Economic value and water productivity of major irrigated crops in the Ogallala aquifer region

Crop water productivity and return after variable cost for three major crops (winter wheat, grain sorghum and maize) in the southwest Kansas were evaluated based on simulated yield using the Decision Support System for Agrotechnology Transfer - Cropping System Model (DSSAT-CSM). Winter wheat and grain sorghum were treated with four irrigation capacities (ICs) (zero, 1.7, 2.5 and 5 mm/day) and an automatic irrigation (irrigation when required). Maize was treated with three ICs (0, 2.5 and 5 mm/day) and an automatic irrigation. Long-term simulations showed that average winter wheat, grain sorghum and maize yields can be stabilized under 1.7–2.5, 2.5 and 5 mm/day ICs with corresponding irrigation of 100–150, 100–250 and 450–500 mm, respectively. The crop water productivities of winter wheat, grain sorghum and maize ranged from 9.8 to 11.8, 12.8–15.0 and 4.2–19.1 kg/ha/mm, respectively. Maize was found to be profitable when grown under both deficit and full irrigation conditions although optimal irrigation application for maize substantially increased the net return after variable cost (RAVC). The median net return after variable cost for rainfed wheat ($252/ha) and grain sorghum ($180/ha) was greater than that for irrigated wheat ($169–$192/ha) and grain sorghum ($104–$110/ha). The RAVC for wheat and grain sorghum did not rise with increase in irrigation and IC, whereas the RAVC for maize increased with irrigation and IC. The lowest and highest RAVC for maize corresponded to IC of 0 ($16/ha) and 5 mm/day ($530/ha). However, this income from growing maize under higher IC may not last long due to rapidly depleting groundwater levels in the underlying Ogallala aquifer. Therefore, the short-term benefits of growing maize under higher ICs need to be compared with the long-term environmental impact, food security and employment opportunities including sustaining the growing municipal and industrial water needs.