Change in soil organic carbon storage as influenced by forestland and grassland conversion to cropland in Canada

Abstract

Conversion of native grassland and forest to agricultural land results in significant losses of soil 20 organic carbon (SOC). However, the quantity of SOC loss upon conversion of native grassland and forest varies with climate, soil texture and agricultural management practices. In this study, we quantified the change of SOC stock as influenced by native grassland and forest conversion to agricultural soils in Canada through a meta-analysis. We determined both the absolute and relative change of SOC from its native state upon the conversion to agriculture. In more humid and temperate region of Eastern Canada losses of SOC upon the conversion of forest to agricultural land varied with soil textures, on an absolute basis, 18 t C ha^-1 for the coarse-textured soil, 43 t C ha^-1 for the medium-textured soil, and 65 t C ha^-1 for the fine-textured soil from its native vegetation; corresponding, on a relative basis, to 22%, 30% and 32%, respectively. On the Canadian prairies, forestland conversion to cropland resulted in losses of 27 t C ha^-1 or 25% for the medium-textured soil whereas there was no change in SOC for the coarse-textured soil. On the Canadian prairies, the conversion of native grassland to agriculture resulted in losses of SOC, on average from 15, 26, and 5 t C ha^-1 in coarse-, medium- and fine-textured soils, respectively. However, because of high inherent variation in SOC stocks among the various soil textures, losses of SOC upon grassland conversion, on a relative basis, were highly variable (14 - 26%), and no statistically significant differences were observed among soil texture classes. The results of this work clearly show that climate and soil texture are main drivers of SOC change after the conversion of native grassland and forest to agriculture and are key factors that must be considered in the development of either national or regional SOC models. The results of this study suggest that more detailed stratification of samples across soil textures and climates improve the accuracy of estimates of SOC loss associated with native grassland and forest conversion to agriculture.