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How to keep nitrogen in the soil where it belongs

Last summer was a dry one for many locations.

Parched plants don’t take up nitrogen as well as those growing in adequate soil moisture. Drought also reduces nitrogen cycling in the soil because microbial activity slows down with the lack of moisture.

These factors can result in excess residual nitrate in the ground come spring. If the weather is rainy, nitrate concentrations could be higher in field drainage.

Matt Helmers, director of the Iowa Nutrient Research Center, says his team conducted a 10-year study on spring drainage and nitrate concentrations from continuous corn and continuous corn with a cover crop. The study included the spring of 2013 after the drought of 2012.

“The year following a drought we saw increased nitrate concentration because of residual soil nitrate levels being higher, and then subsequent drainage and leaching taking that nitrate away,” says Helmers. “But, in both cases, our cover crops can be very effective in helping us reduce that increase in nitrate concentration.”

In addition to cover crops, crop diversity and perennial roots in the landscape will take up some of that residual nitrate, the study found.

“I think it’s important to note that we also have a prairie and a fertilized prairie restored in 2009 at this site,” he says. “And if we look at that cumulative nitrate loss over that 10-year period, we lost less than 10 pounds of nitrogen per acre, illustrating if we can get that perennial system in there, we can have a dramatic reduction on nitrate loss.”

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