Optimizing nutrient stoichiometry for enhanced carbon sequestration in agricultural soils

Nutrients like nitrogen (N), phosphorus (P), and sulphur (S) play a critical role in plant and microbial growth, as well as in stabilizing soil organic carbon (SOC). Humus, the most stable fraction of soil organic matter (SOM), maintains a consistent elemental ratio of C:N:P:S at 10,000:833:200:143. To evaluate how variations in this humus based C:N:P:S ratio affect SOC stabilization, a six-month laboratory incubation was conducted using selected benchmark soil series. The soils were amended with wheat straw (WS) and maize straw (MS), both with and without added inorganic nutrients (N, P, and S), to achieve two target C:N:P:S ratios aligned with humus stoichiometry 15% and 30% (C:N 12; C:P 50; C:S 70). Results showed that the MS30% and WS30% treatments reduced CO₂ efflux by 39% and 33%, respectively, compared to treatments without added nutrients. The MS15% and WS15% treatments also led to a 14% reduction in CO₂ emissions compared to the application of MS and WS alone. Moreover, supplementing WS and MS with nutrients to achieve a 30% humus-based ratio enhanced SOC stabilization by 11-25% over straw-only treatments. The study concludes that aligning organic and inorganic inputs to maintain a 30% humus-based C:N:P:S ratio significantly improves SOC stabilization. This highlights the vital role of balanced nutrient management in promoting carbon sequestration and overall soil health.