Measuring and modelling crop water use of sweet pepper crops grown in screenhouses and greenhouses in an arid region

Abstract

This research studied microclimate and evapotranspiration (ET) of pepper in high tunnel screenhouses and greenhouses. A study was carried out during three consecutive seasons, 2015–2016 (Season I), 2016–2017 (Season II) and 2017–2018 (Season III), in two high-tunnels. One was covered by a plastic sheet (greenhouse) and the other by a porous screen (17 mesh insect net; screenhouse). Other than the covers, the structures were identical. In both houses, microclimate variables were measured simultaneously above the canopy. Evapotranspiration was estimated using six different variations of the Penman–Monteith model. Plant transpiration was measured by the heat pulse technique. Measured transpiration was compared with model estimates of ET to identify the model in best agreement with measurements. Linear regressions between internal and external climatic conditions resulted in R2 values between 0.003 (greenhouse temperature) and 0.99 (greenhouse global radiation). Generally, higher R2 values were obtained for the screenhouse because internal microclimate interacted with the outside more than in the greenhouse. Mean daily evapotranspiration estimated by the six Penman–Monteith models tested was 1.61–4.23 and 1.42–4.43 mm day−1 for the greenhouse and screenhouse, respectively. Mean daily ratio between ET models and transpiration measurements varied between 0.81 and 2.01 with a mean value of 1.20 ± 0.34 (where ± is standard deviation). The comparison between transpiration measurements and the PM models showed that in most cases models based on internal climatic conditions were in better agreement with measurements than those based on the external conditions.