How Cover Crops Reduce Fertilizer Costs and Save Money
- Buz Kloot, Ph.D.
- Sep 14
- 6 min read
Introduction: Beyond Erosion — The Scavenging Power of Cover Crops
At the risk of quoting Ray Archuleta too much, I did spend time with him last week, and he reminded me that cover crops carry a stigma. He said that when he spoke to farmers about the benefits of cover crops, they said, “We don’t have erosion!” End of discussion.
We have already touched on Dr. Ray Weil’s work in an earlier blog, Soil Compaction Fixes: Dr. Ray Weil on Deep Roots & Water. As I reviewed video from our October 2014 visit with Dr. Weil at Steve Groff’s farm in Pennsylvania, I was struck by how well cover crops serve as scavengers, especially of nitrate nitrogen. If that nitrate isn’t taken up in the cover crop in the fall, it will leach out of the root zone during the fall and winter.
In this post, we take a closer look at what Dr. Weil said in that video — and what he and his students have published over the years — to understand more fully the remarkable scavenging power of cover crops.
Cover Crops and the Hidden Depth of Nitrogen
Dr. Ray Weil and his team have conducted detailed soil profile studies on mid-Atlantic farms, extracting soil samples down to depths of 7½ feet (≈2.3 meters). Their findings show that cover crops — especially forage radishes and mixed species planted after silage or grain harvest — actively clean nitrate from deep soil layers.
Without cover crops, nitrate concentrations remain detectable far down the profile, poised to leach beyond the root zone and be lost to the producer forever.
Under cover crops, nitrate levels deep in the soil profile are nearly zero.
In fallow or bare treatments, nitrate concentrations of 5 to 15 parts per million (ppm) can be found all the way down — amounting to roughly 120 lbs of nitrogen per acre.
The implication is clear: cover crops don’t just build organic matter, they scavenge nutrients, intercepting and holding nitrogen that would otherwise be gone.
Weil’s work with Sedghi (2022) underscores this point: “Fall cover crop nitrogen uptake drives reductions in winter-spring leaching” (Sedghi & Weil). The study highlights how timely and well-established cover crops can significantly reduce nitrate loss, especially when planted early after harvest (Sedghi and Weil 2022).
Another study by Hirsh and Weil (2019) documents large end-of-season mineral nitrogen pools in deep soil layers, showing that much of the nitrogen remaining after harvest isn’t easily accessible unless living roots are present to capture it (Hirsh and Weil 2019).
How Planting Date, Cover Crop Species, and Biomass Matter
Not all cover cropping strategies are equally effective, and timing and species selection are critical.
In Maryland, earlier-planted cover crops — especially those seeded soon after harvest or interseeded into standing crops — accumulate more biomass and develop deeper root systems, greatly improving their capacity to scavenge nitrate. Late-planted covers, by contrast, are less effective (“Cover Crops and Nitrate Leaching,” Wisconsin Extension).
Forage radishes, in particular, have taproots that reach nitrate moving downward post-harvest, then winter-kill and release nutrients in time for the next crop (Weil and Notto 2018; Wang and Weil 2018).
The takeaway: it’s not just whether you plant cover crops, but when and what kinds you plant that determine how much nitrogen you retain
Weil and colleagues (2023) have even explored whether adding a small shot of nitrogen fertilizer to cover crops in low-nitrate soils could boost biomass and scavenge more N. Their conclusion: in many cases, the return wasn’t worth the input — a cautionary note for farmers considering that approach (Weil, Stefun, and Lewis 2023).
Why This Matters to Farmers
The nitrogen captured by cover crops isn’t just a soil health benefit — it’s fertilizer value. Weil’s work shows that cover crops can intercept 100–200 lbs of nitrogen per acre that would otherwise slip below the root zone. At current prices, that’s $60–120 per acre you don’t have to replace with synthetic fertilizer.
Compaction and nutrient loss go hand in hand. When roots can’t push through tight layers, they can’t chase moisture or capture nitrogen deeper in the profile. Deep-rooted covers create those natural root channels, giving cash crops access to water and fertility that would otherwise be locked away.
