Role of calcium and nitrogen in stabilization of soilcarbon in forest soils

Brewer, E.A., E.A. Paul, and S.J. Morris

Presented at the All Scientist Meeting (2003-09-12 )

Carbon © sequestration in soils is important for soil fertility and may play a role in short-term mitigation of elevated CO₂.  Unfortunately, the mechanisms for C stabilization are poorly understood.  Previous studies have determined that nitrogen (N) and soil cations, especially calcium (Ca), are essential to C storage.  Our research evaluates the importance of N and Ca in stabilization of soil C.  Laboratory incubations were established using soil from an afforested red pine plantation with relatively low C content. We chose this specific site because earlier field studies have suggested that soils under pine stands with higher Ca content have greater C sequestration. Incubated soils were amended with Ca, added at a rate consistent with adjacent high C soils and N at twice and six times atmospheric deposition rates for this area.  The N and Ca amendments were added separately and together with and without incorporation of litter. The addition of Ca in the form of lime increased the amount of CO₂ lost in the first 95 days of incubation when compared to control soils.  The addition of N at either 2x or 6x decreased CO₂ evolution over the first 30 days of incubation compared to the control.  Incorporation of litter increased CO₂ evolution in all treatments, but lime additions consistently resulted in the greatest CO₂ evolution.  Total CO₂ evolution during the first 116 days from the lime treatments included less CO₂ evolution, compared to control treatments, than can be accounted for by the addition of lime.  As the rates of evolution for these treatments do not currently differ, total C losses from the lime treatments suggest stabilization of soil C by Ca addition.  Increasing the incubation time will allow for better understanding of overall impacts of Ca on C.  Maximizing C sequestration by increasing stabilization may be achieved by Ca addition, but requires greater understanding of the mechanisms controlling C storage in soils.