Effect of tillage direction and slope position on some physical and chemical properties and aggregate stability of soil

Soil tillage is one of the most important practices in agricultural production. Farming and tillage accompanied with slope direction result to not only in increasing soil loss but also in decreasing soil organic carbon content with a consequent reduction in the aggregate stability on steep lands. The aim of this study was to investigate the effect of tillage direction, slope position and slope direction on soil aggregate stability and some physical and chemical properties of soil. For this purpose, soil samples were collected from an area with contour tillage located in the Soil and Water Conservation Research Station of Kuhin and its adjacent area outside the station with up-down tillage. The area was as a shallow valley with the northern and southern faces. Soil samples for both tillage types were taken from upper, middle and bottom of the slope in two depths with three replications (72 samples). Data were analysed based on the nested design. The results showed that most of the soil measured properties were highly affected by soil tillage in which, up-down tillage caused reduction in the soil quality. Furthermore, the results demonstrated that the slope direction and position can only affect soil aggregate stability index, while all four indices of aggregate stability were significantly affected by tillage type. Organic matter content is a major reason for increasing soil aggregate stability in the contour tillage. The position and direction of slope in addition to field management have very complicated effects on soil properties at various depths. Finally it concluded that soil aggregate stability is significantly influenced by all types of changes including the position and direction of slope and soil depth.