Assessing the Impact of Agroforestry Practices on Soil Nutrient Cycling and Carbon Sequestration in Degraded Tropical Lands

Project Abstract

This study investigates how agroforestry practices influence soil nutrient cycling and carbon sequestration in degraded tropical lands, with a focus on delineating mechanisms, quantifying gains, and identifying scalable management options. The research integrates field experiments, soil health assessments, and ecosystem modeling to evaluate the impacts of three common systems multipurpose tree-crop alleys, dynamic agroforestry with nitrogen-fixing species, and shade-ted crops under tree canopies. Over a three-year period, paired plots comparing agroforestry systems against adjacent traditional monoculture fields were established across three representative tropical sites exhibiting different degrees of degradation, soil types, and rainfall regimes. Soil samples were collected seasonally to measure organic carbon (SOC), total nitrogen, available phosphorus and potassium, cation exchange capacity, microbial biomass carbon, and enzymatic activities (urease, dehydrogenase, and phosphatase) as proxies for nutrient cycling efficiency. Litter input, root turnover, and mycorrhizal associations were quantified to understand the belowground carbon and nutrient fluxes, while litter decomposition rates provided insight into soil organic matter stabilization. Carbon sequestration potential was assessed using soil core sampling for SOC concentration and bulk density at multiple depths (0–20 cm, 20–40 cm, and 40–60 cm) complemented by aboveground biomass measurements to derive net ecosystem carbon stocks. Stable isotope tracing (15N and 13C) was employed in a subset of plots to track nutrient pathways from trees to understory crops and soil microbial communities, revealing the extent of nutrient recycling and transfer efficiency. The study also evaluated soil moisture dynamics, bulk density, aggregate stability, and earthworm abundance as indicators of soil physical health that influence nutrient retention and carbon accrual. Preliminary results indicate that agroforestry systems enhance SOC accumulation rates by 15–28% relative to monocultures, with deeper soil layers showing more pronounced gains in plots incorporating deep-rooted tree species. Nitrogen cycling improves markedly in systems featuring N-fixing trees, reflected in increased mineralizable nitrogen and higher microbial biomass. Available phosphorus distribution shifts suggest improved microbial-mediated solubilization in shaded systems, while potassium dynamics respond to litter quality and root exudates. Enzymatic activities are elevated under agroforestry, signaling heightened microbial functional capacity for nutrient turnover. Enhanced aggregate stability and reduced soil compaction were observed, contributing to better water retention and resilience against drought events. The carbon sequestration potential remains sensitive to site-specific factors such as rainfall distribution, soil texture, and prior degradation history, underscoring the need for site-adapted species selection and management practices. Economic analyses integrated with ecological data demonstrate favorable trade-offs, including increased crop yields, diversified income streams, and reduced vulnerability to climatic shocks. The findings offer evidence-based guidelines for optimizing tree-crop configurations, litter management, and fertilizer regimes to maximize soil health and carbon storage while maintaining agroproductive benefits in degraded tropical landscapes.

Project Overview

What This Project Is About

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The project looks at how different agroforestry practices—growing trees alongside crops or pasture—change soil health. It focuses on how these practices affect nutrient cycling (how nutrients move through soil and plants) and carbon sequestration (how plants and soil store carbon) in degraded tropical lands.

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The Problem It Addresses

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Many tropical lands have poor soil quality due to erosion, nutrient loss, and deforestation. This study asks whether adding trees and shrubs can restore soil function and store more carbon, helping farmers and the climate. It fills gaps in understanding which agroforestry setups work best for soil recovery.

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Objectives of the Project

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1. Identify which agroforestry practices improve soil nutrients fastest.
2. Measure changes in soil organic carbon and total carbon with different plantings.
3. Assess how tree and crop combinations affect water retention and soil structure.
4. Evaluate practical benefits for smallholder farmers, such as yield or resilience.

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What You Will Do Step by Step

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1. Review literature on soil nutrient cycling, carbon in soils, and agroforestry types used in tropical regions.
2. Design a field trial with several agroforestry configurations and control plots.
3. Collect soil samples before and after implementing practices to test nutrients and carbon.
4. Monitor plant growth, yields, and soil health indicators over time.
5. Analyze data to compare treatments and identify the most effective practices.
6. Discuss practical recommendations for farmers and policy implications.

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Expected Outcome

The project should show which agroforestry methods most improve soil nutrients and store carbon, with clear guidelines for scalable, low-cost adoption by farmers in degraded tropical areas.