Brewer, Elizabeth (Bradley University, 1501 W. Bradley Ave., Biology Department, Peoria, IL, 61625; Phone: 309-677-3809; Fax: 309-677-3558; Email: email@example.com)
E.A. Brewer*, S.J. Morris, E.A. Paul, G.P. Robertson
A variety of land-use change strategies targeted towards increasing carbon (C) storage in terrestrial systems have focused on converting some agricultural fields to forest. Research to date suggests some strategies are more successful than others at improving belowground C stocks. Our research evaluates the potential use of calcium (Ca) and nitrogen (N) for improving soil C stabilization when agricultural lands are returned to forest. Past work suggests that sandy or acidic soils of the eastern U.S. do not sequester C under pine unless adequate Ca is present. To evaluate the degree to which Ca and/or N additions can increase C sequestration, field plots were established in an afforested red pine stand with low soil C content. Treatments included control (no amendment), addition of CaCl2, addition of NH4NO3, and additions of CaCl2 and NH4NO3. Lime was not used in this study so that contributions of lime-CO2 to atmospheric pools would not be a confounding factor in evaluating C sequestration. Each treatment was also incorporated with litter, to a depth of 20 cm. Biological fractionation incubations were established on soils collected one year after amendment, to evaluate changes in C and N pools. Incubations were also established using soil retrieved from our field site but amended in the laboratory. Amendments included all treatments used in the field but also examined Ca added as lime (CaCO3) amendments to evaluate the differential impacts of Ca source. Overall, our results suggest that impacts of Ca addition on C accrual are dependent of the form of Ca added and method of application, surface versus incorporation. Analysis for main effects and interactions suggest increases in total and resistant C pool sizes with addition of CaCl2 and litter incorporation but there were no differences in mean residence times (MRT). Field respiration measurements showed decreased respiration from CaCl2 amended plots suggesting sequestration. Impacts of N were dependent on whether N was added alone, or in the presence of Ca. Plots with N additions alone showed an increase in total C, compared to plots where N was added with Ca. Field respiration also showed the interaction with increased respiration when N was added with Ca. Nitrogen additions had little impact on N cycling parameters measured either initially or 1 year after amendment, however, CaCl2 decreased N mineralization rates further supporting sequestration. The study supports the hypothesis that Ca and N amendments will increase soil C sequestration. These treatments could easily be incorporated into management schemes and result in increases in soil C in managed systems. Longer-term measurements on these sites are necessary to extrapolate the data collected here to a viable management strategy.