Effects of novel stover valorization pathways on soil organic matter dynamics in a highly weathered soil

Abstract

Soil organic matter (SOM) is vital for soil health and productivity in the highly weathered soils of Sub-Saharan Africa, where crop residue management is crucial for replenishing SOM. Novel circular stover valorization pathways for stover, including oyster mushroom cultivation and vermiculture, can enhance food security while returning organic amendments to soil. However, from an equivalent amount of maize stover, these pathways generate amendments varying in carbon quantity and quality due to differing conversion efficiencies and losses, and their effects on soil carbon relative to conventional stover management remain unclear. We evaluated five maize stover-derived amendments in a 51-day incubation of a highly weathered soil: stover, burned stover, spent mushroom substrate (SMS), vermicomposted stover (VCstover), and vermicomposted SMS (VCSMS), applied at rates reflecting each pathway’s biophysical potential. Novel pathways produced amendments with roughly one-third to one-half the carbon content of stover and lower C/N ratios (43–63 vs. 94). All amendments except burned stover significantly increased heterotrophic respiration. Despite contrasting carbon inputs, bulk soil carbon after 51 days remained unchanged across all novel amendments relative to the control. However, vermicomposted amendments (VCSMS and VCstover) shifted SOM partitioning toward particulate (POM) and away from mineral-associated organic matter (MAOM), with POM rising from 43 % to 51–53 %. This suggests that the vermicomposting pathway could influence early SOM formation, reflecting the combined effects of amendment processing and lower C inputs rather than either alone. Although observed over 51 days, this effect could carry longer-term implications for carbon persistence given MAOM’s greater stability. In the short-term, novel stover valorization pathways show potential to maintain soil carbon while supporting food security.