Effects of Continuous Returning Straw to Maize Tilth Soil on Chemical Character and Microbial Biomass

The experiment was designed to study the effects of continuous returning straw to maize filed on 0-40 cm soil nutrient and microbe,0-20 cm soil microbial biomass in 3-year returning(2007-2010),6-year returning(2005-2010),9-year returning(2002-2010),and non returning field at Pingliang maize breeding experimental station of Gansu agricultural university from 2002 to 2010.The tilth physical and chemical property and variation of main soil microorganism were tested to probe the effectiveness of continuous straw returning on soil nutrients and microorganism environment.The result indicated that continuous straw returning to the maize field coupling with soil shallow cultivation could reduce deep soil bulk density and pH,significantly increase SOM,TN,TP,AN,AP and AK content in 0-20 cm with the rank of H9H6H3CK;but in but 20-40 cm layer,no significant difference was observed except for SOM.Continuous straw returning also increased soil bacteria,fungi,actinomyces quantity in 0-40 cm,H9 had the highest bacteria and fungi increase(152% and 159%,respectively),actinomyces increased 15.1%.MBC in 0-20 cm also increased significantly,indicating that continuous straw returning to the field could improve carbon supply of soil microorganism effectively,and help to increase microorganism.