INTERACTIVE EFFECTS OF WHEEL-TRAFFIC AND TILLAGE SYSTEM ON SOIL CARBON AND NITROGEN

Wheel-traffic induced soil compaction has been shown to limit crop pro ductivity, and its interaction with tillage method could affect soil n utrient transformations. A study was conducted during 1993-1994 to det ermine interactive effects of tillage method (conventional tillage and no-tillage) and wheel-traffic (traffic and no traffic) on soil carbon (C) and nitrogen (N) at a long-term (initiated 1987) research site at Shorter, Alabama. The cropping system at this study site is a corn (Z ea mays L.) - soybean [Glycine max (L.) Merr] rotation with crimson cl over (Trifolium incarnatum L.) as a winter cover crop. Soil organic C, total N, and microbial biomass carbon (MBC) were not significantly af fected by six years of traffic and tillage treatments. However, conven tional tillage compared to no-tillage almost doubled the amount of CO2 -C respired over the entire observation period and during April 1994 f ield operations. Soil respiration was stimulated immediately after app lication of wheel-traffic, but nontrafficked soils produced greater am ounts of CO2-C compared to trafficked soils during other periods of ob servation. Nitrogen mineralization was significantly lower from no-til lage-trafficked soils compared to conventional tillage-trafficked and no-tillage-nontrafficked foils far the 1993 growing season. A laborato ry incubation indicated the presence of relatively easily mineralizabl e N substrates from conventional tillage-trafficked sail compared to c onventional tillage-nontrafficked and no-till-trafficked soils. For th e coarse textured soil used in this study it appears that conventional tillage in combination with wheel-traffic may promote the highest lev els of soil microbial activity.