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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. 

Climate change will increase soil drying, altering microbial communities via increasing water stress and decreasing resource availability. The responses of these microbial communities to changing environments is likely governed by physiological tradeoffs between high yield, resource acquisition, and stress tolerance (Y-A-S framework). We leveraged a unique field experiment that manipulates both drought and carbon availability across two years and three land uses, and we used both metagenomic and bioassay indicators of the three microbial community traits to test the following hypotheses: 1. Drought increases microbial allocation to stress tolerance functions, at the expense of growth and resource acquisition. 2. Because microbes are resource-limited under drought, increased carbon will enable greater expression of stress tolerance. 3. All three key life history traits described in the YAS framework will trade off, especially when resources are limited. Drought did increase microbial physiological investment in stress tolerance (measured via trehalose production), but we saw few other changes in microbial communities under drought. Carbon addition increased resource acquisition (measured via enzyme activity and resource acquisition gene abundance) and stress tolerance (trehalose assay), but did so in both drought and average rainfall environments. We found no evidence of trait tradeoffs, as we found no significant negative correlations between traits (measured via bioassay and metagenomics). In summary, we found C addition, and to a lesser extent, drought, both altered microbial community function and functional genes. However, resources did not alter drought response in a way that was consistent with theory of life history tradeoffs. 

Abstract Long-term climate history can influence rates of soil carbon cycling but the microbial traits underlying these legacy effects are not well understood. Legacies may result if historical climate differences alter the traits of soil microbial communities, particularly those associated with carbon cycling and stress tolerance. However, it is also possible that contemporary conditions can overcome the influence of historical climate, particularly under extreme conditions. Using shotgun metagenomics, we assessed the composition of soil microbial functional genes across a mean annual precipitation gradient that previously showed evidence of strong climate legacies in soil carbon flux and extracellular enzyme activity. Sampling coincided with recovery from a regional, multi-year severe drought, allowing us to document how the strength of climate legacies varied with contemporary conditions. We found increased investment in genes associated with resource cycling with historically higher precipitation across the gradient, particularly in traits related to resource transport and complex carbon degradation. This legacy effect was strongest in seasons with the lowest soil moisture, suggesting that contemporary conditions—particularly, resource stress under water limitation—influences the strength of legacy effects. In contrast, investment in stress tolerance did not vary with historical precipitation, likely due to frequent periodic drought throughout the gradient. Differences in the relative abundance of functional genes explained over half of variation in microbial functional capacity—potential enzyme activity—more so than historical precipitation or current moisture conditions. Together, these results suggest that long-term climate can alter the functional potential of soil microbial communities, leading to legacies in carbon cycling.