Effect of different tillage on soil organic carbon and its fractions in the loess plateau of China

The effects of tillage on total soil organic carbon,microbial biomass carbon,particulate organic carbon and dissolved organic carbon were studied in a long-term trial,which was established in 2004 in the Loess Plateau of China.The results showed that all straw return tillage,no-tillage with straw mulching,shallow rotary tillage and conventional tillage ould significantly influenced SOC of 0～40 cm soil layer,and below 40 cm,there was statistically not significant difference among all treatments.The content of SOC in no-tillage with straw mulching was greater than other treatments,but only within the 0～10 cm soil layer.Below 10～40 cm,it had lower content of soil organic carbon of no-tillage with straw mulching than that of all straw return tillage and conventional tillage.The soil organic carbon storage in 0～100 cm of no-tillage with straw mulching and all straw return tillage were increased by 15.3% and 12.1% respectively compared to conventional tillage treatment.After 5 years of continuous planting maize,the soil organic carbon storage in 0～100 cm was significantly greater under no-tillage with straw mulching(C 67.8 t/hm2)and all straw return tillage(C 65.9 t/hm2)than that under shallow rotary tillage(C 56.4 t/hm2)and conventional tillage(C 58.5 t/hm2).At the soil surface(0～5 cm depth),the highest content of particulate organic carbon,dissolved organic carbon and microbial biomass carbon measured under no-tillage with straw mulching,followed by all straw return tillage,shallow rotary tillage,and conventional tillage,respectively.All straw return tillage could increase labile soil organic carbon pools in 20～40 cm depth.The average content of particulate organic carbon,dissolved organic carbon and microbial biomass carbon of all straw return tillage in 20～30 cm and 30～40 cm depth were increased by 7.3%～121.8%,31.8%～49.3%,and 44.2%～84.6%,respectively,over the conventional tillage.Labile pools were highly correlated with each other and soil organic carbon.Particulate organic carbon,microbial biomass carbon and dissolved organic carbon content increased linearly with increasing soil organic carbon content.