Crop coefficients of a pepper crop grown in plastic greenhouses in Almeria, Spain.

The objective of this work was to improve irrigation scheduling of pepper crops grown in plastic greenhouses in the region of Almeria, Spain. The experimental approach was to determine crop coefficient (Kc) values for a pepper crop grown under representative greenhouse conditions in Almeria, Kc being the ratio between crop evapotranspiration (ETc) and reference evapotranspiration (ETo). Both, ETc and ETo were measured by a water balance using drainage lysimeters in two analogous plastic greenhouses with similar climatic conditions. A pepper crop was grown in the greenhouse where ETc was measured and a perennial grass was grown in the greenhouse where ETo was obtained. A series of Kc values were determined for different crop growth stages. The initial Kc value of approximately 0.2 at 15 days after transplanting (DAT), increased linearly to a maximum value of 1.4 at 80-90 DAT. Thereafter, Kc decreased to 0.9 at 167 DAT, and then maintained a steady, shallow decrease to 0.8 at the end of the growing season (258 DAT). The maximum Kc value determined was higher than reported for peppers grown under outdoor conditions. The higher maximum Kc value in the greenhouse is attributed to management factors that are likely to enhance interception of net radiation by the crop.