Advances in Calibrating SALTIRSOIL at Plot Scale: First Results

SALTIRSOIL (SALTs in IRrigated SOILs) is a capacity-type, steady-state model developed to predict average major ion content (sodium, calcium, magnesium, chloride, sulfate) in the medium to long term in productive well drained soils. Once the algorithm verification was done the objective of our study was to calibrate SALTIRSOIL under one of several water quality and management scenarios in Mediterranean agriculture. Given that drip and basin are the irrigation methods most representative of irrigated agriculture in Valencia (Spain), this calibration is being performed with climate, soil, irrigation water (composition and management) and crop (species and management) information from an experimental plot drip irrigated with well water and cropped to water melon that has been monitored since late spring 2007. To carry out the calibration, firstly we have performed a sensitivity analysis. That is to change an input variable at a time within a range while maintaining the other variables unchanged and measuring the variability in the model output. Secondly, we have compared simulated saturation soil extract composition against measured data. According to the sensitivity analysis SALTIRSOIL calculations seem to be most affected by climate (rainfall) and water quality and less by soil physical characteristics. According to the first predicted-measured comparisons SALTIRSOIL does not seem to be affected by any systematic error and as a consequence, parameterization would not be needed at least under drip irrigation. On the other hand we have observed that i) the longer the climate data record used for the simulations the closer calculated and measured data are and ii) calculated results are closer to space-averaged measured data than to whichever single point measured data. More comparisons under different water quality and irrigation management practices are needed in order to calibrate SALTIRSOIL in the study area.