Optimizing spring cover crop management for productivity, soil health and climate resilience

Progress report for LNE23-481R

Project Type: Research Only
Funds awarded in 2023: $249,267.00
Projected End Date: 11/30/2026
Grant Recipient: University of Maryland
Region: Northeast
State: Maryland
Project Leader:
Dr. Ray Weil
University of Maryland
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Project Information


Cover cropping is a soil health best management practice, but <10% of US farms and <15% of Northeast farms regularly use cover crops (CCs) and fewer manage CCs to maximize benefits for farmers and society. A key question is when to terminate CCs in spring, either mechanically or with herbicides. Farmers typically terminate CCs when small and “easy to deal with.” Delayed termination allows CCs to grow longer and may triple biomass produced, therefore greatly increasing such benefits as erosion control, weed suppression, nutrient cycling, nitrogen fixation, compaction alleviation, and summer water conservation. Farmers who use CCs are increasingly interested in facilitating late CC termination by “planting green” (PG), a practice whereby a cash crop is no-till planted into a living green CC with termination performed either simultaneously or a few days to weeks later.

Increasing climate change concerns have stimulated emerging markets that pay farmers to sequester carbon in soils. Current models have little-to-no basis for estimating carbon in CC roots. Data are therefore urgently needed on how CC termination timing affects root carbon contributions, which are more important than shoot contributions for carbon sequestration. Another issue lacking data and of concern to farmers is that CCs may increase slug problems. Finally, farmers need data on how termination timing affects weeds and soil moisture.  We hypothesize that 1) shoot/root ratios are not constant over time and PG may optimize both root and shoot carbon sequestration;  2) green CCs coexisting with cash crop seedlings may distract slugs and reduce cash crop damage; 3) planting green may optimize weed suppression and summer water conservation.

We will conduct experiments on-station research with coarse and fine textured soils, and on-farm research at four to six collaborating farms. The on-station experiments will test three termination timings relative to cash crop planting (three-four weeks prior; simultaneously with; one-two weeks after) and three CC types (no-cover control; grass-legume or grass-brassica-legume mixture; and pure winter cereal) in a no-till corn-soybean production system. Collaborating farms will use 2-4 treatments (farmer’s choice) per farm. Farmers will conduct all operations and measure yields while researchers will collect data on shoot/root biomass, slug damage, crop stands, seed placement, datalogger-sensed soil moisture and temperature, weed biomass and residue cover at canopy closure, and shoot nutrient content, as appropriate.

Researchers and farmers will keep detailed notes on planter settings, and operational issues such as CC wrapping, seed placement, slot closing, and machine wear. Lessons learned will be promulgated through extension efforts to reduce risk barriers for farmers wanting to grow more effective CCs that are more beneficial for their farm and ecosystem services. Farmers help design the research and those with PG experience will mentor other farmers wanting to try PG. An advisory board will guide the direction of the project, which will strive to include a range of farm types and sizes.

During the first six months of the project, we have recruited and onboarded a graduate student who will conduct much of the day-to-day research operations. Three farmers have planted cover crops and designed on-farm trials to answer questions they have about termination methods and timing. Several additional farmers have indicated an interest in establishing spring on-farm trials using cover crops they already have growing in their fields. The cover crop treatments for the on-station experiments were successfully established by overseeding into standing soybean and corn canopies in September 2023. Dataloggers are presently sensing and recording soil moisture and temperature at two depths on an hourly basis on these experimental fields.

Project Objective:

Research to optimize spring cover crop management with a focus on comparing termination methods and termination timing (from several weeks before to several weeks after cash crop planting). We will learn how these practices affect root and shoot carbon contributions, soil moisture use and conservation, weed and slug pressure, soil health functions, farmer costs and crop yields. Our results will reach 100s of farmers who are on-the-fence about cover crops or use them in ways that provide little benefit, and provide the confidence and information they need to adopt cover cropping with late termination practices that maximize cover crop benefits.


Cover cropping is a widely-recommended soil health best management practice. As a result of attention in the farm press, examples set by respected farmers, and financial incentives provided by various agencies, farmer interest in trying cover crops (CC) and their adoption of CCs increased substantially between 2012 and 2017 Ag census, but is still, <15% in most NE States and <10% in most states nationally. Cover crops are now used on all types of farms, from large-scale grain to small vegetable operations, and even in hoophouses.

