Evapotranspiration for plastic-mulched production system for gradually cooling and warming seasons: measurements and modeling

Abstract

Crop evapotranspiration (ET c ) and crop coeffi - cient (Kc) for drip-irrigated bell pepper grown on plastic- mulched beds for climatically different growing seasons were quantified using drainage lysimeters located in the Southwest Florida. We tested whether: (1) the literature K c (with climatic adjustment) yields accurate ETc estimates; (2) K c values are applicable across the growing seasons that are climatically different; and (3) a thermal-based generic model can be developed to accurately predict K c for gradu- ally cooling (fall) and warming (spring) seasons. Spring ET c (229 mm) was statistically (p = 0.03) higher than fall (189 mm). Seasonal Kc values were also statistically dif- ferent, and average fall value (0.86) was 20 % higher than spring (0.72), confirming Kc's seasonality. The Kc val- ues for the fall were statistically higher than FAO-56 K c 's which underestimated ETc by 22 %. Use of fall Kc overesti- mated spring ET c by 24 %, while it was 12 % underestima- tion for the opposite. These errors were 16-69 % of rainfall and 26-46 % of farm-scale surface flows highlighting the need for accurate ETc predictions. The seasonal differences in K c could be accurately predicted with a generic growing degree days (GDD) model (r 2 = 0.95). The results not only provide an improved ET c estimate for plastic-mulched pep- per in the study area, but also for other regions using the GDD-based model that utilize readily available temperature