Modeling the effects of different irrigation schedules and drain depths for soil salinity management: A case study from Southern Iraq

Abstract

Soil-water-atmosphere-plant (SWAP) relationship model is used to evaluate the impact of current irrigation practices on groundwater table depth, soil salinity and crop yields and to determine optimal irrigation requirements and drain depth for the study area. The results indicate that current irrigation practices of applying 600 mm to wheat and 1000 mm to maize are wasting more than 30% of applied irrigation water as deep percolation, which causes rise in groundwater table, increase in profile salinity and reduction in crop yields. The simulation results reveal that in the absence of an effective drainage system in the study area, a groundwater table depth of approximately 200 cm together with an irrigation application of 5000 m 3 ha -1 for wheat and 6000 m 3 ha -1 for maize will be the most appropriate combination for obtaining optimum yields of wheat (3.0 t ha -1 ) and maize (1.80 t ha -1 ). However, to achieve potential yields, leaching of excessive salts from the root zone through freshwater application would be essential. Therefore a drainage system in these areas should be installed to maintain groundwater table depth around 200 cm. Installation of deeper drains would not be feasible as it will increase the costs and without much gains in crop yields.