Evaluating Nitrate Loss From Manure-Amended Sandy Soils in Wisconsin.

The impact of dairy manure application on nitrate leaching was evaluated at two sites with no manure history. Manure treatment (separated solid manure, separated liquid manure, separated liquid manure plus a nitrification inhibitor, and two treatments with no manure) was the main plot. Each manured plot was split into six subplots with three receiving a single sidedress fertilizer application of 0, 56, or 112 kg N ha^-1 while the others had two sidedress applications totaling 112 kg N ha^-1 with varying percentage of N being applied in each split.  Subplots in one of the no manure treatments received 0 to 280 kg N ha^-1 in increments of 56 kg N ha^-1 while subplots in the second no manure plot received a total of 224 kg N ha^-1 in differing percentages of total N split between two sidedressings. 

After manure application and planting, ceramic suction cup lysimeters were installed 1.5 m below the soil surface to collect water leaching below the root zone in the 0 and 112 kg N ha^-1 subplots of all manure treatments as well as the 224 kg N ha^-1 subplot of one of the no manure treatments. Water samples were collected weekly from installation until two weeks after harvest and were analyzed for nitrate concentration.

Nitrate concentrations ranged from non-detectable (<0.02 mg L^-1) to more than 300 mg L^-1. As expected, fields amended with higher rates of nitrogen fertilizer generally had greater nitrate concentrations. Less nitrate leached from plots amended with separated solid manure compared to separated liquid manure. Nitrate leaching from plots where a nitrification inhibitor was used varied by location.