Sensitivity, Variability, and Statistical Evaluation of Soil Health Indicators in a Silt Loam Soil in Mower County, MN

Abstract

This dissertation focuses on the sensitivity, variability, and statistical evaluation of a subset of soil health indicators and their methodologies prescribed by the Natural Resources Conservation Service in Technical Note 450-03 (updated November 2019) with the aim of evaluating dynamic soil properties (DSPs). All work took place in fine-loamy, mixed, superactive, mesic Hapludolls of Mower County, MN. First, I assessed DSPs across two contrasting agricultural management systems and a reference ecosystem down to 1 m depth with samples separated by soil genetic horizon to determine the sensitivity of DSPs between different land uses within a unique soil. Second, I assessed temporal variability of a subset of DSPs at the same site over the course of a growing season (May-October) and the influence of short-term soil temperature and moisture dynamics. Third, I reviewed past and proposed alternative approaches to modeling depth distribution of soil properties for assessment of differences in soil health by depth. Overall, I found that DSPs were primarily sensitive to management in surface soils (0-5 cm) and subsurface soils (25-40 cm) and varied throughout the course of the season in different degrees depending on the ecosystem, and varied very little as a result of short-term soil temperature and moisture fluctuations. I elaborate on these findings in two data chapters and a statistical review as follows:• In Chapter 2, I present the evaluation of DSPs by depth across two contrasting agricultural management systems and a reference ecosystem to: i) determine the capacity of individual DSPs to distinguish among management practices under static pedoclimatic conditions; ii) evaluate the effect of management on individual DSPs across a soil control section of 1 m; and iii) investigate the value of reference data in determining indicator sensitivity and overall soil health directionality. • In Chapter 3, I present the differences in a subset of soil health indicators across the course of a growing season to: (i) assess seasonal variation, stability, and relationships among these indicators across two contrasting agricultural management systems and a reference ecosystem; (ii) evaluate changes in these metrics within two depths (0-10 cm and 10-20 cm); and (iii) determine the extent to which daily soil temperature and moisture influence seasonal fluctuations of these metrics. • In Chapter 4, I review historical and contemporary approaches to evaluating the distribution of soil properties by depth, propose alternative statistical approaches, and discuss the merits and limitations of each approach. The work presented in this dissertation contributes to the science of soil health by contextualizing DSPs in agriculturally relevant soils of the Upper Midwest and presenting both practical and theoretical approaches to the evaluation of soil health. I discuss the importance of evaluating DSPs over a soil profile to establish soil health changes as a result of management, highlight the value of a reference soil in determining a soils’ DSP potential and soil health directionality, evaluate potential environmental stimuli and constraints on temporal variability of DSPs, and propose alternative methods for statistical evaluation of soil properties in the field of agronomy.