Characteristics of carbon pools in soil profile of typical spring maize regions in northeast China

Objectives  Soil carbon stock represents the level of soil fertility, productivity and sustainability. The present carbon pools in 0−90 cm soil depth were analyzed to understand the effect of the current farmers’ fertilization practices on the carbon storage in typical spring maize regions in northeast China, which is the most important commercial corn production area.

Methods  17 sites in each province of Heilongjiang, Jilin and Liaoning, adding up to 51 sites were chosen for this research in 2012. All the sites were under farmer’s conventional managements for spring maize production. The soil total carbon (TC), organic carbon (SOC), inorganic carbon (IC), particulate organic carbon (POC), microbial biomass carbon (SMBC) and dissolved organic carbon (DOC) in 0−30, 30−60, 60−90 cm soil depth were measured.

Results  In 0−90 cm depth of soils in Heilongjiang, Jilin and Liaoning provinces, the TC stocks were 159.8, 128.5, 108.1 t/hm², the SOC stocks were 141.7, 120.5, 90.2 t/hm², and the IC stocks were 18.2, 8.0, 17.9 t/hm², respectively. The mean SOC stocks in the whole 90 cm soil depth varied significantly among the three provinces (P < 0.05). In 0−30 cm soil depth, the mean TC and SOC stocks were significantly different among the three provinces (P < 0.05). In 30−60 cm and 60−90 cm soil depth, the mean TC, SOC stocks in Heilongjiang were significantly higher than those in Jilin and Liaoning (P < 0.05), and the order of TC and SOC stocks in different soil depths was 0−30 cm > 30−60 cm > 60−90 cm in all the provinces. For soil active carbon pool of 0−30 cm soil depth, the mean POC concentrations, the ratios of POC/SOC, SMBC/SOC and DOC/SOC increased and SMBC concentration decreased with the latitude decreased in all the three provinces, and the significant difference of POC/SOC, SMBC, and DOC/SOC was found among the provinces, respectively (P < 0.05). The mean POC concentration in Heilongjiang were significantly lower than those in Liaoning and Jilin (P < 0.05), and the mean DOC in Jilin was significantly higher than those in Heilongjiang and Liaoning. In 30−60 cm soil depth, the mean POC, POC/SOC, and DOC/SOC were all increased with the latitude decreased in the three provinces, and significant difference in the mean POC/SOC ratio was found among the three provinces (P < 0.05). The mean of POC concentration and DOC/SOC were significantly lower, but that of SMBC was significantly higher in Heilongjiang than in Jilin and Liaoning (P < 0.05). In 60−90 cm soil depth, the mean of POC, POC/SOC, DOC/SOC and SMBC/SOC in Heilongjiang province was significantly lower than that in Jilin and Liaoning provinces (P < 0.05), and the mean of SMBC in Jilin was significantly higher than that in Liaoning province (P < 0.05). With soil depth increased, TC, SOC, IC, and different active soil C pools decreased, while IC/TC in each soil depth increased in each province.

Conclusions  In spring maize regions in Northeast China, Heilongjiang has the highest SOC stock in 0−90 cm soil profile, the change of soil C sequestration and active C pools was not completely consistent because of the integrated effects of temperature, soil parent materials and fertilization, the contribution of inorganic C for TC increased with soil depth increased. Therefore, more attention should be paid to the effect of soil inorganic C on C pools in soil profile.