Effect of Cover Crops and Nitrogen Application Timing on Nutrient Loading through Subsurface Drainage.

It has been estimated that nitrate leaching from artificially drained agricultural fields in the Upper Mississippi River Basin accounts for approximately 65% of nitrogen delivered annually to the Gulf of Mexico.

Therefore, the objectives of this study were to investigate the impact of nitrogen fertilizer application and cover crops on the distribution of soil inorganic nitrogen (N), plant N uptake, and the load of nitrate in subsurface drainage leachate. This experiment was conducted at the Illinois State University Nitrogen Management and Tile Drainage Research Site, in Lexington, IL.

The experimental treatments include a zero control (no Nitrogen fertilizer and no cover crops), fall dominated (80% fall, 20% spring) N application with and without cover crops, and a spring dominated (20% fall, 80% spring) N application with and without cover crops.

A total rate of 225 kg N ha^-1 was applied to all treatments, except the zero control. Spring cover crop sampling revealed an average biomass production of 1107 kg ha^-1 and an average total N uptake of 53.5 kg N ha^-1.

Preliminary results following the first season of cover crop integration indicate that winter cover crops have the potential to reduce nitrate leaching and stabilize a greater concentration of soil NO₃-N in the agronomic and environmental depths of soil (0-80cm), relative to the non-cover crop treatments. Data from the analysis of tile leachate for NO₃-N (kg ha^-1) indicated that fall (33.79) > spring (30.18) > spring CC (30.15) > fall CC (29.78).

However, the average flow-weighted NO₃-N (mg/L) concentrations indicated that fall (6.1) > fall CC (5.3) > spring (4.4) > spring CC (3.7).

First year treatment results of this study indicated that cover crops impacted the distribution of soil inorganic N and the loading of nitrate to the tile despite N application timing.