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Using Legumes To Offset Costly Fertilizer

published: August 13th 2008
source: Noble Foundation

The Samuel Roberts Noble Foundation's researchers and agronomists are studying the possibility of using legumes to offset the need for costly fertilizers. The research could provide a financial savings to farmers and ranchers.

Nitrogen, once only 25¢ per pound, is now 65¢ per pound (or more), an increase of more than 150 percent in the last few years. As these prices increase, the Noble Foundation is taking a second look at winter and summer legumes, such as alfalfa, clovers, medics, vetch and other similar crops, and their ability to add nitrogen back into the soil.

Legumes are known for the significant role they play in agriculture for being high in protein, but they also have the innate ability to fix nitrogen from the air. Their root system, accommodating bacteria called "rhizobia," converts atmospheric nitrogen to ammonia creating a source of fertilizer that could help stem production costs.

"We've hit a critical period in agriculture," said James Rogers, pasture and range consultant and Team Manager. "The way we used fertilizers is gone and may be gone forever. It's vital we discover alternatives to the issue of fertilization, and legumes look to be a positive alternative."

Noble Foundation agronomists with the Forage Improvement and Agricultural divisions, Twain Butler, Ph.D., and John Guretzky, Ph.D., are currently testing several field trials, one of which is a legume-bermudagrass grazing trial on 42 acres. The trial's objective is to discover how legumes impact bermudagrass that is being grazed.

"More than 2.5 million head of cattle are within a 100-mile radius of the Noble Foundation," Guretzky said. "Cattle are the predominant agricultural business in the region so it's important that we find how legumes and grasses can work together to better support the cattle industry."

While legumes are a positive alternative to high fertilizer costs, they do not freely give their nitrogen production away. The primary source of nitrogen transfer comes from decomposition of dead legume plant material to the following grass crop or by recycling urine and dung via grazing to the companion crop.

"To make a legume-grass system work, management must be focused on the legume, not the grass," Rogers said. "Pastures will look different than they have in the past. Without the even distribution of fertilizer (as urine and manure), pastures will look uneven and may have more weeds, but that's OK."

Butler added, "We've always known how important legumes were to agriculture, but there is still a tremendous amount to learn, especially in legume-grass mixtures under grazing."

Because legumes are less persistent than grasses, pastures comprised of grasses and legumes require a higher degree of management than nitrogen-fertilized pastures. The benefits of legume-grass systems, however, are not limited to merely the provision of nitrogen. They also compliment the growth of grasses and extend the production of forage into spring growth periods, when forage from grasses in the southern Plains is unavailable.

"There's no doubt about it, legumes are a key component of agricultural systems either through fixing nitrogen or providing additional quality forages," Guretzky said. "They impact the bottom line, and we're hoping through our research to increase that impact."