Earth Innovations: Cover Cropping

Earth Innovations is a new series from Sound Agriculture that covers the up-and-coming techniques growers are deploying to keep their yields high and their land healthy for generations to come. In each blog post, we break down the benefits and challenges of incorporating new practices, using real growers’ experiences and the Sound Agronomy Team’s expertise.

Cover crops are often praised as one of the best practices to implement to create more sustainable and resilient operations and boost the soils’ microbiome health. But the benefits of introducing cover crops are sometimes obscure. In the first installment of our new Earth Innovations series, we’re exploring the benefits and challenges of cover cropping, as well as steps to consider before jumping in. 

Cover cropping is the practice of planting non-cash crops in order to keep live roots in the ground between seasons or periods of soil rest, which in turn helps to provide protection to the soil and store nutrients in the plant bodies. Growers then end the crop before it goes into the reproductive stage, sometimes before planting their cash crop. The most common method for terminating a cover crop is with herbicides or tillage it into the soil, but other methods, like mowing and crimping, are also effective. 

Cover crops can offer several benefits for growers, including nitrogen fixation, erosion reduction, water capture, and increased soil organic material. 

Nitrogen

“One of the reasons people plant cover crops is to provide additional N to cash crops,” says Sarah Taylor, Sales Agronomist with Sound. ​“Some species can take nitrous oxide from the atmosphere and fix it using root nodules.” 

The root nodules on nitrogen-fixing plants house special bacteria that have formed a symbiotic relationship with these plants. Plants are very good at creating carbohydrates out of water and carbon dioxide through photosynthesis, but they may struggle to access other key nutrients like nitrogen and phosphorus. Certain bacteria can turn atmospheric nitrogen into plant-available forms right in the plant’s root, forming what are called root nodules. In exchange for the nitrogen stores these bacteria supply, the plant provides the bacteria with carbohydrates as a source of energy. 

When the crop is terminated before reproduction, roots and root nodules that are left in the ground will provide an in-season source of nitrogen to the cash crop and reduce the need to apply synthetic fertilizer. 

Erosion

By keeping active roots in the soil all season long, cover crops can help reduce soil erosion and deterioration. Preventing soil loss is important because soil not only supplies organic matter and nutrients, it also holds water and provides habitat for beneficial microbes. 

“Having a cover crop in the ground can stop wind or water erosion from occurring because it prevents a lot of soil movement,” explains Sarah. The plants’ leaves and roots block wind and rain from picking up loose soil and carrying it offsite, robbing growers of nutrient-rich topsoil and potentially impacting nearby air quality or waterways. 

Soil loss is a global issue; the UN’s Food and Agriculture Organization estimates 33% of the Earth’s soils are already degraded and up to 90% could become degraded in the next 30 years. 

This loss has serious impacts for individual growers: degraded soils have reduced productivity, produce lower yields, and require increased water usage, all of which affects a grower’s bottom line. Cover crops are one way growers can protect and preserve their own nutrient-rich top soil. 

Water

Cover crops can have a big impact on a farm’s water quality and retention by helping to percolate and infiltrate rainwater. ​“When it rains,” says Sarah, ​“instead of the water just flooding off and moving away across the field, the water stays in the area where it fell, allowing it to settle into the soil.”

The vegetative canopy provided by a cover crop reduces the speed and intensity of raindrops on the soil. Without this protection, the force of rain on bare soil can break apart soil aggregates, which provide habitat for soil microbes and are responsible for healthy soil structure and adequate oxygenation. The crop’s roots also help the rainwater permeate deeper into the soil and prevent water loss through runoff. This allows growers to sequester rainfall for future use. 

Some growers may be worried that cover crops will increase their irrigation needs. While cover crops may need more water than fallow fields, those crops are actually holding moisture in the soil that will be available when the cash crop is planted. 

“It’s not wasted water to these plants — part of that is also preparing the bed for the cash crop,” says Sarah.

Organic Matter

A soil’s organic matter (OM) content has a significant impact on its health, fertility, and nutrient availability. Soil organic matter is primarily made up of decomposing plant residue and animal wastes and can provide crops with a full spectrum of macro- and micro-nutrients, releasing them more slowly and with less risk of leaching. A high OM content also provides food for beneficial organisms in the soil and supports a robust soil microbiome. 

Building up OM in the soil can be a slow and difficult process, but cover cropping is one of the easiest strategies. Once the crop has been terminated, the plants are left in the soil to be decomposed and turned into nutrient-rich OM.

Kyle Mehmen has been cover cropping on his family’s Iowa farm since 2013 and he’s learned a lot about the practice in the last nine years. 

“Our journey really started out of necessity,” he says. The spring of 2013 was so wet that Kyle and his family had to stop planting without finishing. Faced with the prospect of bare soils until the next spring, they decided to try planting some cover crops. 

