S06 - Session O5 - Horticultural Additives influence soil biogeochemistry and increase Greenhouse gas emissions from peat.

Authors: Bidhya Sharma *, Nigel Roulet, Tim Moore

Peat is used as the chief ingredient of growing media in horticulture. The high cation exchange capacity, water retention capacity, low bulk density, and appropriate physical properties make peat-based growing media desirable for horticulture. Peat in its natural form is acidic and low in nutrient composition. Therefore, for suitability as a growing media, peat is mixed with liming agents, nutrients, surfactants, perlite among several other possible additives. We assessed the change in soil biogeochemistry and Greenhouse Gas (GHG) fluxes because of horticultural additives. We obtained samples of raw peat and additive mixed growing media (n=52) from four different peat extraction companies in Canada. Our analysis shows that the key soil biogeochemical parameters C:N ratio, pH, dissolved organic carbon, bulk density (C) content differs significantly (p < 0.01) between raw peat and growing media. There is a more than a two-fold increase in CO 2 from growing media as compared to raw peat. Further experiment showed the contribution of the longer-term contribution of carbonates borne CO 2 to the total flux. IPCC (2007) calculates that all C from harvested peat is lost in the atmosphere in the first year. However, our initial results estimate less than 10% of C loss in the first year from growing media. Although the influence of horticultural additives in C loss from peat is significant, the current accounting from IPCC is clearly an overestimation.