In order to compare the effects of different straw returning rates on soil total organic carbon

microbial biomass carbon

cellulase activity and catalase activity at different soil depths

an in-situ experiment was conducted in a separate mode of planting and returning. The experiment was conducted with four levels of returning amount

i.e. 0% (R0)

0.44% (R1)

0.88% (R2) and 1.32% (R3)

and three different returning depths

i.e. 0—15

15—30

and 30—45 cm. The result showed that returning for 1 year

soil organic carbon content

microbial biomass carbon content

cellulase activity and catalase activity in 0—15 cm soil layer increased with the increasing amount of straw

and those under R3 treatment had the greatest significantce

which increased by 30.98%

101.16%

172.72%

and 5.40%

respectively. In 15-30 cm soil layer

the contents of total organic carbon

microbial biomass carbon and catalase activity in soil treated with straw were higher than those in R0

but there were no significant differences between R1

R2

R3

while cellulase activity increased with the amount of straw returning. In 30—45 cm soil layer

soil organic carbon content

microbial biomass carbon content and cellulase activity of R2 and R3 were significantly higher than those of other treatments

and no significant differences were in catalase activity of all treatment. Compared with returning for 1 year

the total organic carbon content

soil microbial biomass carbon and cellulase activity during returning for 2 years decreased

with the deree of 8.59%～35.36%

6.74%～29.16%

and 6.18%～31.72%

but catalase activity increased

the largest increase occured in R3 (with the increase of soil depth

the increase rate of 14.14%

10.14%

and 12.11%). This study indicates that in the case of separate mode of planting and returning

the high amount of straw can be returned to the field

and also the soil fertility can be improved effectively.