The results were good — those fields that rested a year with cover crops outperformed their historical yields the next year, he says. But like many growers, Kyle is pragmatic, and he’s hesitant to chalk it all up to cover crops. ​“They certainly didn’t hurt anything,” he says. ​“And we really liked what they did for us from a conservation standpoint.” 

When Kyle started cover cropping, the region had just come out of a few seasons of very rainy springs. ​“Wherever we had a cover crop, we were able to keep soil in place, and that was a huge benefit,” Kyle says. 

Choosing Your Seed Mix

Kyle is very conscious of the climate and location of his family’s farm — Iowa has a short growing season and early frosts, which has influenced not only their cover crop seed mixes, but also how and when they plant.

Some growers plant cover crops in the off season when the cash crop has been harvested and the fields are empty, but Kyle says they plant their cover crops into standing corn and soy around Labor Day. 

“We live far enough north that the idea of harvesting the existing crop and then planting the cover crops doesn’t work with our timing — we just run out of days before frost arrives,” he says. 

Some growers will plant cover crop seed mixes with as many as 10 species, but that just won’t work for Kyle, where most common cover crops will get wiped out by frost within six weeks of planting.

Understanding your farm’s strengths and limitations is key, and the local Natural Resources Conservation Service (NRCS) extension office is a good place to explore what might work for you. 

After years of experimentation, Kyle says his operation has settled on a system that allows them to feel comfortable increasing their cover cropping acreage each year. 

“We do cereal rye ahead of a field that will be planted with soybeans,” says Kyle. ​“We do oats ahead of a field that may be planted with corn so there’s no risk of extra competition for the corn coming up. That’s our base, but we still play with some broad leaves, vetch, and brassicas.” 

Sarah says it’s worth considering crop rotation and variation, even with cover crops. Rotating through crop families can help growers avoid pest pressures and soil diseases and even disrupt weed cycles. 

The Cost of Cover Cropping

Kyle cautions that successfully integrating cover crops takes time, and he encourages growers to think of it as a process

“Since we started learning about cover crops, we toyed with them for five or six years before we really started to scale the practice,” he says. ​“It’s a journey and it’s absolutely not linear.” 

For instance, last year, Kyle had terminated his cover crop and planted in his corn and soy in the spring as usual. ​“But on Memorial Day we had a killing frost, and anywhere that we had high residue or cover crops it froze the soybeans; all the beans were dead,” he says. ​“That’s what I mean when I say it isn’t linear — that was a pretty large setback.” 

But Kyle and his family did not decide to abandon cover crops. ​“Every year that you talk to me is going to be the biggest year that we’ve had in cover crops, because we just continue to scale. We’re not a 100% cover crop farm and I’m not sure if we ever will be, but every year we do a little bit more.” 

Even without unusual weather events, implementing cover crops does have costs. Sarah says some growers shy away from cover crops because of the input cost for seeds, but there are government-funded grants available to farmers that are specifically for cover crops. 

One of the biggest programs is the NRCS Environmental Quality Incentives Program (EQIP), which offers technical and financial assistance to growers interested in implementing a variety of conservation practices, including cover cropping. For growers already using some conservation practices, the Conservation Stewardship Program offers financial incentives and technical assistance for longer-term commitments to cover cropping. Because grant funding is county-specific, growers should contact their local NRCS agriculture extension office as a first step.

Kyle and his family have used EQIP grants throughout the years to help them keep learning and expanding their cover cropping.

“People will ask me if I think the cover crops are paying for themselves. Well, yes, I do think so — otherwise I wouldn’t keep doing it,” he laughs. ​“But I do continue to work with NRCS to keep getting funding to help me with this.” 

For many of the benefits Kyle has seen from cover cropping, it can be hard to assign a dollar value. 

“Any yield benefit or soil health benefit is a long-term play to me,” he says. ​“But we really like the physical things that we can see and can be hard to measure.” If there’s a particularly wet spring, they don’t lose soil anymore, he says, and in drier years, the cover crop roots help hold more moisture for longer. 

“We’re also finding that we are able to eliminate some chemistry early on, especially in our soybeans, because the rye is drowning out the weed competition,” he adds. ​“We really like that.” 

Know Before You Grow

With so much beyond growers’ control, any opportunity to improve on-farm resilience and reduce reliance on inputs is worth some considerations. Introducing cover crops might seem risky, but there are the long term benefits of reduced erosion and soil loss that make it well worth it, as well as providing cash crops with better access to plant-available nutrients by promoting a robust soil microbiome. 

There are a multitude of resources and passionate experts eager to help growers find the cover crop strategies that fit their unique needs and operation, and Sarah encourages growers interested in cover crops to explore their options and discuss their concerns with their agronomist and experts at the local NRCS office.

Kyle’s advice to growers considering introducing cover crops to their operation is to find what works on their farm and start small. Each farm is unique; what works for one grower may not for another, and starting small can help growers reduce financial risk while identifying the best practices and mixes for their farm. 

As of this year, Kyle and his family have cover crops on over 6,000 acres.