The increase of soil mechanical resistance may limit plant growth and productivity. The objective of this paper was to evaluate the effects of wheel traffic caused by a grain harvester (combine) on penetration resistance for two soil tillage systems. The treatments were: no tillage, no wheel traffic and wheel traffic by a soybean harvester; tillage, no wheel traffic and at wheel traffic by a soybean harvester. Soil penetration resistance with a cone penetrograph with electronic readings for each 0.15cm depth, and soil moisture were determined down to a depth of the 40cm, at two soil conditions (dry and wet), on a clayey Haplortox (LE). The combine front-axle load was 5.0Mg and the wheel contact area was 0.283m², yielding a ground pressure of 0.0884MPa. For high soil moisture the soil resistance difference between treatments was low (smaller than 2,0MPa), not limiting to root growth. However, for the second evaluation, about 30 days after the first, when the soil was drier, soil compaction in the layer from 5 to 17cm caused by wheel traffic was observed. Soil water content influenced the values of soil resistance. Critical values, considered as penetration resistance greater than 2MPa, were mainly observed for the no tillage system, specially for the 7.5 to 17.0cm layer. The no tillage system had a greater state of compaction than the tilled soil, because of yearly load accumulations. Soybean yield was not different between the tillage systems, with an average of 3.15Mg ha-1 yield.
soil compaction; no tillage; penetration resistance
