| Rainfed
agriculture and natural ecosystems have in common
that they both depend on the 60% of the rainfall that
does not make it into rivers or aquifers, but is stored
directly in the soil as “soil moisture”
- the green water. Increasing the productivity of
green water used in rainfed agriculture has great
potential to reduce the area needed for agriculture.Agricultural
production of staple crops in Africa, has, over the
last 40 years, increased almost exclusively by area
expansion, at the cost of large areas of natural ecosystems.To
enable sustainable increases in food production in
Africa, agricultural intensification is absolutely
necessary. Increasing the productivity of green water
used in rainfed agriculture - particularly by adding
a limited amount of blue water (from rivers or aquifers)
through supplemental irrigation has great potential.
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| ACTIONS
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| Rainwater
harvesting
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Capturing a larger share of rainfall close to
where it falls not only increases the water
available to plants and people in that location,
but also prevents soil erosion. Rainwater harvesting
can focuson: (1) capturing water for domestic
use, e.g. by collection of rain falling on rooftops
in
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cisterns; or (2) replenishing
green water, e.g. through stone bunds on the contour
line; or (3) increasing blue water available locally,
e.g. through small check dams that either increase
recharge to the groundwater or store water in
small reservoirs. Rainwater harvesting has been
used successfully by hundreds of thousands of
communities, particularly in India, to increase
water for domestic, agriculture and ecosystem
uses. It has brought rivers back to life. But
practised on a large scale in upper watersheds,
it will reduce water available further downstream.
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Rain water harvesting in
Ruhuna Basin,
Sri Lanka
Photograph by Dominique Perera, IWMI
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| Supplemental
and micro irrigation
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Supplemental irrigation with about 100mm of
water, provided during crucial drought spells,
can double rainfed yields from about 1 to 2
tonne of cereals per hectare, increasing water
productivity to 0.5 kg per cubic meter of water
consumed. There are many technologies for supplemental
irrigation that range from farm ponds to micro-irrigation
with shallow groundwater pumped with treadle
pumps.
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Photograph by Frank
Rijsberman, IWMI
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| Increased
infiltration and reduced runoff through land
and water conservation
Improving productivity of rainfed
systems through improved land management techniques
and agricultural production systems.Use of terracing,
contouring and micro-basins are important measures
in maximizing rainfall infiltration into the
soil to increase yields, especially for farmers
in Sub-Saharan Africa, Latin America and South
Asia. Conservation or zero tillage - where crop
residue is used as mulch - is a promising technology.
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FACTS AND FIGURES
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Green
water is represented by the 60% of rainfall
that does not end up in rivers or quifers.
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Green
water exists as soil moisture until it
is evaporated from wet soils or transpired
through plants.
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Approximately
75% of the poor depend on rainfed agriculture
for their livelihoods
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In
Sub-Saharan Africa > 90% of population
depends on rainfed agriculture which generates
between 30-40% of GDP
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Water
productivities of 5000 m3 water/tonne
grain, are common in rainfed systems in
semi-arid regions such as SSA and parts
of Asia.
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The
untapped potential of rainfed systems
is approximately the equivalent of doubling
yields. |
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DEBATES
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Some
experts believe rainfed systems do not
hold more potential. Skeptics
point out that rainfed agriculture has
been the focus of research for many years,
that ideas have been in place for a long
time, yet gains are not forthcoming, and
thus rainfed systems do not hold as much
promise as claimed. |
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Others
believe that evidence exists for greater
potential and poverty reduction from new
approaches to enhancing rainfed agricultural
systems. New propoor small-scale,
low-cost approaches such as treadle pumps,
water bags, and water harvesting are proving
to be the key to unlocking rain-fed potential
and reducing poverty on marginal rainfed
lands. |
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Dependence
on approaches to enhancing rainfed agriculture
involves high risk due to climate variability,
particularly affecting small and poor
farmers. Thus investing in water
resources development and management to
increase the coping ability with rainfall
variability, through methods ranging from
building dams to drought-proofing crops
are crucial. |
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Not
just technologies are needed.
Socio-economic and institutional interventions
are also needed to achieve greater gains
in use of green water. There is a need
for distributed expertise and decentralization. |
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Click
to enlarge
Table of Summary adoption and impact of agricultural
sustainability technologies and practices
on 286 projects on 57 countries. From: Pretty
et al. 2004
Source: IWMI |
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