A field experiment was carried out to investigate the effect of wheat or rape straws incorporation into rice field on soil bulk density

soil nutrients

total organic carbon (TOC)

active organic carbon (LOC)

active organic carbon efficient (ACL)

organic carbon stock (SCS)

carbon management index (CPMI)

rice yield in Hanzhong basin

Shaanxi Province

China. Soil samples were collected at the depth of 0—5 cm

5—10 cm

10—15 cm

15—20 cm

and 20—25 cm soil layer. Results showed that the wheat or rape straw return significantly reduced soil bulk density in soil layer of 0—15 cm; however

wheat or rape straw return had no significant effect on soil bulk density in soil layer of 15—25 cm. Compared to the no straw return treatment

the soil organic carbon contents were significantly increased in the wheat or rape straw return treatments. Meanwhile

the soil TOC and LOC contents decreased with the increasing of soil depth in exception of soil layer in 0—15 cm

where both the contents were highest. The soil TOC had an obvious surface enrichment. The SCS content in soil layer of 0-30 cm was significantly increased by 21.9%～23.5% and 1.7%～6.7% in the wheat straw return treatments and rape straw return treatments

respectively. Compared to the rape straw return treatments

wheat straw returning significantly increased soil LOC

ACL

and CPIM in 10—15 cm soil layer; whereas

soil LOC

ACL

and CPIM in 15—25 cm soil layer in the rape straw returning treatment was higher than that in the wheat straw return treatment. Rice yield was highest in the straw returning treatment with decomposing agent than the straw returning treatment. Correlation analysis showed that rice yield positively related with the soil ACL. The straw return treatment can improve soil organic carbon

crop yield and is one of the most effective farming practices in the Hanzhong basin. Compared to the rape-rice rotation system

full wheat straw returning to field with rotary tillage significantly increased soil carbon sequestration and rice yield under the wheat- rice rotation system.