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The potential for healthy soils to address goals of productivity and sustainability has motivated a global soil health movement. Though this movement involves many groups, farmers’ perceptions are particularly important because they influence whether and how soil health concepts are practiced on farms. We used surveys of Michigan row crop farmers, followed by cognitive mapping exercises and interviews with a smaller subset of farmers, to describe how farmers understand, manage, and evaluate soil health. We report three key findings. First, we found that Michigan farmers believe in the benefits of soil health, but they are less certain of how to manage soil health on-farm. In particular, farmers found it challenging to evaluate how practices alter soil properties they know are important for soil health, including organic matter, compaction, and soil biology. Second, we found that most Michigan farmers are taking steps to improve the health of soils they farm, which was reflected in their current practices. Use of no-till and cover crops was especially prominent, and decisions to utilize them were motivated by yield benefits and water management. Third, we show that farmers primarily assess soil health with traditional agronomic soil tests and qualitative indicators (e.g., yield, crop coloration, and soil texture), which have strong ties to soil type. Overall, our findings emphasize that while Michigan farmers agree on the key properties and outcomes of healthy soils, they are less certain of how their management translates into improved soil health on-farm. Developing faster-responding, outcome-focused indicators as well as local benchmarks guided by soil type may motivate future adoption and retention of soil health practices. 

In nitrogen (N)-limited terrestrial ecosystems, plants employ various strategies to acquire and conserve N, including translocation of N in perennial tissues and stimulation of N fixation in roots and soils. Switchgrass (Panicum virgatum) is a genotypically and phenotypically diverse perennial grass with two distinct ecotypes (lowland and upland) and numerous genotypes. It grows well in low-N soils, likely because of its ability to translocate N and to associate with N-fixing microbes, but little is known about variation in these traits among cultivars or even ecotypes. We measured N translocation, N fixation potential in roots and soils, soil net N mineralization, soil net nitrification, and biomass yields in 12 switchgrass cultivars grown in a replicated block experiment in southwestern Michigan, United States. Lowland cultivars had higher yields, rates of N translocation, soil net N mineralization, and N fixation potentials on washed, nonsterile roots, while upland cultivars exhibited higher N fixation potentials in root-free soil. N resorption efficiencies averaged 53 ± 5% (± standard error) for lowland versus 29 ± 3% for upland cultivars. Additionally, there were significant among-cultivar differences for all response variables except mineralization and nitrification, with differences likely explained by cultivar-specific physiologies and microbial communities. The ideal cultivar for biofuels is one that can maintain high yields with minimal fertilizer addition, and there appear to be several cultivars that meet these criteria. In addition, results suggest substantial N cycle differences among cultivars that might be exploited by breeders to create new or improved high-yielding, N-conserving switchgrass lines. 

Microbial communities help plants access nutrients and tolerate stress. Some microbiomes are specific to plant genotypes and, therefore, may contribute to intraspecific differences in plant growth and be a promising target for plant breeding. Switchgrass (Panicum virgatum) is a potential bioenergy crop with broad variation in yields and environmental responses; recent studies suggest that associations with distinct microbiomes may contribute to variation in cultivar yields. We used a common garden experiment to investigate variation in 12 mature switchgrass cultivar soil microbiomes and, furthermore, to examine how root traits and soil conditions influence microbiome structure. We found that average root diameter varied up to 33% among cultivars and that the cultivars also associated with distinct soil microbiomes. Cultivar had a larger effect on the soil bacterial than fungal community but both were strongly influenced by soil properties. Root traits had a weaker effect on microbiome structure but root length contributed to variation in the fungal community. Unlike the soil communities, the root bacterial communities did not group by cultivar, based on a subset of samples. Microbial biomass carbon and nitrogen and the abundance of several dominant bacterial phyla varied between ecotypes but overall the differences in soil microbiomes were greater among cultivars than between ecotypes. Our findings show that there is not one soil microbiome that applies to all switchgrass cultivars, or even to each ecotype. These subtle but significant differences in root traits, microbial biomass, and the abundance of certain soil bacteria could explain differences in cultivar yields and environmental responses.