Managing Scarce Water Resources in Agriculture in West Asia and North Africa - Restorative Redevelopment of Devastated Ecocultural Landscapes - page 459

increased the benefit by over 50 percent compared with that of the farmer's usual
practice of over-irrigation.
In the highlands of the WANA region, frost conditions occur between December
and March and put field crops into dormancy. Usually, the first rainfall, sufficient
to germinate seeds, comes late resulting in small crop stand when the frost occurs
in December. Rainfed yields as a result are much lower than when the crop stand
pre-frost is good. Ensuring a good crop stand in December can be achieved by early
sowing and applying 50 mm of supplemental irrigation in October. SI given at early
sowing dramatically increases wheat yield and water productivity. Applying 50 mm
of SI to wheat sown early has increased grain yield by more than 60 percent, adding
more than 2 t/ha to the average rainfed yield of 3.2 t/ha (Ilbeyi et al. 2006). Water
productivity reached 4.4 kg grain/m 3 of consumed water (Figure 22.8). These are
extraordinary values compared to water productivity values of wheat of 1-2 kg/m 3 .
SI alone, although it alleviates moisture stress, cannot ensure highest performance
of the rainfed agricultural system. It has to be combined with other good farm man-
agement practices. Of most importance is fertility, particularly in the Mediterranean
region where nitrogen is usually the main deficiency. Absence of nutrient deficiency
greatly improves yield and water use efficiency. Other areas may have different defi-
ciency levels of N or deficiencies in other elements (Figure 22.9). It is always impor-
tant to eliminate these deficiencies to get potential yield and WP.
The use of supplemental irrigation is an example of a concurrent change in both
management practice and water-responsive cultivars to increase water productiv-
ity. The proper varieties need first to manifest a strong response to limited water
applications, which means that they should have a relatively high yield potential. At

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6.2

5.9

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3.1

3

2

2

1

0.8

1

0

Rainfed Sowing SI Deficit SI Full SI

Grain yield (t/ha) Water productivity (Kg/m 3 )

FIGURE 22.8 Wheat grain yield and water productivity at the central Anatolia plateau of
Turkey's highlands under three types of SI management (Sowing SI: 50 mm of SI at sowing
only; Deficit SI: sowing SI plus deficit SI during spring; Full SI: sowing SI plus full SI during
spring) compared to rainfed case. (Adapted from Ilbeyi, A., Ustun, H., Oweis, T., Pala, M.,
Benli, B. 2006. Wheat water productivity and yield in a cool highland environment: Effect of
early sowing with supplemental irrigation. Agricultural Water Management 82:399-410.)