Revised VegSyst model to calculate dry matter production, critical N uptake and ETc of several vegetable species grown in Mediterranean greenhouses

The VegSyst simulation model simulates daily crop N uptake and crop evapotranspiration (ETc) and is a basic component of the VegSyst-DSS decision support system that calculates daily crop N and irrigation requirements of vegetable crops grown in Mediterranean greenhouses. In this work, the VegSyst model was revised to produce version 2 which is simpler and has fewer inputs. VegSyst V2 was calibrated and validated for various species, and species-management combinations. The following changes were made to VegSyst V2. The Almeria Radiation method was included as an alternative to the Penman-Monteith equation to calculate reference evapotranspiration (ETo) because it requires less climate inputs. The growth model was reduced from two phases to one phase, and the maximum fraction of intercepted PAR radiation is now maintained to the end of crop. In autumn-winter grown crops, two values of radiation use efficiency (RUE) are now used with a reduced RUE value for the winter period; a single RUE value is used for spring grown crops. A critical N dilution curve is now used rather than that of a well-fertilized crop. The model was: (a) calibrated for cucumber, zucchini, non-supported melon, watermelon and eggplant, and (b) re-calibrated for pepper and supported melon. Calibration parameters for determining daily crop coefficient (kc) values and for the critical N curves were obtained from previous local studies and published work. Model performance was evaluated for the simulation of daily dry matter production (DMP), critical N uptake (the minimum N uptake to achieve maximum DMP) and crop evapotranspiration (ETc) of several vegetable species. In all species and species-management combinations evaluated, model performance was good for simulation of DMP and was generally acceptable for simulation of ETc, although there were some discrepancies. Where crop N uptake data were available, simulated critical N uptake was consistently lower than the measured N uptake suggesting that the validation crops were not N limited. Differences were observed between the two equations to calculate reference evapotranspiration (ETo), with the Penman-Monteith equation calculating higher values in winter and lower values in summer. In seven of twelve cases, simulation of ETo was more accurate with Penman-Monteith; in five cases, mostly with winter crops, it was more accurate with the Almeria Radiation method. With the modifications, VegSyst V2 is simpler, requires fewer inputs and provides simulation of DMP, ETc and critical N uptake for the most important vegetable species grown in Mediterranean greenhouses.