Assessing the Impact of Biochar Amendments on Soil Microbial Diversity and Nutrient Cycling in Degraded Tropical Soils under Variable moisture Regimes

Project Abstract

Biochar amendments were investigated for their effects on soil microbial diversity and nutrient cycling in degraded tropical soils subjected to varying moisture regimes to understand their potential to restore soil function and productivity. The study utilized a factorial experimental design incorporating three biochar application rates (0, 2 and 6 t ha-1) and three moisture regimes (well-watered, moderate drought, and severe drought) over a 12-month period in a controlled field setting. Soil microbial communities were characterized using high-throughput 16S rRNA gene sequencing and ITS sequencing for bacteria, archaea, and fungi, while microbial functional potential was inferred from shotgun metagenomics and targeted qPCR assays for key nitrogen, phosphorus, and carbon cycling genes (nifH, amoA, narG, nirK/nirS, nirB, nosZ, pmoA, mxaF, acdS, and phoD). Soil inorganic and organic nutrients (N, P, K, C, and Mg) and aggregate structure were measured to link microbial dynamics with physicochemical properties. Biochar treatments led to significant, moisture-dependent shifts in microbial diversity and community composition. In well-watered soils, biochar increased microbial evenness and promoted copiotrophic taxa associated with rapid organic matter turnover, whereas under drought stress, biochar supported drought-tolerant oligotrophic taxa and enhanced the relative abundance of functional genes related to nitrogen immobilization and mineralization, suggesting improved resilience of nutrient cycling under water limitation. Across all moisture conditions, biochar contributed to higher soil organic carbon stabilization and increased cation exchange capacity, with the most pronounced effects observed at 6 t ha-1. Nitrogen cycling genes, particularly those involved in mineralization (nifH, amoA) and denitrification (nirK, nosZ), were more abundant in biochar-amended plots, indicating enhanced potential for N turnover and availability. Phosphorus cycling-associated genes (phoD) and carbon-degrading enzymes (mxaF, pmoA) also showed elevated abundance, implying improved P solubilization and methane oxidation processes in the rhizosphere. Connectance and network analyses revealed a more interconnected microbial network in biochar-treated soils, with keystone taxa including Actinobacteria and Proteobacteria that correlated strongly with nutrient mineralization rates and enzyme activities. Plant growth indicators, including biomass accumulation and root length density, correlated positively with microbial biomass and enzyme activities, particularly under moderate drought with 6 t ha-1 biochar, highlighting the agronomic relevance of biochar for sustaining crop productivity under intermittent moisture stress. The results demonstrate that biochar amendments can modulate soil microbial communities to enhance nutrient cycling and soil health in degraded tropical soils, with moisture regime and application rate shaping the magnitude and direction of the responses. These findings provide mechanistic insight into how biochar mediates microbially driven nutrient transformations and suggest optimized management strategies for restoring soil functions in tropical agroecosystems facing increasing drought intensity. The study offers practical guidance for implementing biochar-based remediation to improve soil fertility, resilience, and sustainable productivity in degraded tropical landscapes.

Project Overview

What This Project Is About

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This project looks at how adding biochar to degraded tropical soils affects the tiny living things in the soil and how nutrients move around. Biochar is a charcoal-like material added to soil to improve health and fertility. The study compares soils with and without biochar under different moisture levels to see what changes occur in microbial life and nutrient cycling.

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The Problem It Addresses

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Degraded soils in tropical regions often have poor fertility and unstable nutrient cycling, which reduces crop yields. Little is known about how biochar changes soil microbes and the way nutrients are released and reused under different moisture conditions. Understanding this helps farmers restore soil health and sustain productivity.

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Objectives of the Project

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1. Explain how biochar amendments affect soil microbial communities.
2. Assess changes in nutrient availability and movement in the soil with and without biochar.
3. Evaluate how varying soil moisture alters biochar effects on microbes and nutrients.
4. Provide practical guidance for using biochar to improve degraded tropical soils.

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What You Will Do Step by Step

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1) Review simple background readings on soil microbes and biochar. 2) Collect soil samples from degraded tropical plots with different moisture levels. 3) Apply biochar to some plots and leave others as controls. 4) Measure basic soil health indicators (microbial activity, biomass, and nutrient levels). 5) Compare results across treatments and moisture regimes using straightforward data methods. 6) Discuss what the findings mean for soil improvement and farming.

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Expected Outcome

Anticipated outcomes include clearer evidence on whether biochar helps microbial communities and nutrient cycling, especially under different moisture conditions, and practical recommendations for farmers on using biochar to rehabilitate degraded tropical soils.