INTRODUCTION

The Breton Plots located in Breton, Alberta were established in 1929 by the Department of Soil Science at the University of Alberta (Dyck & Puurveen, 2023). The plots are categorized into two experiments: the Classical Plots (established in 1029) and the Hendrigan Plots which were established in the 1980s. This site has been at the core of research conducted on understanding the impacts of various agricultural practices including crop rotations and fertilization practices on soil health and crop productivity, becoming one of Canada’s longest running experimental sites. These plots have also been extensively studied for soil organic carbon (SOC) dynamics providing empirical data on how different management strategies influence SOC levels over time. SOC is a crucial component of soil health and plays a critical role in mitigating climate change.

SOC stocks are influenced by key factors such as cropping systems, fertilization, and soil disturbance (Wang et al., 2023), therefore, agricultural research sites such as the Breton Plots become invaluable in evaluating long-term data on cumulative impacts of land management strategies. While the Breton Plots have already been researched for management practices influence on SOC sequestration, many factors including environmental and agricultural practices create a lot of uncertainties around the key underlying controls of SOC accumulation and retention (Zhou et al., 2019). The insights gained from the Breton Plots continue to contribute to the development of empirical data and guidelines for sustainable agriculture, promoting SOC accumulation to ensure soil sustainability and resilience in response to environmental change.

Figure 1: The Breton Plots located in Edmonton, AB, generated using Google Earth

Rationale for the study

With data from the long-term field experiment Breton Plots, this study aims to understand how management practices influence SOC dynamics. The study specifically aims to determine the effects of fallow, amendments, and forage inclusion on the chemical composition of SOC classes which remain poorly researched.

A common assumption is that inorganic fertilizers which include Nitrogen, Prosperous, Potassium and Sulfur (NPKS) boost nitrogen-associated SOC compounds (SOC-N). However this study reveals unexpectedly high SOC-N levels in unamended control plots, suggesting the complexity of underlying soil processes. Additionally, in contrast to the assumptions that greater plant biomass from forage inclusion should enhance SOC across the board, findings from this study indicate this influence may be restricted to certain compounds (e.g., aliphatics), and only in surface soils. Furthermore, the persistence of fallow in some cropping systems raises concerns due to its apparent negative impact on SOC storage.

These discrepancies point towards a need for a better understanding of how distinct agricultural practices influence not just total SOC, but the functional classes as well, because not all agricultural management practices affect soil carbon stocks equally. This study aims to address that gap by evaluating SOC class responses across long-term management practices, offering new insights that could support more effective soil carbon management strategies to building healthier, carbon-rich soils.

Research Objectives

To assess the impact of fallow on the chemical composition and distribution of soil organic carbon classes under varying long-term agricultural management practices.
To evaluate the effects of soil amendments on soil organic carbon composition and to determine whether the influence of amendment type: inorganic fertilizers versus organic manure, differs across management systems.
To investigate the role of forage crop inclusion and green manure in shaping the composition of soil organic carbon classes within distinct agricultural management frameworks.

This study aims to evaluate how different long-term management strategies employed in the Breton Plots affect the chemical composition of soil organic carbon fractions, with the goal of informing improved soil carbon management and promoting sustainable land-use practices.

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