Tillage Effects on Nitrogen Recovery by Corn from a Nitrogen-15 Labeled Legume Cover Crop
1989
Varco, J. J. | Frye, W. W. | Smith, M. S. | MacKown, C. T.
The purpose of this study was to determine the effects of tillage on corn (Zea mays L.) total N uptake and recovery of N from ¹⁵N-depleted legume residue. A conventional tillage (CT) variable was introduced into a 7-yr-old no-tillage (NT) corn study in 1984 by moldboard plowing and disking half of each no N plot having either corn residue (winter fallow) or hairy vetch (Vicia villosa Roth.) cover. Prior to plowing each year, in situ hairy vetch vegetation was removed and replaced with fresh ¹⁵N-depleted hairy vetch vegetation at a comparable rate. In 1984, final total N uptake by corn with vetch cover was 31 kg ha⁻¹ greater with CT than with NT; however, no difference in grain yield occurred. This was a year characterized by limited precipitation during grain fill. In 1985, early season N uptake was greater with CT but there was no difference in final total N accumulated between tillage systems. Averaged across cover treatments, CT resulted in more grain yield than with NT. With vetch, corn N uptake in excess of that with corn residue averaged 60 kg ha⁻¹ yr⁻¹ across tillage systems. Recovery of vetch (¹⁵N (Nᵥ) averaged over years was 32% with CT and 20% with NT. In both years this difference was established by 42 d after planting and the pattern of Nᵥ recovery after this day was similar for both tillage systems. Residual recovery of Nᵥ by corn the second year after application was greater with NT (7%) than with CT (3%). With vetch cover, extractable soil N levels were most elevated early in the growing season, particularly with CT in the 0.1- to 0.2-m soil depth.
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