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%. •Soil pH increased with alkaline treatment biosolids (ATB) applications.•Significant STC and SOC increased in top 30 cm soil depth after biosolid application.•Annual ATB treatments raised long-term soil carbon stock.•Short-term stored C followed order of composted > ATB > anaerobic digested biosolids.•Biosolids-induced C retention coefficients varied by different types of biosolids.