Sorghum-sudangrass

Midwest Cover Crops Council (MCCC-137)

University of Nebraska Extension (G2352)

This publication is intended to provide a starting point for farmers who are new to growing cover crops. With experience, farmers may fine-tune the use of cover crops for their systems.

Introduction

This publication provides an introductory approach to integrating cover crops following wheat and before corn or soybeans. These cover crops can have many benefits, such as erosion control, improved soil health, weed suppression, and quality forage production.

Planning and Preparation
  • Planning—Start planning early. Educate yourself by talking to experienced cover crop users, attending conferences and field days, and reading as much as possible about cover crops. Start small and determine your purpose and objectives for using cover crops. If needed, arrange for equipment, additional labor, or custom operators.
  • Residual herbicides—Consult your agricultural supplier regarding residual wheat herbicides that could cause concerns for newly planted cover crops. If cover crops will be grazed, additional herbicide restrictions may apply.
  • Seed purchase—Order your seed early from a reputable seed supplier to ensure a good germination rate, purity of seed, and that all seed has a seed analysis tag.
Summer Work
  • Dryland vs. irrigation—Irrigation allows for flexibility in managing planting dates and provides some insurance against dry planting conditions. Dryland seedings should occur immediately following wheat harvest in July for warm- and cool-season mixes. If delayed until August, consider changing to a cool-season mix. Contact your local Extension personnel for more information.
  • Residue management—Uniform spreading of chaff and straw is essential during wheat harvest in order to avoid interfering with the cover crop seeding operation.
  • Nitrogen management—If growing a forage crop, a nitrogen application before seeding a cover crop may be beneficial to counteract tie-up caused by stubble. Consider taking soil samples after the wheat harvest to determine nitrate-nitrogen levels. Depending on the prior nitrogen management, wheat yield, and weather, some residual nitrogen should be accounted for. The addition of nitrogen (up to 50 lbs. N/acre) may be beneficial in increasing biomass production of many of the cover crops, e.g., forage sorghum, sorghum-sudangrass.
  • Wheat curl mite—Volunteer winter wheat and some species in diverse cover crop mixes planted after wheat (e.g., sorghums, millets, oats, barley) can serve as a host for wheat curl mites. These mites are vectors for the wheat streak mosaic virus complex. Planting new winter wheat fields within two miles of this existing field may lead to yield losses in winter wheat fields. Applying a burndown herbicide before planting the cover crop may be an option to control volunteer wheat and reduce competition from weeds. Please read the herbicide label and consult with an agricultural supplier or local Extension personnel for more information.
  • Planting cover crop—No-till drill into stubble at least 45–60 days before the 50% frost date for your area. For most of Nebraska, this mix will need to be planted before early September. Use the Cover Crop Selector Tool (in Resources section) for more precise dates for your county. For the highest cover crop productivity, seed immediately after wheat harvest. Seeding depth is limited by the brassica species in the mix (rapeseed) as these are small seeds. A depth of 0.50 inch is best.
  • Seeding rate—Oats are used in most diversified mixes because they are an excellent carrier for the other seeds. Seeding rates per acre are: 16–24 lbs. of oats, 4 lbs. of forage sorghum or sorghum-sudangrass, 2 lbs. of pearl millet, 1 lb. of grain sorghum, 1 lb. of rapeseed, and 4 lbs. of buckwheat.
Figure 1: This diversified cover crop mix seeded right after wheat harvest was able to catch a 2-in rain and got off to a good start (Gary Lesoing)
Spring Work
  • Winterkill—All species in the mixture will usually winter-kill with the onset of hard freezes, which will eliminate the need for any changes to spring management.
  • Cover crop termination—If you have something in the mix that overwinters or germinates and emerges in the spring, the general recommendation is to terminate the mixture approximately two weeks prior to planting the next cash crop. Termination can be achieved using a full rate of glyphosate.
Resources

Cover Crop Selector Tool —available from the Midwest Cover Crops Council, https://www.midwestcovercrops.org

Post Corn, Going to Soybean: Use Cereal Rye (Nebraska Cover Crop Recipe series, MCCC-107)

Post Corn Silage, Going to Corn: Use Cereal Rye (Iowa Cover Crop Recipe series, MCCC-121)

Post Corn Silage, Going to Soybean: Use Cereal Rye (Iowa Cover Crop Recipe series, MCCC-122)

Managing Residual Herbicides with Cover Crops (Institute of Agriculture and Natural Resources, Univ. of Nebraska)

