Effect of Land Use Change on Soil Quality and Clay Mineralogy in Valarude Region of Zanjan Province

Effect of land use type on soil functioning within an ecosystem can be assessed by soil quality indices. Such studies that are carried out to improve land resources quality, lead to control the land degradation and help us to identify the sustainable management. In order to study the effect of land use change from pasture to agriculture on soil quality and clay mineralogy, Valarude region of Zanjan province was selected. Composite soil samples were taken from 0 – 30 and 30 – 60 cm depths of both land uses with three replicates and totally 60 soil samples were prepared. Important soil quality indicators such as bulk density, weighted mean diameter of aggregates, quantities of organic carbon, and total nitrogen, soil microbial respiration rate, amount of microbial biomass C and urease and alkaline phosphatase activities were measured. Results revealed that the land use change from pasture to agriculture, led to a significant reduction in the amounts of organic carbon (62%), total nitrogen (70%), mean weight diameter of aggregates (32%), microbial respiration rate 75%) and microbial biomass C quantity (47%). The assay of enzyme activities showed that alkaline phosphatase activity did not change significantly but urease activity decreased in agriculture land (87%). Mineralogical studies showed that the both land uses had illite, kaolinite; chlorite, smectite and mixed layer minerals and change of land use did not have a significant effect on soil clay minerals. Overall, it can be concluded that a change in land use from pasture to agriculture with widespread agricultural practices, especially intensive tillage activities, may lead to decrease soil quality.