Spring management of cover crops - how termination timing effects soybean growth and yield
Sustainable Production
AgricultureField management
Parent Project:
This is the first year of this project.
Lead Principal Investigator:
Raymond Weil, University of Maryland
Co-Principal Investigators:
Project Code:
Contributing Organization (Checkoff):
Institution Funded:
Brief Project Summary:
The overall aim of this research is to provide information that may help change the mindset about cover crop management just doing the minimum to qualify for payments to managing for maximum cover crop benefits for soil health and profitability. The objectives intend to document the benefits and/or problems of planting earlier and killing later, and develop and test strategies and technologies for establishing cover crops earlier, including airplane seeding, early maturing crop cultivars, and inter-seeding with ground equipment and letting them grow longer in spring, including planting green. Potential benefits include greater nutrient cycling, better weed suppression, more effective water-conserving and increased soil organic matter and biological activity.
Key Beneficiaries:
#agronomists, #Extension agents, #farmers, #NGOs
Unique Keywords:
#cover crops, #interseeding, #planting green
Information And Results
Project Summary

The overall aim of the proposed research is to provide information that may help change the mindset about spring cover crop management from one of terminating as early as possible to get it out of the way and minimize complications at cash crop planting to managing for maximal cover crop performance for soil health and profitability. Maryland has by far the nation’s highest proportion of cropland acres cover cropped. However, farmers enrolled in the state cover crop programs typically plant a single species cereal cover crop and cut short cover crop growth potential in spring by terminating cover crops as early as possible, commonly in late March or early April. Such termination is too early to allow the cover crops to optimally promote soil health, summer water conservation and crop yield. Delaying spring cover crop termination until optimal cash crop planting time, especially planting green instead of killing cover crops two to four weeks ahead of planting, can allow both timely cash crop planting and extended cover crop growth.

Potential benefits of greater cover crop biomass growth include short-term benefits such as greater nutrient cycling, better weed-suppression, and more effective water-conserving in summer, in addition to longer-term benefits of increased soil organic matter and biological activity. The longer-term benefits may include participation in emerging carbon markets which offer per-acre payments for sequestering more carbon from the atmosphere. Yet many are calling into question the ability of cover crops to reliably sequester carbon and mitigate climate change (Popkin, 2022).

Much of the uncertainty about cover crops’ effects on carbon sequestration arises from the fact that most cover crop data is simply about adoption of the practice, not about the performance of the cover crop. The emerging carbon markets are hampered by a high level of uncertainty about cover crop performance and management, and also uncertainty about models used to predict the carbon stored by cover cropping. Perhaps the biggest weakness in these models is the almost total lack of data on belowground (root) carbon contributed by various cover crops at different stages of growth. This project will measure root biomass as well as aboveground biomass since roots are known to contribute more, pound for pound, than shoots to building soil organic matter and sequestering carbon. The aim is to start providing the data needed to make reliable carbon predictions about cover crops impacts on carbon sequestration for more viable carbon markets that benefit farmers.

Preliminary experience suggests that planting into living cover crops may also save time, improve stands, gain additional weed suppression, and possibly reduce slug damage to crop seedlings. Interest in spring cover crop management has been further stimulated in recent years in Maryland since the MDA cover crop program has included an extra incentive to postpone termination to after May 1st.

The aforementioned cover cropping benefits and concerns are of particular relevancy to soybean production because soybeans, unlike corn, do not tend to respond adversely to the early shading and N immobilization that may be associated with planting into living high-biomass cover crops after extended growth in spring. Soybeans therefore stand to benefit from water-conservation, nutrient-cycling (K, S, Ca, Zn, B), compaction alleviation, and slug distraction effects of high springtime biomass cover crops.

Our objectives are to 1) document the impacts (benefits and/or problems) of later termination, and 2) develop 2 and test strategies and technologies for letting cover crops grow longer in spring (including planting green). Using replicated experiments on coastal plain soils at the University CMREC research farm and collaborating commercial farms in 2017-2019 we showed that biomass carbon added to soil and N fixed by legumes was 4 times greater with early May instead of early April termination. There was no drag on yields with either practice so long as a mixture with brassicas and/or legumes was planted. We currently have 2 sites at the Beltsville CMREC research farm with excellent early-planted rye, radish and rye-radish-clover mix cover crops that are in their third year if cover crop treatment implementation. In addition, we are collaborating with commercial soybean/corn farmers on the Eastern Shore. We plan to measure nitrate leaching, cover crop biomass (including root biomass carbon) and nutrient contents, soil water fluctuations and crop growth and yield in 2023. In addition, we plan to expand our study of the impact of cover crop termination timing on slug
damage to both soybeans and corn seedlings on silty soil with restricted drainage and previous slug infestations.

In summary, this project will generate important information on how to better use cover crops for improved soil quality, reduced crop stress, enhanced nutrient cycling, carbon sequestration and profitability.

Project Objectives

The objectives are to determine the effects:
1) of early-established cover crops on soil quality and corn and soybean performance.
2) of early termination of living ground cover in spring on seedbed conditions, pests, soybean crop stands and performance.
3) of single grass species and 3-way mix cover crops on N response by corn.

