In order to discuss the existence forms and the conversion process of the soil organic carbon

and the relationship on different soil organic carbon components under the different tillage method in loess plateau semi-arid area

the soil in different tillage condition had be analyzed by chemical method.The results showed that no-till can increase the content of soil organic carbon.Leaving crops straw affects soil total organic carbon(TOC)

no-till with straw cover(NTS)can significant improve the content of TOC on the surface of the soil

TOC content can be improve 20.77% in semi-arid area after return straw for 17 months.Conventional tillage with no straw(T)and conventional tillage with straw incorporated(TS)can destroy soil construction

go against accumulation of soil organic carbon.There is no significant discrepancy in soil sodium pyrophosphate-extractable carbon(SPPC)among different soil treatments.There is big range of variation on the rate of SPPC in TOC

from 23.70% to 50.60%.NTS has the highest SPPC content

NT has the lowest SPPC content

that is no-till with straw cover is benefit to improve the soil physical chemistry property

but only no-till

doesn't return straw go against the accumulation of the soil organic matter.The content of hot water-extractable carbohydrate(HWCC)accumulation is NTS>NT>TS>T

that is no-till with straw cover benefit to the active organic matter accumulation

to improve the soil physical chemistry property

to provide lots of energy resource to soil microorganism and to benefit soil development.