In the face of rising costs for nitrogen fertilizer, which is derived from natural gas, University of Arkansas Division of Agriculture scientists are turning to nature for a less expensive, more environmentally friendly source.

Dr. David Longer, professor of crop, soil and environmental sciences for the University of Arkansas Division of Agriculture, shows the biomass content of Austrian winter field peas. He is growing the peas, which are a type of legume, as a winter cover crop in test plots to determine if they provide a less expensive source of much-needed nitrogen than traditional nitrogen fertilizers.

Dr. David Longer (photo), professor of crop, soil and environmental sciences at the Arkansas Agricultural Experiment Station, is studying the use of legumes — plants that include soybeans, other beans and peas, alfalfa and clover — to provide a natural source of nitrogen.

“Earth’s atmosphere is nearly 78 percent nitrogen. Legumes have the ability to convert atmospheric nitrogen into an organic form that plants can use,” Longer said. “Corn and thousands of other plants do not have this ability and thus require nitrogen fertilizer to produce significant yields.

“Nitrogen is the most important nutrient for corn growth,” he said. “Corn has extremely high growth and photosynthesis rates and requires large amounts of water and nitrogen.”

Longer’s research partners in the project are Dr. Michael Popp, UA agricultural economist, and Vaughn Skinner, resident director of the Arkansas Agricultural Research and Extension Center in Fayetteville.

“Corn growers are faced with stagnant crop prices and ever-escalating costs of production,” Popp said. “A sizeable supplement of nitrogen from companion crops could significantly lower the production costs.”

Natural gas is the primary feed stock for producing nitrogen fertilizer.  Fertilizer costs are soaring with energy costs while the price of corn remains low, Longer said.

In a preliminary study in 2003, planting corn and soybeans side-by-side showed great promise in reducing the amounts of nitrogen that growers need to apply for maximum corn yield, Longer said.

The current study uses a winter cover crop of Austrian winter field peas that are turned under in the spring, 30 days before planting. Then corn and forage soybeans are planted together in rows.

These soybean seedlings, planted in the row with corn, will help provide nitrogen to the crop. Nitrogen is the most important nutrient for corn and soybeans, a legume, convert nitrogen from the atmosphere to help fill the crop’s needs.

“The delay between plowing the cover crop under and planting the corn allows the peas to begin decomposing,” Longer said.
Decomposition begins “mineralization,” in which the nitrogen in the plant tissue converts to a form the corn can use. It provides a time-released action that continues to provide nitrogen to the corn while the crop is growing.

The soybeans planted with the corn supplement the nitrogen supply.

“The soybean roots grow in the same zone with the corn’s roots,” Longer said. “The soybean roots convert atmospheric nitrogen and produce nitrogen-rich bacterial nodules in their roots, and provide another ‘time-released’ nitrogen supply.”

Test plots will compare combinations of the pea cover crop and soybean-corn intercropping with varying rates of commercial nitrogen fertilizer to see which provide the optimum yield. Longer suspects the natural nitrogen supplements will greatly reduce the amount — and cost — of fertilizer needed to produce a profitable yield.

Popp said reducing the amount of fertilizer is also likely to eliminate one of two applications, which saves fuel costs.

“On 500 acres of production, this could lead to substantial increases in profitability and reductions in price risk for operating costs,” he said.

Longer said the peas and soybeans can benefit the environment as well as the corn grower. They help supply nitrogen to the corn crop during the growing season and add nitrogen and organic matter to the soil over the winter.

“This is nature’s nitrogen,” he said. “You don’t have to worry about nitrates leaching into the soil. And it can’t help but improve soil organic matter over time.”