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New Mexico State University

New Mexico State University

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NMSU Tests Organic Alternative to Chemical Fertilizers

FARMINGTON New Mexico farmers may one day step away from using costly chemical fertilizers, and choose manure as a cost-effective organic alternative. New Mexico State University researchers are studying how producers, especially those raising cattle along with their crops, can also reduce environmental risks by using cattle or poultry manure.


To demonstrate, scientists at NMSU's Agricultural Science Center at Farmington are in the midst of a two-year study using animal waste as an organic fertilizer for corn. "Given the rising costs of chemical fertilizers, the abundance of cattle manure and poultry litter, and the environmental benefits of using animal waste, it's a win-win situation if we can show how to effectively use animal byproducts as fertilizer for local crop production," said center superintendent Mick O'Neill.

Organic fertilizers have many environmental and economic benefits compared with chemical fertilizers, O'Neill said. If applied in the right quantities, organic materials could provide the nitrogen needed for crop growth, but with much less leaching. Organic compounds take longer to break down and they improve soil structure, which increases its water-holding capacity and protects against erosion.

"Organic matter holds onto nitrogen longer," O'Neill said. "With inorganic fertilizer, nitrate leaches out much faster and may contaminate ground water sources. That's what we see happening in the Corn Belt where constant nitrate leaching is harming drinking water."

In addition, since nitrogen is retained longer in the soil, less fertilizer needs to be applied over time, O'Neill said. Most chemical fertilizers are concentrates that supply only one mineral, but organic matter simultaneously adds other needed nutrients to soil.

The challenge is to determine the right quantities of cattle manure or poultry litter to provide enough nitrogen for local crop production.

"We're trying to nail down specific amounts, rates and times to use organic materials," said Sharon Bruce, an NMSU agronomy and horticulture student assisting with the project. "Over-application of animal waste can also create environmental problems, so our goal is to find the right balance."

The study consists of four corn plots one with no fertilizer, one with chemical fertilizer, one with cattle manure and one with poultry litter.

On the chemical and organic plots, the equivalent of 200 pounds of nitrogen per acre was applied. That translates into about 667 pounds per acre of chemical fertilizer, 1.5 tons per acre of poultry litter and 9.6 tons per acre of cattle manure, Bruce said.

The treated plots have split applications with half receiving all the fertilizer when the growing season started and the other half receiving two-thirds at the start and the remainder when the corn silked.

Researchers will compare corn yields at harvest in late November. Meanwhile, they take multiple soil and tissue samples throughout the season to measure nitrogen and mineral nutrient levels. Special attention is paid to acidity levels because humic acid in manure can increase soil acidity and damage crops, O'Neill said.

The study will last at least two years and will include more crops. But even after study results are available, many growers may use cattle manure to supplement rather than replace chemicals, given the huge amounts of waste material required to fertilize fields, O'Neill said.

"That's partly why we're studying poultry litter," he said. "Much less is needed to fertilize and it's widely available on the market, which could make it a more practical alternative."

The Navajo Agricultural Products Industry (NAPI) in Farmington, with 65,000 acres of irrigated land, will probably use study guidelines to begin applying manure from its feedlots, but only as a supplement. NAPI's cattle wouldn't produce enough to cover the farm's corn production, much less other crops, said NAPI Agricultural Testing and Research Lab director John Keenan.

"It's a benefit even if it's just a supplement because our soils are very low in organic matter," Keenan said.