Corn Response to Conventional and Slow-Release Nitrogen Fertilizers across a Claypan Landscape

Improvement of N fertilizer recovery efficiency (NRE) is necessary to reduce excess N entering the environment and to increase economic returns. A 2-yr field trial was established in 2005 in Northeast Missouri to determine the effects of conventional and slow-release N fertilizer sources and landscape position (summit, sideslope, and low-lying) on crop growth and NRE in corn (Zea mays L.) in a claypan soil. Nitrogen fertilizer treatments at 168 kg N ha-1 consisted of pre-plant applied and incorporated polymer-coated urea (PCU), urea, 50% PCU/50% urea mix by weight, anhydrous ammonia (AA), and a nontreated control. Gravimetric soil water content data in 2005 and 2006 indicated that the low-lying position was often wetter than the summit and sideslope positions. Anhydrous ammonia and PCU treatments increased grain yield 1470 to 1810 kg ha-1 over urea in the low-lying position in 2005 and 2006. Corresponding increases in plant N uptake and NRE were observed in the low-lying position in 2005 with use of PCU and AA compared to urea, but not in 2006. Based on the grain yield results in this research and different fertilizer cost and crop prices, gross profit differences for use of PCU and preplant-applied AA compared with urea in the low-lying position could range from $50 to $642 ha-1. These results demonstrate that targeted use of different N fertilizer sources in claypan landscapes may increase grain yields and profitability.