Green Manure

Published in the May 2009 Issue Published online: May 03, 2009 Nancy I. Butler
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Jeff Miller, Miller Research llc, conducts research for improved crop protection in southern Idaho.

During the time of the Dust Bowl, growers did not realize that the devastation was due in part to the lack of crop rotation. Similar results are blamed on the Irish Potato Famine, where that historic farming mistake has been labeled “monoculture.”

Monoculture in the agriculture industry is defined as growing a single crop on the same piece of land season after season.

The potato demise in Ireland was caused by planting the same potato variety over and over in the same place. In addition, there was no resistance to potato blight in that variety and the nutrients in the soil were exhausted.

According to the USDA-ARS, an intensive research program was started following the disastrous “Dust Bowl.” The mission of the USDA in conjunction with Kansas State University was to “…increase understanding of wind erosion processes, develop reliable predictive tools, develop control practices and transfer technology for sustaining agriculture, protecting the environment and conserving natural resources.”

Part of that program includes determining Best Management Practices. Practicing monoculture negatively affects the soil and the crop.

It is recognized that one crop will pull specific nutrients from the soil while other crops will replenish nutrients.

Utilizing BMPs has become a common practice as it is designed specifically and individually. For no two fields or growers are alike.



Rotating crops and fields are the best bets in producing a healthy, high-yield crop.

Cover crops are often considered soil-building as their purpose is to be grown specifically to be worked back into the soil toward the end of the season.

A lot of oilseed radish and a fair amount of mustard are planted as cover crops. Choosing the variety is often up to personal preference and seed salesman. It is advisable to consult with your agriculturalist as well.

By using green manure as a cover crop, or plow-down crop organic matter, nitrogen and other nutrients are added to the soil.



Jeff Miller at Miller Research LLC in Rupert, Idaho, has been doing research on early dying and fungal disease. Miller says, “Green manure products have proven to be very effective and economical in some circumstances.”

Some of the earliest references to the use of green manure are from China in the 12th century B.C. Also, there is proof that colonists brought the practice to North America.

With the introduction of synthetic inorganic fertilizers, the use of green manures declined.

“Green manures,” says Miller, “can actually act as biofumigants.”

“They release the same active ingredient as metam sodium when they are plowed into the soil and when they decompose they release these products that kill the fungi. But green manures do much more than this. They can increase the percentage of decaying organic matter in the soil. This changes the composition of organisms in the soil. The late Dr. Jim Davis showed that incorporation of green manure crops reduced potato diseases without actually decreasing the disease-causing organisms,” said Miller.

There is a looming concern with the possibility of wiping out all the “good guys” in the soil. Fumigants are not selective; they are a broad spectrum killer.

Green manures can reduce disease differently, without killing organisms in the soil.

What university scientists and researchers are shooting for is to stimulate a diverse micro-population to reverse disease.

Through many trials, tests and experiments, they can compile results and create improved methods to make green manures the most effective. Miller explains how eager they are to learn and work with growers. He admonishes growers to contact him or any of the University of Idaho specialists to set up trials and tests.

“However, we don’t want growers to abandon what they have been doing. Call U of I specialists to set up experiments on a small-acre basis first. We are more than happy to help set up trials and tests.” The University of Idaho has a complete listing of specialists on their website, or call Miller at 208-531-5443.