Date of Award

Fall 2017

Project Type

Dissertation

Program or Major

Natural Resources and Environmental Studies

Degree Name

Doctor of Philosophy

First Advisor

Richard G Smith

Second Advisor

Roger T Koide

Third Advisor

David A Mortensen

Abstract

To maximize crop yields, commodity crop production systems typically rely on inputs of fertilizers, pesticides, and irrigation; simplification of crop rotations (e.g., monocultures); and strategic use of soil disturbance (e.g., tillage, cultivation, etc.). While these practices are intended to optimize the soil conditions for crop development and reduce spatial and temporal variability in crop yield, they also impact soil biological diversity and the important agroecosystem services soil communities provide. Identification of management practices that are less prone to causing undesirable changes in the soil food web community are central to improving the sustainability of our agricultural systems. In this dissertation, I examined the effects of two agricultural management practices – conservation tillage and pesticide seed treatments – on the soil food web and soil-derived ecosystem services. The objective of my first study (Chapter 2) was to quantify the effects of zonal and uniform conservation tillage (ridge tillage vs. chisel plow) and strategic crop residue management (or soil functional zone management) on the abundance and diversity of the soil arthropod food web community inhabiting the crop row and inter-row zones in a maize-soybean system. In this two-year field experiment, I demonstrated that by using soil functional zone management, we can create unique zonation of the row and inter-row soil arthropod communities compared to uniform tillage. However, there were tradeoffs associated with this strategy, as the higher abundance of soil arthropods and more non-pest taxa associated with the crop rows under ridge tillage were offset by a more depauperate community inhabiting the crop inter-row compared to the uniformly tilled system. The objectives of Chapters 3 and 4 of this dissertation were to improve our understanding of how pesticide seed treatments (PST) with neonicotinoids affect soil food web communities and the soil functions they regulate. PST with neonicotinoids are widely used in commodity row cropping systems managed with conservation tillage to preemptively protect crop seeds and seedlings from soil-borne diseases and soil-dwelling insects. There is emerging evidence, however, that PST can negatively affect non-targeted organisms, yet its effects on soil arthropod communities are poorly understood. In Chapter 3, I demonstrate with a field experiment that PST with neonicotinoids can alter the abundance and diversity of non-targeted soil fauna spanning multiple trophic-levels with no detectable effect on herbivores – the guild that is the intended target of PST. Lastly, in Chapter 4, I demonstrate for the first time that the initial introduction of PST into a soil community results in dramatic changes in soil community abundance and diversity, while communities with prolonged histories of seed treatment exposure appear to be relatively unaffected by subsequent exposure. Together this research provides insight into how a specific set of conservation tillage strategies, and their often-associated pesticide technologies, impact the community of soil arthropods that are critical to the sustainability of agriculture.

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