Impact of biochar amendments on soil physico-chemical properties and crop yield under varying moisture regimes in a tropical agroecosystem

Project Abstract

Biochar amendments were evaluated for their effects on soil physico-chemical properties and crop yield under three distinct moisture regimes—well-watered, moderate drought, and severe drought—in a tropical agroecosystem over a full growing season. A randomized complete block design with four replications was employed, incorporating three biochar application rates (0, 5 and 15 t ha?1) and six sampling intervals to capture temporal dynamics. Baseline soil properties were characterized prior to treatment, including pH, electrical conductivity, bulk density, total organic carbon, cation exchange capacity, available macronutrients (N, P, K, S), micronutrients, soil texture, bulk density, and aggregate stability. The biochar used was derived from locally sourced agricultural residues, produced by slow pyrolysis at 450°C, ensuring a high surface area and functional groups conducive to nutrient sorption and microbialhabitat provision. Crop performance was assessed through germination rate, above- and below-ground biomass, leaf area index, chlorophyll content, final grain yield, and harvest index. Soil moisture was controlled using regulated irrigation to simulate the three regimes, and rainfall data were recorded to account for natural variability. Soil microbial activity and community composition were analyzed via soil respiration rates, qPCR quantification of key functional genes involved in nitrogen cycling, and 16S rRNA sequencing to track bacterial and fungal taxa shifts in response to biochar and moisture stress. Plant nutrient use efficiency (NUE, PUE, KUE) and nutrient uptake were calculated to elucidate physiological responses under constraint conditions. Throughout the study, biochar amendments demonstrated significant improvements in soil physical properties, including increased water-holding capacity, reduced bulk density, and enhanced aggregate stability, particularly at the 15 t ha?1 rate. Chemical analyses revealed elevated cation exchange capacity and sustained pH buffering, reducing acidity under drought stress and promoting greater nutrient availability. Nitrogen retention was improved in biochar-amended plots, mitigating volatilization losses under high-temperature tropical conditions, while phosphorus availability showed a nuanced response dependent on moisture regime and biochar rate. Crop yield under well-watered conditions benefited from biochar through improved soil moisture retention and nutrient availability, with the highest yield observed at 15 t ha?1. In moderate drought, biochar-treated plots maintained higher biomass and grain yield relative to controls, attributable to improved water use efficiency and microbial-mediated nutrient cycling. Under severe drought, biochar facilitated resilience by preserving soil moisture and providing a protective microhabitat for microbes, though the magnitude of yield gains diminished compared with well-watered conditions. Microbial analyses indicated enrichment of drought-tolerant microbial taxa and functional genes associated with nitrogen mineralization and phosphorus solubilization in biochar-amended soils. Overall, the interaction of biochar application rate and moisture regime significantly influenced soil health indicators, nutrient dynamics, and crop productivity, with the 15 t ha?1 rate offering the most consistent benefits across regimes. The study provides mechanistic evidence that biochar—by modulating physical structure, chemical properties, and the soil microbiome—enhances resilience and productivity in tropical agroecosystems experiencing variable moisture. Recommendations for optimizing biochar rates, integrating with other soil amendments, and tailoring management for drought-prone tropical environments are discussed.

Project Overview

What This Project Is About

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This project looks at how adding biochar to soil changes soil properties like texture, nutrients, water holding, and how these changes affect crop yields. It also tests how different moisture levels (wet, moderate, dry) influence these effects in a tropical farming setting.

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The Problem It Addresses

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Soil quality and water availability limit crop growth in tropical regions. Biochar, a charcoal-like material added to soil, is believed to improve fertility and moisture retention, but results vary depending on climate and moisture. This project explores what works best to boost yields sustainably.

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Objectives of the Project

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1. Describe how biochar changes key soil properties (pH, nutrients, water holding capacity).
2. Evaluate crop yield responses under different moisture regimes with biochar amendments.
3. Compare short-term versus longer-term effects of biochar on soil health.
4. Identify any optimal biochar rate for tropical soils.

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What You Will Do Step by Step

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1) Review simple literature on biochar and soil moisture. 2) Collect soil samples from a tropical field and prepare plots with varying biochar doses. 3) Apply different irrigation levels to each plot. 4) Plant a common test crop and monitor growth, yield, and soil changes. 5) Measure soil pH, nutrient levels, moisture, and bulk density. 6) Record crop yield and quality. 7) Analyze data to see how biochar and moisture interact. 8) Summarize practical recommendations.

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Expected Outcome

Clear understanding of whether biochar improves soil health and yields under different watering conditions, with practical guidelines on application rates for tropical soils.