Slow-Release Fertilizer Effect On Groundwater Nitrogen Concentration In Sandy Soils Under Potato Production.

Abstract: Current nitrogen (N) fertilizer management practices for potato farming have led to elevated levels of N in the local groundwater. Slow-release fertilizer, specifically Environmentally Smart Nitrogen® (ESN) may reduce the amount of N leaching to groundwater; however no field scale studies have been performed in Wisconsin to validate these assertions. A two year field experiment was conducted at the Hancock Agricultural Research Station using Russet Burbank potato, planted in Plainfield sand. Four fertilizer rates, 0 N control, 224 kg ha-1 ESN, 280 kg ha-1 ESN, and current University of Wisconsin-Extension recommended 280 kg ha-1 ammonium sulfate-ammonium nitrate (AS-AN) were used. Conventional fertilizer was applied twice, once on day after planting (DAP) 18 and the second application on DAP 35. Slow-release application occurred once at DAP 18. The study included a complete randomized block design with three replicates creating twelve 14.6 × 15.24 m field plots. Three monitoring wells were installed in each plot to sample groundwater nitrate, ammonium and dissolved organic N. Samples were collected weekly throughout the growing season and monthly after harvest. Samples were assessed for nitrate, ammonium and total N. Results indicate that use of ESN led to reduced concentrations of nitrate in groundwater. Potato growth parameters and yields were maintained between conventional fertilizer and ESN use. This demonstrates that use of slow-release ESN fertilizer is a reasonable alternative to current management practices of AS-AN applications.