Evapotranspiration losses for drip-irrigated watermelon in shallow water table and sandy soil conditions
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Florida has been endowed with abundant water resources; however, with a population growth rate of nearly 23%, demand for water has increased to make water conservation one of the state's priorities. Since agriculture accounts for 45% of total fresh water withdrawals, sound irrigation scheduling and efficient irrigation systems are key for optimum plant growth and conserving water quantity and quality. Estimating the crop evapotranspiration (ETc) by multiplying the crop coefficient (Kc) by the Penman-Monteith reference evapotranspiration (ETo) could help in more efficient agricultural water use. Accurate ETc can only be calculated using locally developed Kc values that take into account local production practices. A study was undertaken to develop crop coefficient (Kc) values for drip-irrigated watermelon, a common vegetable crop grown under plastic mulch in southwest Florida's sandy soils. Four large drainage lysimeters (4.87m 3.65m 1.37m) were instrumented to measure inflow (irrigation and rainfall), outflow (drainage and runoff), and storage (soil moisture). Weather data were also collected. Using a bi-weekly time step, a Kc curve was developed using three seasons of data. The crop coefficient values for Florida were 0.57, 0.89, and 0.76 for March, April and May, respectively. The initial Kc is slightly higher than the values reported in FAO-56. This was mainly caused by the high soil moisture at the soil surface at the beginning of the season resulting from wetting of the soil for bed preparation. The middle and end Kc values were within the range FAO-56 values.
