Determination of optimal regulated deficit irrigation strategies for maize in a semi-arid environment

For a certain overall deficit target, this paper develops a methodology (Optimized Regulated Deficit Irrigation (ORDI)) for determining the stress level (in terms of the rate between actual crop evapotranspiration (ETa) and maximum evapotranspiration (ETm)) that can be applied to each growth period for maximum yield. ORDI is based on the equation proposed by Stewart et al. (1977) and compatible with the MOPECO model. Once the equation is calibrated and validated, ORDI just requires adjusting the determining factors for optimization. Parameters required for the simulation of maize through the equation proposed by Stewart et al. (1977) were calibrated and validated using the experimental data from a three-year maize field trial (2001, 2002 and 2003) under deficit irrigation conditions in Castilla-La Mancha (Spain). The area is classified as semi-arid and the stress levels applied to the crop ranged between 0 and 60% of ETm. The same data were used to validate the use of ORDI in a maize crop through adjusting the determining factors for optimization. Climatic data from the years 2001-2008 were used for calculating the theoretical average distribution of stress, by growth stage, that leads to maximum yield for four overall stress levels (0.6, 0.7, 0.8, and 0.9). These results were inserted in MOPECO to simulate the behavior of a maize crop subjected to different deficit irrigation strategies under the climatic conditions of the years 2009-2011. Depending on the applied stress level and the restrictions imposed to the optimizer, ORDI may increase yield by 10-20% and gross margin up to 167 (sic) ha(-1) compared with an irrigation strategy where the stress level remains constant during the whole growth cycle. Hence, for low water stress conditions, deficit irrigation should be applied during the initial and vegetative development stages. For medium and high water stress conditions, higher deficit should occur during the ripening and grain filling stages. Lastly, this methodology can be applied to schedule the levels of water stress to be applied in future experiments on deficit irrigation with herbaceous crops such as maize. (C) 2012 Elsevier B.V. All rights reserved.