Abstract
The purposes of this study were to develop a dual crop coefficient (K c ) using FAO-56 methodologies and to compare crop evapotranspiration (ETK c ) measured under field conditions for second-crop silage maize in the Southeastern Anatolia Region of Turkey with the ET c estimated using FAO-56 dual K c methodologies. For this study, field experiments were conducted in the 2011 and 2012 growing seasons, and the results were evaluated. To compute dual K c (K cb and K e ), 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 (ET o ) was computed daily using the Penman-Monteith equation. All main and intermediate calculations for the dual Kc 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 0.62 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 K c 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 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 ET c (536 mm) for silage maize. Thus, the FAO-56 dual K c methodology can be used to estimate the crop ET c .
Highlights
Silage maize provides a considerable source of both energy and fiber for animal feeding
We found a difference between the measured ETc and FAO-56’s estimated ETc in 2011, the dual Kc was more accurate because we computed this value based on daily climatological and other data for the growing season
Soil evaporation (Ke) is an important component of ETc during the initial stage in high-temperature climate conditions such as those found in this study area
Summary
Silage maize provides a considerable source of both energy and fiber for animal feeding. It is one of the most valuable forages for ruminant livestock. The Southeastern Anatolia Region of Turkey, silage maize can be grown quickly (in 90–100 days) as a second crop. Second-crop maize consumes large amounts of water due to the climatic conditions in the study area (Yolcu and Cetin, 2015). The water requirements of second-crop maize in this region range from 800 mm to 1000 mm depending on irrigation scheduling for the surface irrigation (Çetin, 1996). Accurate estimations of crop-water requirements and appropriate irrigation scheduling are required to enhance
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