The effects of calcium and nitrogen amendments on soil organic matter dynamics in pine forest stands at Sand Ridge State Forest

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 (SOM) in nutrient poor pine soils. Literature supports that calcium increases soil C content and retention while the benefits of N additions on SOM retention are divided. Increases in SOM resulting from additions of calcium and N to non-agricultural soils would have potential to increase C sequestration in degraded systems. Our study focused on low nutrient pine stands in the Sand Ridge State Forest in central Illinois. Plantations were established at this site on native sand prairie in 1950’s. Soil organic matter in these stands is generally low. Plots were established in 2007 and amended with CaCl₂ and NH₄NO_3.  Amendments were made separately and together on the surface of the soil and incorporated into the soil to 20 cm. For the latter treatment litter was incorporated into soils with amendment mimicking tillage. Carbon mineralization incubations were initiated 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 even 500 days after treatment. Soils amended with calcium alone and in conjunction with N had low rates of C evolution compared to unamended soils. The addition of pine litter to soils increased C release, regardless of soil amendation. Results suggest that Ca additions in forest soils decrease C loss through mineralization. Whether this results in long-term stabilization of soil organic matter or affects 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. Ultimately, long-term C stabilization on nutrient poor soils would increase C stocks and improve site fertility providing outcomes of interest to natural resource managers and policy-makers.