Effects Of Conservation Tillage On The Indicators And Correlations Of Soil Organic Carbon

Based on the long-term field experiments on semi-arid area of the west Loess Plateau since 2001, the paper discussed the soil organic carbon(SOC) and active organic carbon(AOC), whose indicators and correlations responses to the different tillage patterns, by which effects of tillage measures on SOC,readily oxidizable carbon(ROC),microbial biomass carbon(MBC),dissolved organic carbon (DOC) in soil layer of 0～5cm,5～10cm,10～30cm. Four different treatments: no-till with straw cover(NTS), conventional tillage with straw incorporated(TS), no-till without straw cover(NT) and conventional tillage (T) were carried out in a phased rotation systems with spring wheat and field pea. The results indicated1 Effects of conservation tillage on soil organic carbonIn wheat-pea-whea(tW-P-W)rotation sequence, under four different tillage patterns, the average contents of soil organic carbon(SOC) in soil layer of 0～30cm followed the order as NTS>NT>TS>T, while in pea -wheat-pea(P-W-P)rotation sequence, the order was TS>NTS>NT>T.In both rotation sequences, compared with T treatment, the conservation tillage patterns of NTS,TS and NT increased the contents of SOC , conservation tillage is beneficial for carbon sequestration, among of them, NTS treatment was more advantageous to improving the soil organic carbon contents, by which to alleviate greenhouse influence. Thus, it should be recognized as the key approaches to sustainable agriculture and environment.2 Effects of conservation tillage on soil active organic carbon(1) Effects of conservation tillage methods on soil readily oxidizable carbon In wheat-pea-wheat rotation sequence, readily oxidizable carbon (ROC) average contents under four different tillage patterns followed the order as NTS>NT>TS>T, the change of ROC was rapider than SOC,the times of the speed was 6.03,4.27 and 3.30; while in pea -wheat-pea rotation sequence, compared with SOC,the change times was 3.46,1.70 and 2.34, so ROC was more sensitive responses to long-term tillage than SOC. (2) Effects of conservation tillage on soil microbial biomass carbonIn wheat-pea-wheat rotation sequence, microbial biomass carbon (MBC) average contents under four different tillage patterns followed the order as NTS >TS >NT >T, this was also same as the order of SOC, the change of MBC was also rapider than SOC, the times was 14.43,14.66 and 16.66; while in pea-wheat-pea rotation sequence, the order was NTS>TS>NT>T, compared with SOC,the change times was 7.50,6.86 and 6.73, so MBC was more sensitive responses to long-term tillage than SOC. Compared with T treatment, the conservation tillage patterns of NTS and TS increased the contents of MBC greatly.(3) Effects of conservation tillage on soil dissolved organic carbonIn wheat-pea-wheat rotation sequence, soil dissolved organic carbon (DOC) average contents under four different tillage patterns followed the order as NTS> TS> NT >T, this was a little different from the order of SOC, the change of DOC was rapider than SOC,the times of the speed was 9.54,13.41 and 11.74; while in pea -wheat-pea rotation sequence, it was same as the order of SOC, compared with SOC,the change times was 9.01,6.38 and 7.60, DOC was more sensitive responses to long-term tillage methods than SOC.Above all, ROC,MBC,DOC,ROC/SOC,MBC/SOC and DOC/SOC had the same response to the long-term tillage methods with SOC. Meanwhile, all of them had a declining trend with the increasing depth in soil profiles. In both rotation sequences, the indicator of NTS treatment was highest among the different tillage patterns.(4) Effects of conservation tillage on the crop yieldThe conservation tillage patterns of NTS,TS and NT increased crop yields, NTS treatment was more advantageous to improving the yields, it should be recognized as the best tillage pattern.3 Correlation coefficients among SOC, AOC indicators and crop yield studiedCorrelation analysis showed that, the AOC indicators were not only significantly correlated to soil organic carbon, but also significantly correlated to each other, AOC indicators were more sensitive responses to long-term tillage than SOC, they could be indicators for assessing effect on SOC,and the sensitivity of them followed the order as MBC>DOC>ROC/SOC>MBC/SOC>ROC>DOC/SOC. MBC had the same response to the long-term tillage with SOC, and was most sensitive among all the indicators above, so MBC is the best indicator to choose, while to judge the crop yield, ROC and ROC/SOC were more sensitive than the others.