Investigation of plowing depth effect on some soil physical properties.

Tillage or plowing quality is usually evaluated by the soil bulk density and distribution of organic matter. Soil bulk density, which is the sign of compactness and porosity in turn, depends on type of implements, soil organic carbon, tillage method and plowing depth. Plowing depth causes a lot of pulling in tractors and in order to have deep plowings, heavy-duty tractors are needed. To determine the optimum depth of moldboard plow, the bulk density and soil organic carbon of cultivated soil were investigated in this research. The experiments were conducted, using a three-bottom plow with three plowing depths and four depth of soil, in a split plot design, which lasted for three years. Main plots, consisted of three plowing methods (shallow approximately 12 cm, semi-deep approximately 22 cm and deep till age approximately 32 cm) and subplots, consisted of four soil depths (0-10, 10-20, 20-30 and 30-40 cm). The amounts of soil density, soil organic carbon, soil water infiltration and crop yields were measured. The results showed that, deep tillage had the greatest effects on soil densities, soil organic carbon, infiltration rates and crop yields. Mean value of soil bulk density was 1.65 g cm(-3) in shallow tillage which decreased by increasing the plowing depth to 1.53 and 1.151 g cm(-3) in semi-deep and deep tillage, respectively. However, soil bulk density associated with deep tillage was generally higher than that of semi-deep tillage but the differences between the semi-deep and deep tillage were not significant. The soil water infiltration increased from 1.234 cm h(-1), in shallow tillage to 1.405 cm h(-1) in deep tillage. Crop yield by the deep tillage was 6571 kg ha(-1), while the semi-deep tillage and shallow tillage yield were 6389 and 5717 kg ha(-1), respectively. By increasing the plowing depth, the soil organic carbon and crop yields improved but there were no significant differences between the semi-deep and deep tillage system.