Potential of Deficit Irrigation As a Water Conservation Strategy in Water Limited Areas.

Current rates of irrigation water use are unsustainable in many regions, creating an urgent need to identify optimal irrigation strategies for water limited areas. Crop models, like DSSAT, can be used to quantify crop water requirements and predict the impact of water shortages on crop yield. To simulate large areas or future yields, automatic irrigation algorithms are generally used to estimate irrigation dates and amounts. However, these algorithms are not well suited for the study of deficit irrigation strategies under water limited conditions.

To address this constraint, we: (1) developed a new automatic deficit irrigation algorithm for the DSSAT v4.6 crop modelling platform for the simulation of automatic deficit irrigation under limited seasonal water availability, and (2) deployed the new model across the continental US to investigate the potential application of deficit irrigation to mitigate water shortages. The model was first deployed across the continental US without water restrictions. Water supply was subsequently quantified using survey and modeling data. The deficit irrigation algorithm was finally used to estimate the best growth stage specific automatic irrigation VWC thresholds for triggering irrigation applications at each water limited location.

Preliminary results show that, consistent with experimental evidence, higher yields per unit of water irrigated are achieved in CERES-maize with preferential irrigation between panicle initiation and the end of leaf growth. In a similar manner, prioritizing reproductive stages in CROPGRO-soybean produced significantly higher yields per unit water than prioritizing the vegetative stages. The model simulations of plant water stress were in good agreement with experimental observations for a wide range of irrigation regimes and yields. Optimized irrigation schedules based on volumetric water content (VWC) thresholds produced up to 32% more grain weight than uniform deficit irrigation applications throughout the season scheduled based on potential evapotranspiration.