Rye Cover Crop and Gamagrass Strip Effects on NO3 Concentration and Load in Tile Drainage

Authors: Kaspar, Thomas; Jaynes, Dan; Parkin, Timothy; Moorman, Thomas

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2007
Publication Date: 8/31/2007
Citation: Kaspar, T.C., Jaynes, D.B., Parkin, T.B., Moorman, T.B. 2007. Rye Cover Crop and Gamagrass Strip Effects on NO3 Concentration and Load in Tile Drainage. Journal of Environmental Quality. 36(5):1503-1511.

Interpretive Summary: A significant portion of the nitrate (NO3) from agricultural fields that contaminates surface waters in the Midwest Corn Belt is transported to streams or rivers by subsurface drainage systems or “tiles”. Previous research has shown that nitrogen (N) fertilizer management alone is not sufficient for reducing NO3 concentrations in subsurface drainage to acceptable levels, therefore additional approaches need to be devised. One of the reasons that fertilizer management alone will not solve the problem is that most of the NO3 losses to drainage water or deep percolation occur during the fall, winter, and early spring, after harvest and before planting of the corn and soybean crops. Small grain winter cover crops have the potential to increase uptake of NO3 and water during this period in the Midwest Corn Belt and to reduce NO3 losses. Similarly, planting a perennial grass, like gamagrass, in narrow strips directly over subsurface drain tiles within fields planted annually to corn or soybean also has the potential to take up water and NO3 moving to drainage tiles. Our experiment showed that a rye winter cover crop reduced nitrate concentration and load of subsurface drainage water from a corn-soybean rotation. A permanent gamagrass strip above the drainage tile also reduced annual drainage and NO3 load averaged over 4 years. This research will benefit scientists, soil conservationists, and farmers because it shows that small grain cover crops and gamagrass strips can decrease nitrate losses in tile drainage and can be used to reduce nitrate concentrations and loads in surface streams in the Mississippi basin.

Technical Abstract: A significant portion of the nitrate(NO3) from agricultural fields that contaminates surface waters in the Midwest Corn Belt is transported to streams or rivers by subsurface drainage systems or tiles. We compared two cropping system modifications for NO3 concentration and load in subsurface drainage water with a no-till corn-soybean management system. In one treatment, eastern gamagrass was grown in permanent 3.05-m-wide strips above the tiles. For the second treatment, a rye winter cover crop was seeded over the entire plot area after both soybean and corn harvest and then chemically killed before planting the following spring. Twelve 30.5 x 42.7-m subsurface-drained field plots were established in 1999 with an automated system for measuring tile flow and collecting flow-weighted samples. Both treatments and a control were replicated four times and treatment comparisons were conducted from 2002 through 2005. The rye cover crop treatment significantly reduced subsurface drainage water flow-weighted NO3 concentrations in all 4 years and NO3 loads in 3 of 4 years. The rye cover crop treatment, however, did not significantly reduce cumulative annual drainage. Averaged over 4 years the rye cover crop reduced flow-weighted NO3 concentrations by 59% and loads by 62%. The gamagrass strips did not significantly lower flow-weighted NO3 concentrations, but significantly lowered cumulative annual drainage by 26% and NO3 loads by 24% averaged over the 4 years. A rye cover crop grown after both corn and soybean and gamagrass strip over the drainage tile have the potential to reduce the NO3 loads delivered to surface waters by subsurface drainage systems.