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Boosting Topsoil Quality
Dan DeSutter asks a seemingly easy question: If you invested money with money managers who lost half of it, what would you do?
Easy answer: They’re outta there.
Swap money for soil carbon, though, and the answer is harder to face. That’s the U.S. soil carbon loss over the last 60 years, says the Attica, Indiana, farmer.
“Carbon is the key ingredient in soils,” adds Ray Archuleta, a Natural Resources Conservation Services (NRCS) conservation agronomist in Greensboro, North Carolina. “Soil organic matter is 58% carbon.”
Organic matter has a number of benefits, such as being a reservoir of nutrients and boosting water-holding capacity. Soil carbon holds the key to even more benefits.
“We can have soils with 10% organic matter that still don’t cycle water and nutrients,” says Archuleta. Instead, having active carbon is key. That’s because soil teems with thousands of living organisms, including soil microbes like bacteria and fungi.
Without active carbon in soils, it is like living in a mansion eating little cocktail wieners every night,” says Archuleta. “We have to feed the microbes (with active carbon). If you give them food, they release ammonium that can add 17 to 60 pounds (per acre) of nitrogen (N) to the crop.” These microbes also can spur release of nutrients like phosphorus and zinc to crops, he adds.
Of course, having the soil to retain carbon and organic matter comes first. There’s good news on that front. The latest USDA/NRCS National Resources Inventory shows cropland soil erosion decreased 41% from 1982 to 2010. Annual water erosion rates declined from 1.67 billion tons to 982 million tons during this time frame. Meanwhile, annual wind erosion losses dipped from 1.38 billion tons in 1982 to 740 million tons in 2010.
Still, maintaining a thin black line of topsoil that determines bounty or despair is challenging. Archuleta cites a Colorado dust storm that occurred in January 2014.
“I never thought we would experience a dust bowl, but we did,” he says. “The majority of our soils are degraded all over the planet. When I go to a farm, I assume soils are degraded unless I’m shown otherwise.”
Soil Cores and their Characteristics
Next time you’re by a fence line, plunge a shovel into it. The loose, pliable soil permeating with microbial activity mimics the tallgrass prairie present before European settlers arrived.
“When the tallgrass and mixed-grass prairie was tilled, the oxygen it added increased the rate of organic matter decay,” says Dwayne Beck, manager of the Dakota Lakes Research Farm near Pierre, South Dakota. “When organic matter decreases, the ability of the soil to maintain good structure decreases. The porosity collapses, and the water-holding capacity of the soil decreases. The soil particles are too close together.”
Over time, such soils begin to hold less water. A fenceline with native prairie grass and deep soils can hold up to 10 inches of water down to four feet deep, Beck says.
A bordering conventionally tilled field may hold only six inches at the same depth.
“With a smaller soil bucket to hold water, soils get wetter faster and dry out faster,” Beck says.
Changing weather patterns play a role as to why farmers may believe they struggle with wet soils at planting and dry ones several weeks later, says Beck.
“The problem with soils being too wet at planting and too dry afterward is the lack of resilience in the soil,” he points out. “Our soils are really starting to degrade after 100 years.”
How do you do it?
Beck once talked with a road builder who asked why farmers disked their fields.
“He told me, ‘I have friends who are farmers, and they say they disk their fields to loosen up the soils. When I build roads, I disk to make them hard,’” recalls Beck.
The road builder was right.
“When you till, you beat organic matter and pore space out of the soil. It’s the organic matter that holds those pores together,” says Beck. Decreased pore space and organic matter slice natural nutrient release, water infiltration, and a host of other benefits.
“No-till is not where you stop,” Beck says. “It is where you start by not beating the soil.”
Says Archuleta, “Zero-till emulates the natural ecosystem. Mother Nature does not till. She uses earthworms, dung beetles, ants, termites, and roots.”
No-till isn’t enough, Archuleta says. Cover crops are another vital system component.
“No-till failed in many parts of the country because farmers forgot the most important part,” says Archuleta. “Cover, cover, cover the soils with living roots 24-7. No-till will not work without covers.”
Back in the early 1990s, DeSutter set several goals. Then, he and his wife, Barbie, started farming.
“I wanted to be a good neighbor and keep my soil and nutrients at home,” he says. “I also wanted to figure out a competitive advantage. I’m in the commodity business, and over the long haul, the average person breaks even. I needed to do better.”
He’s been able to do that by building soil quality. “I have a systematic approach, one in which everything links to each other,” he says.
