INFLUENCE OF HIGH AXLE LOADS AND TILLAGE SYSTEMS ON SOIL PROPERTIES AND GRAIN CORN YIELD

The effects of various tillage systems in combination with different l evels of high axle load traffic on soil bulk density, penetration resi stance and corn (Zea mays L.) grain yields were studied for a 3 year p eriod on a silt loam soil. The tillage systems were zero tillage, fall chisel plowing and fall mold-board plowing. Traffic treatments involv ed the annual post-harvest imposition of a 12 Mg axle weight on 100%, 25%, and 0% of the plot surface area. The 0% treatment involved contro lling all field traffic with the use of a wide span tractor. Only in t he third year were differences in soil bulk density resulting from loa ding significant within all three tillage systems at the 5-10 cm depth interval. At a depth of 20-25 cm (below the maximum depth of tillage) differences in soil bulk density resulting from loading were never si gnificant regardless of the tillage system or year. Differences in pen etrometer resistance in the 0-10 cm depth interval resulting from load ing were generally only significant in zero tillage, but they were oft en significant within all tillage systems in the 12-22 cm depth interv al. The maximum depth to which loading caused significant increases in penetrometer resistance was 35 cm Corn grain yields were significantl y higher for the traffic-free treatments within only one tillage syste m (moldboard) in only 1 year (1988) of the experiment. In general, axl e loads of 12 Mg did not result in reduced grain corn yields regardles s of whether they were imposed on 25% or 100% of the plot surface area .