ossibilities of using dual $K_c$approach in predicting crop evapotranspiration of second-crop silage maize

Abstract

The purposes of this study were to develop a dual crop coefficient ($K_c$) using FAO-56 methodologies and to compare cropevapotranspiration ($ET_c$) measured under field conditions for second-crop silage maize in the Southeastern Anatolia Region of Turkeywith the $ET_c$ estimated using FAO-56 dual Kc methodologies. For this study, field experiments were conducted in the 2011 and 2012growing seasons, and the results were evaluated. To compute dual $K_c$ ($K_cb$ and $K_e$), all climatological data involving the seedling andharvesting dates, growth stages, water holding of soil at field capacity and at wilting point, soil evaporation layer, and crop characteristicswere 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. Thereference evapotranspiration ($ET_o$) was computed daily using the Penman–Monteith equation. All main and intermediate calculationsfor the dual $K_c$ and its components $K_cb$ and $K_e$ were based on the FAO-56 guidelines. The $K_cb$ values were computed as 0.15, 1.27, and 0.62for 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 sameorder. 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$ET_c$ rate occurred in midseason, which had an average maximum value of 10.8 mm day–1. The $ET_c$ of silage maize for optimal dry matterduring the growing season in the years of the study was 519 mm as the average of two growing seasons. The FAO methodology thusinsignificantly overestimated the seasonal $ET_c$ (536 mm) for silage maize. Thus, the FAO-56 dual $K_c$ methodology can be used to estimatethe crop $ET_c$..