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UBC Theses and Dissertations

Understanding the impact of irrigated agricultural systems on soil organic carbon storage Emde, David


Over the last 200 years, conversion of noncultivated land for agriculture has substantially reduced global soil organic carbon (SOC) stocks in upper soil layers. While many agricultural management practices have been well-studied, the specific effects on SOC of cropping systems that incorporate irrigation are poorly understood. Given the large, and expanding, agricultural landbase under irrigation across the globe, this is a critical knowledge gap for climate change mitigation. I undertook a systematic literature review and subsequent meta-analysis of data from studies that examined changes in SOC through time on irrigated agricultural sites across the globe. I followed this work with a regional assessment of mineral-associated organic carbon (MAOC) deficits in irrigated perennial cropping systems of the Okanagan Valley, British Columbia. In the meta-analysis study, I investigated changes in SOC with the following objectives: i) to examine the impact of irrigated agriculture on SOC storage, ii) and to identify the conditions under which irrigated agriculture is most likely to enhance SOC. In the regional assessment of MAOC deficits, I compared specific surface area (SSA) and fine fraction soil texture in combination with random forest and stepwise multiple regression with Akaike Information Criterion modelling in order to iii) determine the best model approach for estimation of MAOC, iv) determine if there is a MAOC deficit present in Okanagan soils, and v) identify the Okanagan soil types with the greatest potential to store additional MAOC. Overall, the meta-analysis indicated that irrigated agriculture has increased SOC stocks by 5.9% globally; however, changes in SOC varied by climate and soil depth. Models using random forest with either SSA or fine fraction soil texture produced the most accurate estimates of current MAOC concentration. By employing a 90th quantile method, we further determined that woody cropping systems across the Okanagan Valley have the potential to store an additional 28.5 million kg of MAOC in the top 30 cm of the soil profile. This work sheds light on the nuances of SOC change across irrigated agricultural systems, outlines the viability of MAOC deficit modelling, and will help guide future research on the impacts of irrigated agriculture on SOC.

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