Irrigation scheduling to maximize crop gross margin under limited water availability

Abstract

MOPECO uses the optimized regulated deficit irrigation (ORDI) methodology to determine the irrigation schedule that maximizes the gross margin (GM) of annual crops when the availability of irrigation water is limited. To this end, it is necessary to determine the functions that relate GM to the gross irrigation water (IG) supplied to the crop. Given that MOPECO is designed for implementation by farmers using online tools, the time required to obtain the “GM vs. IG” function must be low. Thus, the objective was to develop and validate a methodology to generate the most accurate “GM vs. IG” function with a low calculation time that takes into consideration the effect of irrigation uniformity on final yield. Five sub-models were developed and evaluated with barley, onion and maize for the semi-arid conditions of Castilla-La Mancha (Spain). The sub-models included one or more of the following variables: yield (Y); effective precipitation (Pef); soil moisture (S); and its distribution uniformity at plot level (CU). The sub-model “Y-Pef-S-CU” achieved the best fitting. The other sub-models (Y, Y-Pef, Y-Pef-S, and Y-Pef-CU) provided solutions that were very close to the optimum, with low calculation time. Nevertheless, the best fit of each sub-model to the optimum function was achieved in different sections of this function. Therefore, the five sub-models are complementary, and it is advisable to use them simultaneously thanks to their low calculation time requirements (3.9 s). The validation with the three crops showed that in farms where irrigation uniformity and water price are low and harvest price is high, it is economically advisable to apply higher irrigation depths than the crop irrigation requirements. Nevertheless, as improving agricultural water productivity is key for sustaining the environment, tools like MOPECO may help to maximize GM and increase water use efficiency by means of deficit irrigation strategies.