The expansion of conventional row crop agriculture has altered soil biodiversity and function across the Midwest United States. The tallgrass prairie ecosystem that historically dominated this region is characterized by rich soil food webs that carry out important ecosystem services; therefore, restoring prairies within agricultural landscapes may reverse the harms wrought by intensive agricultural management. Prairie strips are a farm conservation practice in which tallgrass prairie vegetation is established in row crop fields, comprising up to 25% of a field area in linear strips ranging from 30 to 120 feet in width. Prairie strips reintroduce many features of the tallgrass prairie ecosystem to row crop farms, including increased plant, insect, and wildlife diversity, enhanced pollination, and reduced erosion and nutrient runoff. It remains unknown whether prairie strips also reintroduce belowground biota and soil processes characteristic of the tallgrass prairie. In this dissertation, I investigated the belowground changes associated with prairie strip establishment in Michigan and Iowa cropping systems. In Chapter 1, I measured soil microbial community composition during the first four years of prairie strip establishment within two low-intensity cropping systems in Michigan. I found that prairie strips quickly enriched prairie-associated microbial phyla and functional groups within just a few months after prairie strip planting, that land use history is an important driver of prairie strip microbial community composition, and that prairie strips did not affect microbial communities of surrounding cropland soils, suggesting that prairie taxa do not spill over into surrounding cropland soils early in their establishment. To understand whether prairie strips have a stronger effect on adjacent cropland soil microbial communities later in their succession, I conducted a similar study at a site in Iowa with more mature prairie strips in Chapter 2. I showed that similar to newly planted prairie strips in Michigan, 12 year old prairie strips altered soil microbial communities beneath the prairie strip, but not in adjacent cropland soils. Prairie strips also increased soil microbial biomass carbon and potential enzyme activities beneath the prairie strip, and increased potential activity of some extracellular enzymes in adjacent cropland soils. In Chapter 3, I measured early soil carbon indicators and soil organic matter fractions during three years of prairie strip establishment and at multiple distances from prairie strips in two cropping systems. This study showed that prairie strips do not exhibit a linear increase in soil carbon indicators during three years of establishment, but some indicators do show a temporary increase compared to surrounding cropland. Prairie strips increased soil active C relative to adjacent cropland in 2 of the 3 years we measured. Prairie strips did not increase soil active C in surrounding cropland soils, nor did they increase C stocks in organic matter fractions after 3 years. Early increases in prairie strip soil active C suggest that prairie strips will show more pronounced increases in soil C stocks relative to cropland in coming years. Finally, in Chapter 4, I examined prairie strips’ effect on insecticide movement across the landscape and insecticide degradation by soil microbial communities. I measured the neonicotinoid clothianidin in soil, plant tissue, and groundwater. Prairie strips at this site accumulated neonicotinoids in plant tissue, but at concentrations below levels toxic to pollinator insects. This study also showed that prairie strips planted in cropland managed with neonicotinoid-treated seeds do not reduce neonicotinoid runoff into downslope soils. Lastly, I report findings from an experiment that tests degradation of neonicotinoid insecticides by soil microbial communities in prairie strips and surrounding cropland. Altogether, this dissertation shows that prairie strip effects on surrounding cropland is minimal, but beneath the strips, prairie strips quickly restore soil biota and soil C cycling functions of the tallgrass prairie.
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