How Herbicide Labels Restrict Using Cover Crops as Forage (Institute of Agriculture and Natural Resources, Univ. of Nebraska)

Corn and Soybean Herbicide Options for Planting Cover Crops for Forage in Fall (Institute of Agriculture and Natural Resources, Univ. of Nebraska)

Residual Herbicides and Fall Cover Crop Establishment (Purdue Extension Weed Science publication)

Terminating Cover Crops: Successful Cover Crop Termination with Herbicides (Purdue Extension publication WS-50-W)

Wheat Stem Maggot Adult Monitoring: A Pest of Cover Crop-to-Corn Transitions (Institute of Agriculture and Natural Resources, Univ. of Nebraska)

Research Update on Cover Crops after Winter Wheat Harvest (Institute of Agriculture and Natural Resources, Univ. of Nebraska)

Authors

Gary Lesoing and Katja Koehler-Cole, University of Nebraska-Lincoln (Note: This publication was adapted with consent from MCCC under a joint project to produce customized introductory guidance about cover crops for all member states/provinces.)

Reviewers

Caro Córdova, Nathan Mueller, and Jennifer Rees, University of Nebraska-Lincoln; Eileen Kladivko, Purdue University; Anna Morrow, Midwest Cover Crop Council

The Midwest Cover Crops Council (www.midwestcovercrops.org) aims to facilitate widespread adoption of cover crops throughout the Midwest by providing educational/outreach resources and programs, conducting new research, and communicating about cover crops to the public.

Funding for this project was provided by McKnight Foundation.

December 2022

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or a part of an individual’s income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410 or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer. ©2022 by MCCC. All rights reserved.

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Midwest Cover Crops Council (MCCC-135)

This publication is intended to provide a starting point for farmers who are new to growing cover crops. With experience, farmers may fine-tune the use of cover crops for their systems.

Introduction

The following recipe provides an introductory approach to integrating a cover crop into a wheat-based rotation with soybean or corn. Planting a cover crop blend that predominantly consists of cool-season species and is winter-killed adds diversity and provides soil armor through summer and spring. However, in some situations added ground cover in the spring in combination with excess soil moisture could be a problem unless winter cereals (winter rye, wheat, or triticale) are included in the mix.

