Soil carbon is known to be highly spatially variable, especially across the landscape with diverse topography and soil parent materials. Moreover, performances of different conservational management practices, such as no-till or cover-crop-based management in terms of their effects on soil carbon also substantially vary across landscapes, making up-scaling based on small-scale experimental data difficult. We are studying the factors affecting soil carbon variability and the interactions between such factors and land use and management practices in their effects on soil carbon processes.
Chemically-intensive management of row crop production systems have raised serious concerns about their sustainability and ability to provide key ecosystem services. Using cover crops in the rotation can reduce fertilizer needs and increase carbon sequestration. The questions we are addressing are: how consistent can be performance and carbon sequestering role of cover crops across landscapes with diverse topography? What are the mechanisms by which they contribute to soil carbon processes? What can we expect in terms of cover crop usefulness in future variable climate?
Soil structure defines sizes and characteristics of soil pores, thus creating physical micro-environments for microbial activities and playing a major role as both an arena and a product of soil organic matter stabilization and dynamics. Microorganisms are vital actors of soil systems. Their ability to move and grow in a structurally and chemically heterogeneous soil environment governs belowground processes of biomass transformation into soil organic matter and defines its further fate, e.g., stabilization within soil matrix or loss to the atmosphere as emitted CO2. Our goal is to produce experimental evidence, numeric quantification, and modeling of the effects of soil pores on decomposition of plant residues, decomposition of native soil organic matter and involvement of microorganisms in these processes.
Soil aggregates play an important role in a number of soil processes, e.g., water flow and solute transport, carbon sequestration, and microbial activity. Quantitative characterization of the management effects on intra-aggregate porosities will enhance our ability to understand functioning of soil macro-aggregates and the mechanisms of their contributions to various soil processes, including carbon sequestration. Computed micro-tomography can address internal physical structure of soil aggregates at micron resolutions. We explore how differences in the intensity of soil disturbance, frequencies of wetting/drying patterns, amounts of organic matter, microbial and faunal activities may substantially alter the intra-aggregate pore characteristics, including porosity, pore sized distributions, and heterogeneity in pore distribution patterns.
Aggregates play an important role in carbon processes and carbon sequestration. Carbon is believed to be protected within them by a variety of mechanisms. We are addressing the details in the mechanisms of such protection by finding where the organic matter is located within the aggregates and how its locations are related to aggregate pores and fluxes through them. Combination of computed tomography and traditional carbon measurements enable answering these questions.
Lack of understanding of the mechanisms controlling microbial activity at aggregate-size scales in soils under most typical to rural watershed land uses and agricultural practices reduces modeling capabilities and accuracy in predicting fate and survival of microorganisms, including fate of pathogenic microorganisms. We look at how differences in soil tillage practices and land uses influence intra-aggregate pore structures of soil aggregates, affecting E. coli fate and transport.
Funding for this research has been provided in part by the NSF LTER Program at KBS, Michigan Agricultural Experiment Station, and USDA-CSREES National Research Initiative: Water and Watersheds Program.