Adoption of CCing is only a first step. Like cash crops, CCs require thoughtful systems management to maximize benefits. One issue limiting CC effectiveness is that most farmers terminate CCs relatively early, which inhibits CC benefits. As a result, most farmers experience little or no increase in crop yields or observable increase in soil organic matter from CCs. They are therefore not motivated to continue using CCs or invest in their management. Typically, farmers terminate their CCs about a month ahead of cash crop planting when CCs are small because “covers are easier to kill when small”, “the residues need a few weeks to dry down and become easy plant through”, “they want to get that job out of the way”, to avoid CCs “getting away from” them, to avoid residue “winding around planter closing wheels”, to avoid possible competition with crops for stored soil moisture, or to reduce anticipated slug damage to emerging cash crops.

A  key research question is when to terminate CCs, either mechanically or with herbicides. Delaying termination as late as possible in spring allows CCs to grow longer and may triple biomass produced, therefore greatly increasing such benefits as carbon sequestration, erosion control, weed suppression, nutrient cycling, nitrogen fixation, compaction alleviation, and summer water conservation. Farmers who use CCs are increasingly interested in facilitating late CC termination and greater CC benefits by “planting green” (PG), a practice where a cash crop is no-till planted into a living green CC with termination performed either simultaneously or a week or two later. This relatively new and still rarely used practice could greatly improve CC benefits on thousands to even millions of annual cropland acres on Northeast farms of all sizes.

To be willing to try PG practice farmers need information on planting techniques and equipment settings and how to reap increased benefits while avoiding pitfalls. One issue is the lack of data addressing farmer concerns that CCs may increase slug problems if not terminated early. Farmers also need better data on how termination timing affects weeds and soil moisture.

Increasing climate change concerns have stimulated emerging markets that pay farmers to sequester carbon in soils. Current carbon sequestration models such as COMET-Farm (USDA/NRCS, 2022) have little-to-no basis for estimating carbon in CC roots. Data are urgently needed on how CC termination timing and PG affect carbon contributions and soil organic matter, especially belowground, as root contributions are nearly twice as effective as shoot contributions for carbon sequestration.


Click linked name(s) to expand/collapse or show everyone's info
  • Dr. Sarah Hirsh (Educator and Researcher)
  • Mark Townsend (Educator)



Compared to early termination and planting into dead CC residues, planting green with properly adjusted equipment will:

  1. Achieve equally good seed placement, furrow closure and stand uniformity;
  2. Conserve summer soil moisture and reduce crop water stress;
  3. Reduce weed biomass before canopy close;
  4. Not affect slug numbers but decrease slug damage to cash crops;
  5. Increase above- and below-ground plant carbon inputs, increase stabilized soil carbon and Active Carbon in 0-30 cm soil by third year;
  6. Reduce time and herbicide used for CC management.
  7. Increase yields in site-years with wet spring and dry summer.
Materials and methods:
  1. Treatments: Proposed treatments with rationale for selection.

Replicated experiments use one cash crop (e.g. soybean, dry beans, sweetcorn, dent corn) or rotations of cash crops according to farmer preferences. On-station trials use a soybean-corn rotation with each cash crop represented in each year.

Treatments will comprise factorial combinations of CC termination times and CC species (see below). For on-station trials nine factorial combinations (marked by * below) will be used (3 termination times x 3 CC species = 9 treatments). For on-farm trials, farmers choose two termination times and 2-3 cover crops to give four to six treatment combinations.

Early, Mid and Late termination dates (in relation to optimal cash crop planting date for the site):

  1. *Early: 2-4 weeks prior to cash crop planting (01-10April in Maryland). Chosen to represent current standard practice killing CC while small and “planting brown”.
  2. *Mid: simultaneous with cash crop planting (planting green, 20-30April in Maryland). Chosen to represent the most common, least complex PG.
  3. *Late: 1-2 weeks after cash crop planting. In Maryland, planting green in late April but waiting until mid-May to terminate allowing CC to maximize aboveground biomass and reach reproductive stage necessary for roller-crimping.

