Abstract
Biculture of nonlegumes and legumes could serve as cover crops for increasing main crop yield, while reducing NO3 leaching. This study, conducted from 1994 to 1999, determined the effect of monocultured cereal rye (Secale cereale L.), annual ryegrass (Lolium multiflorum), and hairy vetch (Vicia villosa), and bicultured rye/vetch and ryegrass/vetch on N availability in soil, corn (Zea mays L.) yield, and NO3-N leaching in a silt loam soil. The field had been in corn and cover crop rotation since 1987. In addition to the cover crop treatments, there were four N fertilizer rates (0, 67, 134, and 201 kg N ha(-1), referred to as N0, N1, N2, and N3, respectively) applied to corn. The experiment was a randomized split-block design with three replications for each treatment. Lysimeters were installed in 1987 at 0.75 m below the soil surface for leachate collection for the N 0, N 2, and N 3 treatments. The result showed that vetch monoculture had the most influence on soil N availability and corn yield, followed by the bicultures. Rye or ryegrass monoculture had either no effect or an adverse effect on corn yield and soil N availability. Leachate NO3-N concentration was highest where vetch cover crop was planted regardless of N rates, which suggests that N mineralization of vetch N continued well into the fall and winter. Leachate NO3-N concentration increased with increasing N fertilizer rates and exceeded the U.S. Environmental Protection Agency's drinking water standard of 10 mg N l(-1) even at recommended N rate for corn in this region (coastal Pacific Northwest). In comparisons of the average NO3-N concentration during the period of high N leaching, monocultured rye and ryegrass or bicultured rye/vetch and ryegrass/vetch very effectively decreased N leaching in 1998 with dry fall weather. The amount of N available for leaching (determined based on the presidedress nitrate test, the amount of N fertilizer applied, and N uptake) correlated well with average NO3-N during the high N leaching period for vetch cover crop treatment and for the control without the cover crops. The correlation, however, failed for other cover crops largely because of variable effectiveness of the cover crops in reducing NO3 leaching during the 5 years of this study. Further research is needed to determine if relay cover crops planted into standing summer crops is a more appropriate approach than fall seeding in this region to gain sufficient growth of the cover crop by fall. Testing with other main crops that have earlier harvest dates than corn is also needed to further validate the effectiveness of the bicultures to increase soil N availability while protecting the water quality.
Highlights
Improving soil quality and crop productivity is central to sustainable agriculture
Winter cover cropping has emerged as a promising practice to help attain this goal
The benefits of winter cover cropping include providing ground cover to protect soil from erosion[1], increasing input of organic matter to soil, and removing the residual soil inorganic N to minimize NO3 leaching and contamination of groundwater[1,2]; some winter cover crops are more beneficial than others
Summary
Improving soil quality and crop productivity is central to sustainable agriculture. Winter cover cropping has emerged as a promising practice to help attain this goal. Soil, and weather conditions, different plant species with contrasting chemical characteristics have been used as winter cover crops. When planted after fall harvest, nonleguminous cover crops reduced N leaching by 20 to 69 kg N ha1 depending on the region, cropping system, cover crop species, and the amount of supplemental N applied[2,3,4]. Nonleguminous cover crop residues, have no effect or even adverse effects on production of a succeeding main crop[5], possibly because of N immobilization[6] or production of allopathic compounds[7]; while serving an important function of decreasing N leaching and increasing soil organic C and N accumulation, it is not beneficial to the production of a succeeding crop
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