This project is funded by the Forest Biology Research Cooperative and the Forest Soils Laboratory. It is the PhD research of Deoyani Sarkhot. The chair of her committee is Dr. N. Comerford with Dr. E. Jokela as the co-chair.

Pine plantations of the southeastern US are regional carbon sinks. In spite of huge increases in woody biomass, studies have shown little to even a negative effect of soil management on the carbon content of extremely sandy soils in North Florida. It is unclear how these soils can sequester and protect soil C, particularly given the common conception of them having weak soil structure and aggregation. This study was conducted to examine the carbon profile of sandy soils and evaluate the effect two different management intensities (and a range of genotypes) have on soil carbon pools.

Deoyani will be defending her dissertation in November, 2006. The field and laboratory work is complete and her research is being prepared for publication.

Our conclusions to date are:

Dry sieving of these sandy soils is a useful method for size fractionation of very sandy soils. The size fractions were significantly different in all the properties studied, though there was no continuous change with decreasing particle size. The mechanisms regulating this carbon distribution need to be determined.

The preliminary data showed that aggregate-protected SOC accounted for 30 to 50 % of the carbon in these sandy soils, indicating the importance of physical protection. Hence it is essential to understand the mechanisms of aggregation as well as the effects of intensive management on aggregate-protected carbon in order to ensure sustainable land management.

The carbon pools used in this study are indicative of important soil processes. For example, the light fraction, which consists mostly of broken bits of roots and litter, is directly related to the input of carbon to the system. The aggregate-protected carbon and the energy level required for complete dispersion are indicators of aggregate stability and hence the potential of carbon sequestration through physical protection. These methods, therefore, can help not only in understanding the impacts of forest management on SOC, but also the soil processes involved.
Intensive management reduced soil C in both macro and micro-aggregate fractions in just 4 years. It was probably due to the reduction in fine root turnover, especially the understory roots. Although this might be compensated by the higher above ground storage, further study is necessary to determine the potential long-term effects on carbon sequestration capacity of the soil.

The following figures illustrate some of these points:

This graph shows that dry and wet sieving of these very sandy soils give very comparable results.

This graph illustrates the % of OM that can be found in the light, medium and heavy density fractions of each particle size class. Note that light fraction diminishes in importance with decreasing size.