Changes in carbon fractions with corn straw incorporation and comparison of carbon sequestration efficiency in Phaeozem derived from two parent materials in China

Returning corn straw to soil improves soil carbon sequestration in the Phaeozem regions of Northeast China. This research was to investigate the changes in soil carbon fractions of Phaeozem derived from loess and laterite PM with corn straw incorporation and quantify the influence of the key factors on soil carbon accumulation in order to improve the soil carbon stabilization efficiency. A simulative laboratory incubation experiment was conducted over 12 months using Phaeozem derived from loess and laterite PM and eight corn straw doses. Results showed that the clay mineral of Phaeozem was dominated by a mixed-mineral illite-smectite layer, illite, vermiculite, kaolinite, and smaller amounts of montmorillonite. Clay mineral species of topsoil were identical with its PM. The LOC and HOC of six soils increase with increase in straw incorporation level. The promoting effectiveness of straw incorporation on C accumulation declined when the C inputs reached a certain level. At 15% straw incorporation levels, the LOC and HOC of six soil increased by 1.86–3.01 g kg −1 and 1.33–2.22 g kg −1 than CK, respectively. The increment of LOC and HOC of six soils followed the trend of LHAp > LLAp > RHAp > RLAp > LC > RC. At 15% straw incorporation levels, the RLOC of RC (419%) and LC (296%) was greater than topsoil (103–254%) and the RHOC of RC (90%) and LC (61%) was much greater than topsoil (9–26%). Further analysis suggested that C input, TSOC, and clay content were the most influential variables on carbon sequestration efficiency. They accounted for about 73% of the variations of RLOC and RHOC. The relative contributions of 2:1 clay to RLOC and RHOC were about 10% and 15%, respectively and that of 1:1 clay were about 4.4% and 3.5%, respectively. In conclusion, both the topsoil and PM of Phaeozem have considerable C-stabilizing capacity and the C sequestration efficiency of topsoil and PM derived from loess was greater than those for topsoil and PM derived from laterite.