Irrigation water productivity trends in rice-wheat grown under partially reclaimed sodic soils

Productive use of water reflects better food and nutrition for families, more income, and productive employment. Targeting high water productivity can reduce the cost of cultivation of crops and lower energy requirements for water withdrawal. For several decades, researchers have made efforts to enhance water use efficiency. The primary objectives of these efforts were to conserve water rather than reflect the economic gains of water use. With the growing demand for water by sectors other than agriculture, the focus has changed, and the emphasis is more on the net economic return per unit of water used. This objective can be well addressed by assessing the water productivity of irrigation practices as the term water productivity is used to more accurately characterize the relationship between the output or income (such as biomass or yield) and the volume of water resource. At the same time, WUE measures the ratio or percentage of effective water demand to water consumption. Considering this concept, this paper presents the performances of different irrigation regimes in rice and wheat crops grown under a sodic environment regarding water productivity. The irrigation regimes are a combination of varying depths and varying irrigation schedules. In rice crops, ten combinations of irrigation regimes were developed by varying two irrigation depths (5 and 7 cm) and five scheduling techniques (2 DAD (days after the disappearance of ponded water), 3 DAD, 5 DAD, 7.5 kPa and 10 kPa in rice. Similarly, two irrigation depths (3 and 5 cm) and five scheduling techniques (30% SMD (Soil Moisture depletion), 50% SMD, 70% SMD, IW/CPE ratio -0.8 and IW/CPEratio 1.0 in wheat crop. One control each in rice and wheat considering farmers' practices in the area was considered for comparison. The results reflect that the irrigation regime of applying 5 cm irrigation depth at 3 to 5 DAD in rice may result in higher irrigation water productivity (IWP). The observed values of water productivity in rice were 1.18 and 0.9 when 5 cm irrigation depth was scheduled at 5 DAD and 3 DAD respectively. In the wheat overall irrigation regime, applying 5 cm irrigation depth at the IW/CPE ratio 0.8 performed better. The irrigation water productivity value observed in this case was 2.27 kg/cubic m of water used. The results were further analyzed to decide the best-performing schedule for the RW cropping systems by combining the results under different irrigation regimes. Applying 5 cm irrigation depth at 5 DAD in rice and at an IW/CPE ratio of 0.8 may lead to optimum water utilization and higher crop yield, in the RW cropping system,.