Why is the first principle of soil health management to keep the soil covered? And do cover crops grow up to the current hype?
Keeping the soil covered and maximizing living roots encourages the soil to stay in place, for nutrients to remain intact, and for water to soak into the soil rather than run off. Keeping soil covered also moderates soil temperatures so moisture can be retained for a longer period of time.
Mary Michael Lipford Zahed, Graduate Research Assistant at Virginia Tech’s School of Plant and Environmental Sciences and Eastern Shore Agricultural Research and Extension Center, shares insightful demonstrations of cover crops and their impact.
Take a look at how the various soil management practices affect the runoff in the photo below. The trays of water at the top are designed to simulate rainfall on the trays of soil samples below. The buckets of water in front of the trays show the amount and transparency level coinciding with each tray.
On the left, the soil sample is covered with straw and taken from a no-till field of cover crop mix residue. The sample was taken three months after the termination of the cover crop. The least amount of water ran through this soil sample and into the bucket, and the water ran clear!
In the middle, the soil sample was taken from a field that was tilled but still had some cover. The corn husks and fodder kept the soil covered, which helped some of it remain in place. However, the intense disturbance of the soil broke it up so that it was more prone to runoff.
On the right, the soil was sampled from a tilled field with no residue. Without the coverage and living roots, the soil eroded into the bucket below.
If Mary Michael's visual demonstration has you considering cover crops, Robert "Bob" Waring of Brandon Farms has another reason to give them a try.
"It's the economics of these cover crops that are helping us with the times that we're getting ready to face," said Bob in Episode 24-15 of 4 The Soil: A Conversation.
Over the past 15 years, Bob has grown his fertilizer (nitrogen, phosphorus, and potassium) and farm profitability through timely cover crop mixtures and management. Hairy vetch and black oats have worked well in his corn and soybean rotations and helped Brandon Farms dramatically reduce fertilizer and pesticide costs.
Bob's farm, Brandon Farms of Dunnsville, Virginia, was the first in the Commonwealth to undergo a soil and economic case study with the American Farmland Trust (AFT). They found a net benefit of $55 per acre when producers implemented soil health practices, specifically cover crops and nutrient management. Overall, the study showed that cover crops can help reduce input costs.
"That was a great experience," said Bob. AFT looked at Brandon Farms' historical data and then collected data such as the oxygen coming out of vetch and the phosphorus and potassium being cycled through black oats and vetch.
If you are new to cover cropping, Bob recommends finding a legume like clover, cowpeas, or Austrian winter pea that fits in your system as a starting point.
Finding a cover crop that suits your system is a process, similar to finding the best times to plant and terminate them. Mary Michael shared another demonstration of these factors from N.C. Farms in eastern Virginia.
Mary Michael took the above picture of a field on N.S. Farms, owned and operated by brothers Aaron and James Black, on January 30, 2024. The image shows the impacts of early and late planted hairy vetch. The previous fall, on September 9, 2023, the plot on the left was aerially seeded using a combine-mounted cover crop seeder and then drilled four weeks later on October 21, 2023. The autumn biomass growth was statistically higher in the early planted hairy vetch due to getting significantly more rain.
"Where I think we need to focus efforts in the future with that is focusing on biomass. With biomass and cover crops comes more nutrient cycling," said Bob. "Certainly bringing soil health into the conversation is important, and most farmers are open to that direction."
Burrow In
Episode 24-15: Growing Fertilizer and Farm Profitability with Robert Waring of Brandon Farms Part 1 with 4 The Soil: A Conversation https://www.spreaker.com/episode/episode-24-15-growing-fertilizer-and-farm-profitability-with-robert-waring-of-brandon-farms-part-i--60676333
Brandon Farms, VA Soil Health Case Study with American Farmland Trust
https://farmlandinfo.org/wp-content/uploads/sites/2/2024/05/brandon-farms-soil-health-case-study.pdf
Publications and Education Resources webpage of Virginia Cooperative Extension Office: https://www.pubs.ext.vt.edu/
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