Long-term effects of land use on soil aggregate stability.

Abstract

A b s t r a c t. In the study presented here, the long-term effects of two land uses of forest and tea garden on soil aggregate stability as an indicator of soil quality were investigated at three landscapes in Lahijan, North Iran. In each landscape, soil samples were collected from two slope positions and two depths of adjacent forest and tea garden, and were analyzed for their physical and chemical properties including aggregate size distributions by dry and wet sieving. Soil properties and aggregate stability indices were compared for the two land uses by the algorithms of nested design. The results showed that organic matter content, hydraulic conductivity, field capacity moisture content, mean weight diameter, and geometric mean diameter of the soil aggregates were significantly lower for the tea garden than for the forest, while bulk density and fractal dimension of aggregates were higher. Traffic and cultural operations, combined with increased organic matter decomposition in the tea garden, disintegrated the large aggregates into smaller aggregates (0.25-0.5 mm), resulting in a lower proportion of large aggregates in these soils. All measured soil properties were statistically the same for two depths of 0-15 and 15-30 cm, except for organic matter, field capacity and permanent wilting point. There were also no differences between two slope positions regarding the soil properties. K e y w o r d s: land use, aggregate stability, soil erosion, slope position, humid climate