How much soil carbon gets stored long-term after land application of biosolids?

Title: How much soil carbon gets stored long-term after land application of biosolids?

By Mike Badzmierowski, PhD

(Dr. Mike Badzmierowski is a postdoctoral researcher in the School of Plant and Environmental Sciences at Virginia Tech. He received his PhD in 2019 from Virginia Tech, where he focused on the use of biosolids as a soil amendment and how different biosolids processing methods may affect greenhouse gas emissions and carbon sequestration potential. He is leading a team partially funded by the Virginia Biosolids Council to understand carbon sequestration of land-applied biosolids)

Biosolids are mostly organic materials resulting from the treatment of wastewater that has undergone additional treatment, mostly at municipal wastewater facilities. Biosolids are produced in significant quantities around the world and often applied to land, frequently on agricultural fields, forests, mine lands, and urban areas. Land application of biosolids can increase soil organic carbon, improve soil physical and chemical characteristics, and reduce fertilizer needs and water usage [1,2,3]. Many of the soils on which biosolids are applied are low in organic matter and thereby soil organic carbon. Applications of biosolids are generally expected to increase organic matter content for some time and may act as a carbon sink under certain land management scenarios.

Decades of biosolids soil research has indicated variation in soil organic carbon changes from biosolids land application. The variability of soil organic carbon stock changes is most likely a result of various factors such as climatic conditions, soil properties, land use management, biosolids characteristics, application strategies (i.e., rate, surface-applied or incorporation, one-time or repeated applications), and timing between last application and sample measurement. Determining the potential of soil organic carbon stock change from biosolids land application is a critical step for biosolids generators and users to potentially gain access to carbon credit markets. The best way to give a clear and comprehensive overview of results across many studies is a systematic review and meta-analysis.

A systematic review pools together all results of a particular topic to give one complete interpretation of research results. A meta-analysis is the statistical approach to combining data found during the systematic review process. Systematic reviews provide transparency for every decision that was made along the review process (and there are many!). All decisions are documented by generally two people and all data is made available upon finishing the review to reduce bias of the reviewers, produce reliable and accurate conclusions to stakeholders, and improve reproducibility of the work. Systematic reviews involve a detailed and comprehensive protocol developed a priori to reduce bias in study selection, appraisal of study quality, and synthesis of relevant studies. Critical appraisal of included studies is an important step in systematic reviews. This step allows researchers to determine the trustworthiness and value (or weaknesses) of a particular studies’ methods and results. For example, some studies may lack replication in their experiment or use soil measurement methods that may not be seen as the “gold standard.” It is important that the result of a systematic review provides the most accurate conclusions due to its potential implications in future policy.

I am leading a team of reviewers in conducting the most comprehensive, transparent, and open-access synthesis of soil carbon stock changes from land applied biosolids to date. Our systematic review will answer the question, “what is the impact of biosolids application on long-term soil carbon sequestration rates?” We look to explore this main question with the follow-up, “do biosolids processing methods and characteristics, application method, soil properties, land management and other modifiers affect rates of carbon accumulation from land-applied biosolids?”

Our protocol has been published as an open access article in the Environmental Evidence journal ( [4]. Our approach includes the use of online databases (i.e., Web of Science Core Collection, CAB Abstracts, Scopus, ProQuest Dissertations & Theses Global, Open Access Theses and Dissertations), search engines (Google Scholar and Microsoft Academic), and specialist websites to find published and non-published field studies and of biosolids land-application effects on soil organic carbon stocks. We used English search terms and predefined inclusion criteria of: (1) a field study of at least 24 months that reports soil organic carbon/matter stocks; (2) has two types of treatments: (i) a control (non-intervention AND/OR synthetic fertilizer) AND (ii) a biosolids-based amendment; and (3) information of amendment properties and application dates and rates to estimate the relative contribution of the applied materials to SOC changes.

At the time of this publication, we have screened over 16,000+ abstracts. Of these 16,000+ abstracts over 1,100 were deemed relevant enough to investigate at the full-text level. The team has recently met over video conference to confirm our critical appraisal criteria as we are beginning to extract data from included studies. At the completion of the systematic review, the goal is to create an open access “biosolids and soil measurements database” to improve future research and identify knowledge gaps in understanding carbon accumulation of biosolids-applied land.

This work is funded by the Virginia Biosolids Council and the Metropolitan Washington Council of Governments.

  1. Annabi M, Le Bissonnais Y, Le Villio-Poitrenaud M, Houot S. Improvement of soil aggregate stability by repeated applications of organic amendments to a cultivated silty loam soil. Agr Ecosyst Environ. 2011;144(1):382–9.
  2. Hargreaves JC, Adl MS, Warman PR. A review of the use of composted municipal solid waste in agriculture. Agr Ecosyst Environ. 2008;123(1):1–14.
  3. Khaleel R, Reddy K, Overcash M. Changes in soil physical properties due to organic waste applications: a review 1. J Environ Qual. 1981;10(2):133–41.
  4. Badzmierowski MJ, Evanylo GK, Daniels WL, Haering KC.What is the impact of human wastewater biosolids (sewage sludge) application on long-term soil carbon sequestration rates? A systematic review protocol. Environ Evid. 2021;10,