Project Deliverables

There are currently sole and mixed-species cover crops planted for this project on 2 sites with replicated plots on the CMREC Beltsville research farm. We plan to measure winter/spring nitrate leaching, spring cover crop growth and root matter, slug activity, soil moisture dynamics, and cash crop response on these sites if this project is funded.

April- May 2023
Measure cover crop shoot biomass a three termination times.
Sample cover crop roots for total dry matter and carbon
Terminate cover crops on early, mid and late dates
Plant corn and soybean crop into cover crop treatments
Monitor changes in soil temperature and water.
Counts slugs in clayey field before and after ecrops are planted
Assess slug damage to soybean and corn seedlings in clayey field
Do stand counts

June-July 2023
Do final stand counts for soybeans an corn in both soils
Measure corn V5 seedling grwth, dry matter and N content
Measure soil nitrate to 30 cm deep (PSNT)
Monitor soil water and temperature

August-September 2023
Monitor soil water and temperature
Inter-seed cover crops into standing corn (August) and soybeans (September)
Harvest corn by combine and by hand sampling
Determine corn yield and grain size
Harvest soybeans by hand sampling (for smaller subplots) and by combine

October-November 2023
Monitor soil water and temperature
Determine soybean yield and grain size.
Determine cover crop ground cover
Present results to national conference

December 2023-January 2024
Sample fall cover crop biomass
Dry and grind fall cover crop biomass
determine cover crop dry matter and N content
Analyze data, write reports

February-March 2024
Analyze data
Write reports
Present results

Progress Of Work
Final Project Results

Updated May 29, 2024:

View uploaded report PDF file

Benefit To Soybean Farmers

Cover crops have receive increasing attention from mainstream grain farmers across the US, with the total acres planted to cover crops increasing by 50% from 10 million in 2012 to 15 million in 2017 (USDA/NASS, 2019). Still, this is an increase from 2.8 to 4.3% of US cropland planted to cover crops. In contrast, nearly 50% of Maryland’s cropland has been planted to cover crops in recent years. Cover crops are used by most farmers in Maryland and on a greater proportion of cropland than in any other state. This high adoption rate is largely a result of the Maryland Department of Agriculture offering generous ($45- 95/acre) subsidies for planting cover crops. The main purpose of these cover crop supports is the reduction cropland nitrogen losses to the Chesapeake Bay. However, these programs payout based on cover crop planting and termination, not on cover crop performance. While any cover crop is better than none, cover crop management and performance is often sub-optimal. Typically, a cereal like rye or wheat is planted in October and terminated in March with minimal achievement of ground cover, root and shoot biomass or even N capture.

The cover crop conversation in Maryland is often dominated by program payments rather than by soil health and crop
production benefits that effective cover cropping could offer. As farmers can claim payments upon cover crop termination, they understandably may terminate as early as possible in spring – too early for optimal nutrient cycling, water conservation, weed suppression, soil health, and crop yield enhancement. In addition, traditional recommendations suggest burn-down or plow-in be done two to three weeks before planting, ostensibly to avoid residue conditions that cause hair-pining with no-till planters and also to avoid allelopathic and N immobilization inhibition of crop seedlings. This loss of potential cover crop growing degree days in April/May before cash crop planting can cut cover crop performance by more than half. The recent addition to the MACS program of an extra $10/acre incentive for allowing cove crops to grow at least until May 1st is a step in the right direction and was based in part on our research supported by the Maryland Soybean Board.

Research in our lab also showed that that nitrogen and carbon benefits from cover crops can be enhanced by extending the cover crop season with early interseeding and late termination, especially planting green (Sedghi et al., 2022). The latter study showed that extending the cover crop season provided a good return on investment by the Maryland Department of Agriculture’s $10/acre extra incentive for late termination. Most cover crop benefits are closely related to the biomass produced which in turn is a function of the growing degrees days available, especially in spring. Yet there is much confusion and uncertainty in policy makers’ minds about the efficacy of cover cropping for soil health and carbon benefits . Many published studies on cover cropping simply compare some cover crop to no cover crop without much information on cover crop management or effectiveness, often failing to even report the cover crop biomass achieved (Ruis and Blanco- Canqui, 2017). Most cover crop research is done on single species cover crops and those that focus on mixtures usually focus on the relative seeding rates (Poffenbarger et al., 2015; Quinn et al., 2021; Rorick and Kladivko, 2017). Yet recent regional (Boniface, 2022) research indicates cover crop management, especially termination timing and associated growing degree days, outweighs seeding rates in determining CC performance.

Planting green is a system that allows the cover crop to have the maximum number of growing degree days without delaying timely cash crop planting. Very little research has been published on planting green, the planting of cash crops into green living cover crops. Pennsylvania is a state with a long history of no-till and cover crop innovators and considerable experience with planting green. Many of the lessons learned the hard way by farmers growing green in Pennsylvania have been summarized by the Pennsylvania No-till Alliance (Groff, 2017). They advise that planting green is not for beginning no-tillers as it requires attention to details of planter adjustments and modifications and a sharp eye on weather conditions and soil moisture (Reed et al., 2019b).

The United Soybean Research Retention policy will display final reports with the project once completed but working files will be purged after three years. And financial information after seven years. All pertinent information is in the final report or if you want more information, please contact the project lead at your state soybean organization or principal investigator listed on the project.