Doctoral Dissertations

Date of Award

12-2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

Sindhu Jagadamma

Committee Members

Forbes Walker, Xinhua Yin, Daniel Yoder

Abstract

Soil health assessment is important for making informed sustainable management decisions in production systems. An established standardized method to quantify soil health is lacking and the validity of the existing methods across agroecoregions and cropping systems is not yet proven. Therefore, this study aims to evaluate the feasibility of widely discussed three soil health tests - Haney’s Soil Health Test (HSHT), Comprehensive Assessment of Soil Health (CASH), and Alabama Soil Health Index (ASHI) to assess soil health in diverse cropping systems of Tennessee. Since these approaches were originally developed for specific agroecoregions, we hypothesized that these tests are not sensitive to detect soil health changes due to management differences for the cropping systems of Tennessee. Our feasibility criteria depended on the sensitivity of soil health scores and underlying indicators to management changes. To conduct this research, we leveraged three ongoing cropping system experiments in Tennessee that include a suite of tillage, cover crops, and N rate treatments. These experiments are: (i) continuous soybean (Glycine max L.) (SS), (ii) corn (Zea mays L.)-soybean rotation (CS), and (iii) continuous cotton (Gossypium hirsutum L.) (CC) systems. Our results showed that all three existing tests (HSHT, CASH, and ASHI) failed to differentiate soil health in long-term conventional systems from that in conservation systems. Therefore, a weighted soil health index (WSHI) was developed for a regionally-realistic soil health assessment of these cropping systems. The WSHI used soil health indicators sensitive to the tested cropping systems and scoring functions meaningful within the region. Finally, soil health gaps (SHG) between the regional benchmark soils (i.e., unmanaged grasslands and woodlots) and cropland soils were calculated. Results revealed that WSHI was more effective in discerning soil health differences between conservation and conventional managements of Tennessee cropping systems compared iv to already existing tests. Additionally, SHG between unmanaged and intensively managed soils reiterated the degree of soil health degradation from cultivation. The SHG approach shows promise as a standardized method to compare soil health across agroecological regions.

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