Possibilities of using dual Kc approach in predicting crop evapotranspiration of second-crop silage maize.

The purposes of this study were to develop a dual crop coefficient (Kc) using FAO-56 methodologies and to compare crop evapotranspiration (ETc) measured under field conditions for second-crop silage maize in the Southeastern Anatolia Region of Turkey with the ETc estimated using FAO-56 dual Kc methodologies. For this study, field experiments were conducted in the 2011 and 2012 growing seasons, and the results were evaluated. To compute dual Kc (Kcb and Ke), all climatological data involving the seedling and harvesting dates, growth stages, water holding of soil at field capacity and at wilting point, soil evaporation layer, and crop characteristics were input into a spreadsheet program. The crop stages observed were 15, 25, 40, and 12 days for the initial, crop development, midseason, and late-season stages, respectively, in 2011, and 12, 23, 43, and 13 days, respectively, for the same stages in 2012. The reference evapotranspiration (ETo) was computed daily using the Penman-Monteith equation. All main and intermediate calculations for the dual Kc and its components Kcb and Ke were based on the FAO-56 guidelines. The Kcb values were computed as 0.15, 1.27, and 0.62 for the initial, midseason, and late-season stages, respectively. However, these figures were 0.15, 1.15, and 0.5 in the FAO-56 in the same order. The dual Kc was 0.64, 1.27, and 0.67 in this study for the initial, midseason, and late-season stages, respectively. The maximum ETc rate occurred in midseason, which had an average maximum value of 10.8 mm day-1. The ETc of silage maize for optimal dry matter during the growing season in the years of the study was 519 mm as the average of two growing seasons. The FAO methodology thus insignificantly overestimated the seasonal ETc (536 mm) for silage maize. Thus, the FAO-56 dual Kc methodology can be used to estimate the crop ETc. [ABSTRACT FROM AUTHOR]