Cover Crop Research

 

Dr. Etienne Sutton, University of Michigan conducted cover crop research for 3 years. She got her PHD and she shared research results at a field day in Williams County on the Allen Dean farm. Her research centered on getting more cover crop biomass and either tying up nitrogen (N) and phosphorus (P) or creating more N.

For the last 3 years (2022-2025), she monitored cover crop fields in Michigan, Ohio, Indiana, Illinois and Minnesota. A total of 125 fields (2022), 138 in 2023, and 281 in 2025. The majority of the fields were cereal rye (121 fields) and cover crop mixtures (117) with the remaining being grass and legume or clover cover crop fields. Almost all the cover crops (88%) were planted after regular field crops with less than 10 percent after vegetable crops. About 52% were drilled, 32% broadcast, and the rest were aerially applied (drone or plain). Her major research centered around maximizing biomass and increasing N content or uptake in cover crop biomass (CCB).

Why shoot for high CBB? High CBB increases soil organic matter and nutrient soil retention, increases water infiltration, and decreases soil erosion. High N content in CCB improves water quality and decreases N fertilizer cost. Also, increasing P content does the same thing.

Since CBB is so variable, Dr. Sutton wanted to find out how to improve it. CBB often varies from zero to 6 ton/acre with N content varying from zero to over 300#/acre. She found that cereal rye is often planted later after either corn or soybeans while cover crop mixtures often get planted earlier after small grains, mostly wheat. With a slightly longer growing season being planted after wheat (30 days) and more rain (almost 5 inches); cover crop mixtures had a distinct advantage.

Typically, cover crop mixtures had much higher CCB and much higher total N sequestered. Grasses take up N but legumes and clovers not only absorb N but also make their own N. The most important factors for increasing CBB was having multiple species of cover crops growing together that complement each other, planting earlier, using manure or compost, getting extra or adequate rain, planting into good loamy productive soils, and drilling or getting the cover crop seed incorporated into soil.

When the cover crop is terminated is also important. Extending the cover crop growing season from Mid-April to Mid-May increased CCB from 200# to 2000#/acre on average. This decreases weed pressure and helps dry out the soil. Nutrient uptake of both N and P mirrors the amount of CCB produced. How much N is released (especially from grasses) depends upon the carbon:nitrogen ratio (C:N) which is also associated with higher lignin and higher C:N ratios. Less than 24 C:N, N tends to be released to the next crop, greater than 24 C:N and N is tied up. Legumes like vetches (Hairy, common), winter peas, and even red clover in this study had higher N content and much lower C:N ratios. Grasses sequester left over N and oats, cereal rye, annual rye grass and even winter wheat were the best.

Dr Sutton also looked at cover crop roots. Mixtures had the most roots while rye was close behind with many fine and medium size roots and clover had the least with many coarse roots. Mixtures had the most N and P. Mixtures had 2X more P than either cereal rye (a grass) or crimson clover. The mixture and the clover tied for total N at 102#/acre while the cereal rye had 65# of N in the roots. As a crop matures and starts to bloom in the spring, both N and P mover up into the leaves and stems.

Finally, Dr Sutton looked at farm resilience. Increasingly, heavy rains in the spring seem to hamper crop planting. Dr. Sutton viewed satellite data from 2009 to 2019 for the state of Michigan. She found that the increased usage of cover crops actually improved planting times. Probably due to improved water infiltration and better drainage. Under average spring conditions, cover crop fields have similar planting dates as those without cover crops. The problem is that most farmers tend to wait because they think the cover crop fields are wetter. Actually, they may be slightly wetter, but they also have better aggregate stability to hold up heavier equipment. This means they can be planted at the same time or even earlier than most farmers think. Planting delays are actually reduced in heavy rainy seasons with cover crops according to Dr. Sutton’s research. Lastly, using cover crops more than 3 years increases soybean yields 1% and corn yields 1.5% with more stable yields over time.