Current nitrogen (N) fertilizer management practices for vegetable farming have led to elevated levels of nitrate-nitrogen in the local groundwater. A study was conducted at the Hancock Agricultural Research station to determine if controlled release fertilizer, specifically Environmentally Smart Nitrogen (ESN®), could reduce groundwater N concentration. Field experiments were conducted using Russet Burbank potato and Overland sweet corn, planted in Plainfield sand. Four fertilizer rates in potato were evaluated: 1) 0 N control, 2) 224 kg ha-1 of N as ESN®, 3) 280 kg N ha-1 as ESN®, and 4) 280 kg N ha-1 as a split application of ammonium sulfate (AS) and ammonium nitrate (AN). Sweet corn fertilizer rates were: 1) 0 N control, 2) 168 kg N ha-1 as ESN®, 3) 168 kg N ha-1 as ASurea-urea, and 4) 224 kg N ha-1 as AS-urea-urea. Both studies included three replicates to create twelve 14.6 m by 15.2 m field plots. Three groundwater monitoring wells placed diagonally across plots were installed and sampled weekly during the growing season and monthly during winter for assessing nitrate. Bromide tracer was used to evaluate solute flux and spatial distribution of N leaching potential among plots. Bromide tracer showed that plot size was sufficiently large with no plot-to-plot contamination from N migration and the time for groundwater to flow to adjacent plots is longer than the growing season. Therefore, in-season contamination is minimal, and thus nitrate measurements were from respective plots. Trends indicate that ESN® reduced the amount of nitrate leaching to groundwater. However, highly variable background nitrate concentrations in the groundwater made it difficult to show statistical significance. The effective use of groundwater monitoring wells requires careful consideration of depth to groundwater, groundwater flow direction, and variability of groundwater nitrogen concentration.
Soil Science Extension
University of Wisconsin Madison