Cover Crops Update
If the amount of recent coverage given to cover crops in various media outlets is any indication, using cover crops for curing all the ills associated with herbicide-resistant (HR) weeds is the next big thing. How I wish that was true, but my years in agronomic research have taught me that there is no panacea for any of the many maladies that affect soybean production.
The premise supporting the use of cover crops is that they should become an integral part of any cropping system that seeks to become more sustainable and supportive of conservation agriculture. They are incorporated into most cropping systems to provide environmental and soil productivity benefits. Recently, they have been touted as an effective tool to aid in the management of HR weeds.
The integration of cover crops into a crop production system should be considered a long-term investment for conserving and/or improving soil and water resources. Their use as a tool against HR weeds should become a part of this broader use.
For row crop producers in the Midsouth, the major categories of winter cover crops to consider are either grasses (wheat, cereal rye, oats), legumes (vetches, peas, clovers), or a mixture of the two.
There are already several cover crops articles posted on this website. Click the following links to view those articles.
Cover Crops–MSSOY White Paper–updated Sept. 2016
Cover Crops and Corn Stover Removal blog–posted Oct. 2015
Timing of Cover Crop Termination for the Southeast blog–posted Feb. 2016
Cover Crop Termination with Herbicides blog–posted Oct. 2015
Cover Crops blog–posted Aug. 2015
In the below narrative, I cite recent resources that pertain to cover crops, and provide a brief summary of the content of each linked article.
2016 Cover Crop Survey–CTIC, SARE, ASTA. Results from the fourth annual Cover Crop Survey are summarized. Data were collected from 2,020 respondents from 48 states; Arkansas, Louisiana, Mississippi, and Tennessee were in the lowest responding group of states. 70% of the respondents described themselves as commodity crop farmers; i.e., they grow corn, soybeans, wheat, cotton, or grain sorghum. The number of acres of cover crops per respondent has grown from about 140 acres in 2011 to an estimated 339 acres in 2016.
Unfertilized Cover Crop May Reduce Nutrient Losses from Tennessee Fields–UTIA. Univ. of Tenn. scientists Hawkins and McClellan used a Soil and Water Assessment Tool (SWAT) or model to determine that farmers can significantly reduce the amount of nitrogen and phosphorus lost from row crop fields by incorporating an unfertilized winter wheat cover crop into their crop rotations.
Increasing Water Use Efficiency/Drought Tolerance and Yields with Cover Crops–utcrops.com. Author Tyson Raper, Univ. of Tenn. Cotton and Small Grains Specialist, found that soil moisture measurements suggest that a wheat cover crop increased water infiltration into the soil, and water retention by soil. This suggests that cover crops may aid in the prevention of yield penalties that result from slight to moderate soil water deficits.
A Few Thoughts on Incorporating/Managing Cover Crops–utcrops.com. Author Tyson Raper presents a summary of available information on advantages of single-species monocot covers vs. species mixtures, and timing of cover crop termination.
Cover Crops before Soybean Improve Soil Health–Iowa State Univ. Drs. Castellano, Archontoulis, Helmers, Mueller, and Leandro present a summary of the results of their USB-funded project. They found that cover crops before soybean produce significantly more biomass than cover crops before corn, which in turn increased soil nitrogen retention by 100% without affecting soybean yield.
Functional Diversity in Cover Crop Polycultures Increases Multifunctionality of an Agricultural System–J. of Appl. Ecology 2016. Authors Finney and Kaye present results from a unique study that was designed to determine how increasing species richness of a cover crop (cover crop with multiple species) may or may not impact the resulting ecosystem (weed suppression, N retention, cover crop biomass N, N supply during subsequent summer crop season) and yield of the following summer crop.
Evaluating Cover Crops and Herbicides for Glyphosate-Resistant (GR) Palmer Amaranth Control in Cotton–Weed Tech 30:2016. Authors Wiggins, Hayes, and Steckel report results from this West Tenn. study that was designed to evaluate Palmer amaranth control when integrating cover crops with PRE residual herbicides. Cereal rye and winter wheat cover treatments provided the best Palmer amaranth control, while treatments with crimson clover and hairy vetch covers had the greatest number of Palmer amaranth plants. Their conclusions were that high-residue cover crops in combination with the PRE herbicides used in the study did not adequately control Palmer amaranth, but these inputs can be a part of an effective GR Palmer amaranth management strategy when combined with additional late-season weed control inputs.
