When a farmer uses cover crops, it tends to stand out. Particularly when viewed against the brown dried-down residue of cash crops and fields of bare ground ready for winter, the lush green of new growth emerging late in the season shouts that something different is happening.
What benefits can cover crops bring to an operation, and what trade-offs must be made? We asked Justin McAllister, Bunge regenerative agriculture lead and soybean farmer, whose family legacy spans nearly 175 years on their land in northern Missouri, about his experiences with cover crops.
“I farm with my Dad, Gary, who has been using no-till with a large portion of our soybeans for 20 to 30 years, it’s only been the last seven years or so that we’ve experimented with our use of cover crops,” McAllister said. “We’re in year three of doing cover crops as part of our crop rotation with our beans, and so far, I get enough benefits from them that I can justify doing it on its own merits.”
Benefits of Cover Crops
Better Soil Erosion Control
Ryegrass, similar to the winter rye pictured here, helps prevent soil erosion in McAllister’s experience.
At the top of the list for McAllister is soil erosion control. In his fields, cereal ryegrass — a perennial — goes in right after the bean harvest, he explained. “I have something growing in that field with the winter cover crops,” he continued. “In the spring, when I go in with my cash crop, I can plant right into it while it’s green. Then I terminate the cover crop. My fields are never bare, which helps keep the field from eroding via wind-driven soil erosion or, particularly around here, water-driven soil erosion.”
Improved Soil Health and Structure
“I have a lot of clay content in certain fields, and I’ve noticed that the soil is looser when something is growing continuously,” McAllister said. “With my no-till fields, I feel I am planting into a better seedbed that is not as compacted.”
Living roots also make a difference in water infiltration and moisture retention in those fields, boosting soil fertility. “Looser soil allows for better water infiltration, so moisture penetrates down into the soil instead of running off,” he said. “And that can benefit the cropping system later in the season.”
“Last year, we had a dry spell toward the end of summer,” he explained. “My soybeans planted into cover crop ground managed the heat and dryness better. Those plants stayed healthier compared to the non-cover crop ground.”
Herbicide Savings & Effectiveness
Fields laying bare or fallow for long periods could give weeds a chance to gain a foothold. “Where I am dealing with some herbicide-resistant weeds, the cover crops can make a difference,” he pointed out. “Cereal rye’s large root system choked out waterhemp and prevented germination entirely,” McAllister said he dropped a more expensive residual chemical from his herbicide program because the cover crops aided weed control by preventing competing weeds from growing.
“It costs $20 to $25 an acre for cover crops,” he continued. “I made that cost back in herbicide savings alone — even with the added pass to terminate the cover crop.”
There are several ways to think about cover crops and nutrient management. With water control, less runoff leads to fewer nutrients washing out of your fields, and the planted cover crop species/mix can also benefit the following crop.
“Even though I haven’t experimented with it yet, I agree with others that say more diverse cover crop mixture can bring extra benefits,” McAllister said. “Legumes don’t need a nitrogen-fixing species in fields. But I can see where someone following with corn would benefit from adding nitrogen credits through a nitrogen fixation cover crop.”
Building Organic Matter
“We do soil sampling, and we have a lot of different soil types here,” says McAllister. “One field in particular, where I have had great success with cover crops, has high clay content. No matter what I do, it will always have high clay content. You can’t change the soil type or soil quality by planting cover crops, but you can enhance its biomass over time. And the cover crop aids your soil health by avoiding compaction and allowing the soil to stay a little looser by having those plant roots constantly growing in it.”
Trade-Offs of Cover Crops
You can’t talk about the benefits of cover crops without mentioning trade-offs. McAllister said employing cover crops requires more thought and attention, mainly when planting into a green cover. “The timing of cover termination depends on several factors, not the least of which is rainfall,” he said. “Too late in a dry year steals moisture needed for cash crop germination. Too soon in a wet year, and you may have trouble getting in there to plant.” If mishandled, either of these situations can cost you a few bushels of yield with your cash crops.
Other trade-offs include the price of seed and a potential extra pass across the field to plant or terminate. “Every farm and every field are different,” McAllister said. “It all depends on your goals for the season. You may not get the same benefits from the direct savings that offset costs on my farm, but most farms can still benefit from the long-term effects.”
The Legacy Effect: Biodiversity and Sustainability
Considering the immediate costs of beginning a cover crop program is essential. Growers must be able to absorb the initial cost of seed and the potential of a slight yield loss as they get started. However, the long-term effects on a farm can be impactful.
The benefits can be very substantial from planting cover crops as they become the key to a no-till conversion. Avoiding tillage allows you to run lighter equipment, spend less time in the field, and consume less fuel. Other benefits include providing natural weed control which reduces reliance on herbicides and herbicide resistance. Cover crops can also limit soil erosion, improve water infiltration and moisture retention, and foster soil health with a more resilient soil structure resulting in a healthier farm that can withstand more of what nature throws at it.
Sustainable agricultural research has concluded an operation will become a sustainable ecosystem — a farm prepared to produce reliably for future generations.