Brassica Cover Crop Effects on Nitrogen Availability and Oat and Corn Yield

Cover crops are used to scavenge residual soil nitrate, with the goal of reducing N losses from agricultural fields and increasing subsequent N availability. Two experiments were conducted to determine fall-planted brassica cover crops' effect on N availability for rotational crops. The first evaluated five species-brown mustard [Brassica juncea (L.) Czern], hybrid turnip (Brassica rapa L. x B. napus L.), radish (Raphanus sativus L.), rapeseed (Brassica napus L.), and white mustard (Sinapis alba L.)-in rotation with oat (Avena sativa L.). The second evaluated radish in rotation with corn (Zea mays L.). End of season cover crop biomass averaged 1160 to 6170 kg ha(-1) across experiments, locations, and years. Biomass did not differ by species. Nitrogen accumulation was generally greater than 70 kg ha(-1) (range 31-136 kg ha(-1)). In the subsequent spring and summer, brassica cover crops reduced soil nitrate N levels relative to a no-cover control by 0 to 132 kg ha(-1). In Exp. 1, all brassicas reduced oat N accumulation by >= 77 kg ha(-1) and oat biomass by >= 1255 kg ha(-1) in June 2012, relative to the control. Mustards reduced oat grain yield by 505 kg ha(-1) in 2011, while radish increased oat yield by >= 578 kg ha(-1) in each year. In Exp. 2, radish did not affect corn V8 biomass N concentration, grain yield, or response to N fertilizer. Nitrogen taken up by brassica cover crops often is not available when the subsequent crop needs it.