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TECHNICAL REPORTS

Surface Water Quality

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

USDA-ARS, National Soil Tilth Laboratory, Ames, IA 50011

^* Corresponding author (Tom.Kaspar{at}ars.usda.gov).

Received for publication October 27, 2006. A significant portion of the 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 N fertilizer management alone is not sufficient for reducing NO₃ concentrations in subsurface drainage to acceptable levels; therefore, additional approaches need to be devised. We compared two cropping system modifications for NO₃ concentration and load in subsurface drainage water for a no-till corn (Zea mays L.)-soybean (Glycine max [L.] Merr.) management system. In one treatment, eastern gamagrass (Tripsacum dactyloides L.) was grown in permanent 3.05-m-wide strips above the tiles. For the second treatment, a rye (Secale cereale L.) winter cover crop was seeded over the entire plot area each year near harvest and 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 initiated in 2000 and replicated four times. Full establishment of both treatments did not occur until fall 2001 because of dry conditions. Treatment comparisons were conducted from 2002 through 2005. The rye cover crop treatment significantly reduced subsurface drainage water flow-weighted NO₃ concentrations and NO₃ loads in all 4 yr. The rye cover crop treatment did not significantly reduce cumulative annual drainage. Averaged over 4 yr, the rye cover crop reduced flow-weighted NO₃ concentrations by 59% and loads by 61%. The gamagrass strips did not significantly reduce cumulative drainage, the average annual flow-weighted NO₃ concentrations, or cumulative NO₃ loads averaged over the 4 yr. Rye winter cover crops grown after corn and soybean have the potential to reduce the NO₃ concentrations and loads delivered to surface waters by subsurface drainage systems.

Abbreviations: DOY, day of year • USEPA, United States Environmental Protection Agency • UTM, Universal Transverse Mercator

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