Modelling for improved irrigation water management in a temperate region of Northern Spain

This study refers to a region with temperate climate due to Atlantic influence and variable rainfall during the spring–summer season. Surface irrigation is traditionally practiced in this region, but this system is being progressively replaced by sprinkler irrigation. To assess the irrigation requirements and to select the most appropriate irrigation management practices, an irrigation scheduling simulation model was used after calibration/validation. Several alternative schedules were generated and evaluated according to impacts on yields and on percolation of excess applied water referring to each soil type and to conditions of very low, average, high and very high demand. Irrigation requirements under very low and very high demand conditions vary largely, in the range 124–358 mm for silage maize and 34–275 mm for grass pasture. Schedules refer to different soil water thresholds, and fixed (40 mm) and variable net irrigation depths, which range from 30 mm to 54 mm. Moreover, the different schedules were studied according to differences in the soil water-holding capacities of four soil types present in the area. In addition, the irrigation schedule previously proposed for supporting modernisation was evaluated. It showed an even worse performance in relation to those produced in this study. It was observed that, when sprinkler systems are well designed to produce high distribution uniformity, several alternative sprinkler schedules that minimise yield losses due to crop stress and percolation can be implemented. Findings suggest that a schedule with a constant application depth of 40 mm is best for immediate implementation, while a schedule with variable irrigation depths could be adopted when supported by a geographic information system and more sophisticated advisory facilities.