Soil-Specific, Late-Season Nitrogen and Potassium Applications to Increase Corn Yields in the Mid-Atlantic Coastal Plain

Corn grain yields can be limited by nitrogen (N) and potassium (K) availability on sandy coastal plain soils when soil moisture is adequate for high yields. This study evaluated irrigated corn grain yield response to late-season (just prior to tassel) N and K fertilizer applications, and enabled the proposal of a method to predict potential for corn to utilize late-season N applications based on soil moisture. In an experiment to evaluate late-season fertilizer application rates, N and K were applied in a complete factorial of five N and K rates ranging from 0 to 112 kg ha-1. Additionally, water use of high yielding corn was measured, and historical weather patterns evaluated in an effort to predict the need for late-season fertilizer applications based on soil moisture. Grain yield was increased significantly by late-season N applications in three of four experiments. Potassium applications did not affect yield, and there were no interactions between N and K. Significant drainage due to high rainfall levels in 2000 prohibited further refinement of corn water use data for Virginia climatic conditions. Historical weather patterns, potential evapotranspiration of corn, and soil water holding properties were evaluated. In order to provide corn with adequate moisture during a two-week moisture-sensitive critical period beginning at tassel, soils must be near field capacity at the start of the period and receive above-average (75th percentile) rainfall during the period.