Recovery of Nitrogen‐15–Labeled Hairy Vetch and Fertilizer Applied to Corn

Abstract

Knowledge of the plant and soil recovery of nitrogen (N) from legume cover‐crop residues and fertilizer is needed to improve corn N use efficiency. Nitrogen‐15 labeled ammonium sulfate (AS) or hairy vetch (Vicia villosa Roth.) residues were applied at planting or AS at the six‐leaf stage (sidedressing) to silage corn (Zea mays L.) grown in 38‐cm–diameter by 60‐cm–deep microplots containing a Jungdong loam (coarse loamy, mixed, mesic, Typic Udifluvents) in Suwon, Korea. The recovery of the labeled N sources was followed over 2 yr into the corn grain, stover, and the 0‐ to 15‐cm depth of soil. Recovery of labeled N in the first‐year corn was 32% of the planting‐applied AS, 15% of planting‐applied hairy vetch (HV) residues, and 46% of the sidedress AS. Conversely, the post‐harvest soil contained more labeled N from the HV residues (38%) compared with planting AS (15%) or sidedress AS (14%). Total first‐year recoveries of 15N in crop plus soil after harvest were 47% for planting AS, 54% for HV residues, and 60% for sidedress AS, which are consistent for high summer rainfall (850 mm) climates. The second‐year corn showed low availability of residual 15N, although HV residues supplied about twice as much N (3.5%) as AS (1.5%). These results are consistent with other studies and show that AS is about twice as effective as legume residues in supplying N to a crop, whereas legume residues contribute about twice as much N to the soil.