The variable response of dryland corn yield to soil water content at planting

Farmers in the central Great Plains want to diversify crop rotations from the traditional monoculture system of winter wheat-fallow. Corn (Zea mays L.) could work well as a rotation crop, but inputs are expensive and farmers would like to know the chances of producing a certain yield before investing in seed, fertilizer, herbicides, etc. Information on the yield response of corn to available soil water at planting could help guide the crop choice decision regarding corn. This study was conducted to determine if a predictive relationship exists between dryland corn yield and available soil water at planting time and, if such a relationship exists, to use it to assess the risk in obtaining profitable yields. Yield and soil water data from 10 years of a dryland crop rotation study at Akron, CO were analyzed by linear regression to determine predictive relationships. The yield-soil water content production function was highly variable, with values ranging from 0.0 to 67.3 kg ha-1 per mm of available soil water in the 0 to 1.8 m soil profile at planting. The differences in yield response to soil water were related to the amount and timing of precipitation that fell during the corn growing season. Because dryland corn yield is highly dependent on precipitation during reproductive and grain-filling stages, soil water content at corn planting cannot be used alone to reliably determine whether corn should be planted in a flexible rotational system. The predictive relationships developed in this study indicate that under typical amounts of available soil water at corn planting, profitable corn production under dryland conditions is a risky and speculative activity in the central Great Plains of the United States.