‘Grow-your-own’ N boosts yield

The latest research on farmers growing their own nitrogen shows the management practice hedges against a volatile off-farm inputs market, and results in increased yields and income.

The research by Iowa State University agronomy professor Matt Liebman and his associates was discussed at a recent field day at the ISU Ag Engineering and Agronomy Research Farm in September.

The event was sponsored by Practical Farmers of Iowa, the USDA Agriculture Research Service, Iowa State University and the U.S. Testing Network.

Results show that from 2003 through 2010, extending a two-year corn-soybean crop rotation with small grains and forage legumes increased corn yields 5 to 9 bushels per acre and soybean yields 5 to 7 bushels.

The three-year rotation (corn–soybean–oat/red clover) provided about $284 per acre in net returns to land and management compared to $277 for the two-year rotation (corn–soybean) and $282 for the four-year rotation (corn–soybean–oat/ alfalfa–alfalfa).

Key Points

Growing own nitrogen increases yields and hedges against volatile N prices.

Extending crop rotation by adding forage legume trims cost of purchased inputs.

Goal is to maintain a high level of production while improving environment.


This study supports earlier research showing farmers who use legumes as their major source of nitrogen and apply manure for extra on-farm nutrients, protect themselves from the rising prices of off-farm inputs, and it stabilizes their farm’s income.

This comes as no surprise to conventional farmers like John Gilbert, 62, a self-described “veteran of the farm crisis of the 1980s.” Gilbert farms 800 acres in Hardin County, and his operation now includes forage, dairy cattle and hogs.

“I don’t want to expose myself to more financial risk,” says Gilbert. “Land is out of my price range, so we have to intensify our management of what we have. Farmer-owned livestock has done that for us.” He says his forage land stands up to drought and flooding, plus he has a use for the grass and legumes. “This system will work for us through thick and thin,” says Gilbert.

Do more with less

Liebman, Wallace chair for Sustainable Agriculture at ISU, says farmers can do more with less and yield more with lower external inputs. “It’s about maintaining high levels of production while improving the environment,” he says, including diversifying with legumes to improve soil quality and integrating livestock into the operation to cut reliance on synthetic fertilizers.

Liebman’s numbers show this approach can greatly reduce chemical use without jeopardizing yields, an increasingly important factor as weeds and pests adapt to herbicides and pesticides.

Compared with the two-year rotation system, nitrogen fertilizer use during 2003-10 was decreased by 76% in the three-year rotation and by 84% in the four-year rotation. Herbicide use was 85% less in the three-year rotation and 89% less in the four-year rotation.

For farmers without their own livestock, the high livestock numbers across the state allow them access to manure from neighboring facilities. Liebman used purchased manure in his analysis of three different systems, and the three-year rotation still outperformed the other two rotations, both economically and agronomically.

Earl Hafner, 65, an organic farmer from Panora, who spoke at the field day later, said this research makes using an extended crop rotation to reduce inputs “a no-brainer, but it takes a different mindset. If you’re farming 3,000 acres, it means you’ve got to have a cultivator and have someone on it, you can’t just call the
co-op to spray.”

Hafner, who began converting his 1,800 acres and beef herd to organic in the late 1990s, isn’t out to convert fellow farmers to organic. “We don’t have to be organic to have healthy food,” he says. “We have to have good soil biology. You can call that a biological farmer if you want to.”

To Hafner, extending his rotation with cover crops makes good economic and environmental sense. “If you go in behind soybeans and plant cereal rye, it means you’re feeding the soil biology during winter,” he says. “I turn that into the top 4 inches of soil; 6 inches of rye in the spring will absorb $170 worth of water-soluble nutrients that you’re saving. By July, when your corn or beans are having a major pull on nutrients; those nutrients are available to the crop.”

The added bonuses of increased yields and better weed control through the allelopathic qualities of cover crops only build the case for the extended rotation.

Gilbert adds one more consideration: “It’s the type of system landowners need to recognize is important if we’re going to have a new generation of farmers. At that stage it becomes more economical for a person of limited means to use their skills to raise perennial forages, rather than be buying a lot of inputs.”

Liebman has been working with ISU economist Craig Chase, ISU plant pathologist Leonor Leandro and University of Illinois soil scientist Michelle Wander. He also works on this study with Mark Tomer and Tom Sauer from the USDA-ARS National Laboratory for Ag and Environment at ISU.

Erem writes from Cedar County.

This article published in the November, 2011 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.