Assessing the Trade-Offs of 20 Years of Management on Sequestration, Stabilization, and Stratification of Soil Organic Matter.

Amidst concerns over rising atmospheric levels of CO₂, there is a strong impetus to better characterize the global carbon cycle, as well as identify management opportunities capable of mitigating greenhouse gas emissions.  Agricultural soils are often depleted in organic matter (SOM) relative to pre-cultivation levels.  Thus, soil carbon sequestration (SCS) on agricultural lands has been widely touted as a promising way to offset greenhouse gas emissions, while providing the additional benefit of overall improved soil fertility, increased water holding capacity, and reduced erosion.  However, there is still great uncertainty as to contemporary saturation potentials, as well as the tradeoffs of various management practices, especially amidst climate uncertainty and increasing demands for agricultural intensification.  

The Russell Ranch Long Term Research Experimental Site provides a rare opportunity to assess the trade-offs of various crop rotations, nutrient management systems, and irrigation strategies on long-term carbon sequestration. Traditionally, soil carbon research has been limited to the surface soil, providing an incomplete picture of SOM dynamics, focused on a zone highly susceptible to tillage and neglecting mechanisms that contribute to movement of SOM down the soil profile, such as preferential flowpaths, sloughing of roots, root respiration and exudation, bioperturbation, reprecipitation of carbonates, and through the cracks of shrink-swell soils, and the interactions thereof. 

Carbon dynamics operate on various timescales, are spatially heterogeneous, and are best characterized by, not only change in overall quantity, but in tandem with metrics of physical and chemical stability.  As such, my research characterizes not only the change in the amount of SOM at various depths and across various management practices over 20 years, but also relevant attributes of the physical environment (i.e. texture and mineralogy) and chemical structure that can better inform global models regarding the stability of soil carbon and its response to disturbance.