Development and field validation of a decision support system for irrigation scheduling of open field vegetable crops based on determining soil evaporation and plant transpiration

Usually, irrigation scheduling is based on a soil water balance approach that considers reference evapotranspiration and crop coefficients as inputs. However, this procedure is based on an empirical database of crop coefficients available from the literature and it does not take into account field variability in canopy vigour, among other factors. This study compared a novel irrigation model (Riego-Asesor, RA), that separately determines soil evaporation and plant transpiration, with the standard irrigation farmer practices (F). Three experiments, two in endive and one in muskmelon, were carried out in south-eastern Spain. The irrigation volume applied, crop aboveground biomass, water content, relative chlorophyll content (SPAD) and yield were determined. The results showed water savings up to 7.5% in the RA treatment when compared with the F treatment. Water savings were limited because the farmer’s watering regime was already well adjusted to the crop water needs and because of the leaching fraction applied due to the high salinity level of the irrigation water. No statistically significant differences in aboveground biomass, water content, SPAD and yield were observed between treatments. The results confirmed that the proposed model mimics quite well the farmer’s irrigation scheduling without employing on-the-ground sensors. Nevertheless, further developments are needed in order to better estimate the leaching fraction and to determine evapotranspiration under deficit irrigation conditions.