Cover Crops Information
By now, all Midsouth soybean producers know about the myriad reasons for and advantages from integrating cover crops [CC] into a crop production system. Depending on CC species, major reasons for using them are 1) managing primary nutrients left by or used by a preceding or following summer cash crop, 2) weed suppression in the summer cash crop, and 3) a reduction is sediment losses that arise from erosion. The information in the following articles provides useful information pertaining to these subjects.
Does residue incorporation influence available nitrogen release from cereal rye and tillage radish cover crops under controlled conditions? by Greub and Roberts, Univ. of Ark. [Soil Sci. Soc. Am. J. 2023;87:324-336] reports the following.
• An aerobic laboratory incubation of soil containing residues from cereal rye and tillage radish CC’s was conducted to determine the effect on the mineralization and nutrient cycling potential of residues from these CC’s when grown in the midsouthern U.S.
• CC residues were added to soil on an equivalent nitrogen [N] basis. Thus, the amount of CC residue that was added varied between the two CC species used in this study.
• Incubation temperature was kept at 23°C to mimic the average soil temperature at Kibler, Arkansas.
• CC species used in this study influenced rate of residue decomposition and N mineralization.
• Immobilization of N was lower for tillage radish residue than for cereal rye residue regardless of the residue being left on the soil surface vs. its being incorporated.
• Results from this study indicate that tillage radish may possibly be more effective at synchronous N release than cereal rye. However, both species have the potential to provide similar amounts of inorganic N over the same period of time, but at different rates and timings of release.
• The bottom line based on these results is this: 1) CC species influences both rate of N mineralization from and decomposition of CC residue; and 2) residue incorporation by tillage vs. no incorporation will influence the rate of plant-available N release from the residue.
Agronomic and economic implications of cover crop and phosphorus fertilizer management practices for water quality improvement by Nelson et al. [J. Environ. Qual. 2023;52:113-125] provides the following information.
• Data were collected from a 4-year [2015-2019] field study conducted at a site near Manhattan, Kansas to determine the impacts of three phosphorus [P] management practices [no P, fall-broadcast P, and spring-injected P] and CC’s [winter wheat alone or winter triticale + rapeseed or winter wheat + rapeseed] on yields, net returns [no government payments included], and water quality in a no-till corn-soybean rotation production system.
• The most profitable treatment was fall-broadcast P fertilizer with no CC. However, this treatment also had the greatest P loss and near greatest sediment loss.
• The lowest-cost methods for reducing P and sediment losses were no P fertilizer without a CC, spring-injected P fertilizer without a CC, and spring-injected P fertilizer with a CC, respectively.
• The no-P fertilizer treatment resulted in the lowest production of CC biomass and corn grain over the 4 years of this study.
• Soybean grain yield was not affected by P fertilizer treatment over the 4-year period of the study, but the authors state that continual production of soybean without P fertilizer addition would be expected to result in lowered soybean grain yield over the long term.
• CC adoption was the only effective method for decreasing sediment losses in this study.
• The authors concluded that producer adoption of the best practices identified in this study will likely require monetary incentives, and that sufficiency P fertilization vs. P fertilization to build-and-maintain soil P levels for corn and soybean grown in rotation should be evaluated as an alternative P fertilization management practice.
Mechanisms of weed suppression by cereal rye cover crop: A review by Silva and Bagavathiannan [Agron. J. 2023;115:1571-1585] reports the following results.
• Cereal rye is used as a CC to 1) reduce soil erosion in the off-season between summer cash crops, 2) reduce leaching of nutrients that are not used by a summer cash crop, 3) reduce fertilizer inputs, 4) increase soil organic matter, and 5) suppress weeds that might compete with a summer cash crop.
• A cereal rye CC evidently suppresses weeds by multiple mechanisms, including competition for resources needed for weed growth and development. Climate and management of this CC species determine the dominant weed suppression mechanisms that are attributed to it.
• Results reported in this review indicate that high biomass production by cereal rye is not always a requirement for weed suppression benefits to occur, although weed suppression was much less variable when biomass levels were high. A majority of the sources reviewed for this article indicate that a greater cereal rye CC biomass results in greater weed suppression, especially of small-seeded weed species, when biomass residue is left on the soil surface vs. incorporated.
