Abstract: A two growth seasons experiment was conducted to study the effects of different tillage methods, straw-returning, and their interaction on the dynamic change of organic carbon content in 0-20 cm soil layer during the whole growth period of winter wheat. An obvious change was observed in the soil organic carbon content. Treatments with straw-returning had higher soil organic carbon content than treatments with no straw-returning, and conservation tillage induced higher soil organic carbon content than conventional tillage. In all treatments except conventional tillage, the organic carbon content in 0-10 cm soil layer was higher than that in 10-20 cm soil layer. In treatments with straw-returning, the organic carbon content in 0-10 cm soil layer decreased in  order of deep soiling (PS)＞rotary tillage (PR)＞no tillage (PZ)＞normal ploughing (PH)＞conventional tillage (PC), while that in 10-20 cm soil layer was PC＞PS＞PR＞PH＞PZ, suggesting that conservation tillage could improve the organic carbon content in 0-10 cm soil layer. Multi factor variance analysis showed that tillage method, straw-returning, and their interaction had significant effects on the organic carbon content in 0-20 cm soil layer at various growth stages of winter wheat.

Key words: conservation tillage, straw-returning, soil organic carbon, winter wheat, soil colloidal phosphorus, speciation, transference, analysis technology.