Saturday, 15 July 2006

Soil Quality Indicators Response to Long-Term Grazing Exclusion as a Recovering Strategy in Some Rangelands in Central Iran.

Mohammad A. Hajabbasi, Isfahan Univ of Technology, College of Agriculture, Dept of Soil Science, Isfahan, Iran, Mehdi Sharifi, Agriculture and Agri-Food Canada, Potato Research Centre, PO Box 20280, Fredericton, NB E3B 4Z7, Canada, and Mohsen Sheklabadi, Isfahan Univ of Technology, College of Agriculture, Soil Science Dept, Isfahan, Iran.

Overgrazing and conversion of rangelands to crop lands have resulted in great decline in physical, chemical and biological quality of soil resources in Iran as well as elsewhere in the world. Complete grazing exclusion was one of the main and old strategies which have been used for recovering of these degraded soils. This investigation was conducted to understand the changes of soil functions, resulting from exploitive management, and the effectiveness of long term complete grazing exclusion (>20 years) as a recovering strategy, using some soil quality indicators. Adjacent protected and disturbed sites were identified in each of four study areas, including two rangelands in semi-humid, a rangeland in semi-arid and a rangeland in arid climate in central Iran. Soils are derived from calcareous parent material and classified as Typic Haploxerepts, Typic Calcixerepts, Typic Haploxeralfs, and Typic Haplocalcids (Soil Survey Staff, 1999). Soil Organic Carbon (OC), Particular Organic Matter (POM), Total Nitrogen (TN), Mean Weight Diameter of aggregates (MWD), bulk density (ρb) and calcium carbonate (CaCO3) of the sites in 3 depths (0-5, 5-15 and 15-30 cm) were determined. The comparison of protected and disturbed rangelands for measured soil quality indicators showed that conversion was decreased POM in 0-5 cm of soil depth by 33% and did not have any significant effects on other soil quality indicators. Dry rangeland had significantly lower values of TN in 0-30 cm and POM and ρ b in 0-15 cm depth compare to semi-arid and semi-humid rangelands. The semi-arid rangeland had the highest TN and lowest ρb among others due to the site location (2 percent slop) and type of vegetation while others located on the 25-35% slope. Overall, complete protection of rangelands did not have any significant effect on soil quality indicator except for POM which shows lack of success for this strategy in the area. The study illustrates importance of local climate, grazing intervals and native vegetation interactions in sustainable rangeland management system. Future efforts in finding the best management system for recovering degradated rangelands in central Iran are required.

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