Managing Scarce Water Resources in Agriculture in West Asia and North Africa - Restorative Redevelopment of Devastated Ecocultural Landscapes - page 462

i mProved W ater P rodUCtivity in i irrigated a griCUltUre
The WANA region contains vast deserts—about two-thirds of the region receives
less than 100 mm annual rainfall and about three-quarters of WANA receives less
than 200 mm annual rainfall (Table 22.1). If water (surface or subsurface) is avail-
able, irrigation is practiced. In these dry areas, irrigation agriculture produces most
of the food. However, water productivity is generally low and soil and water quality
are continuously declining. Soil salinity and water logging are other problems in
WANA irrigated areas. The root causes for these chronic problems in the irrigated
land are poor on-farm water management and lack of sufficient drainage and salt
leaching. Despite its scarcity of irrigation water in the region, it is still abused and
wasted. It has been reported that farmers, on average, apply 60 percent more water
than the crops need (Oweis et al. 2000).
In most WANA countries, water for irrigation is generally managed by public sec-
tors where local institutions are very weak. Policies of water allocation and use do
not provide incentive for water savings. Expanding irrigated areas without additional
water resources poses another source of pressure for more efficient use of water. The
return for irrigation water in the region is low, and varies from one crop to another.
However, substantial improvements in water productivity can be achieved by irriga-
tion management and adjusting cropping patterns.
Higher water productivity (yield per unit of water) is usually associated with
higher land productivity (yields per unit of land). This parallel increase in yields and
WP, however, does not continue positively all the way. At some high level of yield
incremental yield increase requires higher amounts of water to achieve. This means
that water productivity starts to decline as yield per unit land increases above certain
levels. This means that the amount of water required for producing the same amount
of wheat at high yield levels is higher than the water requirement at lower levels. This
is mainly due to increased losses of evaporation, etc. In this case and when water is
more limiting than land it would be more efficient to produce lower yield while the
saved water may better be used to irrigate new land than to produce maximum yield
with excessive amounts of water at low water productivity. For summer crop under
full irrigation, deficit irrigation also improves WP. This, of course, applies only when
water, not land, is limiting resource and without sufficient water to irrigate all the
available land.
The association of high water productivity values with high yields has important
implications for the crop management for achieving efficient use of water resources
in water scarce areas. Policies for maximizing yield should be considered carefully
before they are applied under water-scarce conditions. Guidelines for recommending
irrigation schedules under normal water availability may need to be revised when
applied in water-scarce areas.
The identification of appropriate crops and cultivars with optimum physiology,
morphology, and phenology to suit local environmental conditions is one of the
important areas of research within cropping system management for improved water
productivity. Under water scarcity many crops may be phased out of economical
production. In many countries of WANA, inefficient crops are still being produced
with very high water costs.