A modeling approach for agricultural water management in citrus orchards: cost-effective irrigation scheduling and agrochemical transport simulation.

The water flow and the mass transport of agrochemicals in the unsaturated and saturated zone were simulated in the extended alluvial basin of Keritis river in Crete, Greece (a predominantly flat and most productive citrus growing area) using the hydrological model MIKE SHE. This model was set up based on information on land use, geology, soil structure, meteorological data, as well as groundwater level data from pumping wells. Additionally, field measurements of the soil moisture at six different locations from three soil depths (0.1, 0.2, and 0.3 m) were used as targets to calibrate and validate the unsaturated flow model while for saturated condition, groundwater level data from three well locations were used. Following the modeling approach, the agrochemical mass transport simulation was performed as well, based on different application doses. After the successful calibration processes, the obtained 1D modeling results of soil moisture-pressure related to soil depth at different locations were used to design a proper and cost-effective irrigation programme (irrigation timing, frequency, application rates, etc.) for citrus orchards. The results of the present simulation showed a very good correlation with the field measurements. Based on these results, a proper irrigation plan can be designed at every site of the model domain reducing the water consumption up to 38% with respect to the common irrigation practices and ensuring the citrus water productivity. In addition, the effect of the proposed irrigation scheduling on citrus yield was investigated. Regarding the agrochemical concentration in the groundwater for all dose cases was below the maximum permissible limit. The only exception was for the highest dose in areas where the water table is high. Thus, this modeling approach could be used as a tool for appropriate water management in an agricultural area estimating at each time and location the availability of soil water, contributing to a cost-effective irrigation plan.