Date of Award
Master of Science
Plant, Soil and Environmental Sciences
Donald D. Tyler
F. F. Bell, G. M. Lessman
Soil erosion and rapidly increasing nitrogen fertilizer costs are two major problems confronting West Tennessee corn producers. Cover crops grown during fall and winter can substantially reduce erosion especially if used in conjunction with no-till corn planting. Including nitrogen fixing legumes in cover crops could supply a part of the nitro gen needed for a succeeding corn crop. An objective of this experiment was to determine whether as much nitrogen is supplied to succeeding corn crops by the residues left on the soil surface in a no-tillage system as compared to incorporation in a conventional tillage system. A field experiment using a split plot design was conducted to determine the effects of different cover crops, tillage systems, and nitrogen rates on corn. The four tillage-cover crop treatments con sisted of conventional tilled no cover, conventional tilled wheat-vetch, wheat-vetch no-tillage, and wheat no-tillage. The four nitrogen rates used ranged from 0 to 168 kg N/ha. Conventionally tilled corn following a wheat-vetch cover crop significantly outyielded conventionally tilled corn following no cover crop in plots receiving 0 and 56 kg N/ha. Since the yields from the 112 and 168 kg N/ha were similar, differences in yields at the 0 and 56 kg N/ha rates were attributed to greater nitrogen availability in the wheat-vetch plots as compared to the no cover plots. Corn yields were significantly lower in no-tillage corn following a wheat cover crop than in no-tillage corn following a wheat-vetch cover crop at 0, 56, 112, and 168 kg N/ha nitrogen rates. Soil nitrate-nitrogen levels were lower in the wheat no-tillage plots than in the iiiiv wheat-vetch no-tillage plots. This may indicate that less soil nitrogen mineralization occurred in the wheat no-tillage plots as compared with the wheat-vetch no-tillage plots due to higher carbon:nitrogen ratios in the residues of the former. Corn following conventionally tilled wheat-vetch outyielded corn following no-tilled wheat-vetch at the 56, 112, and 168 kg N/ha rates. Results from this experiment indicate that the availability of soil nitrogen to corn is influenced by tillage and cover crops. Soil nitrogen was more available to corn following wheat-vetch as compared to corn following wheat. Soil nitrogen was less available in no-tilled corn with wheat-vetch than conventionally tilled corn with wheat-vetch at the 0 and 56 kg N/ha rate. This indicates that more nitrogen fer tilizer may be needed to produce corn yields in no-tillage systems com parable with conventionally tilled corn yields.
Stevens, William E., "Cover crop, tillage, and nitrogen effects on corn. " Master's Thesis, University of Tennessee, 1982.