Biosolid Application Enhances Carbon Stocks in Soil.

Biosolids produced from sewage treatment facilities are increasingly applied to agricultural, and degraded mined lands for improving soil health, and increasing soil organic carbon (SOC) stocks. Although many case studies have been reported on increased SOC as influenced by land application of biosolids, there remains a lack of comprehensive quantification assessment on the overall trend and magnitude of changes in SOC, and its sequestration. A Meta-Analysis (MA) was applied to quantitatively compare results derived from 298 paired-treatments of data across 25 countries. The MA compared SOC changes over two main categories: soil carbon storage and rate of carbon sequestration. Data were meta-analysed using the Comprehensive Meta-Analysis Professional Version 3 and “R” programs. The MA revealed that biosolids addition increased average net soil carbon stock and sequestration rate in soils (2.25±0.32 Mg SOC ha-1) compared with non-biosolids conditions (1.16±0.18 Mg SOC ha-1). Meta-regression revealed that the biosolids-associated factors including application rate, time after application, and application frequency as clear drivers for soil carbon sequestration and also identified their optimal conditions to maximise soil carbon stocks. For example, multiple applications of biosolids are required to promote carbon storage in soils for long term. Overall, this study shows land application of biosolids can be used to increase soil carbon stock, and therefore has the potential to be a direct strategy for soil carbon sequestration. Key Words: Soil Organic Carbon Sequestration, Biosolids, Meta-Analysis, Carbon Sequestration