Assessing The Nitrogen Credit Of Radish As a Cover Crop.

Oilseed radish (Raphanus sativus L) has become a popular cover crop option in the Midwest for the late summer, especially among no-till farmers. However, little, if any information is available on brassica cover crops, radish included. The objective of this project was to determine the effects of radish as a cover crop, specifically quantifying the uptake and release of nitrogen, as well as compaction and nematode suppression. Radish cover crops were planted in mid-August in three field sites located in Southern and Northeast Wisconsin. Each radish treatment was accompanied by a no cover crop treatment, and all treatments were split into increasing amounts of nitrogen fertilizer. Soil samples (0-1’ and 1-2’) were collected within each plot and analyzed for extractable nitrate using KCl extraction and colorimetric analysis using a microplate reader. Radish biomass (above ground and root) was collected from a 9 ft² area within each whole plot prior to winterkill and analyzed for total dry matter production and total nitrogen uptake. Soil samples (0-1’) were collected for each plot and analyzed for nematodes. Nematodes were isolated from the soil by a series of washings through increasingly smaller sized sieves. The samples were then examined under a microscope to identify and quantify both root lesion nematodes and soybean cyst nematodes. Soil compaction was measured in each plot using a portable constant-rate cone penetrometer. Soil moisture was determined as gravimetric soil moisture with a soil moisture probe. Results from the 2012 growing season indicates that radish increased soil nitrate early in the growing season, but dry growing conditions limited corn yield and response to N. Nitrate data from this year of normal rainfall will determine if these results are consistent. Seasonal variation in soil compaction, soil moisture, and nematode populations will also be presented.