Incorporation of stoichiometric CNPS inputs in soils with variable clay content

Abstract Purpose: Evidence exists for a constant C, N, P, and S content in the stabilized fine fraction pool of organic carbon in soils globally. This study aimed to test C:N:P:S stoichiometry to increase the rate of organic matter mineralization and soil organic carbon (SOC) stabilisation following straw incorporation in soils with varying clay content. Objectives were to (i) determine whether stoichiometric CNPS input affected mineralisation by increasing CO2 production, (ii) quantify the effect of nutrient limitation (N, P or S) on CO2-C and (iii) determine if enhanced mineralisation could be detected in the stable C fraction (FF-C) after one incubation cycle. Methods: Straw was incorporated in soil at a rate of 8 t ha-1 with or without stoichiometrically balanced nutrients to convert a target 30% fresh C-input to SOC. Results: Both treatment and soil type had a statistically significant effect on the total amount of CO2-C production (p<0.001). A positive significant relationship was observed during peak concentration of CO2-C between C2 (C-input) and N1 (balanced stoichiometric CNPS input) in two soils with higher clay and silt content (loam soils), with nutrient-limiting treatments responding accordingly. No significant treatment effect was observed for FF-C, as an indicative response of SOC stabilisation in heavier textured soils. This suggests that lighter soils may take a longer time to respond to stoichiometric CNPS inputs to achieve stabilised SOC. Conclusion: In conclusion, Multiple C addition cycle may be required to show both the straw mineralisation and SOC stabilisation response to stoichiometrically balanced inputs of CNPS.