ABSTRACT
The beneficial effects of reduced tillage and winter legume crops on the yields of cotton may result from enhanced N availability as well as from improved soil tilth and other advantageous changes these practices cause in the soil environment. To assess the relative importance of these factors, N status of cotton was determined by collecting petioles and leaf blades between first bloom and end of the effective bloom period from cotton grown under different tillage and N fertilizer regimes after wheat, vetch and fallow cover crops. Analyses of these plant components indicated that while petiole nitrate (NO3-) and leaf blade N both tended to show the same effects of management practices on N status of cotton, leaf blade N was less variable than petiole NO3- and was generally a more sensitive and reliable indicator of N status. Using blade N to assess N nutrition showed that no-till management increased N status of cotton grown on Gigger silt loam after fallow or a wheat cover, but had no effect after winter vetch. Leaf N contents suggested that a vetch cover could supply most of N required to obtain maximum yields of cotton grown on this soil. In contrast, reduced tillage appeared to reduce N availability to cotton grown on a Sharkey clay regardless of cover crop, and the N contributions of vetch were less evident. The increased yields obtained on Sharkey clay by reduced tillage and a vetch cover appear to result primarily from an improved soil environment rather than from enhanced N availability.
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