Determination of evaporation and transpiration components of crop evapotranspiration of lettuce grown under greenhouse conditions

This study aimed to separately compute the evapotranspiration (ETc) components of curly lettuce (Lactuca sativa var. Caipira) grown under different irrigation levels into evaporation (E) and transpiration (T). For this purpose, the study was carried out in the autumn growing season in 2020 in a plastic greenhouse located in the experimental area of Akdeniz University Faculty of Agriculture in a randomized plot design between 16.10.2020 and 22.12.2020. In order to investigate the effect of water stress on ET and its components, three different irrigation water levels (I100: for full irrigation treatment (100%), I66 for 66% (I100 x 0.66) and I33 for 33% (I100 x 0.33)) were selected. During the experiment, the pots were weighed at most once every two days, and irrigation was carried out in all treatments when 30-40% of the water holding capacity in I100 declined. The amount of water required to be applied to the all irrigation treatments was conducted in a controlled manner to ensure that the depleted moisture was brought to the field capacity. In the research, plant transpiration was determined by using two methods by directly measuring (Tr(o)) and by predicting with a model (Tr(e)). A strong positive relationship was obtained between Tr(o) and Tr(e). However, it was also found that this relationship decreased with the increment of water stress. In the research, evaporation from the soil was determined in two ways: evaporation from bare soil (E) and evaporation from planted pots (Es) except the area covered by percentage of plant cover. In the research, it was concluded that water stress significantly affected the lettuce plant height, root length, cover percentage, leaf area index (LAI), number of leaves, fresh and dry head weights and root weights (p<0.01). In the research, an exponential relationship between Es/ET and LAI was found in all treatments. According to the method used in the research and the conditions of the region, it was concluded that the calibrated models can be used for accurate prediction of lettuce ET values and partitioning of ET into its components.