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Cover Crops ProjectCover crops have been a major focus of WICST. They can play a key role in diversifying and reducing purchased inputs in many cropping systems that include a small grain (wheat, oats or barley) or canning crops (sweet corn, peas and beans). In addition to evaluating the agronomic and management aspects of numerous possible cover crops for the upper Midwest, the Trial has evaluated their value as a nitrogen source for corn. WICST has also conducted numerous on-farm and on-station trials of several cover crops, and in recent years has worked to fine-tune management and reduce risks associated with relying on cover crops for nitrogen. The two most successful cover crops we studied were medium or common red clover and hairy vetch. By fall freeze both usually contained nearly 100 lbs. of N/a in the tops and roots. Other cover crops studied included sweet clover, oats, dormant and non-dormant alfalfa, berseem clover and annual medic. Cover crops were sensitive to soil conditions. The cover crops we worked with were more successful on silt loams than sandy loams, and establishment was inconsistent on the more poorly drained Lakeland site. Red clover worked best frost seeded into winter wheat in our CS3. Seed is broadcast onto frozen and cracked soil in mid-March after snow melt. Seedlings remain relatively small until wheat harvest, at which time they have full sunlight and three months to grow and fix atmospheric nitrogen. Total nitrogen accumulation typically exceeds 100 lbs./a by the end of the growing season. Hairy vetch can be successfully planted after wheat harvest and produce appreciable biomass and nitrogen yields. On the two occasions (out of 18 site-years of the trial) when the red clover failed to establish well, the vetch produced an average of 115 lbs./a of nitrogen, providing an excellent “back-up plan” that reduces one of the potential risks of relying on a companion-seeded cover crop for nitrogen. We note, however, that on droughty soils, late July plantings can be riskier than frost seeding. Cover crops can provide most or all of the nitrogen required by corn growth. Trials to determine whether supplemental nitrogen was worthwhile found that additional nitrogen (either starter or sidedressed) produced a significant yield increase only about one-fourth of the time. The exceptions always occurred during years with cool springs, when there is a slow release of legume nitrogen. We recommend that producers perform the pre-sidedress nitrate test if the cover crop growth was modest or the spring particularly cool, and use sidedress nitrogen accordingly. (When justified, sidedress nitrogen was more economic than starter in our trials.) Legume nitrogen is made available to corn in a timely fashion. Except in particularly cool springs, legume nitrogen release is generally well timed to correspond with nitrogen uptake in corn. Cover crops provide substantial erosion control benefits. Cover crops generally provided 80-100% soil coverage minimizing the erosive impact of fall rain within a month of planting. Cover crops can be managed economically. When the cost of purchased nitrogen is low, the value of the nitrogen alone does not usually justify the cost of a legume. However, other benefits such as reduced herbicide use, improved yield of other crops, reduced risk of nitrate leaching, improved soil texture, diminshed erosion potential and reduced fossil fuel use make cover crops more attractive. As energy prices increase, cover crops become increasingly more attractive. Economics of cover cropsFarmer collaborators with the WICST project initially cited cost as their number one concern about using cover crops to replace synthetic nitrogen. WICST has studied several systems to determine whether cover crops can be an economically competitive source of nitrogen. Major findings are as follows: If the sole benefit of the cover crop were nitrogen, purchased synthetic nitrogen would be more economical when energy prices are low. The legume nitrogen plus the “rotation effect” generally makes the cover crop systems comparable to or only slightly less profitable than the systems relying on synthetic nitrogen. However, when the price of N fertilizer is high, cover cropping becomes more attractive. In addition to comparing CS2 and CS3, we compared a corn-oat-corn rotation with a corn-oat/red clover-corn rotation and a corn-oat/hairy vetch-corn rotation. We found that the gross margins of the cover crop systems were comparable to the corn-oat system that relied on synthetic nitrogen. Companion seeded red clover was generally more economical than vetch, due primarily to lower seed and establishment costs. There are excellent agronomic and economic reasons for farmers to experiment with cover crops. Our research suggests that cover crops are more economical than many farmers realize, and they offer clear benefits for soil quality, reduced nitrate leaching, and a way to expand corn-soybean rotations for pest and disease control. |
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