Disk-till vs. no-till maize grass- and alfalfa-reference single (average) and basal (dual) crop coefficients

Disk-till (DT) and no-till (NT) maize (Zea mays L.) water use, crop growth characteristics, and microclimatic differences have been shown to differ. With these differences, it becomes essential that maize be managed differently under these tillage practices in terms of irrigation, and hence, it is indispensable that tools to effectively implement irrigation management be developed. However, water management tools such as crop coefficients that account for tillage practices are extremely rare. To investigate and develop better management tools, this research aimed to develop single (average) (K-c) and basal (dual) (K-cb) daily grass- and alfalfa reference crop coefficients (K-co and K-cr, respectively) using measured crop evapotranspiration at two carefully and cautiously -managed producer fields (disk-till and no-till fields) at Holdrege, Nebraska for 2011, 2012, and 2013 growing seasons. Both K-c and K-cb differed among DT and NT maize in that NT maize showed lower K-c and K-cb during pre-anthesis and higher K-c and K-cb during post-anthesis, and the period of maximum K-c and K-cb occurred later in the crop growing season. Specifically, the magnitude of these differences in K-c values were 56%, 29%, 1%, 8%, 47%, and 41% for May, June, July, August, September, and October, respectively, i.e., greater in early and late season, but smaller in mid-season. Kcb presented similar trends within the season. K-cb exhibited 70% lower magnitudes than K-c, due to minimized evaporation effects on or around precipitation events and hence had reasonably strong relationship with leaf area index. Daily crop coefficients were correlated with two types of base scales: days after planting (DAP) and cumulative growing degree days (CGDD). It is demonstrated with evidence that CGDD was a better predictor of seasonal variation in K-c and K-cb. The relationships between K-c (both K-cr and K-co) and K-cb (both K-cbr and K-cbo) vs. DAP and CGDD for both DT and NT maize during the three growing seasons in the form of transferable polynomial equations were also presented. The crop coefficients for DT and NT maize and their estimation equations presented in this research are novel and have immense application in the task of accurate quantification of maize evapotranspiration and manage irrigation under these two contrasting systems.