July 7, 2014: Jane Fyksen-Agri-view
Cover crops are becoming a valued workhorse in farmers’ fields, fitting niches in cropping and grazing systems. Interest has grown, particularly in forage radishes.
Cover crops provide many benefits. They reduce erosion by holding soil in place, increase soil microbial activity and nutrient cycling, reduce excess nitrogen and increase soil carbon. Their plant biomass helps to build soil organic matter, too.
Cover crop varieties range from grains like cereal rye, legumes such as hairy vetch, and brassicas like radish and rapeseed.
Prevent plant became a common phrase across the Corn Belt last year, and many upper Midwest farmers had their first chance to try cover-crop radishes on those prevent-plant acres, reports Ryan Stockwell, a Medford farmer and senior agriculture program manager for the National Wildlife Federation.
Radishes reduce soil compaction due to the plant’s large taproot, reports Stockwell, adding that they attract soil livestock, the microbes, worms, fungi and more in the soil providing nutrient cycling for cash crops.
Farmers who have planted radishes for many years have seen improvements in water infiltration and soil health. Stockwell mentions that one benefit of radishes that may become more evident is weed control for the year following radishes.
Admittedly, since a cover crop radish does not overwinter and only a carcass is left the following spring, its weed control potential seems hard to believe; however, a recent article in Agronomy Journal from author Yvonne Lawley at the University of Manitoba investigates the nature of radish’s weed control.
Lawley, along with John Teasdale from U.S. Department of Agriculture’s Agricultural Research Service in Beltsville, Md., and Ray Weil from the University of Maryland, looked at what mechanism of weed suppression a forage radish cover crop employs.
Stockwell reports that experiments were conducted to determine if the forage radish cover crop suppresses weeds via plant chemicals or direct competition with weeds in the fall. Since radishes winterkill in Wisconsin and other parts of the upper Midwest, they are physically present and growing during the fall. This research suggests that weed suppression by radishes is 
due to direct competition in the fall, not plant chemicals.
Cover crop radish needs to be planted early, around early August, for sufficient growth. Stockwell drilled radishes after wheat harvest last year in Taylor County.
“I had almost zero broadleaf weeds and a small amount of grass weeds this spring, much less weed pressure than in years past,” he notes. “The radish cover crop made weed control very easy.”
Read Stockwell’s latest post on cover crops at http://blog.nwf.org/2014/05/evidence-builds-no-till-and-cover-crops-make-working-lands-more-wildlife-friendly/.
Five-year cover crop study noted
Iowa State University released results of a 5-year cover crop on-farm yield study. This work by Iowa Learning Farms and Practical Farmers of Iowa found that cereal rye cover crops added to a corn-soybean rotation seems to have little effect on yield.
Ten Iowa farmers participated in this 5-year project between 2009 and 2013. They established side-by-side strips of corn or soybeans with a winter cereal rye cover crop, as well as strips using no cover crop.
The cover crop was either drilled after harvest or aerially seeded into standing crops each fall. At each site, the cover crop was terminated with herbicide the following spring.
When the project started, farmers were concerned the winter cereal rye would negatively impact their corn or soybean yields, but after harvest each year, they discovered that was not the case. The properly managed cover crops had little-to-no negative effect and, in some cases, actually improved the yield of soybeans.
“When I first started the trial, I thought the following crop would suffer because of the competition for water and nutrients,” admits participating Butler County, Iowa farmer Rick Juchems. “That has been proven wrong with stronger yields and better soil quality.”
Juchems’ corn yields remained steady, and he saw a slight improvement in soybean yields on the cover crop acres last year as well as in 2011.
Iowa researchers and participating growers found that weather variability may affect soil properties such as water infiltration and carbon and nitrogen concentration more strongly than cover crop usage. While year significantly affected many measured parameters, cover crop treatment did not appear to result in any changes.
In contrast, research in Maryland did not find any changes in organic matter content in soils there after 13 years, though some parameters like aggregate stability did change, and some seasonal differences were seen.
