Influence of vegetable cultivation methods on soil organic carbon sequestration rate

The rapid increase of vegetable land area plays an important dynamic factor on soil organic carbon(SOC) pool change in agricultural soil in China.How vegetable cultivation methods influence the SOC storage is of great concern for revealing the change of SOC pool in agricultural soil.Three vegetable cultivation methods such as field cultivation(FC),seasonal greenhouse(SG) and perennial greenhouse(PG) method and their influences on profiles distribution of SOC content and SOC sequestration rate with cultivation history were investigated and studied by in situ soil sampling in Cangshan County,Shandong Province,where vegetable production is the most popular and typical in China.Totally,76 soil samples were collected from 16 soil profiles in vegetable land cultivated in the three methods and analyzed for SOC content and bulk density to calculate SOC density and sequestration rate.Results showed that SOC content declined significantly as the increase of soil depth.From soil surface layer(0—20 cm) to subsurface layer(20—30 cm) cultivated in PG method,the mean SOC content declined by 50.2%,which was the largest decrease and significantly different from that in SG(by 38.4%) and FC method(by 26.9%). While from soil subsurface layer to subsoil layer(30—60 cm) cultivated in SG method,the mean SOC content declined by 15.6% as the largest decrease,and that in PG and FC cultivation method declined by 8.9% and 5.1% respectively.Obviously,the change of SOC content with increase of soil depth was mostly conducted in the soil layer of 0—30 cm,these vegetable cultivation methods could hardly influence SOC in the deep layer(below 30 cm). Further,the mean change rates of SOC content from soil surface to subsurface layer as well as to other deep layers in the two greenhouse cultivation methods(PG and SG) were significantly higher than in FC cultivation method,as the better condition of irrigation and fertilization in the two greenhouse cultivation methods leads more accumulation of SOC in soil surface layer and subsurface layer than in FC method.As long term vegetable cultivation,a trend of SOC accumulation was shown apparently in these soil profiles cultivated in the three methods.The mean SOC sequestration rate of soil surface layer cultivated in PG、SG and FC method was 0.64,0.36,0.20 Mg·hm-2·a-1,and that of whole soil profile(0—100cm) was 1.44、2.73,1.60 Mg·hm-2·a-1,respectively.The SOC sequestration rate of soil surface layer ranked in the order as: PGSGFC,resulting mainly from that economic input for irrigation and fertilization of the two greenhouse cultivation methods(PG and SG) was much more than that of FC method;while the SOC sequestration rate of whole soil profile ranked in a different order as: SGFCPG,as a result of influence of their original soil physical and chemical properties.Though the three vegetable cultivation methods all increased the SOC pools,significant differences in SOC sequestration were shown from each other in the present study.Thus,it is an important route to accelerate SOC sequestration rate in agricultural soil by choosing a reasonable cultivation method.