The Form and Vertical Distribution of Soil Nitrogen as Affected by Forage Radish Cover Crop and Residual Side-Dressed N fertilizer

Forage radish (Raphanus sativus L. var. longipinnatus) is an increasingly popular winter cover crop in the mid-Atlantic region of the United States. This crop can be used to scavenge residual soil nitrate (NO3-) and ammonium (NH4+), with the goal of reducing nitrogen (N) loss from agricultural fields and increasing N availability for subsequent crops. In the present work, two sites in Maryland were examined to investigate the influence of forage radish cover crop and residual N fertilizer from corn side-dressing on the forms and vertical distribution of soil N and the yield of subsequent no-till silage corn (Zea mays L.). Forage radish dry matter ranged from 1,965 to 3,360 kg ha -1 for shoots and 1,531.5 to 3,740 kg ha -1 for fleshy taproots. Forage radish had a marked influence on the distribution of NO3--N in the soil profile; in the spring following a radish cover crop, NO3 --N was concentrated in the surface soil, with no accumulation in deep soil, even at the highest fertilization rate of 168 kg N ha-1. The cover crop had no significant influence on the NH4+-N or total N profile. The average silage corn yield was significantly improved following cover cropping. In addition, the yield increased with the highest N fertilization rate but was not affected by low or medium N fertilization rate. In conclusion, a radish cover crop captures large quantities of residual N from the deep soil following N side-dressing and can improve the yield of subsequent silage.