Planning and Preparation
  • Planning—Consult with university Extension staff, local NRCS staff, and experienced producers to gain insight on the practice. Start small while exploring new practices. In South Dakota, timeliness is important due to the shorter growing window. Always focus on your objectives, such as whether you are growing the cover crop for ground cover, fall grazing, nutrient cycling, etc.
  • Small-grain variety and planting—Small-grain varieties such as wheat or oats do not need to be changed or modified to incorporate cover crops following grain harvest or haying. Planting small grains early in the spring is important for good growth and development, which also typically results in earlier harvest and allows more time for cover crops to grow before a frost.
  • Residual herbicides—A blend consisting primarily of cool-season cover crops such as cereal grains (oat, barley), brassicas (radish, turnip, rapeseed), and legumes (field pea), and some warm-season grasses such as millet and sorghum-sudangrass have shown good tolerance to commonly used herbicides. If the cover crop is intended for grazing in the fall/winter, it is critical to follow grazing restrictions stated on the herbicide label.
  • Seed source—Planning ahead and ordering seed early with the objective in mind is important. Most cover crop seed dealers have their own pre-mixed blends but are willing to custom-mix upon request. Follow the seed label and review the individual species to make sure that the growth habit of each is ideal for the planting time. If opting for a mix of only one or two species, labeled varieties usually perform better than variety not stated (VNS) seeds.
Summer/Fall Work
  • Harvest—Harvest wheat/oats at the normal time. If weed pressure is high, you can spray glyphosate or other herbicides with the least residual effects. Herbicides are a better option than tillage as stirring the soil can dry it out and reduce germination. Baling small-grain residue is common in South Dakota but can make establishment of the cover crop difficult where the windrows were present.
  • Timing of planting—In South Dakota, wheat and/or oats are generally harvested from the second week of July to the first week of August. Planting cover crops immediately following harvest is recommended so that the seasonal window can be maximized. A mix consisting mostly of cool-season annual species grows well as temperatures start to gradually decrease. Use the Cover Crop Selector Tool (in Resources section) for precise seeding dates.
  • Planting method—Determining seeding depth is tricky when planting a mix with various seed sizes. Drilling to a moderate depth of 0.50–0.75 inch will be good for most mixes. Tilling or soil disturbance is not recommended as this may cause unwanted weed growth.
  • Cover crop types—Diversity of species in a mix is good and typically will provide the best benefits. The general rule of thumb is to select cover crops that are of contrasting growth habit to the subsequent cash crop. For example, if the next season’s cash crop is corn, planting cover crop blends that have a higher proportion of cool-season broadleaves is suggested; if the next season’s crop is soybean, then a mix with more cool-season grasses would be ideal. If wheat or other small grains are to be raised for seed purposes, cover crop blends that contain winter cereals (e.g., winter wheat, winter rye, winter triticale) are not suggested.
  • Seeding rate—Seed size and proportion in the mix determines the seeding rates. For example, a mix high in large-seed species such as peas and oats can be higher than the ones dominant in brassicas. Typically, the seeding rate of commonly marketed cover crop mixes can range from 15 to 30 lbs./acre. The full seeding rate of individual species can be found in Cover Crop: Common Species and Properties of South Dakota (see Resources).
  • Tillage—Tillage or soil disturbance is not suggested.
  • Fertility—Fertilizer is not usually required for a cover crop mix with well-balanced species. However, producers who have livestock and intend to maximize growth for fall/winter grazing have shown interest in using low rates of fertilizer. Although there are no specific guidelines on fertilizer rates for various cover crop blends, using nitrogen rates in the range of 30–40 lbs. N/acre can enhance cover crop growth and establishment, especially following high-yielding wheat crops.
  • Grazing—Producers who prefer to grow cover crops after small grains for grazing in the fall/winter can slightly increase the proportion of cool-season grass species such as oats and barley. Include at least 60% grasses in the mix for grazing. To assist in calculating the amount of grazing your cover crop can offer, refer to the Grazing Cover Crop Calculation App (in Resources).
Figure 1: Frost-killed cover crops seeded after oats in southeast South Dakota (Peter Sexton)
Spring Work
  • Starter fertilizer—No modifications to your typical fertilization program are required for planting soybean or corn. However, there are a few considerations for planting corn. After a cover crop has winter-killed, get a current soil test to look at nitrates and sulfur. Cover crops can sequester nitrogen, which is a desired attribute to reduce leaching or runoff. But mixes with a high proportion of Brassica species (radish, turnip, rapeseed) can use quite a bit of sulfur. Soil-testing and applying these nutrients as needed to minimize the chance of nutrient deficiency is a good practice.
  • Termination—Typical cover crop blends should winter-kill in South Dakota. However, mild winters can leave a few plants the next spring. Timely scouting and herbicide application as needed is suggested for uniform control of cover crop plants that survived the winter. Some mixes with winter annuals such as winter triticale, cereal rye, or winter camelina will require spring termination.
  • Soybean or corn planting—It is usually best to no-till plant cash crops into the dead/dry or standing cover crop. Almost all modern planters and drills are fully capable of planting soybean or corn into terminated cover crop residue. Check planting depth and seed furrow closure shortly after beginning.
  • Scouting—After planting soybean or corn, scout for crop emergence and population. Additionally, scout for weeds since cover crop residue can often delay emergence of annual weeds, which may delay the application of post-emergence herbicides.
Figure 2: This photo shows cover crop growth mid-September in Lake County, SD. The field was seeded after cereal rye was hayed in June (David Karki)
Resources

Cover Crop Selector Tool—available from the Midwest Cover Crops Council, www.midwestcovercrops.org

Cover Crop Species Selection for Grazing (USDA-NRCS publication SD-FS-56)

Herbicide Residual Effects on Cover Crops after Wheat (South Dakota State University Extension)

Cover Crop: Common Species and Properties of South Dakota (USDA-NRCS)

Grazing Cover Crop Calculation App (Jotform app)

Author

David Karki, South Dakota State University Extension (Note: This publication was adapted with consent from MCCC under a joint project to produce customized introductory guidance about cover crops for all member states/provinces.)

Reviewers and Contributors

Eric Barsness, USDA-NRCS; Anthony Bly, South Dakota State University Extension; Eileen Kladivko, Purdue University; Anna Morrow, Midwest Cover Crops Council

The Midwest Cover Crops Council (www.midwestcovercrops.org) aims to facilitate widespread adoption of cover crops throughout the Midwest by providing educational/outreach resources and programs, conducting new research, and communicating about cover crops to the public.

Funding for this project was provided by McKnight Foundation.

December 2022

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or a part of an individual’s income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410 or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer. ©2022 by MCCC. All rights reserved.

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