Decomposition of Soil Organic Carbon and Turnover of Soil Microbial Biomass Carbon under Condition o

Decomposition of organic carbon,i.e.soil native carbon plus hybrid elephant grass straw carbon,and turnover characteristics of soil microbial biomass carbon(SMBC)in a yellowbrown earth were studied by using porous carborundum tube method under condition of rotation between upland crop and paddy rice for 1 year(1998～1999).Results indicated that decomposition of organic carbon proceeded rapidly at the early period and then slowed down.The decomposition amount of organic carbon during the first 7 d made up 37%～41% of that during a whole year;decomposition of organic carbon proceeded rapidly again after rice was transplanted,then slowed down.The original organic carbon was decomposed in total of 545%～1732% after 1 yearThe decomposition amount of organic carbon increased with the increment of straw added.Straw application not only accelerated the decomposition of organic carbon,but also compensated the loss of soil native carbon.SMBC increased rapidly at the early period and then decreased,and increased again after rice was transplanted,and then decreased gradually.The utilization rate of organic carbon by soil microorganisms varied from 096% to 338%,and it could be improved greatly due to straw application.Turnoverrate of SMBC changed from 100 to 113 a-1.Straw addition could promote SMBC and its turnover rate,and enhance the ability of supply and maintenance of soil nutrients.Decomposition patterns of organic carbon showed similar to dynamics of SMBC,which indicated that the decaying rate of organic carbonwas the external expression of soil microbial activities.