Adaptation of VegSyst-DSS for macronutrient recommendations of fertigated, soil-grown, greenhouse vegetable crops

VegSyst model v3 was calibrated and validated to simulate daily and seasonal P, K, Ca and Mg uptake of soilgrown sweet pepper and muskmelon crops in greenhouses in SE Spain. The model adequately simulated P, K and Mg uptake in three validation crops of sweet pepper, and Ca uptake in one crop. P, K, Ca and Mg uptake were accurately simulated in one validation muskmelon crop. The decision support system VegSyst-DSS v2 was developed by adding a component for recommendations of P, K, Ca and Mg for pepper and muskmelon to VegSyst-DSS vl. The new DSS component, which combines with VegSyst model v3, calculates: (i) daily P, K, Ca and Mg requirement (in kg ha-1) and (ii) nutrient concentration recommendations for fertigation nutrient solution, considering soil available/exchangeable content and simulated crop uptake. Recommended concentrations of P, K, Ca and Mg (in mmol L-1) are calculated from simulated uptake of each nutrient and crop evapotranspiration (ETc). Scenario analyses were conducted for nutrient recommendations of representative cropping cycles of pepper and melon with hypothetical soils of relatively low, medium and high P, K, Ca and Mg availability, obtained from a local soil database. The scenario analyses showed most soils had ample available soil P, and required minimal applications of P. For soils with relatively high levels of available nutrients, DSS recommendations were much lower (20-60%) than fanning practice. For soils with a medium supply of available nutrients, the DSS recommendations were generally approximately 60% of fanner practice, except for K in pepper and Ca in muskmelon. For soils that were relatively low in available nutrients, the recommendations were generally similar to or slightly less than farming practice. The crop and greenhouse specific recommendations of VegSyst-DSS v2 can appreciably reduce the application of P, K, Ca and Mg while meeting crop requirements.