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 15 N 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 15 N, 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.

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Reduction of greenhouse gas (GHG) emissions from upland crop field as well as paddy field is being required, but little information on GHG emissions according to cultivation practices in upland field is available. Soil GHG emissions during the growing season were investigated in the field of three decades rotation and tillage treatments which were consisted of plow, chiesl tillage and no tillage in west central Indiana, USA in 2006. Seasonal cumulative CO 2 emissions were not different among treatments. CH 4 emission increased a little in plow tillage during early soybean growing season. Most of N2O emission occurred during early corn growing season after N-fertilizer application from mid June to mid July, and was significantly affected by tillage practices in which seasonal cumulative N2O emission was significantly higher under chisel tillage. N 2 O emission under no-tillage was lower about 64% and 39% than that under chisel tillage and plow tillage, respectively. No-tillage practice with rotation of corn and soybean seems to be promising in point of less GHG emission and less labor for cultivation without grain yield reduction.