Effectiveness of oat and rye cover crops in reducing nitrate losses in drainage water

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

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2012
Publication Date: 5/16/2012
Citation: Kaspar, T.C., Jaynes, D.B., Parkin, T.B., Moorman, T.B., Singer, J.W. 2012. Effectiveness of oat and rye cover crops in reducing nitrate losses in drainage water. Agricultural Water Management. 110:25-33. DOI:10.1016/j.agwat.2012.03.010.

Interpretive Summary: A significant portion of the nitrate from agricultural fields that contaminates surface waters in the Mississippi River basin comes from corn and soybean fields with subsurface drainage systems. Previous research has shown that nitrogen fertilizer management alone is not sufficient for reducing nitrate concentrations in drainage water to acceptable levels. Therefore, additional approaches like cover crops need to be studied. One of the reasons that fertilizer management alone will not solve the problem is that most of the nitrate losses to drainage water occur during the fall, winter, and early spring, after maturity and before planting of the corn and soybean crops. Small grain cover crops, like rye and oats, can grow and take up nitrate and water during this period and thus, have the potential to reduce nitrate losses. Questions remain as to whether a rye cover crop planted year after year will remain effective at reducing nitrate loss or whether an oat cover crop, which only grows in the fall, can reduce nitrate loss significantly. Our experiment showed after nine years of annual use that a rye winter cover crop continued to reduce the nitrate concentration of drainage water from a corn-soybean rotation, but was slightly less effective than during the first four years of use. An oat cover crop growing only in fall reduced nitrate concentrations about half as much as the rye cover crop. This research will benefit scientists, soil conservationists, and farmers because it shows that small grain cover crops decrease nitrate losses in tile drainage and can be used in conjunction with other practices to reduce nitrate losses to surface streams in the Mississippi basin.

Technical Abstract: Much of the NO3 in the riverine surface waters of the upper Mississippi River basin originates from artificially drained agricultural land used for corn (Zea mays L.) and soybean (Glycine max [L.] Merr.) production. Cover crops grown between maturity and planting of these crops are one approach to reducing NO3 losses. Our objectives were to determine whether a rye winter cover crop after more than four years of annual use and an oat fall cover crop seeded before harvest could effectively reduce drainage NO3 losses. The oat fall cover crop was broadcast seeded into living corn and soybean crops before harvest and was killed by cold temperatures in late fall. The rye winter cover crop was planted with a grain drill after corn and soybean harvest, overwintered, grew again in the spring, and was killed with herbicides before planting of the main crops in the spring. These treatments were evaluated against a control in subsurface-drained field plots with an automated system for measuring drainage flow and collecting proportional samples for analysis of NO3 concentrations. The rye winter cover crop significantly reduced drainage water NO3 concentrations by 48% over five years, but did not significantly reduce cumulative loads due to variability in cumulative drainage. The rye cover crop was not as effective as it was in a previous study at this site, but still provided a reasonable reduction in NO3 concentrations. The oat fall cover crop reduced NO3 concentrations by 26% or about half the reduction of the rye cover crop. Contrary to previous research the oat treatment caused a reduction in corn and soybean yield in some years. Both cover crops have the potential to reduce NO3 losses to surface waters from agricultural drainage systems.