Assessment of rice husk–based biochar in smallholder farming: A case study of Lipa Farmers Cooperative, Philippines

Thesis Abstract

The adoption of rice husk–based biochar by smallholder farmers in Lipa, Philippines, faces constraints related to soil fertility variability, limited access to soil amendments, and uncertain yield responses under tropical agroecologies. This study addresses the knowledge gap on whether rice husk–derived biochar can enhance soil quality, crop productivity, and smallholder livelihoods within a cooperative framework, while examining adoption barriers and farmer perceptions. The aim is to evaluate agronomic, economic, and social outcomes of incorporating rice husk biochar into smallholder maize–vegetable rotations managed by the Lipa Farmers Cooperative. Specific objectives include (1) determining the effect of biochar on soil physical properties (bulk density, pore space) and chemical properties (pH, cation exchange capacity, available nutrients) over two cropping cycles; (2) assessing crop performance (germination rate, growth indices, yield, and nutrient uptake) of maize and leafy vegetables under biochar amendment at field and on-farm microplot scales; (3) analyzing economic feasibility and livelihood impacts (costs, net returns, risk indicators) for member households; (4) identifying determinants of biochar adoption, perceived risks, and knowledge transfer dynamics within the cooperative; and (5) developing a context-specific management guideline for rice husk biochar production, application rates, and soil–crop combinations. A mixed-methods research design combines quantitative field experiments and survey data with qualitative insights. The population comprises 350 registered members of the Lipa Farmers Cooperative, with a stratified random sample of 120 farmers for surveys and 12 extension staff for in-depth interviews. Field experiments employ a randomized complete block design with four treatments control, 5 t ha–1 biochar, 10 t ha–1 biochar, and 15 t ha–1 biochar, replicated across 4 blocks. Biochar is produced from locally sourced rice husk, characterized for ash content, fixed carbon, lignin, and pH, and applied to calibrated plots preceding the main cropping season. Data collection instruments include standardized soil sampling protocols, soil moisture and nutrient sensors, plant biometric measurement sheets, harvest yield records, and structured questionnaires complemented by semi-structured interview guides. Validity and reliability are ensured through pilot testing, Cronbach’s alpha for survey scales, and triangulation across methods. Analytical techniques encompass descriptive statistics, ANOVA and repeated-measures ANOVA to assess soil and crop responses, multiple regression to identify predictors of yield, cost–benefit analysis to evaluate economic viability, and thematic analysis for interview transcripts. The theoretical framework integrates the Sustainable Intensification theory and Technology Acceptance Model (TAM) to interpret agronomic performance, adoption drivers, and perceptions, with a conceptual model linking biochar properties to soil functions, crop productivity, and household welfare. Key expected findings include significant improvements in soil porosity, aggregate stability, pH buffering, and available phosphorus and potassium with increasing biochar rates, corresponding to enhanced maize and leafy vegetable growth, higher biomass accumulation, and increased yields relative to controls. Economic analysis is anticipated to show positive net returns at 10 t ha–1, with diminishing marginal gains at 15 t ha–1 due to immobilization effects and higher input costs. The study is expected to reveal adoption determinants such as perceived yield benefits, access to biochar production training, peer recommendations, and trust in extension services, while highlighting constraints including labor requirements, initial investment, and uncertainties about long-term soil impacts. The contribution to knowledge comprises context-specific evidence on rice husk biochar’s agronomic efficacy, economic viability, and socio-technical determinants within a Southeast Asian smallholder cooperative, offering a scalable model for integrating biochar into crop-livestock–horticulture rotations. The main conclusion is that rice husk–based biochar can be a technically feasible and economically viable soil amendment for smallholders in Lipa when integrated with farmer education and supportive extension services, with optimal benefits achieved at 10 t ha–1 for the studied rotations. Recommendations include (i) adopting a cooperative-led biochar training and quality-control program; (ii) establishing community-based biochar production hubs to reduce transaction costs; (iii) developing risk-mitigation strategies such as staggered application schedules and crop-specific rates; and (iv) conducting longitudinal monitoring to verify long-term soil health and productivity outcomes, and to refine the management guideline for broader regional deployment.