Environmental Engineering Reference
In-Depth Information
spring. As a consequence, terminal drought stress occurs causing low yields. This
was avoided by early planting with cultivars developed by ICARDA that are cold
tolerant. On-station as well as on-farm trials have demonstrated that increases in
yield and water productivity of 30 to 70 percent are possible by adopting early
sowing. Currently, winter chickpea is spreading fast among the farmers in the
WANA region.
In the winter rainfall environment of the WANA region, delaying the sowing
date will prevent crop germination and seedlings establishment because of the
rapid drop in air temperature starting generally in November. In the lowlands of the
Mediterranean region, where continuous cropping prevails as pure cereal or cereal-
legume rotations, mid-November was found to be an optimum sowing time for cere-
als. Every week delay after this time results in a 200-250 kg ha
-1
yield decrease.
If the onset seasonal rain is delayed, early sowing can be realized with the help of
supplemental irrigation systems.
Methodologies to help farmers determine the appropriate supplemental irri-
gation management have been developed. Since rainfall amount cannot be con-
trolled, the objective is to determine the optimal amount of SI that results in
maximum net benefit to the farmers. Knowing the cost of irrigation water and the
expected price for a unit of the product, maximum profit occurs when marginal
product for water equals the price ratio of water to the product (Figure 22.11). The
figure shows the optimal amount of SI to be applied under different rainfall zones
and various price ratios.
450
250
300
350
400
450
500
400
350
300
250
200
150
100
50
0
0
0.4
0.8
1.2
1.6
2
2.4
2.8
3.2
Ratio of Unit Water Cost to Unit Product Sale Price (C/P)
FIGURE 22.11
Optimal seasonal depth of supplemental irrigation of durum wheat at
Aleppo, Syria versus the ratio of unit water cost to unit wheat grain sale price for different
probable seasonal rainfall (mm).
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