Interactions of Vegetation and Soil Chemistry as Controls On Soil C Sequestration.

Soil carbon sequestration is the result of the interactions of soil chemical and biological factors.  Understanding the consequences of management on SOC pools can aid in our understanding of the controls on C sequestration.  Our studies have focused on a range of managed afforested sites.  While most of our study sites are on former agricultural lands, some are on former sand prairies.  We have found C retention in sandy soils vs. above ground litter pools is determined by the interaction of vegetation and soil chemical components.  There is a link between calcium and C retention in a number of sites that appears dependent upon the species planted and movement of Ca through the profile.  Of recent concern is C retention in managed forests, which leads to the question could calcium be used as an amendment to increase SOC. To evaluate Ca additions as a management tool, we established plots in C poor pine forest sites in Michigan and Illinois.  Rather than add a stable, mined form of calcium to soils we added CaCl₂ alone and in concert with N and with incorporation of litter pools.  Our results suggested increases in total and resistant C pool sizes with addition of CaCl₂ and litter incorporation, but without changes to the mean residence times of SOC. Data from field respiration measurements supported laboratory data showing decreased respiration from CaCl₂ amended plots suggesting sequestration.  These results suggest that soil C sequestration is currently being managed intentionally or unintentionally through the choices made at time of planting. Careful manipulation of the controls on C sequestration within managed sites could increase SOC so as to provide gains in terrestrial C storage, more important however, would be the improvements to soil fertility and site productivity that are associated with soils with large SOC pools.