Radish traps nitrogen

by Matt Ruark, UW-Madison Soil Scientist view the origional article in the AgriView

Cover crops are grown between main crops such as wheat, corn or soybeans when soil would otherwise be bare. Cover crops can control erosion, build soil and suppress weeds. A radish cover crop provides those benefits and more. The long radish root creates deep channels in soil that will help subsequent crops to reach moisture in the soil below.

Radish also safeguards water quality by absorbing nitrogen in the form of nitrates from the soil. It leaves less nitrogen in soil — nitrogen that could potentially run off into streams and lakes.

We wanted to know more about radish nitrate uptake and any impact in the following growing season. So researchers established test sites at three Wisconsin locations for three years. At each site a radish cover crop was compared to no cover crop. The radish cover crop was planted in August after wheat harvest. Corn was planted the following spring.

The research showed radish significantly reduced nitrate content in soil compared to no cover crop. The finding confirmed the results of several earlier studies that radish absorbed nitrogen in the form of nitrates from the soil. The research supports use of radish as a cover-crop and as a “trap crop” for fall-applied nitrogen.

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But what happens to that nitrogen afterward remains unknown. There was no consistent evidence nitrogen was returned to the soil when the radish crop decomposed. Radish did not supply nitrogen to the corn crop. Researchers concluded that in the Upper Midwest, nitrogen in radish could not replace fertilizer.

Radish’s decomposition pattern needs to be studied more. Perhaps radish could be more beneficial if mixed with a winter-hardy cover crop.

The Wisconsin Fertilizer Research Council funded the research, with additional support from the Leo Walsh Graduate Fellowship. Visit dl.sciencesocieties.org for more information.