UNIVERSITY PARK, Pa. — For corn, using dairy manure and legume cover crops in crop rotations can reduce the need for inorganic nitrogen fertilizer and protect water quality, but these practices also can contribute to emissions of nitrous oxide — a potent greenhouse gas.
That is the conclusion of Penn State researchers, who measured nitrous oxide emissions from the corn phases of two crop rotations — a corn-soybean rotation and a dairy forage rotation — under three different management regimens. The results of the study offer clues about how dairy farmers might reduce the amount of nitrogen fertilizer they apply to corn crops, saving money and contributing less to climate change.
The results are important because although nitrous oxide accounts for just 7% of U.S. greenhouse gas emissions, it is significantly more potent than carbon dioxide or methane when it comes to driving climate change, according to Heather Karsten, associate professor of crop production/ecology in the College of Agricultural Sciences. Nitrous oxide is almost 300 times more powerful than carbon dioxide and remains in the atmosphere for more than 100 years.
“This research suggests that all nitrogen inputs — manure, legumes and fertilizer — contribute to nitrous oxide emissions,” she said. “But farmers could reduce nitrous oxide emissions if they could apply manure after the crop is planted, closer to when the corn begins to take up nitrogen.
"And if they could apply manure only when the crop needs it by “side-dressing,” she added, "they likely could use less inorganic nitrogen fertilizer. But equipment for side-dressing manure into a growing corn crop is not yet widely available."