Cover Crops are an Effective Tool to Reduce Nitrogen Loss
Nitrates and water quality are receiving increased attention across Iowa. To effectively address the problem, it’s important to understand where and why nitrogen loss is occurring. A study by Rogovska et al. examined how tillage, cover crop, and in-situ bioreactors affected nutrient loss at the USDA Long-Term Agroecosystem Research Experiment near Ames. ¹
One key finding was that eliminating nitrogen fertilizer did not eliminate nitrogen loss. After 10 years of crop production without nitrogen fertilizer, nitrogen loss to drainage was not statistically different than plots receiving N fertilizer. Plots receiving about 175 pounds of N per acre lost an average of 13.86 pounds of nitrogen per acre per year through tile drainage. Plots receiving no nitrogen fertilizer lost 10.72 pounds per acre annually*. This suggests that fertilizer is not the only source of nitrogen loss.
* results adjusted from kg N/ha to lbs N/ac.
Why does nitrogen loss occur? Iowa’s fertile soil contains large amounts of nitrogen stored in organic matter. Through mineralization, soil microbes convert organic nitrogen into inorganic forms such as nitrate and ammonium. This biological process starts when soil conditions are fit for microbial activity. There are times during the year when microbes are actively mineralizing nitrogen, but plants aren’t actively growing and using the nitrogen, creating the potential for loss. In the article by Iowa Agricultural Water Alliance, Raising Better Crops and Minimizing Our Impact on the Environment2, ISU Professor Dr. Michael Castellano explains the mismatch between natural nitrogen cycles and a normal corn and soybean growing season.
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