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Cover crop mixture of canola, red clover, Austrian winter pea, and cereal rye

Enhancing Cover Crop Benefits With Species Mixtures And Organic Reduced Tillage Systems

By Charlie White, Sustainable Agriculture Extension Associate, Penn State Extension

Added December 9, 2013. Research at Penn State and with collaborating farmers has been investigating two new strategies of cover crop management in organic farming systems: planting mixtures of cover crop species and using a roller-crimper to kill cover crops without tillage. The roller-crimper system uses a rolled-down mat of cover crop residue to suppress weeds in the following corn or soybean cash crop without the need for cultivation. Using cover crop mixtures, on the other hand, generally requires a tillage and cultivation regime typical of organic field crop production. Both of these cover cropping strategies help to increase the ecosystem services provided by cover crops such as erosion control, weed suppression, nitrogen supply and retention, resources for beneficial insects, and crop yields.

At a recent field day we rated ecosystem service provisioning based on observations and measurements in four cover crop systems of interest: a cereal rye monoculture, a red clover monoculture, a mixture of canola + Austrian winter pea + red clover + rye, and a reduced tillage system where a mixture of triticale +hairy vetch was killed with the roller-crimper. All of these cover crop systems were planted after wheat harvest in one year and were followed by a corn silage crop in the next year.

The rye monoculture scored well for nitrogen retention and weed suppression services due to aggressive uptake of residual soil nitrogen and high biomass production that outcompetes weeds. Rye lacked in most other services, however, including providing resources for pollinators and beneficial insects and supplying nitrogen. Corn silage yields following rye were the lowest at 13.5 T/ac.

The red clover monoculture scored well in a set of services opposite to rye. Nitrogen supply and silage yield, at 21 T/ac, were the highest of all the cover crop systems. Red clover lacked in erosion control and weed suppression due to the slow establishment of the cover crop in the fall, however. Nitrogen retention also lacked due to slow establishment and because red clover, being a legume that fixes nitrogen from the atmosphere, is not as aggressive at taking up residual soil nitrogen as non-legume species are.

The four species mixture of canola + pea + red clover + rye was more balanced in the set of services that it provided. Weed suppression and nitrogen retention were as good as the rye monoculture and nitrogen supply and crop yields were nearly as good as the red clover monoculture. Corn silage yields following this treatment were 19 T/ac. Because canola flowered for 1 to 2 weeks prior to termination in the spring, this mixture also provided a greater level of resources to pollinators and beneficial insects than either the red clover or cereal rye monocultures did.

Roller crimper used to terminate cover crops without tillage

The reduced tillage cover crop system of triticale + hairy vetch provided the greatest and most balanced set of services. By mixing grass and legume species together, both nitrogen supply and nitrogen retention services were provided. This system also maximized erosion control and weed suppression due to the cover crop residue left on the soil surface after rolling. The high residue environment also provided a good habitat for beneficial insects and we observed a striking increase in the number of beneficial ground dwelling insects such as spiders and ground beetles in this system. Because the cover crop in this system is allowed to grow several weeks longer than is customary, the hairy vetch flowers for 2 to 4 weeks, increasing the resources for pollinators and beneficial insects. Maintaining high crop yields has sometimes been an issue in organic reduced tillage systems. However, in this year of the experiment, we estimated corn silage yields to be 19.5 T/ac, which is similar to the yields achieved in the organic system that used traditional tillage and cultivation to kill the cover crop and control weeds in the crop.

As we seek to get more efficient cropping systems, from the perspectives of crop yields, maintaining environmental quality, and managing labor, using cover crop mixtures and reduced tillage practices appear to be strategies worth considering.

Charlie White is a Sustainable Agriculture Extension Associate with Penn State Extension’s Crop Management Team. Charlie’s research and extension activities are focused on how cover crops and cover crop mixtures can be used to meet farm management objectives such as improving soil health, enhancing nutrient cycling, and reducing input costs. Contact Charlie by phone or email: 814-863-9922; cmw29@psu.edu.

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