Transformation and stabilization of straw residue carbon in soil affected by soil types, maize straw addition and fertilized levels of soil

Soil organic carbon (SOC) sequestration is influenced by incorporation of maize straw and application of fertilizers, in intensive agricultural regions. However, there is a limited understanding of the transformation and stabilization of the newly added carbon (C) in soils applied with different amounts of straw residue. The aim of this study was to quantify the relationship between straw C input and SOC sequestration across soil types. We applied 13C-labeled maize straw (at amounts of 0 g, 1 g, 3 g, 5 g, 10 g per 100 g dried soil), combined with an in-situ carborundum tube method, in fertilized and non-fertilized Phaeozem and Luvisol soils at experimental sites in Northeast China. Over a period of 360 days, we found that the added amounts of maize straw, and fertilization, affected the residual rates, distribution and stabilization of extraneous new C. Fertilized treatments resulted in lower residual rates of maize straw at the end of the experimental period compared with non-fertilized treatments. We observed that the increased SOC from maize straw amendment (1.08 g C kg−1, the average for all treatments) could not compensate for the loss of native SOC (2.49 g C kg−1 soil, the average for all treatments) with 1 × C maize straw input. However, 5 × C and 10 × C straw addition were enough to offset the native SOC loss. An increase in maize straw incorporation with non-fertilized treatments caused the largest increase in new SOC formation which was highest (84.5%) for 10 × C maize straw input at the end of 360 days incubation at the Luvisol site. With increasing C input, turnover rate was observed to increase from 0.06 (1 × C) to 5.07 year−1 (10 × C), and the C turnover in each level of maize straw addition decreased with incubation time. These results demonstrate that soil type, fertilizer application, and a threshold amount of maize straw input are needed to drive net SOC sequestration.