Corn Nitrogen Management Following Daikon Radish and Forage Oat Cover Crops

Core Ideas Daikon radish and forage oat cover crops following winter wheat sequestered residual autumn soil NO₃–N levels. Nitrogen availability to the ensuing corn crop may be reduced when preceded by radish or oat cover crops. When using radish or oat cover crops, increased 5×5 starter rates (> 45 kg N ha‐1) may be required if full SD is delayed until V11. Radish and oat cover crops preceding corn did not provide a subsequent N fertilizer replacement value but may still be effectively utilized as soil conservation tools. Cover crops (CC) preceding corn (Zea mays L.) may influence subsequent nitrogen (N) availability, but it is not clear whether N strategies require adjustment. Field studies conducted in 2015 to 2016 evaluated the effects of a daikon radish [Raphanus sativus (L.)], forage oat [Avena sativa (L.)], and no CC following winter wheat [Triticum aestivum (L.)] on soil chemical properties, corn growth, grain yield, and profitability. Nitrogen management strategies were equalized to 179 kg N ha–¹ and included pre‐plant incorporated (PPI) N, poultry litter (PL) PPI (61 kg N ha–¹) plus sidedress (SD) N V11, starter N (45 kg N ha–¹) subsurface banded (5 cm below and 5 cm beside the seed, 5×5) followed by V4, V11, or V4 plus V11 SD, and a zero N control. Cover crops reduced autumn soil NO₃–N levels 78 to 84% relative to no CC but occasionally reduced N during critical corn uptake periods. Cover crops did not increase soil base cation availability to the ensuing corn crop. When 5×5 starter was followed by full SD at V11, CCs reduced yield 3.2 to 3.9% and profitability 11.8 to 13.2% compared with no CC indicating reduced efficacy and possibly greater 5×5 requirements to maintain yield potential until SD time. In the zero N control, CCs reduced grain yield 11.8 to 14.2% and increased yield response to N 63 to 79% suggesting reduced N availability. Radish and oat CCs provided a trap crop for autumn residual N, but N management strategies may need to account for reduced N availability.