Modelling soil tillage and mulching effects on soil water dynamics in raised-bed vegetable rotations

Reduced tillage and mulching may bring about new production systems that combine better soil structure with greater water use efficiency for vegetable crops grown in raised bed systems. These are especially relevant under conditions of high rainfall variability, limited access to irrigation and high soil erosion risk. Here we evaluate a novel combination of empirical models on water interception and infiltration, with a soil-water balance model to evaluate water dynamics in raised bed systems on fine Uruguayan soils to analyze the effect of reduced tillage, cover crops and organic matter addition on soil physical properties and water balance. In the experiment mulching increased water capture by 9.5% and reduced runoff by 37%, on average, leading to less erosion risk and greater plant available water over four years of trial. Using these data we calibrated and evaluated different models that predicted interception+infiltration efficiently (EF=0.93 to 0.95), with a root mean squared error (RMSE) from 0.32 to 0.40mm, for an average observed interception+infiltration of 28.8mm per day per rainfall event. Combining the best model with a soil water balance resulted in predictions of total soil water content to 1m depth (SWC_T) with RMSE ranging from 4.5 to 10.3mm for observed SWC_T ranging from 180.4 to 380.6mm. Running the model for a four-year crop sequence under 10 years of Uruguayan historical weather revealed that reduced tillage required on average 141mmyr^-1 less irrigation water than conventional tillage combined with organic matter application, thus enabling a potential increase in irrigated area of vegetable crops and crop yields. Results also showed the importance of inter-annual rainfall variability, which caused up to 3-fold differences in irrigation requirements. The model is easily adaptable to other soil and weather conditions.