CCs species used (including a no-cover crop winter -weeds only control):

  1. *No CC (winter weeds only). A no-cover control included as the standard practice for many farmers who are still on the fence about using cover crops.
  2. *Winter cereal (Cereal rye or other winter cereal chosen by farmer). Most common standard cover crop. In Maryland winter wheat is the most popular, while cereal rye is second most popular and the most often recommended for its winter hardiness and effectiveness nitrogen capture.
  3. *Grass-brassica-legume mixture (farmer choice from each group). This 3-species CC works well in the mid-Atlantic, with rye, radish, and crimson clover being most popular species. This CC provides aggressive fall growth and nutrient cycling by brassica, and long-lasting mulch from cereal, but without the nitrogen immobilization and yield drag single-species cereal CCs often entail.
  4. Grass-legume mixture (farmer choice of species). Similar to #3 above, but no brassica for famers with brassica crops in rotation or desire to limit CC seed costs.


  1. Methods: Experimental design, experimental unit size, and treatment application.

On-station experiments. Randomized complete block design with split-split-plot arrangement of treatments within blocks. Experiment will be repeated on two sites representing range of Mid-Atlantic soils, one excessively well-drained sandy soil and the other moderately well-drained clayey soil. Main plots have either corn or soybean cash crop. Subplots are three CC species treatments: no cover, 3-species mix, and cereal rye. Subsubplots are termination dates: early, mid, and late. Experimental unit is the subsubplot which will measure 30 ft x 60 ft to accommodate farm-scale equipment. The experiments have four replications at each site and conducted for 3 years using same treatments on each experimental unit, giving 6 site-years of data.

On-farm trials. Four to six on-farm trials will be conducted. Each will use a randomized complete block design with three replicate blocks. If possible, the same plots will be used for a treatment two to three consecutive years on a given farm. Four to six treatments  (farmer's choice of 2 termination times x 1-3 CC species treatments) will be applied in simple strip plots with a total of 6 to 18 plots (experimental units) per farm. On-farm plots sized to accommodate farmer's land and equipment.  Each trial will feature one cash crop (farmer’s choice) in a given year. For combine-harvested cash crops, plots will be long enough (>150ft) to obtain reliable data from calibrated yield monitors. Smaller plots may be used for crops requiring smaller equipment or hand-harvesting. Treatments randomly assigned to plots within each block. Blocks laid out to maximize uniformity within the block. Replicate blocks on a farm not necessarily in one field. Cover crop establishment and termination and cash crop planting and harvesting accomplished by the farmer using their normal equipment.

For both on-station and on-farm trials cash crop planter adjustments will be optimized for plant and soil conditions, meaning adjustments may be made between plots with different treatments.

  1. Data Collection: Data to be collected and collection protocols. (*only on-station, **only at slug-infested sites).
  • CC Shoot biomass just before termination. Three 50 cm x 50 cm quadrats per experimental unit clipped to 1 cm from ground and separated by species with dry matter recorded after drying to constant weigh at 65o
  • *CC Root biomass and root/shoot ratio on each kill date. At three locations in each experimental unit, a 20x20x20 cm cube of soil will be excavated with a square spade, the CC shoots cut 1 cm above soil surface, and cube of roots washed with sprayer over nest of screens until clean roots are obtained. Dry weights obtained for roots and shoots. Dry tissue ground analyzed for C and N (LECO).
  • **Slug counts every 3 days from before early termination through establishment of cash crop with two true leaves (no longer susceptible to slugs). Counts 8-11 am using 30 cm x 60 cm roofing shingle traps.
  • **Slug damage to cash crop in each experimental unit (scored from 0-5 as per (Stefun, et al., 2021) every 3 days from emergence through 2nd true leaf stage.
  • Assessment of seed placement and emergence counts using three 1-meter rows per experimental unit.
  • Cash crop population density at 2 leaf stage counting three 1-meter rows per experimental unit.
  • Hourly volumetric soil moisture and temperature readings at two soil depths in two replicates of no cover control and early and late termination plots for 3-species CC (8 METER Group capacitance sensors per site).
  • **Soil moisture content during critical spring and summer dry periods as indicated by dataloggers. Measured using handheld meter with sensor for volumetric content or by soil core methods for gravimetric analysis. Three locations in each experimental units at 0-10 cm and 20-25 cm depth.
  • Weed biomass just before crop canopy closure. Three 50 cm x 50 cm quadrats per experimental unit clipped to 1 cm; drying to constant weigh at 65o
  • Residue cover at canopy closure. At three locations in each experimental unit a vertical photo edited to contrast soil and residue will be analyzed for percent residue cover.
  • Cash crop yields. Calibrated combine yield monitor or hand harvest of two middle rows at least 20 ft long for corn or soybeans.
  • Detailed record of observations regarding soil, crop, and equipment status.
  1. Data Analysis and Presentation of Results: Statistical methods to be used and the forms in which results will be presented. Describe plans

