryland farming systems and they
are fed on weeds taken from crops, salvage
crops, crop stubbles, weedy fallows, and
pasture on adjacent marginal lands. There
is no ley farming (as in Australia), and few
special-purpose pastures. Animals are always
corralled at night. The return of manure to
the fields is important to the nutrient cycle
but inefficient and insufficient, except for
fields close to the corral. Animals produce
valuable income in dry regions and research
to integrate them into the dryland cropping
system could include new feed sources such
as leguminous forages. The general shortage
of water, means there is little or no scope
for biophysical complementation between
annual crops and trees, and hence little point
in mixing stands of annuals and trees.
Run-off can readily be captured in the
subtropics, and local water harvesting for
cropping is important to the drylands of many
developing countries. Although strategic
supplemental irrigation can increase wateruse efficiency in grain crops, it rarely makes
economic sense to use expensive water for
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Australia
this purpose. Inevitably, there is better return
from higher value crops, such as out-of
season horticulture. Finally, dryland cropping
is the heart of agricultural system modelling,
because the major input, soil water supply,
has been thoroughly quantified, and can even
be predicted with some accuracy through
seasonal forecasting, and because its effect on
most crops is also well quantified.
Implementing the strategies
Adoption of new practices may be slowed
by the riskiness of dryland environments,
but many of the improvements listed above
can reduce the risk. However, complex
interventions are unlikely to be adopted
quickly or fully. Research into dryland
cropping will require special attention to
adoption pathways and must involve farmer
participation.
ACIAR will favour research into techniques for
improving productivity and sustainability in
dryland cropping that have a high chance of
success and good prospects for widespread
adoption by dryland farmers.
Phone: +61 2 6217 0500
Email: [email protected]
Fax: + 61 2 6217 0501
Web: <www.aciar.gov.au>