Articles

Evaluating Nurse Crops to Improve Legume Cover Crop Performance

Performance of winter-hardy legume cover crops can improve with the use of a winter-killed oat nurse crop compared to cereal rye, including at later sowing dates. Legume performance varies widely based on weather conditions near establishment, but crimson clover and hairy vetch are the most consistent performers.

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Updated:

December 16, 2025

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Crimson clover and spring oat mixture in late spring. Credit: Grant Hoffer, 2024

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Investigators

Grant Hoffer, Research Technologist, Penn State Weed Science Program
John Wallace, Ph.D., Associate Professor and Extension Weed Management Specialist

Background

Winter-hardy legume cover crops can improve production and conservation benefits by supplying nitrogen to grain corn. However, crop rotation and climate within the Northeast region often limit the establishment window and growing degree days (GDDs) necessary for consistent establishment of legume cover crops. Moreover, residual soil fertility and fall GDDs can impact legume performance when used in mixtures with grass cover crops.

Members of the Northeast Cover Crop Council (NECCC; northeastcovercrops.com) coordinate distributed experiments across the Northeast region to improve cover crop management recommendations and decision support tools. In this report, we share Pennsylvania results from a coordinated NECCC project focused on improving the management of winter-hardy legume cover crops.

Objective

The goal of this project was to evaluate how fall planting date and small grain (oats, cereal rye) companion cover crops affect the performance of four winter legume cover crops (balansa clover, crimson clover, hairy vetch, winter pea), including winter survival, spring biomass production, and nitrogen provisioning.

Methods

We replicated the coordinated experiment twice (2023–2024; 2024–2025) at the Penn State Russell E. Larson Agricultural Research Center in Rock Springs, Pennsylvania. The experiment consisted of three factors, including four legume species, three nurse crop treatments, and two sowing dates. Legume species included balansa clover (8 lb/ac), crimson clover (20 lb/ac), hairy vetch (20 lb/ac), and winter pea (40 lb/ac). Nurse crop treatments included a no-nurse-crop control, oats (30 lb/ac), and cereal rye (30 lb/ac). Sowing dates include three and six weeks before the historical first frost date (October 25). To facilitate these sowing dates, we established plots after a small grain crop using no-till methods, 7.5-inch row spacing, and a burndown application seven days prior to sowing. We harvested and weighed cover crop biomass by species between May 10 and 17, which represents average corn planting dates in this region.

Results

Spring cover crop biomass production (mid-May) varied significantly by year (Figure 1). Fall establishment conditions in 2024–2025 were much drier than conditions in 2023–2024, likely causing the significant reduction in legume biomass observed between sampling years. In general, planting three weeks before the typical frost date significantly improved biomass production for all legumes except winter pea. Earlier sowing dates are generally considered to optimize legume performance. However, our results suggest that sowing earlier may increase weed and nurse crop competition.

Among species, crimson clover produced the greatest amount of biomass, followed by hairy vetch and balansa clover, with winter pea producing the least amount of biomass. General trends indicate that legume performance improved when sown with an oat nurse crop compared to cereal rye, which suggests that fall and spring competition with rye resulted in reduced legume performance. Legume performance with an oat nurse crop was comparable or improved compared to legume monocultures at both sowing dates.

A matrix of legumes and year are shown, with balansa clover, crimson clover, hairy vetch, and winter pea shown from left to right, 2024 data shown in the top row and 2025 data shown in the bottom row. The vertical axis is pounds per acre of legume biomass, which ranges from zero to approximately 3,000 pounds per acre. Light blue bars show the six weeks before average frost date planting, while dark blue bars show the three weeks before average frost date planting. Later planting results in higher biomass in most cases. — Figure 1: Spring biomass (mid-May) produced by each legume species by study year and separated by accompanying grass nurse crop.

Conclusion

Our results demonstrate that weather conditions during the fall establishment period are a primary driver of legume performance. The use of an oat nurse crop may help to maximize legume performance by reducing spring competition compared to cereal rye, while improving fall conservation benefits related to groundcover. Among legume species, crimson clover and hairy vetch produced the most biomass in each year, whereas balansa clover and winter pea performance was lower and more variable among years. Our results will be included in a synthesis of replicated trials across the Northeast region to improve NECCC management recommendations.

Acknowledgements

Coordinated research by the NECCC receives in-kind contributions in the form of cover crop seed donations. We thank Art Siller (University of Massachusetts; project lead) and other NECCC contributors to this project.