Effects of conservation tillage on soil organic carbon fractions under pea-wheat rotation

Long term field experiment on the responses of soil organic carbon(SOC)and active organic carbon(AOC)to different tillage patterns were conducted in Dingxi City located on the western Loess Plateau.The experiment was set with two rotation sequences,phase 1started with field pea(Pisum sativum)followed by spring wheat(Triticum aestivum)(P→W),whereas,phase 2started with spring wheat followed by field pea(W→P).The effects of conventional tillage and three conservation agriculture patterns,conventional tillage(T),conventional tillage with stubble incorporation(TS),no till with no stubble(NT)and no till with stubble retention(NTS)were studied.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 0~5,5~10,10~30,30~50and 50~80cm.It was shown that the conservation tillage patterns,NTS,TS and NT,increased the concentration of SOC,ROC and MBC.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.Total SOC content was significantly increased in 0~30cm soil layer,while it decreased in 30~80cm soil layer in NTS,NT and TS treatment.