Soil C Mass and Energy Budgets for Managed Forest Soils in California.

Managed forests in California will play a considerable role in a robust C economy where wood, fiber, bioenergy, CO2 storage and tradable C credits are valuable commodities. Currently soil C stocks are not certified or traded under any condition (post harvest secession (control) or management (fertilizer, herbicide and herbicide+fertilizer –HxF). Accurate quantification of soil organic matter (SOM) and its stability related to various managed forest conditions are vital to both basic science and in support of C credit certification. Standardized measurement protocols and basic relationships between site productivity, treatment (inputs) and soil C are needed to support estimation and projection of C stocks across the landscape. To address this we conducted research employing soils from long term silvicultural experiments for traditional mass balance soil C estimates and analysis with Differential Scanning Calorimetry (DSC) to elucidate energetic budgets and stability relationships.
We found that fertilizer alone (3.6 kg/m2) and HxF (3.3) were significantly different from control (2.6) and herbicide alone (2.5) for soil C at 0-10 cm. Fertilized soil had increased soil C to 30 cm. Energy yield was significantly greater for fertilizer alone (2076 j/kg-soil) than all other conditions and showed greater energy release at lower temperatures (~330C). Herbicide alone had the lowest C and energy yield at all depths. We feel the measurement of both C mass and associated energy (amount and stability distribution) provide rich information about the stability and status of SOM that illustrate differences in inputs governed by forest type and treatment. We hesitate to claim this characterizes ‘soil quality’ but feel it provides an approach and metrics that will enable comparison across forest soils and lead to a better understanding of relationships between soil quality and SOM and greatly assist the quantification soil C across the landscape.