Effects on soil carbon storage from municipal biosolids application to agricultural fields.

This study investigated the influence of biosolid applications on soil carbon storage and evaluated nutrient management strategies affecting soil carbon dynamics. The research assessed alterations in soil pH, soil carbon stock, and soil nitrogen content within short-term and long-term biosolids-amended soils in Bible Hill, Nova Scotia, Canada, extending to a depth of 0-60 cm. The findings indicated an increase in soil pH with alkaline treatment biosolids (ATB) applications across both study sites, with a legacy effect on soil pH noted in the long-term biosolids-amended soil following a single ATB application over 13 years. Both sites demonstrated significant increases in soil total carbon (STC) and soil organic carbon (SOC) within the 0-30 cm soil depth after biosolid application, and soil inorganic carbon (SIC) accounted for approximately 5-10% of STC, specifically in the surface soil layer (0-15 cm). In the long-term study site, annual 14, 28 and 42 Mg ATB ha-1 treatments resulted in a substantial rise in soil carbon stock (59.5, 60.1 and 68.0 Mg C ha-1), marking a 25% increase compared to control soil. The SOC content in biosolids-amended soil showed a declining trend with increasing soil depth at both study sites. Notably, the carbon stock in the short-term site was observed in composted biosolids (COMP) > ATB > liquid mesophilic anaerobically digested biosolids (LMAD) from the 0-60 cm soil depth. Approximately 79-80% of the variation in SOC response at both sites was concentrated within the top 30 cm soil. Soil total nitrogen (STN) showed no significant differences at the short-term site, and STN in biosolids-amended soil decreased with increasing soil depth at the long-term site. Biosolids-induced C retention coefficients (BCR) for ATB remained consistent at both sites, ranging from -13% to 31.4% with a mean of 11.12%. BCR values for COMP ranged from 1.9% to 34.4% with a mean of 18.73%, while those for LMAD exhibited variability, spanning from -6.2% to 106.3% with a mean of 53.9%.

A comparison of Tier 1, 2, and 3 methods for quantifying nitrous oxide emissions from soils amended with biosolids.

Municipal biosolids are a nitrogen (N)-rich agricultural fertilizer which may emit nitrous oxide (N2O) after rainfall events. Due to sparse empirical data, there is a lack of biosolids-specific N2O emission factors to determine how land-applied biosolids contribute to the national greenhouse gas inventory. This study estimated N2O emissions from biosolids-amended land in Canada using Tier 1, Tier 2 (Canadian), and Tier 3 (Denitrification and Decomposition model [DNDC]) methodologies recommended by the Intergovernmental Panel on Climate Change (IPCC). Field data was from replicated plots at 8 site-years between 2017 and 2019 in the provinces of Quebec, Nova Scotia and Alberta, Canada, representing three distinct ecozones. Municipal biosolids were the major N source for the crop, applied as mesophilic anaerobically digested biosolids, composted biosolids, or alkaline-stabilized biosolids alone or combined with an equal amount of urea-N fertilizer to meet the crop N requirements. Fluxes of N2O were measured during the growing season with manual chambers and compared to N2O emissions estimated using the IPCC methods. In all site-years, the mean emission of N2O in the growing season was greater with digested biosolids than other biosolids sources or urea fertilizer alone. The emissions of N2O in the growing season were similar with composted or alkaline-stabilized biosolids, and no greater than the unfertilized control. The best estimates of N2O emissions, relative to measured values, were with the Tier 3 > adapted Tier 2 with biosolids-specific correction factors > standard Tier 2 = Tier 1 methods of the IPCC, according to the root mean square error statistic. The Tier 3 IPCC method was the best estimator of N2O emissions in the Canadian ecozones evaluated in this study. These results will be used to improve methods for estimating N2O emissions from agricultural soils amended with biosolids and to generate more accurate GHG inventories.