INVESTIGATING THE FEEDBACKS BETWEEN SOIL HEALTH AND PEST MANAGEMENT PRACTICES IN FIELD CROPS
ABSTRACT Field crop growers are increasingly aware of the benefits for managing healthy biologically active soils, such as improved nutrient cycling and decomposition, and soil structure. Of equal importance to growers is the management of crop pests, which may include pesticides that have unintended effects on soil biological function. Historically, soil health and pest management are rarely integrated, despite that both practices are aimed at enhancing and maximizing productivity. The goal of this research was to explore the feedbacks between soil health and pest management tactics in field crops, and to quantify the influence of pest management on soil biological function, specifically biological control and decomposition. A three-year field experiment (2017-2019) was conducted in a corn-soybean-corn rotation, and evaluated the influence of two management practices: (1) preventative pest management, with pesticide-treated seed and foliar sprays, and a scouting-based IPM, on pest regulation (chapter one), and soil fertility and decomposition (chapter two). To assess pest regulation, I measured predator activity-density and predation at the soil surface, and the biological control potential of soil-borne entomopathogenic fungi (EPF). Aboveground predators were measured via pitfall trapping and predation dynamics were assessed with a standard sentinel-bait assay. Belowground biological control potential was determined using a sentinel-bait bioassay to quantify the abundance of entomopathogenic fungi. To determine decomposition and nutrient cycling, I measured soil fertility (pH, organic matter, macro- and micro- nutrients) and % wet aggregate stability. Soil microarthropods were measured via Berlese funnel extraction and decomposer activity was determined through microbial extracellular enzymes and bait lamina strips. Over the course of the experiment, I found that the use of seed treatments and foliar applications together negatively suppressed total predator activity-density, spider activity-density, predation, and the infection potential of soil-borne entomopathogenic fungi, compared with no pesticide use in one out of three years of the field study. I also found that pest management practices had minimal impacts on the soil physicochemical properties compared to biological factors. I observed increased microbial enzyme activity and feeding activity in preventatively managed fields, and both practices increased the abundance of decomposer microarthropods, depending on taxa and pesticide input. There were higher abundances of two collembolan families (Isotomidae and Entomobryidae) and three mite taxa (Oribatida, Mesostigmata, and Astigmatina) in IPM and preventative practices, and a suppression of one mite taxa (Prostigmata) in preventative management in all three years of the study. Overall, the use of pesticides did not improve crop yield in either corn or soybean. These results highlight that the use of seed treatments within an IPM practice may not always be necessary for maximum crop productivity. Taken together, my findings suggest pest management practices may have unintended consequences for above and below ground soil biological control, and diverse impacts on decomposer community composition and function, with responses varying by biotic compartment, season, and the specific active ingredients used. These results emphasize the need for further research exploring the mechanisms underlying the responses of soil biota to pesticidal seed treatments and foliar applications to better align practices for managing both soil health and agricultural pests in field crops.
Biological Control; Decomposition; Field Crops; Neonicotinoids; Pest Management; Soil Health
Master of Science
dissertation or thesis