Impact Of Stocking Rate On Soil Microorganism Of Semi-arid Grassland At Eastern Gansu Province

Soil microorganism plays important role in keeping soil fertility and maintaining ecosystem health.Numbers of microbes were studied for the soil of grassland under various stocking rates at the Loess Plateau of eastern Gansu province,China in 2006-2007.Components of fungal and bacterial flora were identified with the aid of Biolog Microbial System.The characteristics of microbial distribution in time and space were also studied.The main findings were summarized below.The total number of microorganism is decreasing with the increase of the stocking rate which the lowest number of microorganism was obtained from the paddocks with stocking rate of 8.7 sheep unit/ha.The numbers of fungi,bacteria and actinomycetes isolated varied with stocking rates.In order of decreasing number the number of microorganisms ranked as bacteria＞actinomycetes＞fungi.More number of microbial organisms were isolated from soil at the depth of 10-20cm than from those at 0-10cm and 20-30cm depths.During the year the highest number of microbial organisms was obtained in July.About 38 fungal genera and 17 species in total were isolated from various paddocks during the entire experimental periods.The species most frequently isolted was Rhizoctonia which was followed by species of Penicillium,Fusarium,Aspergillus,Trichoderma and Humicola.The most frequently isolated fungal species is Fusarium juruanum.There were 38 bacterial species in total isolated.The most frequently isolated bacterial speices are Kocuria rosea and Macrococcus carouselicus which were followed by Cellulomonas flavigena,Rhodococcus coprophilus,Cellulosimicrobium cellulans and Leuconostoc carnosum.About 20 bacterial species was found from the paddocks grazed at 8.7 sheep unit/ha,whereas 19 bacterial species were identified from the paddocks with the stocking rate of 2.7 sheep unit/ha or 5.3 sheep sheep unit/ha,only 16 bacterial species were found from the paddocks grazed at the stocking rate of 0 sheep unit/ha. Rhodococcus coprophilus was the most frequently isolated species in paddocks grazed at rate of 8.7 sheep unit/ha.Cellulomonas flavigenaw was the predominant species in the soil of paddocks grazed at 0 sheep unit/ha.Kocuria rosea was most frequently isolated from the paddocks grazed at 2.7 sheep unit/ha.Arthrobacter woluwensis was most in and 5.3 sheep unit/ha.