干旱区生态环境知识资源中心

Aggregation is an important process related to structure of the soil This study examined soil aggregation indices in a semi-and rangeland in the northern Negev region of Israel. The purpose of the study was to investigate to what extent the soil aggregation is affected by hillside aspect, surface cover and grazing The soil of four types of surface cover - shrub patch, intershrub area, flock trampling route and rock fragment cluster - was sampled in an area subject to grazing and in grazing exclusion plots At the peak of the growing season and at the end of the dry season, sampling was conducted from two depths (0-2 and 5-10 cm) on a north- and south-facing hillside. We determined the aggregation indices of <250 mu m, >2000 mu m, >8000 mu m the mean weight diameter Differences were found between hillside aspects as well as among the types of cover. Grazing affected the fraction >8000 mu m The aggregation indices of the trampling routes were distinct from those of the intershrub area It is proposed that in semi-arid rangelands, uneven grazing pressure in the intershrub area creates spatial heterogeneity in soil aggregation properties, which affect the spatial redistribution of soil resources and primary production. (C) 2010 Elsevier Ltd All rights reserved