Time of Desiccation Effects on Plant Composition and Subsequent Nitrogen Release from Several Winter Annual Cover Crops
Efficient utilization of N contained in cover crop residues by the subsequent summer crop requires an understanding of temporal patterns of N release as related to specific management strategies. The objective of this research was to determine, under field conditions, changes in plant composition and subsequent patterns of N release resulting from two desiccation dates approximately 2 wk apart (early and late) for rye (Secale cereale L.), crimson clover (Trifolium incarnatum L.), and hairy vetch (Vicia villosa Roth) cover crops. Averaged over 2 yr the late desiccation treatment resulted in increases in cover crop dry matter of 39, 41, and 61% for rye, crimson clover, and hairy vetch, respectively. Corresponding increases in total N content of the respective cover crops were 14, 23, and 41%. Significant differences in cellulose, hemicellulose, and lignin contents were found among cover crop residues between desiccation times. Nitrogen release from decomposing cover crop residues was monitored using nylon mesh (53 µm) bags. In general, the order of N release was hairy vetch > crimson clover > rye. Cover crops desiccated early decomposed faster, however, the relative magnitude of these N release patterns differed sharply between years. The percentage of initial residue N remaining after 16 wk for the early desiccation date in 1984 was 53, 14, and 13% for rye, crimson clover, and hairy vetch, respectively, compared with corresponding values of 59, 42, and 35% in 1985, which was characterized by a relatively dry growing season. Estimates of N released from each cover crop indicated that the potentially larger available N pool resulting from a delay in desiccation was offset by the slower rate of N release, especially for rye and crimson clover.
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