Below ground residues were more conducive to soil organic carbon accumulation than above ground ones

Abstract

Long-term intensive cultivation generally affects even soil fertility by decreasing the soil organic carbon (SOC) content. The returning of maize residues to the soil is documented as an effective measure to increase SOC and improve soil productivity. However, limited information is available on the turnover and storage of organic carbon (C) caused by the addition of different maize residue types to soil with different soil fertility levels. For this purpose, a 540-day in-site field experiment was carried on soils with low and high fertility levels amended with three types of 13C-labeled maize residues (root, stem and leaf) in Northeast China. The abundances of 13C in the soil samples were measured on the 60th, 90th, 180th, and 540th days after incubation. The results showed that the residual rate of the residue-derived C was higher in the high-fertility (HF) soil than that in the low-fertility (LF) soil on the 60th day (an average of 56.6% vs. 52.37%, P < 0.05). At the end of the experiment, the content of the residue-derived C in the root-amended treatment (0.5 and 0.4 g kg−1 in the HF and LF soils, respectively) was higher than that in the stem-amended (0.4 and 0.3 g kg−1 in the HF and LF soils, respectively) and leaf-amended (0.4 and 0.3 g kg−1 in the HF and LF soils, respectively) treatments. The residual rates of the root-, stem- and leaf-derived C were 20.1%, 15.6%, and 15.4% in the LF soil and 20.4%, 18.3%, and 18.2% in the HF soil, respectively. The results revealed that the HF soil had higher capacity to retain exogenous residue C, and the residue-derived C contribution from below ground residues (roots) to SOC should be more important than that from above ground parts (leaves + stems) in a long-term period.