Long-Term Corn Yield Impacted by Cropping Rotations and Bio-Covers under No-Tillage–Agron. J. 108:2016. In a long-term Tennessee study, authors Ashworth, Allen, Saxton, and Tyler found that legume cover crops resulted in increased yield of corn that was grown in a rotation with soybean. Their results also indicated that winter wheat as a cover crop prior to corn in this rotation is detrimental to corn yield.
Costs and Benefits of Cover Crops: An Example with Cereal Rye–Univ. of Ill. farmdoc daily. Authors Schnitkey, Coppess, and Paulson provide an example of the costs associated with cover crops, using cereal rye as an example. This estimate of $20.60/acre is based on $13.10/acre for drilling and $7.50/acre in seed costs based on 30 lb./acre @ $0.25/lb. This cost estimate will be $28.10/acre if the cereal rye is planted at a more likely rate of 60 lb./acre. In a no-till system where a $5/acre herbicide charge is included, the estimate is $25.60/acre ($33.10/acre with a 60 lb./acre seeding rate).
Rolling Rye to Control Tough Weeds. This Univ. of Georgia video provides an in-depth presentation on rolling tall cereal rye, including equipment needs.
AgFax Weed Solutions Oct. 2016–agfax.com. A series of short articles that provide 1) major reasons for using cereal rye as a cover crop to assist in managing HR weeds, 2) how cereal rye may impede the sunlight needed for pigweed germination, 3) how to initially deal with cereal rye biomass, 4) using legumes with cereal rye, 5) how a properly rolled cereal rye cover crop with high biomass can reduce pigweed germination and emergence, and 6) the long-term benefits of a cereal rye cover crop.
When Should I Terminate My Cover Crop.–utcrops.com. Author Garret Montgomery of the Univ. of Tenn. gives the pros and cons of early vs. late termination of both single species and mixed species cover crops in relation to soybean or corn planting.
Terminating Cover Crops-What’s Your Plan–Iowa State Univ. Authors Anderson, Vittetoe, and Hartzler present details about plus pros and cons for using herbicides, rolling/crimping, and tillage to terminate cover crops. They also provide links to other articles about cover crop termination.
Here are some points gleaned from all of the above.
• The first step when deciding to use cover crops is to define the purpose for their inclusion so that subsequent input and management decisions support that purpose; i.e., is the purpose to control HR weeds, remedy soil compaction, protect highly erodible soil, scavenge soil nutrients left from a preceding crop, increase soil organic matter, provide N to a following crop, etc.?
• One of the main points gleaned from all of the cover crops literature is that a one-cover-crop-fits-all approach likely will not result in the intended result. This is supported by the research of Finney and Kaye (cited above). An example follows.
In a corn-soybean rotation, using winter wheat or cereal rye after the corn crop will scavenge soil N that may not have been used by the corn crop, thus preventing it from leaving the site. The cereal rye may also provide some weed control prior to planting the following soybean crop. Using a legume such as hairy vetch after the soybean crop likely will provide some N for the next year’s corn crop, thus reducing the amount of N fertilizer that will be required.
• Cereal rye appears to be the best cover crop species for suppressing HR weeds, especially Palmer amaranth.
• A roller with the chevron design is likely the roller of choice to use when terminating a cover crop with the rolling method.
• If cereal rye is allowed to grow tall before terminating with a roller, a planter with a trash removing/handling attachment will likely be required to clean a space for the planted row of the following crop.
• With any cover crop, establishment of a suitable cover is paramount. This requires the proper species selection for the latitude, as well as suitable environmental growing conditions following emergence of the selected cover crop species.
• No cover crop will result in complete control of problem weeds such as HR Palmer amaranth.
• Some of the above articles mention the potential allelopathic effect from a terminated cereal rye cover crop. However, there is little if any research evidence that this does in fact occur. Click here for a detailed article on allelopathy.
• Planting a row crop into a terminated cover crop likely will require a planter that is equipped with special attachments to handle or plant through cover crop residue.
• It is likely that a cover crop will be used on a limited acreage within an individual producer’s total operation to perform a specific function such as controlling HR weeds, remedying soil compaction, protecting highly erodible soil, scavenging soil nutrients left from a preceding crop, or increasing soil organic matter.
• Costs attributed to cover crops used in a row-crop production system should be determined by using the proper inputs and rates of those inputs. These costs will vary considerably based on the tillage system used, the crop rotation, the cover crop species, and the method of cover crop termination. This is the information that is most urgently needed so that the cost/benefit of cover crop incorporation into a crop production system can be determined.
Click here for the White Paper on this website that is an up-to-date summary of cover crop subjects.
Composed by Larry G. Heatherly, Oct. 2016, larryheatherly@bellsouth.com.