Possibilities of using dual K c approach in predicting crop evapotranspiration of second-crop silage maize

Abstract

Introduction Silage maize provides a considerable source of both energy and fiber for animal feeding. It is thus one of the most valuable forages for ruminant livestock. The average composition of corn silage is 27% dry matter, 8% crude protein, 45% neutral-detergent fiber, 28% acid-detergent fiber, 22% cellulose, and 26% starch (Bittman and Kowalenko, 2004). In the study area, the Southeastern Anatolia Region of Turkey, silage maize can be grown quickly (in 90-100 days) as a second crop. However, 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). However, drip irrigation enables the saving of water compared with furrow irrigation (Yazar et al., 2002). Thus, accurate estimations of crop-water requirements and appropriate irrigation scheduling are required to enhance the optimization and efficiency of applied water for silage maize, ensuring its sustainability. On the other hand, the irrigation-water requirements for silage maize vary depending on the region's climate and soil conditions, the irrigation methods, and the farmers' practices. In arid and semiarid regions, it is thus important to estimate the actual crop evapotranspiration (ET c) for the growing period to ensure appropriate irrigation practices and scheduling (Kenjabaev et al., 2014). Estimating cropwater consumption accurately is necessary to ensure sustainable irrigation management (Katerji and Rana, 2008). One of the main ways in which to estimate the ET c is to use the FAO-56 crop-coefficient (K c) approach (Allen et al., 1998), in which ET c is estimated using standard agrometeorological data and a crop-specific coefficient, K c , which is based on the relationship among crop physiology, atmosphere, and agricultural practices. The dual-crop-coefficient approach is generally used for irrigation scheduling, such as for drip irrigation (Allen Abstract: The purposes of this study were to develop a dual crop coefficient (K c) using FAO-56 methodologies and to compare crop evapotranspiration (ET 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 u...