Effects of Conservation Tillage on Soil Organic Carbon Fractions

In order to explore responses of soil organic carbon(SOC) and active organic carbon(AOC) to different tillage patterns,long-term field experiments have been conducted at Lijiabu town of Dingxi city,Gansu province in semi-arid area of the western Loess Plateau since 2001.Readily oxidizable carbon(ROC) and microbial biomass carbon(MBC) were considered as indicators of AOC,and were measured together with SOC in soil layers of 0-5 cm,5-10 cm and 10-30 cm.Four different treatments such as no-till with straw cover(NTS),conventional tillage with straw incorporated(TS),no-till without straw cover(NT)and conventional tillage(T) were designed in a rotation system between spring wheat and field pea.It was shown that the conservation tillage patterns,e.g.NTS,TS and NT,increased the concentration of SOC,ROC and MBC as well as ratios of ROC to SOC and MBC to SOC.This suggested that conservation tillage was beneficial for carbon sequestration,by which to alleviate greenhouse influence.Thus,it should be recognized as the key approaches to sustainable agriculture and environment in semi-arid area.In both rotation sequences,NTS treatment showed the highest values in the concentration of carbon among the different tillage patterns;meanwhile,carbon fractions had a declining trend with the increasing depth along the soil profile.Correlation analysis showed that AOC indicator had the similar response to the long-term tillage patterns and was more sensitive than SOC.The correlation coefficients of them followed the order as MBCROCMBC/SOCROC/SOC,while the sensitivity of them followed MBCROC/SOCMBC/SOCROC,so MBC was the best carbon indicator to choose.