Validation of on-farm crop water requirements (PrHo) model for horticultural crops in an unheated plastic greenhouse.

摘要

Most greenhouse crop transpiration models presented in the literature have been calibrated and validated over short periods, sometimes less than a week, with the same conditions for calibration and validation. The objective of this paper is to analyse the performance of the PrHo v 2.0 ( copyright 2008 Cajamar; www.fundacioncajamar.com) model during the entire cropping season in an unheated plastic greenhouse. PrHo is a software that estimates crop evapotranspiration (ETc), based on the FAO model (Doorenbos and Pruitt, 1975), that has been previously calibrated for greenhouse-grown vegetable crops (Fernandez, 2000). It includes two sub-models, the reference evapotranspiration (ETo) sub-model and the sub-model for the crop coefficients (Kc). The ETo sub-model estimates greenhouse ETo values from exterior solar radiation values, using a radiation model previously calibrated for local conditions. With this model it is possible to adjust irrigation to particular crop conditions, such as white washing. The Kc sub-model calculates Kc values from sowing/planting to effective full cover as a function of thermal time, calculated using greenhouse air temperature (Fernandez, 2000; Orgaz et al., 2005). Therefore the evolution of Kc values includes variability in crop growing cycles and planting dates. PrHo v 2.0 calculates the ETc for the main greenhouse horticultural crops in real time ("ETc real") or using average climatic data ("ETc average"). The calculated PrHo values of ETc in real time were compared with average ETc values measured during entire cycles of pepper crops. There was very good agreement between the estimated and measured ETc values, even for low ETc values of 1 mm d-1. The evolution of calculated ETc values closely followed that of measured ETc values.