Data will be analyzed using R, SAS and SYSTAT software. On-station trials analyzed as split-split-plot RCB across two soils with soils, blocks within soil, and termination dates random effects while CCs and cash crops are fixed effects. On-farm trials use simple RCB analysis with general linear models. For data such as slug counts and soil moisture, transformations will likely be needed to meet assumptions of normality. Results will be back transformed.  If transformations are insufficient, non-parametric tests such as Kruskal-Wallis and Inman tests will be used to determine significant differences. Trends over time for variables like slugs, soil moisture, and CC growth presented using line graphs and regressions. Cover crop and soil data will be presented in tables and graphs as well as in illustrated info-graphics for outreach to farmers.

Research results and discussion:

In early Fall/late summer 2023, cover crops to receive spring management treatments were planted on collaborating farms and at the  Central Maryland Research and Education Center (CMREC), in Beltsville, MD.  At CMREC, the cover crops were broadcast overseeded into standing corn canopies in late August 2023 and into standing soybean canopies at leaf yellowing in early September. Due to nearly a month without any significant rain, the cover crops didn't germinate until mid-September. Different rates of side-dressed nitrogen had been applied in June to corn plots as part of a prior agronomic experiment on the site.  During the first year of the project cover crop experiments, this differential N could theoretically affect the cover crop performance in spring 2024 due to the effect of corn vigor in competing for light during early cover crop growth before corn harvest and due to possible residual N remaining on the soil for use by the cover crop plants.  To assess this potential carry-over effect at CMREC, fall biomass was hand-harvested in December 2023 for the radish-crimson clover-rye mixture (3-Way) cover crop that was intersown into the corn before harvest. This data was collected for all four replications at the sandy soil site, and two of the replications at the silty-clay soil site.  A statistically significant difference in aboveground cover crop dry biomass was observed between the high (160 or 180 lb N/acre) and low (0 lb Nacre) side-dress rate (Figure 1).  The range of biomass values from about 600 to 1000 kg/ha is lower than expected for an early intersown cover mixture at this location, probably due to lack of rain during the early cover crop growth period. In addition, the N rate applied to corn in June differentially affected the rye and clover components of the cover crop, the higher N applied to corn in June increasing the relative amount of rye while decreasing the amount of clover (Figure 2).  These results would be expected since the main competitive advantage of the clover is its ability to fix its own nitrogen, while the faster-growing rye would be more competitive where more N was available in the soil.  We conclude that 1) N applied at the higher rate was not efficiently used by the corn crop since residual N was available to stimulate the growth of the rye cover crop in September-December.  This was true across both the sandy and silty clay soils.  In addition, the differential effect on species in the fall biomass suggests that we might see the effect of N applied to corn in one year affect the performance and N-fixation ability of the following cover crop in the spring of the next year.  Although we will not apply different rates of N to corn in 2024, we will monitor the cover crop biomass from all termination date subplots at the time of early termination (early April) to determine if this effect has carried over in the spring.

Bar graoh of cover crop biomass in fall versus N rate applied to corn the previous June.
Figure 1. Total biomass dry matter above ground in Late November 2023 for the 3-Way mixture cover crop as affected by N rate applied to corn in June 2023. 
Color coded stack-bar graoph showing clover decreasing and rye increasing with N applied to corn.
Figure 2. Applying a higher rate of N to corn in June 2023 increased the December 2023 rye above-ground biomass, but decreased the clover biomass component of the 3-Way cover crop mix intersown into standing corn before harvest in August 2023. Means across sandy and silty clay soils.

Participation Summary
3 Farmers participating in research

Education & Outreach Activities and Participation Summary

Educational activities:

3 Consultations
1 Published press articles, newsletters
1 Webinars / talks / presentations

Participation Summary:

10 Farmers participated
50 Number of agricultural educator or service providers reached through education and outreach activities
Outreach description:

During the first 6 months of this research project, no outreach activities were implemented, other than a farmer extension newsletter story about the establishment of the new project and a workshop presentation that discussed spring cover crop management in organic systems for the Mid-Atlantic Crop Scholle in Ocean City Maryland in November 2023. We are planning field days for when there are things to see in the field at the research sites.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.