Impact of Organic Mulch on Maize Yield under Variable Rainfall in Smallholder Farms

Thesis Abstract

Soil moisture stress and erosion risk in smallholder maize production under increasingly erratic rainfall patterns necessitate practical resilience strategies for yield stability. This study investigates the impact of organic mulch on maize yield under variable rainfall in smallholder farms, addressing the gap in context-specific, on-farm adaptation strategies within moist tropical agroecosystems. The aim is to quantify how different mulch types and application regimes influence maize grain yield, water-use efficiency, soil moisture dynamics, and nutrient availability under contrasting rainfall scenarios. Specific objectives include (1) comparing yield responses of maize to surface mulch derived from farm-approved organic materials (coconut husk, maize stover, and composted leaf litter) across three rainfall regimes (typical, drought-lean, and heavy rainfall years) over two cropping seasons; (2) assessing mulch-mediated changes in soil moisture content, temperature, and infiltration rates; (3) evaluating the effects on soil chemical properties (organic carbon, available phosphorus, and mineral N) and nutrient uptake; (4) analyzing economic viability considering mulch production, application costs, and maize market returns; and (5) identifying farmer-perceived constraints and adoption drivers through participatory diagnostics. A mixed-methods approach was employed. The study was conducted in three representative smallholder communities across a gradient of soil types within the maize belt, with a total population of approximately 600 hectares under maize cultivation. A randomized complete block design with split-plot arrangement was used across four farms per site, totaling 12 experimental plots per site and 36 plots overall. Mulch treatments comprised three organic mulch types (coconut husk, maize stover, composted leaf litter) and a no-mulch control, each applied at 5 and 10 tons per hectare, with three replicates per treatment, and monitored over two consecutive cropping seasons. Data collection instruments included calibrated soil moisture sensors (Time Domain Reflectometry) and soil temperature probes for in-situ microclimate monitoring; grain harvest yields; laboratory analyses for soil organic carbon, total nitrogen, available phosphorus, exchangeable potassium, and cation exchange capacity; and foliar tissue analyses for N and P concentrations. A structured farmer questionnaire and key-informant interviews were conducted to capture socio-economic factors, labor requirements, and perceived constraints. Validity and reliability were ensured through pre-testing of instruments, calibration of sensors, and triangulation across field measurements and farmer surveys. Data analysis followed a robust sequential approach. Descriptive statistics characterized baseline conditions and treatment means. Repeated-measures ANOVA tested mulch effects on yield, soil moisture, and soil properties across seasons and rainfall regimes, with post hoc Tukey tests for pairwise comparisons. Multivariate regression models quantified the relationship between mulch treatments, soil moisture, nutrient availability, and maize yield, controlling for soil type, planting density, and rainfall amount. Structural equation modeling (SEM) explored direct and indirect pathways linking mulch use to yield through soil moisture retention and nutrient dynamics. Economic analysis included partial budgeting and cost-benefit ratios to determine return on mulch investment under different rainfall scenarios. Theoretical framing drew on the Conservation Agriculture and Resource Conservation theories, with a supplementary application of the Water-Amplification Hypothesis to interpret moisture retention effects. Expected findings anticipate that organic mulch will significantly improve maize grain yield under drought-lean years, primarily through enhanced soil moisture retention and moderated soil temperatures, with the greatest gains for maize stover mulch at 10 t ha?1. Compost-based mulch is expected to boost soil organic carbon and available nitrogen modestly, while coconut husk may improve moisture retention but exhibit slower nutrient release. The study will likely demonstrate improved water-use efficiency and favorable economic returns when mulch is produced and applied as part of an integrated soil fertility and moisture management strategy. The contribution to knowledge includes empirically grounded recommendations for mulch selection, application rates, and adoption pathways tailored to smallholder contexts under variable rainfall. Policy implications emphasize scalable, low-cost, on-farm mulch systems as climate-resilient practices. In conclusion, organic mulch is expected to be a viable strategy to stabilize maize yields amid rainfall variability, with implications for agronomic practice, farmer livelihoods, and regional food security, supported by evidence-based guidelines for dissemination and extension. Recommendations include farmer training modules, community mulch cooperatives, and integration with soil health monitoring to sustain long-term productivity.