Madeline Luthard

Current Projects:

Microbial carbon cycling in agricultural soils

Soil texture is an influential ecosystem property that mediates the physical, chemical, and biological soil environment. In this project, we evaluate soil texture as a potentially important driver of variation in microbial carbon cycling. Microbial activity dictates the formation and persistence of soil organic matter, which represents a pool of nutrients that can contribute to soil fertility and that can be stored over long timescales. To investigate carbon cycling in diverse soil texture environments, we measured microbial substrate use efficiency in a laboratory microcosm experiment with soils from natural and constructed texture gradients. After adding a nutrient source enriched in carbon-13 to the soil microcosms, we used isotope tracing methods to track the fate of carbon-13 into microbial biomass, soil organic matter, and respired carbon dioxide over a three-month laboratory incubation. Results from this project feed into the development of a web-based nitrogen decision support tool, led by Dr. Charlie White, that can be used by Pennsylvania farmers to predict nutrient supply to crops from soil organic matter and decomposing cover crop tissues. By understanding soil textural controls on microbial growth and nutrient use, farmers and land managers can improve their site-specific nutrient management and soil health objectives.

Cover crops for nitrogen management

Cover crops are just one of many Best Management Practices that can be implemented to benefit farmers and the environment. Different cover crop species provide different benefits, and practitioners often select cover crop species based on their ability to either supply nitrogen to soil or prevent nitrogen losses. At our lab’s long-term cover cropping research trial, we look at trends in soil nitrogen patterns under different cover crop treatments: six single-species treatments, five multi-species mixture treatments, and one no cover crop control. Now, we are analyzing over a decade of data to quantify potential reductions in leaching from soils managed with cover crops. To evaluate leaching patterns under each cover crop treatment and across a natural gradient of soil texture, we measure inorganic nitrogen in surface soil samples (20 cm), anion exchange resins that trap nitrate leached below the active plant rooting zone (25 cm), water from lysimeters buried underground (35 cm), and deep soil cores (up to 80 cm). Drawing together the insights from these distinct pools of data allows us to understand how cover crop species traits and functional diversity contribute to desirable ecosystem services that can be leveraged by farmers. Prior research at this site found that all cover crop treatments reduced nitrogen losses compared to the no cover crop control and suggested that species mixtures can be designed to balance nitrogen supply with the prevention of nitrogen losses (Kaye et al., 2019). Overall, this research tests fundamental ecological theory related to biodiversity and ecosystem functioning while also providing actionable management recommendations to farmers.