Impact of long-term tillage and organic amendments on soil organic carbon sequestration and aggregate stability in a coastal saline soil ecosystem

Project Abstract

Long-term tillage practices and organic amendments significantly influence soil organic carbon (SOC) dynamics, aggregate stability, and overall soil health in coastal saline environments, where high salinity and shallow groundwater often constrain productivity. This study integrates a multi-year field experiment with complementary laboratory analyses to quantify the effects of conventional tillage, reduced tillage, and no-till systems combined with organic amendments (compost, farmyard manure, and biochar) on SOC sequestration rates, aggregate distribution, and soil structural stability in a coastal saline soil (CSS) ecosystem. A randomized complete block design with split plots ( tillage as main plots; organic amendments as subplots) and four replicates was employed across a 5-year period. Soil samples were collected at 0–15, 15–30, and 30–60 cm depths to capture vertical SOC stratification and microaggregate protection. SOC was measured by dry combustion, and active carbon pools (permanganate oxidizable C and hydrolyzable C) were quantified to assess labile carbon dynamics. Aggregate size distribution and mean weight diameter (MWD) were determined using wet sieving to evaluate the influence of tillage and amendments on macro- and microaggregate stability under salinity stress. Wet aggregate stability (WAS) and air-dried aggregate stability (ADAS) were assessed to infer resistance to dispersion and erosion. Soil salinity (ECe), pH, bulk density, moisture content, and exchangeable sodium percentage (ESP) were monitored to disentangle salinity-driven effects from tillage and amendment impacts. Plant-available nutrients (N, P, K, Ca, Mg) and micronutrients were measured to link soil quality changes with potential productivity outcomes. The study employs a holistic carbon budget framework that partitions SOC into particulate organic carbon (POC), mineral-associated organic carbon (MAOC), and total SOC, enabling assessment of stabilization mechanisms under CSS conditions. Modeling tools, including a generalized linear mixed model (GLMM) and non-linear SOC mineralization models, are used to identify significant interactions among tillage, amendments, depth, and salinity level. The anticipated results indicate that no-till with organic amendments, particularly biochar and compost combinations, enhances SOC sequestration by promoting MAOC formation and protecting C within resistant aggregates, while reducing soil bulk density and improving WAS in the 0–30 cm layer. Reduced tillage with manure is expected to favor macroaggregate formation but may offer variable SOC gains depending on salinity gradients. Depth-wise trends reveal diminishing SOC gains with increasing depth; however, organic amendments mitigate SOC losses in deeper horizons by sustaining aggregate porosity and reducing dispersion under high ESP. The study will also document changes in salinity stratification, ESP, and soil structure as mediating factors for SOC stabilization. The outcomes aim to inform best management practices for CSS ecosystems, optimizing tillage regimes and organic amendment strategies to maximize SOC sequestration, enhance aggregate stability, and sustain crop productivity in the face of salinity intrusion and climate variability. Policy-relevant recommendations will be provided for coastal agro-ecosystems prioritizing sustainable soil management, carbon storage, and resilience.

Project Overview

What This Project Is About

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A plain-language overview of how soils change when farmers use different tillage practices and add organic materials, and how these changes affect soil carbon storage and soil structure in coastal areas with saltier soils.

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The Problem It Addresses

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Soils in coastal regions often lose carbon and become less stable when tilled in conventional ways, especially with salty conditions. The project investigates how long-term farming methods and adding organic matter can improve carbon storage and soil structure, which benefits fertility and resilience.

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Objectives of the Project

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1. Understand how long-term tillage affects soil carbon and aggregate stability in coastal saline soils.
2. Evaluate the effect of organic amendments on soil carbon sequestration.
3. Compare traditional tillage with reduced-tillage or no-till systems under saline conditions.
4. Assess changes in soil structure and water-holding capacity with different practices.
5. Provide practical recommendations for farmers on sustainable soil management in coastal zones.

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What You Will Do Step by Step

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1. Review relevant literature on tillage, organic amendments, and soil carbon in coastal soils.
2. Design a field or controlled experiment with different tillage and amendment treatments.
3. Collect soil samples at multiple depths and measure organic carbon and particle stability.
4. Analyze data to see how treatments influence carbon and soil structure over time.
5. Interpret results and relate them to real farming practices in coastal areas.

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Expected Outcome

Clear evidence on which tillage and organic amendment practices best enhance carbon storage and soil stability in coastal saline soils, plus practical guidelines for improving soil health and sustainability.