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U research guides growers on cover crop selection, planting date

ST. PAUL, Minn. -- Cover crops are any green crops grown between cash crops. They come in many different varieties, but until recently little information was available to help growers decide which varieties to select and exactly when to plant them.

Common uses of cover crops include reduction of soil erosion, weed prevention, nutrient scavenging and alleviation of soil compaction. They are most easily used after small grains, canning crops, and silage, but can also be used in the corn-soybean rotation.

The difficult growing conditions of 2011 provided a unique circumstance for collecting cover crop data. Researchers and educators from University of Minnesota Extension, University of Minnesota Southwest Research and Outreach Center, and Albert Lea Seed House partnered with North Central Region Sustainable Agriculture Research and Education (NCR-SARE) on the establishment of cover crop plots to be used for education and outreach.

The cover crop plots were established in areas that were too wet for spring 2011 planting; conditions were similar to those for prevented-plant acres. The year's weather extremes allowed us to study the agronomics of cover crops under both wet and dry conditions.

Cover crops included: tillage radish, oats, field pea, winter rye, sudangrass, sorghum-sudangrass, pearl millet, cowpeas, tillage radish-oats-field pea mixture, oats-cowpea mixture, oats-berseem clover mixture, and oats-crimson clover mixture. Site conditions included: after corn with standing water that prevented planting, after alfalfa with soil too wet to plant, and after oat harvest. Two planting dates were used: Aug. 17 and Sept. 9, 2011. Plant cuttings were taken Oct. 27, 2011.

Data showed that under the 2011 growing conditions in Lamberton, Minn., cover crops had the most above-ground growth when planted in mid-August with the previous cash crop of field corn, except in the tillage radish. No single cover crop species consistently had the most above-ground plant matter for each planting date or site.

The top plant-matter producer was the oats-cowpea mixture planted Aug. 17 with the previous cash crop of corn (4,539 pounds dry plant matter per acre). The lowest plant-matter producer under all plot conditions was the cowpeas (zero pounds dry plant matter per acre). No samples were taken from the plots planted in the 2011 oat field. Conditions were too dry for growth.

University of Minnesota researchers and Extension educators contributed to a cover crop decision tool that can be found at the Midwest Cover Crops Council website: To join the Minnesota Cover Crop Listserv, email me at

Jill Sackett is a conservation agronomist with University of Minnesota Extension and Rural Advantage.