Impact of Precipitation Timing and Soil Water at Planting On Wheat and Corn Yields in the Central Great Plains.

A diversified dryland cropping system of no-till winter wheat-corn-fallow has become more common in the Central Great Plains in recent years.  This cropping system of both fall and spring planted crops optimizes the time a crop is available to intercept the precipitation.  The summer fallow period in this 3-year system also maximizes the amount of water stored in the soil profile prior to planting back to winter wheat.  The success of a winter wheat crop has been linked to precipitation during the fallow period and the efficiency of that water storage within the profile.  The success of a corn crop has been observed to be linked to rainfall during the reproductive stage in July and August.  We evaluated 22 years of wheat and corn yields collected at three locations ranging from 400 to 425 mm yr^-1 of average precipitation as impacted by stored soil water, and rainfall during fallow, vegetative, and reproductive periods in a multivariate analysis.  Locations represent a range in open pan evaporation from 1600 to 1975 mm.  Wheat grain yields were significantly impacted by initial soil water at all 3 locations.  Fallow period rainfall was also significant in both the low and high potential evaporation locations for wheat yield.  Corn grain yields were strongly impacted by soil water at planting and reproductive period precipitation but not by vegetative period rainfall.  Multivariate analysis showed how critical reproductive precipitation was for spring planted crops but not for fall planted winter wheat.  The fallow precipitation period was critical for wheat but not for corn yields.  This analysis demonstrates the importance of looking at the complete cropping sequence and rainfall distribution in order to optimize the precipitation patterns most likely to benefit the crops grown in the system.