Partial substitution of chemical fertilizer with organic amendments affects soil organic carbon composition and stability in a greenhouse vegetable production system

Abstract Understanding soil organic carbon (SOC) composition and stability is necessary for long-term carbon (C) sequestration. Fertilization is known to modify SOC stability and composition; however, inconsistent results have been reported. Here, we evaluated the changes in SOC composition and stability through multiple methods in an 8-year fertilization experiment under greenhouse vegetable production (GVP) systems in Tianjin, China. This experiment was designed to supply an equivalent amount of nutrients (N, P 2 O 5 and K 2 O) but variable amount of C through different exogenous organic resources (ORs) input. Five treatments were included based on substitution of chemical fertilizer nitrogen (N) with different exogenous ORs: no N (no nitrogen inputs), 4/4CN (CN, nitrogen in chemical fertilizer), 2/4CN + 2/4 MN (MN, nitrogen in pig manure, high-quality ORs), 2/4CN + 2/4SN (SN, nitrogen in corn straw, low-quality ORs) and 2/4CN + 1/4 MN+1/4SN. Organic fertilization strategies promoted SOC accumulation and reduced SOC stability by increasing labile C fractions, whereas chemical fertilizer alone had a negative effect on SOC accumulation by consuming labile C fractions but enhanced SOC stability. Notably, the characteristics of high temperature, nutrient availability and C inputs in organically managed soils in GVP systems weaken the influence of ORs quality on SOC stability. Consequently, high doses of C inputs (11.5 and 18.5 Mg ha –1  year –1 in 2/4CN + 1/4 MN+1/4SN and 2/4CN + 2/4SN treatments) induced lower SOC stability than low doses of C inputs (4.5 Mg ha –1  year –1 in the 2/4CN + 2/4 MN treatment), irrespective of ORs quality. In addition, strong correlations were found between SOC thermal characteristics and SOC chemical and 13 C NMR spectral properties, indicating that thermal analysis techniques can characterize SOC stability effectively.