Organic matter growth is one way to gauge a soil quality increase. In one of DeSutter’s fields, soil organic matter has increased from 2% to 4% over 20 years. A couple benefits of increased organic matter include:
• Free nitrogen. Every 1% increase in organic matter adds 1,000 pounds per acre of N in the top 12 inches of his soil; 2% to 4% of this mineralizes annually. A 3% mineralization rate translates into an average 60 pounds of free nitrogen annually.
“That’s like a $40-per-acre annuity each year,” says DeSutter.
• Increased water-holding capacity. Every 1% increase in organic matter in the top 12 inches of soil adds 16,500 gallons per acre in soil water-holding capacity. DeSutter figures the 27,154 gallons in an acre-inch of water can translate into the equivalent of a 1.2-inch August rainfall. At a critical time during the fill period after pollination, the extra water-holding capacity from a 2% organic matter boost tallies an extra 20 bushels per acre. At the $5-per-bushel corn prices of 2013, that generates an additional $100 per acre in profit.
One tool he’s used to glean benefits like these came about by accident. He assisted a Purdue University crop scientist who had planted annual ryegrass on DeSutter’s farm for a research project.
“We were fixing a tile hole during the first week of April,” DeSutter says. “When we looked down in the hole, we could see the annual ryegrass roots going down four feet.”
DeSutter reasoned that such a deep-rooting cover crop could shatter compaction and could boost water infiltration much better than tillage.
“Within six months, I sold a deep-tillage tool and started focusing on planting cover crops on every acre,” he says. “I found something more effective than that piece of steel could ever be.”
Unlike tillage, he reasoned, cover crops could spur microbial activity and boost soil quality. “A key is keeping the top 12 inches of the soil profile moist,” he says.
When this layer dries out, symbiosis between roots and soil microbes halts. These include microbes like soil fungal hyphae, which boost soil structure and add chemical compounds that bind soil aggregates and build soil carbon and organic matter. Cover crops combine with cash crops to create a year-round moist mulch.
Although annual ryegrass perked DeSutter’s interest in cover crops, he shifted to cereal rye because he felt it had better winter survivability.
“The 3-foot-high cereal rye keeps soil moist because it provides a nice mulch barrier on top of the soil,” he says.
Although cereal rye is his base cover crop, others he laces into the mix include:
• Hairy vetch
• Austrian winter peas
• Crimson clover
• Oilseed radish
“A mixture is always best,” he says. “One plus one doesn’t always make two. Sometimes it makes three. Sometimes, I get more growth out of them together than I do by themselves.”
DeSutter has interspersed continuous corn with soybeans and winter wheat for cash crops. Economics is the main reason. Crop diversity enhances biological activity, too.
Beck says incorporating diverse cover and cash crops helps build soil carbon content and higher organic matter content.
“This corn-soybean thing is collapsing,” says Beck. While corn adds much soil carbon to the soil, soybeans do not. Diverse rotations that add soil carbon while still balancing the diet of soil microbes can build organic matter.
No-till and cover crops are keys in DeSutter’s strategy. Still, other factors like tiling most of his farm are important. Other essential factors include:
• Fertility. Managing the carbon-N ratio with no-till and cover crops is crucial, says DeSutter.
“When I no-till and add a cover crop, I tie up that N early on,” he says. “Microbes eat the N first and release it to the plant later in the season. If I try cover crops and don’t manage N right, I get a pale corn crop early on.”
Besides manure, he spoon-feeds fertilizer several times during the growing season to ensure N access to crops at all times.
“Last year with cover crops, I applied 2 gallons per acre of 10-34-0 with the seed and applied 100 units of nitrogen with the cover crop-killing herbicide,” he adds. “I then sidedressed the balance of nitrogen. The crops were green right out of the gate. I have to feed N early on, but I get it back later in the season during critical reproductive phases.”
• Weed control.
Marestail concerns soybean farmers in DeSutter’s area. “The most effective thing against it is a good stand of cereal rye,” says DeSutter. Although herbicides are still needed, cereal rye aids control by first smothering the marestail.
• Cover crop kills.
Complete cover kills with herbicide are paramount so the cover crop does not compete with the main cash crop.
“Systemic herbicides are very temperature sensitive,” says Mike Plumer, a former University of Illinois Extension educator who’s now an independent conservation consultant. “The plant must be actively growing for them to work.”
Cover crop kills are greatly curtailed in cold and/or cloudy weather, he adds.
Steps to boost soil organic matter and carbon are ways to protect both your soil and your bottom line. “When I do things to make my soil more productive, there is an economic benefit,” says DeSutter. “It may not be measurable at times, but if I go forward to improve the soil resource, I will get it back.”