Designing a Soil Health Index for Sustainable Agricultural Systems.
Creators: name: Khandoker, Munisath
Publisher: name: Lancaster University
Year: 2024

description: Soil health is vital for agriculture and agro-ecosystems. Healthy soils
 act as a reservoir and cycling system for water, air, organic matter, and
 nutrients essential for crop growth and as a habitat for a diverse array
 of organisms, including bacteria, fungi, insects, and worms, contributing
 towards ecosystem stability and resilience. However, soil health cannot be
 directly measured effectively with one indicator. Instead, soil health
 assessments typically rely on a range of measurements of essential
 biological, physical, and chemical indicators. Due to the complexity and
 highly integrative nature of soils, it is difficult to develop general
 soil health indices. 
 
 
 The main goal of this thesis was to develop a soil health index that was
 able to quantify soil health for different agricultural land uses and soil
 textures across the UK. With the aid of Rothamsted Research’s long-term
 experiments of known history and land management, we aimed to collect
 measurements of crucial physical, biological, and chemical soil health
 indicators using traditional methods. Then, using structural equation
 modelling (SEM), we hoped to create a robust soil health assessment. When
 designing a soil health index, selecting the most informative indicators
 of soil health is essential. To achieve this, we initially focused on
 enhancing existing soil monitoring methodologies and exploring novel
 technologies that can streamline this process. In Chapter 2, we evaluated
 the SLAKES smartphone application as a tool for measuring soil stability.
 Results from the SLAKES application were compared with the established Le
 Bissonnais method. Results showed SLAKES could differentiate between
 different management types on clayey soil, but were less sensitive when
 tested with sandy soil. Despite this lower sensitivity, we conclude that
 the SLAKES app can be a legitimate method to measure aggregate stability,
 providing a faster and easier method for researchers and land managers
 compared to conventional methods. 
 
 
 In Chapter 3, we evaluated the use of extracellular enzymes,
 N-acetyl-β-glucosaminidase (NAG), acid phosphatase (PHO) and β-glucosidase
 (GLU), as promising soil health indicators. The objective was to
 investigate which of these soil enzymes, if any, could be used as a
 comprehensive biological indicator for soil health by examining the
 relationships between microbial enzyme activity in a range of soils with
 contrasting chemical and physical properties. We observed that grass
 treatments relative to all other plots showed increased levels of
 enzymatic activity, followed by arable and fallow, respectively.
 Furthermore, enzyme activity correlated with other observed soil health
 indicators. 
 
 
 Using learnings from the previous two chapters, the Chapter 4 study aimed
 to create meaningful metrics for soil health that influence agricultural
 production and other ecosystem services. We included a range of soil
 measurements relevant to soil health, including physical, chemical, and
 biological soil indicators under contrasting agricultural land uses and
 soil types. We found that SEM allows for a comprehensive understanding of
 the complex relationships within the soil health system. It was
 particularly beneficial when dealing with multiple indicators and latent
 variables that contribute to overall soil health. Based on our results, we
 believe soil scientists can leverage SEM to refine soil health assessment
 models and improve the accuracy of their measurements, as well as
 understand the effects of agricultural management practices on soil
 health.
 
 
 From selecting the most informative soil health indicators to carefully
 considering the measurement methods used for these indicators, this study
 demonstrates the multifaceted nature of designing a soil health index.