Estimating strawberry crop coefficients under plastic tunnels in Southern Spain by using drainage lysimeters

Water is the major limiting factor in the irrigated agriculture of Southern Spain. This fact is even more determining for strawberries cultivated in the vicinity of environmentally sensitive areas such as the Doñana National Park; the major protected wetland of Europe. In the last few years, there is a growing interest on maximizing the efficient use of irrigation water in this area, aiming to achieve the equilibrium between agricultural practices and environmental protection. This work shows the local crop coefficients (Kc) for strawberries (Fragaria x ananassa cv. Sabrina) grown under plastic tunnels in the coast of Huelva (Spain). Crop coefficients were estimated in situ during the 2014/15 and 2015/16 seasons by using three drainage lysimeters installed along the raised beds where plants were grown, and filled with the same soil (sandy soil). Estimated Kc values were defined on the basis of the agro-climatic information provided by two weather stations located inside and outside of the tunnels (macro-tunnels). Values ranged between 0.3 and 0.8, when outside data were used, and between 0.4 and 1.4, when using the climatic data provided by the weather station inside the macro-tunnel. However, discrepancies in estimations of Kc inside were observed depending on the methodology used to determine the reference evapotranspiration (ET0) under the plastic tunnel. Polygonal and polynomial models were fitted to Kc data versus the days after planting (DAP) and the growing degree days (GDD) in order to provide a useful tool for growers to be able to estimate crop water needs. These results represent an important contribution for the improvement of irrigation water use in strawberry cultivation in the Southern Spain.