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soil

Formation and stabilization of organic matter

Formation and decomposition of organic matter have always been two sides of the same coin, but understanding of what links them has changed significantly. Previously, because decomposition is so well predicted by the recalcitrance of litter, it was thought that long-term, persistent organic matter should be unpalatable to microorganisms. New understanding is that all organic matter is decomposed at some point; organic matter stabilization happens when microbially processed compounds bind into aggregates or onto mineral surfaces. I am involved in several projects—from field observation1, 2 to lab experiments3, to modeling exercises—that aim to quantify the relative importance of different controls on decomposition and formation of organic matter. I am also working to generate robust regional and local targets of potentially achievable soil carbon levels.

Effect of soil organic matter on agriculture and environment

Building soil organic matter in agricultural systems can be beneficial because it provides nutrients to crops, retains moisture, decreases carbon in the atmosphere, and reduces erosion. Despite decades of general knowledge of the importance of soil organic matter, there is very little predictive and quantitative knowledge of how building soil organic matter contributes to agricultural and environmental goals. In other words, there is a need for quantitative predictions of how much of an increase in soil organic matter would be needed to achieve a specific agronomic or environmental target4. I lead an NCEAS-based working group that uses data synthesis to generate more predictive and quantitative understanding of the impacts of soil organic matter on agriculture and environment. In my empirical work, I use lab experiments and field observation to quantify the nature and magnitude of the impact of organic matter. I have demonstrated recently5 that different types of organic matter may have contrasting impacts—some positive, some negative—on agricultural outomes, challenging the notion that more organic matter is generally better for agriculture.

Impact of land use on biological communities and activity

Microbial processes are the biogeochemical engine propelling all ecosystems. Early thinking in microbial ecology assumed that microbial communities—and their functioning—would be nearly uniform around the world because microbes disperse so efficiently. Any differences in rates of ecosystem processes would therefore be attributable to different abiotic conditions governing thermodyanmic processes, not the microbial communities themselves. Recent work in meta-genomics has demonstrated strong differentiation among microbial communities in different environments. I am particularly interested in the consequences of human-driven environmental change on microbial communities and their functioning. Much of my work in this area has focused on agricultural systems in the tropics, where I have shown strong differences in soil bacterial communities based on farm management in Kenya6 and forest use history in Malaysia7. I have also suggested that real-world changes in microbial communities due to land management may not be great enough to significantly impact ecosystem processes8, even though strong lab-enduced experimental gradients in microbial communities have been shown to impact process rates.

Text mining and the evolution of soil concepts

The use of "health" as a metaphor for ecosystems has a long history that has been documented and critiqued by environmental philosophers. The advent of soil health discourse has been framed by some as an important conceptual advance that prioritizes the ecology of soil. Others argue that soil health is a simple re-branding of older notions, like soil quality, fertility, and tilth. As part of our SNAPP working group, I am applying quantiative text modeling strategies, drawn from sociology, to understand the history of the soil health concept. I am drawing data from academia, media, and social media to investigate what actors are shaping the discourse around soil health and how the use of the concept has evolved and relates to older notions of "good" soil.

Relatedly, there is growing interest in applying soil health practices and concepts to new systems, like rangelands and forests. I am collaborating with working group members on a conceptual history of the health of different types of ecosystems to think through whether the metaphor and measure of soil health, as it has been developed in row crop agriculture, should be applied to other systems. In other words, is soil health equal to ecosystem health?