By Shannon Burkdoll

Green manure was the subject of a recent workshop attended by about 125 Montana farmers and ranchers during the state’s very first organic conference Dec. 5 in Great Falls.

	"Healthy soil is a vital system to your productivity, and earthworms are ecosystem engineers."

“With minimum tillage, green manures will increase the soil’s earthworm activity and are beneficial to the soil’s arthropods,” said Helen Atthowe, a Missoula County Extension agent. Green manures also encourage beneficial insects such as ground beetles—a natural predator of miller moths—and spiders—an effective control for grasshoppers, she said.

This increased earthworm activity can influence the soil’s productivity by increasing the amount of nutrients and airflow in the soil, said Jill Clapperton, Ph.D., who researches transitions to organic systems on an experiment station near Lethbridge, Alberta, Canada. “Healthy soil is a vital system to your productivity, and earthworms are ecosystem engineers” she said. “They mix the soil and create soil that is more microbially active. Creating a predator-prey relationship is part of the nutrient cycle” Clapperton said that while it’s advantageous to encourage native earthworm activity through practices such as growing green manures, one should never introduce earthworms brought in from the outside.

Choosing the right green manure

Atthowe said she prefers white clover for irrigated intensive vegetable production. “For a warm season crop, white clover is a good green manure and living mulch when kept mowed,” she said. “It’s a constant residue and we’ve seen an extraordinary increase in yield and vegetable quality. We’re picking about 60,000 pounds per acre.” Yellow clover is also a good choice, she said. It blooms earlier than the vegetables and attracts flies and wasps to prey on harmful insects, she explained.

Herb Sand has experimented with peas, lentils and sweet clover as green manures on his organic wheat farm near Ophiem, Mont. Sand said the sweet clover flourishes in his light-sandy fields, not only fertilizing the soil but eliminating weed problems. “Sweet clover is biannual and won’t compete with other crops, but it will in a wet spring,” he said. “The second year it is very aggressive. My neighbors are convinced sweet clover is toxic to wild oats.” Sweet clover is inexpensive and creates a lot of tonnage for a green manure mulch or cattle feed, he said, adding that it also has a deep root system well suited to breaking up a hardpan field. “I seed the sweet clover with my wheat in an air seeder because I want it to grow in between the wheat where the weeds grow,” Sand explained.

But sweet clover isn’t always the best answer, he said; it is hard to get a good stand going, it doesn’t sequester as much nitrogen as other legumes, and is sometimes hard to manage as it can get away from you, especially over a wet June. “If it gets too tall, you have to disk it with two swipes or plow it to get through it,” Sand said.

Peas provide a more even stand over a field and lock in more nitrogen than clover, he said. They can be seeded with ordinary drills and are fairly drought tolerant, but they are more expensive and don’t provide as much organic matter, Sand said. Lentils can also be seeded with ordinary seed drills, he said, and they can be worked into the ground without a disk. Lentils can be left standing while other crops are harvested, Sand said, whereas sweet clover needs more management; however, he said, lentils provide little organic matter and are hard to harvest because they only grow between six to eight inches tall. “Lentils should be rolled because they are so short,” he said. Sand stressed the importance of getting into rotations with green manures, as well as crops for sale, to better benefit the soil and productivity.

Mikel Lund of Scobey, Mont., turned to chickling vetch to get his “green fix” after using sweet clover and peas. Lund said he decided to try something new after the clover weevils took over his sweet clover production. Though chickling vetch is new to Montana, Lund said it produces good nodules and has improved the soil quality on his organic wheat farm. “Last year my lowest protein was 13.7 and I had 60- to 61.5-pound wheat,” he said. “It’s quality all the way, and it’s easy to sell.”

David Oien, an organic grain producer in Conrad, Mont., uses a 70-year-old mulching technique to provide his soil with green nutrients by planting medic as a manure crop. Medic is a cousin to alfalfa and a hard-seed legume that germinates over time. Former Montana State University researcher, Jim Simms developed a brand of medic out of wild black medic and a strand already existing in Montana, said Oien. “Now it’s in every state,” he said. Though it’s considered a weed in some Montana regions, Oien said black medic grows well with wheat in dryland systems and saves moisture by shading the soil. Black medic has had some successes, he said, including a no-till operation in North Dakota and a dryland Saskatchewan farm.

To till or not to till

While Sand and Lund till their green manures to mix them into the soil, Atthowe’s green manure program requires minimum tillage to mix the clover with her west-central Montana soils. She tills her fields in spring to help reduce stress on the earthworm population (tillage in the summer and fall, she said, can decrease earthworm production). “The soil is covered most of the year. A light tillage in the spring rips a lot of the residue that is left [from the winter months].” Including the dying, dead and very, very dead in the compost residues is important to the green manure’s productivity, Atthowe said. “It’s a habitat for beneficials,” she said.

	"Biodiversity is your biggest insurance and gives your system flexibility, resilience and resistance to what you throw at it."

Montana State University researcher Perry Miller works in primarily no-till organic systems. While one study cited showed no-till and tilled systems had similar results, Miller said the no-till has greater long-term benefits than the tilled systems. The project was completed near Culbertson, Mont., and in a Swiftkern, Saskatchewan operation. The wheat responded better to the tilled lentil fields in the short-term but took five years to return to the normal soil composition. The Saskatchewan experiment had the same results. “Green manure pays relative to cost,” concluded Miller. “In six years, the no-till systems outweighed the tilled systems. We focused heavily on conserving water and coincidentally the performance dramatically improved in Saskatchewan.”

While tillage systems may provide farmers with short-term results that look good, Miller said, the no-till systems provide farmers with healthier soils that produce higher quality crops. In 2003, he said, an organic study producing conservative yields ran dry in a no-till system. “Organic is favorable during drought,” he said. “But here’s one no-till researcher who’s sitting here a little surprised.”

Clapperton agreed that no-till operations were most beneficial to organic operations. Tillage systems can play havoc on earthworm activity, therefore reducing nutrient production in the soil, she said. “Biodiversity is your biggest insurance and gives your system flexibility, resilience and resistance to what you throw at it. If you do till, try to do it in the spring. If you do it in the fall, make sure you do it in good forage to maintain mycrorrhizea, which make the plants more competitive for space, increase its drought and disease resistance and increase the uptake of mobile minerals.”

Con't to part 2 of our series on the MOO conference>