Cover crops are a key tool for managing soil health and fertility. Farmers that use cover crops in rotation with other crops can improve weed and disease suppression, improve soil infiltration, increase nitrogen and other nutrients and increase soil resilience during extreme weather events. Some farmers, both in organic and traditional cropping systems, have embraced the practice. Until recently, little research has been conducted to help farmers select cover crop mixtures to achieve the best outcomes.
Beginning in 2014, a group of collaborators from across the northeast have worked on a project led by Penn State University and funded by a USDA Organic OREI grant. Justin K. O’Dea, a Field Crop and Vegetable Extension Educator with Cornell Cooperative Extension of Ulster County, was one of the project team members at the time (he has since transferred to the Washington State Extension) and has been sharing the research findings through a series of workshops this spring.
“We studied mixed species cover crops for a variety of factors to determine which ones would provide the best results,” he said.
Using one plant type, such as a brassica, improves soil infiltration thanks to deep taproots, while a legume is an aggressive nitrogen fixer. Mixing multiple species combines the benefits of all species types into one planting.
“Understanding the benefits of multi-species means you’ll be getting more out of that planting and make it more economically feasible to use cover crops than when using a single species cover crop,” he said.
O’Dea highlighted five species, a blend of grass, legume and brassica crops, that when used in combination, significantly improved multiple factors of soil health.
- Tritcale. This grassy cover crop is cross between rye and wheat. It aids in building soil structure to improve stabilization and encourages nutrient recovery.
- Winter canola. This brassica is part of the mustard family. Because of its deep taproots, it radically helps with infiltration. It is also good at catching or recovering nitrogen and demonstrates mild disease and weed suppression attributes.
- Austrian winter pea. This is an over winter, annual legume. All legumes, including the Austrian winter pea, are used for nitrogen fixing.
- Crimson clover. Crimson clover is a popular cover crop legume. It grows faster than red clover and if it survives the winter, it catches a lot of nitrogen.
- Medium red clover. This legume that is the most winter hardy of all three, but it is the slowest growing because it develops underneath a main crop canopy.
While each species brings significant benefits to the soil it is planted on, O’Dea points out that using a mixture of species provides a wider variety of services at the same time.
“For example, the combination of tritcale and winter canola together is extremely weed suppressive,” he said.
The following seeding rate has been suggested and found to be successful at this point. The Ulster County Extension worked with farmers to run trials and land owners were given the option of planting a cover crop of their choosing in a strip next to the five species mix to compare performance of the two areas.
Increasing cover crop diversity increases the beneficial functions for soil health. The relationship is non-linear meaning that there is a point at which adding more diversity does not significantly improve the mixture function or outweigh management or monetary costs.
“A single species may maximize one or two functions, whereas mixtures provide a broader suite of functions,” he said.
Cover crops are the number one management practice that affects soil quality and health is tillage. In regions that have been growing annual crops for a long time, the decline of soil quality is inevitable.
The research at Penn State University is the first step in finding the right mix of cover crop species that provides multifunctional benefits while meeting grower needs. Further research is needed to continue developing the most effective multi-species cover crop solution.