Farmers gather to learn latest science on nitrogen fertilizer

Written by Jonathan Eisenthal

An audience of farmers packed a meeting room in Rochester last week to hear from six experts representing the spectrum of scientific investigation into nitrogen fertilizer and the associated compound, nitrate, to hear the latest information about techniques for fertilizing crops while reducing nitrates in the environment.

The nitrate forum, convened by Minnesota Agricultural Water Resource Center (MAWRC), welcomed Bruce Montgomery, a scientist from Minnesota Department of Agriculture, who is in charge of its nitrogen fertilizer management review. Montgomery assessed how agriculture is doing controlling nitrate loss and where it can be improved. He praised the willingness of all the farmers he has encountered on these issues, to join with them to help solve situations where wells show presence of nitrates in drinking water above the standard for human health, 10 parts per million.

He noted that the yield of corn per unit of fertilizer has increased dramatically (meaning less fertilizer per pound of corn is being used), which is a great success story.

Montgomery noted that two major areas of the state–the Central Sands (stretching north from the metro area) and the southeastern region, are particularly sensitive to nitrate movement into groundwater, and that different crop regimens may in future be brought to bear, to reduce these problems. He noted that some areas had success using “nitrogen scavenger” crops like alfalfa–actually feeding high-nitrate water into these crops to cleanse the water.

Dr. Carrie Laboski, an expert from the University of Wisconsin, shared an overview of the complex chemical workings of the nitrogen cycle. With knowledge of this chemistry in mind, management decisions that improve water quality can be made. The timing of fertilizer and the use of “inhibitors” that slow the transformation of ammonium (NH4) into nitrate (NO3)–a process known as mineralization. This can be the key to making nitrates available at the right time for crops to make use of them, so they don’t end up moving into the water table. Environmental factors can influence mineralization, which is a chemical process actually governed by bacteria and microbial fungi in the soil. Mineralization hastens under conditions that favor that flourishing of these microbes–soil temperatures in a certain range and a certain level of soil moisture. “Mother Nature has the final say,” Laboski acknowledged. As understanding of the weather and how it acts on this cycle becomes more and more refined as time goes on, but chance can disrupt even the most careful stewardship.

Other experts included Eric Cooley from Wisconsin Discovery Farm Network, speaking about data that compares nitrogen loss from surface water versus the flow from tile drainage systems; Waseca crop scientist Jeff Vetsch discussed his research on maximizing the impact of fertilizer while minimizing nitrate loss; and Iowa State University’s Steve Ensley gave practical advice on the signs and impacts of nitrate toxicity on livestock animals. He noted the most pertinent information for this growing season, marked by drought, that livestock operators who have to haul water for cattle and other animals should, at all costs, use a separate tank devoted to water, rather than hauling water in a tank that has been used to transport nitrogen fertilizer. Even after careful washing of such a tank in order to haul water, an Iowa cattle operation suffered significant cattle losses to nitrate poisoning.

Ensley offered a cautionary note for farmers who raise their own corn to feed cattle who cut their drought losses by green-chopping stunted corn. Farmers cut the plants down, stalks and all, for cattle feed. Unlike silage, which is mature corn that has been cut and allowed to cure for a period of time, this immature green-chopped corn can contain super-high levels of nitrates–in excess of 10,000 ppm–two to three times the level considered safe for cattle. The danger increases if the crop is cut down shortly after a rain, which oftentimes stimulates the withered plants to take up even more nitrates into their stalks.

 

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