Arable soil that have been no-tilled and covered with crop residues for several years developes anorganic matter,plant
nutrients
and microbial activity redistribution with a large content near the soil surface and decrease with depth.The concentrations of organic matter,total nitrogen and phosphorus are all remarkably increased in no-tilled soils and the activity of soil enzymes are higher in
no-tillage soils than that in plowed soils.No-tillage leads to an increase in microbial biomass near the soil surface,in the depth of 0-7.5cw microbial biomass was 51.7% higher than that in plowed soils.The higher levels of microbial biomass occur in spring and autumn while wheat is in seedling and not able to absorb much
nutrients from soil.In this period, microbial biomass begins to accumulate and conserve nutrients in a biologically active form. In summer,when crop growth and development is rapid, microbial biomass declines as nutrients mineralization increases to promote crop growth. The average amount of untrients immobilized by microbes in 0-30cm soil layar is slightly more than that of the annual uptake of crops;on the other hand, no-tillage makes biomass largely dormant,in the depth of 0-30cm soil,active microbial bionmass in plowed soil is 25.3% greater than that in no-tillage soil.