Water scarcity is usually the biggest yield-limiting factor in dry areas. Supplemental irrigation – providing small quantities of water at crucial growth stages, to supplement rainfall – can increase both yield and water productivity, which is the quantity of grain produced per unit of water used.
ICARDA researchers studied yield and water productivity in different crops, at different levels of supplemental irrigation. The results will help farmers make informed decisions on irrigation.
Using water more efficiently
Experiments were conducted at ICARDA’s Tel Hadya research station on five crops – bread wheat, durum wheat, faba bean, chickpea and lentil. Four levels of supplemental irrigation (SI) were tested, over multiple seasons: zero, full SI (enough water to fill the root zone profile), two-thirds of this amount (2/3 SI), and one-third of this amount (1/3 SI).
The results for grain yield illustrate two things: even small quantities of SI provide substantial benefits, and the incremental benefits taper off at higher SI levels.
For example, 1/3 SI gave large yield increases in all crops. Compared to zero- SI, yields increased by 180% in bread wheat, 206% in durum wheat, 93% in chickpea, 80% in lentil and 50% in faba bean.
With more irrigation, i.e. moving from 1/3 to 2/3 SI, yields continued to increase, but more slowly. Compared to 1/3 SI, yields increased by 22% to 36% in different crops. All five crops yielded the most grain under full SI, but in most cases, yields gradually began tapering off at higher SI levels.
Trade-offs between yield and water productivity
Maximum grain yield does not necessarily mean maximum water productivity. In areas with severe water shortages, it may be useful (for the national interest, if not for individual farmers) to maximize water productivity, even at the cost of slightly lower yields. Particularly in cereals, considerable amounts of water can be saved – for example by applying 2/3 SI rather than full SI – without a significant reduction in yield. The saved water can be used to irrigate other fields
These experiments are helping to measure the trade-offs between grain yield and water productivity. In bread wheat, for example, one option is maximum water productivity (12 kg/ha/mm) with a yield of 5.4 tons per hectare.
Another option is maximum yield (7 tons) with water productivity of 10.6 kg/ha/mm. Water productivity in wheat was highest at 2/3 SI. But for legume crops, water productivity was highest at full SI – highlighting the difficulties involved in making irrigation decisions in real-world farming systems.