VARIATIONS OF SOIL PHYSICAL CHARACTERISTICS UNDER THE INFLUENCE OF CROP ROTATION AND SOIL TILLAGE SYSTEMS

This paper presents the evolution of certain physical soil characteristics (bulk density, degree of subsidence, total porosity, resistance to penetration), as part of a three-year soybean-wheat-corn rotation, with the implementation of conservative soil tillage (minimum tillage) with: rotary harrow, paraplow and chisel plough. The experiment has been conducted on a phaeozem argic soil type in Transylvanian Plain, with average multiannual rainfall of 500 mm and an average multiannual temperature of 9.2 degrees C. The soil physical condition within the asolament, depending on the implemented tillage system, has been assessed by the bulk density evolution, by the total porosity, by the subsidence degree and by the penetration resistance. Bulk density reveal, during the entire experimental period, for all three crops, a better aeration at 0-20 cm depth (arable layer) for the annual plough tillage variant, respectively 1.13-1.23 g/cm(3) and values of 1.18-1.38 g/cm(3) in minimum soil tillage variants. Phaeozem argic porosity as related to the humus content (43.5%), leads to a minimum required porosity of 52%, and determinations performed show in all variants, both in the conventional tillage ones and minimum tillage ones, values equal to or above the minimum limit. The soil subsidence degree has been influenced both by the tillage system and the crops within the rotation, particularly in the first 20 cm. The soil resistance to penetration measurements reveal that in all conventional and conservative tillage variants, the plant root penetration is not obstructed. In conclusion, concerning the subsidence degree and soil resistance to penetration, the conservative tillage systems with rotary harrow, chisel plough and paraplow are suitable for autumn wheat culture. Also, within the soybean-wheat-corn rotation, the evolution of the subsidence degree and penetration resistance keeps within the normal range.