And while agronomists may emphasize nitrate leaching to streams or groundwater, the farmer’s bottom line is simpler: every pound that leaches out is a pound you’ve already paid for and won’t see again. Cover crops keep that nitrogen cycling in your field, where it can work for the next crop instead of disappearing.
Where Do the Nutrients Come From?
It’s worth stepping back to ask: if cover crops are scavenging nutrients, where did those nutrients come from in the first place? The answer is twofold.
A lot of folks assume that most of the nitrogen in their crops comes straight out of a fertilizer bag. The surprise is how little of that fertilizer nitrogen actually reaches the plant — research shows much of it is lost to the air or leaches away in water. The real “bank account” for nitrogen is the sky overhead: the atmosphere is nearly 79% nitrogen gas (N₂). Legumes and soil microbes tap into that vast supply, turning it into forms crops can use.
By contrast, nutrients like phosphorus, potassium, calcium, and the metals come from the slow weathering of rock already in the soil. And here’s where biology really matters: the more biologically active the soil, the more those rock-bound nutrients are made available. Roots, fungi, and microbes release organic acids and enzymes that free up phosphorus, potassium, and other minerals that would otherwise stay locked away.
As Drs.Weil and Brady note in The Nature and Properties of Soils (15 edition) that the bulk of a plant’s body doesn’t come from the soil minerals at all. Carbon, hydrogen, and oxygen — derived from carbon dioxide and water — make up roughly 90–95% of a plant’s dry weight, with nitrogen adding another 1–5%. That means well over 90% of the biomass of every corn stalk, soybean plant, or radish root comes directly from the atmosphere. Soil minerals supply the rest — small in percentage, but essential in function.
This perspective reframes the role of cover crops: not only do they scavenge nitrogen that would otherwise leach away, they also help cycle the mineral nutrients that rocks and soil biology slowly release. In doing so, cover crops connect the atmosphere above and the geology below into the living fabric of healthy soil.
Conclusion: Rethinking “Clean” Soils and What We’ve Left Behind
For years, the conversation about cover crops has been boxed in by one line: “We don’t have erosion.” As if erosion control were the only reason to plant them. Weil’s work shows us something different: cover crops are not just about protecting the surface — they are about reaching into the soil profile, pulling back nitrogen that would otherwise slip away, and making it available for the next cash crop.
When we think about soil fertility, we often focus on the top foot or so — the zone we sample, till, or fertilize. But a surprising amount of nitrogen and other mobile nutrients can be lurking — or leaking — deeper than that. Weil’s research challenges us to think deeper — literally — about where nutrients go after harvest and how cover crops give us a tool to pull back what many assume is gone.
For farmers willing to look below the surface, cover crops offer a way to reclaim nitrogen that was never truly “lost” — just waiting for a root to find it. And with nitrogen prices where they are, that’s not just a soil health story — it’s money in the bank.
Selected Works by Ray Weil (Please get in touch with us if you have trouble finding these references)
Hirsh, Sarah M., Sjoerd W. Duiker, Jeff Graybill, Kelly Nichols, and Ray R. Weil. “Scavenging and Recycling Deep Soil Nitrogen Using Cover Crops on Mid-Atlantic, USA Farms.”
Agriculture, Ecosystems & Environment, vol. 309, 2021, art. no. 107274.
Sedghi, Nathan, and Ray R. Weil. “Fall Cover Crop Nitrogen Uptake Drives Reductions in Winter-Spring Leaching.” Journal of Environmental Quality, vol. 51, 2022.
Weil, Ray R. “The ‘Cover Cropping’ Renaissance.” The Earth and I, 22 Aug. 2023.
Weil, Raymond. Spring Management of Cover Crops: How Termination Timing Affects Soybean Growth and Yield. Maryland Soybean Board Research Report, University of Maryland, 2024.
Temple, Laura. “Does Fertilizing Cover Crops Boost Nutrient Capture?” Soybean Research & Information Network, 4 Dec. 2023
Weil, Raymond. Soil Health and Nutrient Flows with Enhanced Cover Cropping and Soil Management. Thriving Agricultural Systems in Urbanized Landscapes, 2025.
Weil, Ray R., and Nyle C. Brady. The Nature and Properties of Soils. 15th ed., Pearson, 2017.
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