Evaluating deficit irrigation scheduling strategies to improve yield and water productivity of maize in arid environment using simulation

Water scarcity and rising temperatures are creating serious concerns over the sustainability of agriculture systems in arid regions of the Middle East and North Africa. The aims were (i) to calibrate and evaluate the Decision Support System for Agrotechnology Transfer (DSSAT) model using detailed experimental datasets on maize (Zea mays L.) yield and water productivity in an arid Mediterranean environment and (ii) to determine the impacts of various irrigation scheduling strategies on maize yield and water productivity in arid sandy soils and produce irrigation scheduling recommendations that maximize the marginal benefit per unit water applied. The goodness-of-fit statistics comparing the observed and simulated crop phenology, grain yield, dry matter, evapotranspiration (ET), and soil water content indicate that the model simulates these crop and soil variables reasonably well for a medium-maturity maize hybrid (similar to 110 days to physiological maturity) commonly grown in the study region. Long-term simulations (1984-2018) using the well-calibrated model were performed and included three irrigation scheduling strategies: (i) soil water-based irrigation scheduling, (ii) ET-based threshold irrigation scheduling, and (iii) growth-stage ET-based irrigation scheduling. In the soil water-based, four levels of maximum allowable depletion (MAD) of available soil water content (AWC) were tested using the auto-irrigation option of DSSAT. Results indicated that MAD 50% is recommended for scheduling irrigation in arid sandy soils for potential irrigation water saving without unacceptable yield loss. The ET-based threshold consisted of a combination of four cumulative net ET threshold (ETH) triggers of 14, 21, 28, and 35 mm and five ET replacement levels of 50%, 70%, 90%, 110%, and 130% ET using the DSSAT ET-based auto-irrigation option. Based on this irrigation strategy, it is more favorable to irrigate at the high frequency of ETH 14 or 21 mm than low frequency of ETH 35 mm, even when replacing 130% ET, as high drought-stress during the crop development and reproductive stages were observed for ETH 35 mm due to the omission of key irrigation events. In the growth-stage ET-based, two levels of irrigation of 100% ET and 60% ET estimated based on the crop coefficient approach were tested with different combinations of targets during the vegetative and reproductive growth stages. Results indicated that meeting crop ET requirements during the reproductive stage is more essential than during the vegetative stage for greater yield and enhanced WUE, particularly when available seasonal irrigation water is less than seasonal full crop ET requirements. In water limited environments, reasonable yield and enhanced WUE can be achieved by applying a deficit rate of 40% ET during the vegetative stage and 80% ET during the reproductive stage or scheduling irrigation based on soil water content to ensure AWC of 30% in the top 0-30 cm soil layer throughout the growing season. Concepts developed in the present study can be adapted to effectively manage irrigation scheduling for medium-maturity maize hybrids in arid sandy soils with low AWC and organic C content.