• Nitrogen immobilization into cereal rye plant tissues is especially important when it is grown before a legume crop such as soybeans.
• Allelopathic potential of any CC is difficult to measure in field environments. Thus, the effect of cereal rye CC allelopathy is subjective and should not be considered an important contributor to weed suppression in field settings.
• The authors state that “adequate management of cereal rye is essential to maximize its benefits as a CC”. Management factors such as planting time and method, quality of planted seed, seeding rate, fertilization, and termination timing and method should be considered important since they will affect biomass production. The authors also state that the physical barrier effect from a cereal rye CC is the best known mechanism for weed suppression.
• And finally, the authors state that “the integration of a cereal rye CC into a crop production system is a valuable strategy for managing herbicide-resistant weeds...”.
Fall-winter cover crops promote soil health and weed control in the southeastern clayey soils by Aime et al. [Agron. J. 2023;115:242-360] reports the following.
• This short-term research with CC’s was conducted in the Piedmont region of South Carolina on a kaolinitic clay soil.
• A MG VI soybean variety was planted in mid- or late-June as the summer cash crop at least 7-8 weeks after CC termination.
• Seven CC treatments were used in the study, and included cereal rye and crimson clover used alone, and varied mixtures of cereal rye, crimson clover, turnip, oat, radish, Austrian winter pea, hairy vetch, and wheat.
• Cereal rye alone or in a mixture with other CC species produced the greatest amount of biomass. Cereal rye in a mixture comprised 50% or more of the biomass production.
• Yield of soybean following a cereal rye CC either alone or in a mixture was among the highest yielding treatments.
• The highest biomass-producing CC’s resulted in weed control that was equal to or greater than that of a chemical fallow treatment.
• The authors concluded that their results suggest that rye either alone or in the mixtures used in this study will be a suitable CC treatment based on biomass production, weed suppression, short-term improvements in soil health as indicated by their measured parameters, and soybean yield performance.
• And finally, the authors concluded that their results provide the rationale for soybean producers in the southeastern U.S. to grow cover crops vs. a chemical fallow during the fall-winter season between soybean crops.
• Caveat. The results from this short-term study lead to the following point. Economic benefit from CC use will not likely be realized in the short term since the expense associated with CC inclusion will not be recouped. This is further emphasized in an article titled “Don’t abandon cover crops after one tough year” by Becky Brathal, a crops educator with Univ. of Wisconsin Extension.
An article by Mindy Ward titled “Solve the cover crop conundrum” provides links to online tools that can be used by producers to refine their decisions about CC use.
• A Cover Crop Species Selector allows producers to select the CC or CC mixture that should work best to meet their defined goal.
• A Cover Crop Nitrogen Calculator will allow a producer to select a CC species or mixture that can supply N to a following cereal cash crop.
• Two additional tools–a Cover Crops Economics Calculator and a Cover Crops Seeding Rate Calculator–should be available online in the coming months. Click here to access online CC tools as they become available from Precision Sustainable Agriculture.
An Aug. 14, 2023 article titled “Enroll Now: Farmers for Soil Health Offers Financial Assistance for Cover Crop Adoption” provides information about a farmer-led initiative that offers cost-share programs to farmers who plant CC’s for 3 years. This program is a collaborative effort among varied commodity groups that include the United Soybean Board. The objective of this initiative is to create a farmer-led program that will advance the use of soil health improvement practices such as CC’s. This initiative is provided through Farmers for Soil Health, and details about the program can be accessed on their website. .
Remember that the important points about CC use are: 1) define the objective(s) and intended outcome(s) from CC use in order to select the appropriate CC species; 2) ensure that quality seed of the selected CC species are planted at the proper seeding rate for the seed lot that is used [click here for an article about this]; 3) ensure that proper planting practices are used so that an adequate stand of the CC is achieved; 4) choose the proper timing and method for terminating the CC; and 5) realize that the cumulative benefits from cover cropping with any species will likely only accrue over the long term [arguably >10 years]. These subjects are covered in the White Paper on this website that provides details about CC use in crop production systems. Also, click here [filter by sustainability, then search cover crops] to access numerous articles on this website that deal with various aspects of CC use.
Composed by Larry G. Heatherly, Aug. 2023, larryh91746@gmail.com