A 4-year trial in Illinois found fewer significant changes in soil properties and no differences in soil organic matter. In another Illinois study, increased organic matter after 5 years of cover cropping was attributed to high cover crop biomass and a relatively high nitrogen concentration of the biomass through the inclusion of vetches as well as rye.
Management is key when incorporating cover crops into a corn-soybean rotation. Knowing which cover crop to plant, when and how to plant and terminate the cover crop are necessary to success.
A four-page summary of the Iowa study is available at www.extension.iastate.edu/ilf/content/cover-crop-research. There is more information regarding cover crops at www.extension.iastate.edu/ilf/content/cover-crop-resources.
Single species versus multiple species
A replicated trial on a farm in the northcentral part of Michigan’s Upper Pennisula (UP) explored the option of multi-species cover crops and compared three cover crop selections and a fallow treatment, reports Jim Isleib with Michigan State University Extension in the UP.
The cover crops included Marathon red clover, a hybrid sorghum sudangrass and a multi-species cover crop mixture from North Dakota containing soybeans, lentils, forage peas, sweet clovers, turnips, oilseed radishes, pearl millets, forage oat and sunflowers.
The cover crops were planted at the end of June and allowed to grow through the year, with livestock grazing simulated by mowing off about half of the sorghum sudangrass and multi-species mixture in late September and leaving the mown material on the plots. This grazing was included to demonstrate the way multi-species cover crops are managed on North Dakota farms, notes Isleib.
After tilling the cover crop under in the spring, oats were planted and oat yields were compared in August to determine the impact of the different soil-building cover crop after just 1 year. Soil samples also were collected, following the cover crop and following the oat. No fertilizer was used in this project.
Oat yield following the cover crop treatments in this trial gives a single indication of the impact of a single-year cover crop treatment. Other factors, including weed suppression, were not included in this trial, notes Isleib, who admits that this 2-year trial was not expected to result in dramatic changes in crop yield or soil conditions, as “cover crops are understood to be a long-term investment in soil health and crop performance with benefits becoming more apparent over several seasons.”
Here are the oat yields (at 13.5 percent moisture) from prior-year cover crop treatments: Fallow, 92 bushels; red clover, 92 bushels; sorghum sudangrass, 102 bushels; multi-species cover crops mix, 109 bushels.
“The sorghum sudangrass and multi-species cover crop treatments resulted in better oat yields the following year, compared with red clover and fallow treatments. Soil testing before the trial showed a fertile soil high in organic matter. The organic matter dropped during and after the trial, probably due to thorough tillage of the pre-existing old sod prior to seeding cover crops and resulting oxidation and decomposition of raw organic matter. The inclusion of a cover crop can be expected to help maintain soil organic matter following the initial plow down of an old, dense sod and in following cropping years,” Isleib reports.
He also dials in on cover crop seed cost and the value of oat yield above fallow treatment, with oats at $3.85 a bushel.
• Fallow: 0 seed cost per acre, 0 additional oat yield, 0 additional profit per acre.
• Red clover: $33.12 seed cost per acre, 0 additional oat yield, minus $33.12 an acre.
• Sorghum Sudangrass: $15 seed cost per acre, 10 bushels more oats, $38.50 an acre more oat value, $23.50 additional profit per acre.
• Nitrogen Builder cover crops mix: $24 seed cost per acre, 17 bushels more oats, $65.45 an acre more oat value, $41.45 additional profit per acre.
Isleib says that there was not a statistically significant difference between oat yield following sorghum sudangrass and the Nitrogen Builder cover crop treatments. Soil tests following the cover crop showed a modest increase in phosphorus, potassium, magnesium, calcium and cation exchange capacity (CEC) under the Nitrogen Builder cover crop treatment. Soil organic matter, pH and lime index content were reduced.
“The Nitrogen Builder multi-species cover crop treatment compared favorably to the fallow and mono-culture cover crop treatments included in the trial,” reports Isleib.
For more information, visit www.covercrops.msu.edu.
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