Validation of an adapted soil-plant model to study the water and nitrogen flows of Colombian greenhouse tomato systems

The purpose of the present work was to validate a soil-plant model to represent, besides crop growth, the soil water and nitrogen dynamics. We used a soil model developed for temperate conditions coupled to a tomato growth model calibrated and validated locally. Additionally, the evapotranspiration module was changed to the one of Stanghellini, which is recognized as more appropriate to estimate the evapotranspiration inside greenhouse crops, especially for tomato. The last significant modification corresponded to change the soil temperature module since the original model version incorporates an approach able to simulate the soil temperature only under temperate seasonal climate variations. The model, which is programmed in the R statistical language, uses as inputs climate data (solar radiation, air temperature, humidity and wind speed), soil characteristics (e.g., pH, nitrogen content, bulk density and moisture, lower limit, field capacity and saturation), crop management practices (e.g., planting date, plant density, cycle duration), as well as irrigation and fertilization strategies. The field data for the validation came from an experiment carried out in the main greenhouse tomato production area of Colombia. The model was validated by comparing the simulated values against the observed ones. Two goodness-of-fit measures were used to evaluate the model fit: Nash-Sutcliffe modeling efficiency (NSE) and percent bias (PBias). The plant model, soil water movement and soil temperature showed satisfactory performance according to the measures employed. Although the experimental data demonstrated that the simulated soil nitrogen contents follow the observed tendency, the NSE score showed the poor soil N module performance. Based on the above, extra future calibration and validation experiments are needed to improve the accuracy of the proposed model.