Nitrogen Cycling With Oilseed Radish Cover Crop in Indiana Crop Rotations.

The oilseed radish (Raphanus sativus L.) cover crop can scavenge large quantities of N in the fall, but its rapid decomposition in spring may release N too early for the succeeding cash crop to benefit, thereby allowing N to leach out of the root zone. It was hypothesized that planting oilseed radish (OSR) in combination with a higher C: N ratio cereal cover crop would tie up N longer in the spring and reduce premature N release. The objectives of this one year study in west-central Indiana were to determine the effects of OSR and OSR bicultures on soil ammonium (NH₄-N) and nitrate (NO₃-N) concentrations with time, depth, and distance from the OSR tuber compared to the no cover crop control. The experimental design was a randomized complete block with four cover crop treatments and three replicates at each of four sites. The cover crop treatments included OSR (var. Groundhog), OSR/oat (Avena sativa L.), OSR/cereal rye (Secale cereale L.), and a control (no cover crop). Detailed soil sampling with depth and distance from the OSR tuber was performed in the spring, to observe the timing and pathways of N release. Cover crop treatment had more of an effect on soil NO₃-N concentrations than on soil NH₄-N concentrations. Oilseed radish, OSR/oat, and OSR/rye soil NO₃-N concentrations were highest at the surface and decreased with depth, while control soil NO₃-N concentrations increased with depth. Soil NO₃-N concentrations increased with time at the 0-15 cm depth but stayed relatively constant with time at the lower depths over the March-April sampling period. Soil NO₃-N concentrations were also higher closer to the OSR tuber than farther away from the OSR tuber. This research is part of the USDA-NIFA, “Cropping Systems Coordinated Agricultural Project: Climate Change, Mitigation, and Adaption in Corn-based Cropping Systems.”