Performance assessment of AquaCrop model for estimating maize (Zea mays L.) evapotranspiration and its components in micro irrigation systems under mulch conditions

The aim of this study was to simulate the effect of micro irrigation systems under mulch conditions on evapotranspiration, soil surface evaporation and plant transpiration of forage maize using AquaCrop model. In this study, the AquaCrop model’s performance was tested using data for silage maize (Zea mays L.) under surface drip, subsurface drip and permeability clay pipe irrigation systems with mulch conditions in the semiarid environment of Karaj, Alborz during 2014. According to the NRMSE index, in the calibration and validation stage (7.74% and 10.7%), the accuracy of this model to simulating forage maize biomass was acceptable, and AquaCrop simulated well the biomass yield (B-yield) of silage maize. The model had moderate efficiency for simulating corn evapotranspiration.The performance of the model in maze evapotranspiration simulation was better in PCI-M1 treatment than other treatments. So that, it had the lowest value of nRMSE and the highest value of R2. There was no good correlation between the observed and simulated values in estimating soil surface evaporation and high nRMSE values in these treatments (2.96 and 3.23%) indicate the inefficiency of the AquaCrop model in estimating soil surface evaporation. The positive MBE index in both DI-M1 and SDI-M1 treatments indicates that the model overestimates the soil surface evaporation and does not estimate close to the observed values. Statistical evaluations between observational values and plant transpiration simulation showed a moderate correlation between observed and simulated values. The value of NRMSE index for canopy cover was calculated to be more than 30% in all treatments, which indicates the poor performance of the model. In these treatments, the maximum amount of canopy cover simulated using the AquaCrop model is more than the observed values.