Evaluation of biochar-amended soils on nutrient use efficiency and yield in maize under variable rainfall regimes

Project Abstract

In this study, we evaluate how biochar amendment to soil influences nutrient use efficiency and maize yield under simulated variable rainfall regimes, addressing a critical need to sustain productivity amid climate variability. The research integrates a field-based long-term experiment and controlled-environment analyses to dissect the mechanisms by which biochar modulates soil physical and chemical properties, nutrient dynamics, and plant physiological responses. A randomized complete block design (RCBD) with factorial treatment combinations of biochar application rates (0, 5, and 10 t ha?1) and rainfall regimes (optimal, moderate-drought, and severe-drought) was conducted over two growing seasons across two agro-ecological zones. Biochar derived from locally available agricultural residues underwent standardized pyrolysis (500°C) to ensure high pH, high surface area, and stable cation exchange capacity. Soil resource indices, including total and available nitrogen, phosphorus, potassium, micronutrients, pH, cation exchange capacity, bulk density, porosity, water holding capacity, and aggregate stability, were measured pre- and post-application, with seasonal monitoring of soil moisture dynamics using tensiometers and capacitance probes. Maize growth parameters—emergence, leaf area index, chlorophyll content, biomass accumulation, and phenology—were tracked alongside yield components such as ear number, kernel number per ear, 100-kernel weight, and harvest index. Nutrient use efficiency was quantified through uptake efficiency, agronomic efficiency, and partial factor productivity for N, P, and K under each treatment and rainfall condition. Isotopic tracing with 15N-labeled urea (where feasible) complemented the assessment of nitrogen use pathways, including mineralization rates and immobilization processes in biochar-amended soils. To elucidate the underlying mechanisms, soil enzyme activities (urease, phosphatase, dehydrogenase), microbial biomass carbon, and microbial community structure (via 16S rRNA and ITS sequencing) were analyzed to determine biochar-induced shifts in soil biota and functional potential. Key findings indicate that biochar application significantly enhances soil water retention and porosity, mitigating moisture stress under drought regimes. Nutrient availability, particularly inorganic N and P, improved with biochar due to sorption-desorption dynamics and reduced leaching, leading to higher nutrient use efficiency and greater biomass production. Under drought, biochar-treated plots maintained higher photosynthetic rates and stomatal conductance, translating into improved kernel set and grain yield relative to non-biochar controls. The magnitude of benefit correlated with biochar rate, rainfall regime, and soil texture, with loamy soils showing the most pronounced gains. However, interactions between high biochar rates and severe drought sometimes resulted in increased immobilization of N, underscoring the need for optimized timing of fertilizer inputs and careful consideration of biochar characteristics such as feedstock, pH, and ash content. The study provides robust evidence that biochar amendments can enhance nutrient use efficiency and maize yield under variable rainfall by improving soil physical structure, stabilizing nutrient availability, and fostering beneficial soil microbial processes. The findings offer practical recommendations for farmers and policy makers on biochar deployment as a climate-smart soil amendment, including rate guidelines, integration with N management strategies, and considerations for tailoring applications to specific soil types and rainfall projections.

Project Overview

What This Project Is About

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Objectives of the Project

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