Temperature, sowing and harvest dates, and yield potential of maize in the southwestern US

Abstract. Since sowing date of maize is sensitive to climate variability and changes, it is critical to examine how sowing dates affect maize yields in various temperature regimes in the southwestern US. In doing so, the ApsimRegions model, regionally extended version of the APSIM model, has been run over the southwestern US region at 32 km resolutions over the 21-year period from 1991 to 2011. The meteorological forcing dataset was North American Regional Reanalysis (NARR) and irrigation was assumed to be applied at a 95% soil water-holding capacity. The interannually-fixed and -variant sowing date runs (fixed and optimal run, respectively) showed 50~300 % increases of the yield potential over selected regions by optimizing sowing date. For the optimal run, it was found that earlier sowing dates are favorable for higher yields primarily by increasing the length of growing season in cold mountaineous regions. In these regions, warmer than normal conditions in the sowing period tend to advance the sowing date to result in yield increases. Over the low-elevation warm regions (e.g., the southern parts of the Central Valley and Arizona), yields are less correlated with sowing dates and the length of growing season, perhaps because growing season temperatures are high enough for fast growth. Instread, in those warm regions, maize yields are sensitive to temperature variations during the sowing- and late growing season due to the adverse effects of extremely high temperature events on maize development. Theses results indicate that appropriate adaptations for sowing date can enhance yield significantly, but the positive effect of advanced sowing on the maize yields in warmer spring is constrained in the cool environmental regions rather than the warm environmental regions in the southwestern US.