The effects of calcium and nitrogen amendments on soil organic matter carbon sequestration in Sand Ridge State Forest pine stands

Background/Question/Methods Concern over the increase in atmospheric CO₂ content has created interest in the mechanisms that increase and stabilize organic matter in soils.  The present study examined the impacts of calcium and nitrogen on soil organic matter in nutrient poor pine soils.  There is ample literature that calcium increases soil C content and retention. The impacts of N additions on soil organic matter retention are divided.  Some studies have found increased C turnover and some stabilization.  Calcium and N are relatively inexpensive and easily applied to soils.  Resultant increases in soil organic matter would have potential to increase C sequestration on the terrestrial surface in degraded systems.   Our study focused on low nutrient pine plantation stands in the Sand Ridge State Forest in central Illinois.  Pine plantations were established at this site on native sand prairie in 1950’s.  Soil organic matter in these stands is generally low.  Amendments consisting of CaCl₂ and NH₄NO₃ were made in the summer of 2007.  Amendments were made separately and together on the surface of the soil and incorporated into the soil to a depth of 20 cm.  For the former treatment litter was removed and replaced before amendment. For the latter treatment litter was incorporated into soils with amendment in a treatment that roughly mimicked tillage.  There were two blocks containing each of the above treatments established in two pine stands.  Carbon mineralization incubations were initiated in the laboratory to examine the initial effects of each of these treatments. 

Results/Conclusions

There were significant differences detected in the amount of C released from soils 200 days after treatment.  Calcium alone and with N had low rates of C evolution.  Calcium and Ca/N added with pine litter had higher C release than control but less than when litter was added without amendment or with N alone. Results suggest that Ca additions in forest soils decrease C loss through mineralization.  Whether this results in long term stabilization of soil organic matter; without affecting plant nutrient availability remains to be seen.  Forest plots will be evaluated for the next several years to determine the extent to which these trends continue and the impacts on above and belowground communities.