Impact of Biochar and Mulch on Soil Carbon Sequestration under Maize Farming Systems

Thesis Abstract

Soil carbon dynamics in maize-based agroecosystems are increasingly influenced by farmer-driven soil amendments, but the combined effects of biochar and mulch on long-term soil organic carbon sequestration under field conditions remain inadequately quantified. This study addresses the knowledge gap by evaluating how biochar application and organic mulch integration interact to enhance soil carbon stocks, stability, and priming effects, alongside impacts on soil physical and microbial properties. The aim is to quantify the individual and interactive effects of biochar and mulch on soil carbon sequestration, soil respiration, and maize yield over a two-year cropping cycle in temperate-continental maize systems. Specific objectives are (i) to determine the effects of varying biochar application rates (0, 10, 20 t ha-1) and mulch levels (0, 5, 10 Mg ha-1) on soil organic carbon (SOC) stocks in the 0–20 cm and 20–40 cm depths; (ii) to assess changes in SOC fractionation (light fraction, mineral-associated organic carbon) and soil microbial biomass; (iii) to evaluate priming effects via soil respiration and dissolved organic carbon fluxes; (iv) to examine impacts on maize growth, yield, and root aerenchyma under different amendment regimes; and (v) to analyze economic feasibility and practical recommendations for farmers. The methodology employs a randomized complete block design with a factorial 3×3 treatment arrangement replicated four times across a 1.6 ha experimental field in a maize-dominant cropping system. The population comprises field plots receiving biochar sourced from locally produced agricultural residue and locally sourced rice husk mulch. Data collection instruments include soil core sampling for SOC fractionation and mineral-associated carbon analysis by density fractionation and loss-on-ignition; chemical analyses for total organic carbon, inorganic carbon, and aggregate-associated carbon; microbial biomass carbon via substrate-induced respiration and phospholipid fatty acid profiling; soil respiration measurements using Li-Cor infrared gas analyzers; maize biometric data (plant height, leaf area index), phenology tracking, and grain yield assessment; and economic data through input costs, labor, and gross margin calculations. Instrument validity is ensured through calibration with standard reference materials and participation in external proficiency testing for soil carbon fractions; reliability is established via duplicate sampling and inter-laboratory cross-checks. Data analysis integrates mixed-effects models to test main and interaction effects of biochar and mulch on SOC stocks, SOC fractions, microbial parameters, and crop performance, with year and block as random factors. Regression analyses identify predictors of SOC accumulation, while repeated-measures ANOVA analyzes temporal changes in soil properties. Structural equation modeling examines causal pathways linking amendments, soil properties, microbial activity, and maize yield. A decomposition analysis estimates carbon sequestration potential under each treatment over the study period, and a simple cost-benefit model evaluates profitability and break-even points for farmers. Plausible hypotheses anticipate synergistic enhancement of SOC sequestration in combined biochar-plus-mulch treatments, greater stabilization of mineral-associated carbon, reduced soil respiration priming, and improved maize yield stability under moderate amendment levels. Expected findings include (i) significant increases in SOC stocks, especially in the 0–20 cm layer, with the highest gains under 20 t ha-1 biochar plus 10 Mg ha-1 mulch; (ii) increased proportions of mineral-associated organic carbon and aggregate-size fractions indicating enhanced stabilization; (iii) moderated soil respiration and improved microbial vigor suggesting optimized priming effects; (iv) positive effects on maize growth and grain yield, particularly in integrated amendment regimes; and (v) favorable economic indicators suggesting practical adoptability under smallholder to commercial farming scales. The study contributes to knowledge by delivering field-based, regionally relevant evidence on the combined influence of biochar and mulch on soil carbon sequestration, highlighting mechanistic links to soil physical structure and microbial ecology, and providing empirically grounded recommendations for agroecological management. The main conclusion posits that integrated biochar and mulch strategies offer a robust, scalable approach to increasing SOC stocks and stabilizing carbon in maize systems, with co-benefits for soil health and productivity. Recommendations include optimizing amendment rates for site-specific conditions, integrating biochar and mulch within existing residue management practices, and policy support for incentivizing carbon-sequestration-friendly maize production.