Report to the Oregon Processed Vegetable Commission
Dan Sullivan, Dept of Crop and Soils
Enhanced efficiency fertilizer (EEF) technologies have the potential to improve the crop N use efficiency (NUE) as well as minimize negative environmental losses compared to conventional fertilizers. The EEF fertilizer products consist of urea plus additives (to inhibit N loss). The major pathways for N loss in our sweet corn cropping systems are 1) N leached below the root zone as water soluble nitrate-N (NO3-N), and 2) gaseous ammonia loss (NH3-N) to the atmosphere following a surface urea application.
Field studies and a laboratory incubation study were conducted in 2014 to evaluate the potential for benefit from EEF products via reduced nitrate-N leaching. Three products were evaluated: ESN (polymer coated urea), SuperU (prilled urea containing both a urease and nitrification inhibitor), and Instinct (urea + nitrification inhibitor). Concentrations of soil ammonium-N and nitrate-N were measured in the lab and in the field to assess product efficacy in controlling nitrate-N release vs. urea alone. In general, about 20 to 50% of the urea-N applied was protected from conversion to nitrate-N for the first 3 to 6 weeks after fertilizer application. In a field trial at the OSU Vegetable Farm, corn ear yields were not different for urea alone vs. the EEF products applied at the same N rates. This field trial was managed to maximize opportunity for nitrate leaching (8.6 inches water was supplied via extra irrigations plus rainfall during the first 6 weeks after planting). We conclude that EEF products had measurable efficacy in slowing the rate of conversion of urea-N to leachable nitrate-N. However, even under a “worst case” leaching scenario on a medium-textured soil, the use of inhibitors was ineffective in achieving a corn ear yield response.
A field study was conducted to quantify gaseous ammonia loss from surface-applied urea (without tillage to incorporate fertilizer), and to evaluate SuperU for efficacy in reducing gaseous ammonia loss. Passive flux masts were used to capture and quantify ammonia lost during the first weeks after fertilizer application. Despite favorable soil moisture and temperature conditions for ammonia loss, the measured ammonia loss for urea alone was very small (< 2% of urea-N applied), so it was not possible to quantify benefit from SuperU. Additional research is needed to verify these results (insignificant gaseous ammonia loss) across a wider range of soil, crop management and weather scenarios.