Table 1 Search specifications and string for each database or search engine

Bibliographic databases

 CAB Abstracts from CAB Direct

All fields (does not have a “Topic” field)

(soil) AND (carbon OR “soil OC” OR SOC OR “soil organic C” OR “soil organic carbon” OR “organic matter” OR “soil OM” OR SOM OR “soil organic matter”) AND (biosolid* OR sewage OR sludge OR “sewage sludge” OR biosludge OR milorganite OR “human solid waste” OR “waste amend*”)

All years (1915–present)

 ProQuest Dissertations & Theses Global

Abstract

ab(soil) AND ab(carbon OR "soil OC" OR SOC OR "soil organic C" OR "soil organic carbon" OR "organic matter" OR "soil OM" OR SOM OR "soil organic matter") AND ab(biosolid* OR sewage OR sludge OR "sewage sludge" OR biosludge OR milorganite OR "human solid waste" OR "waste amend*")

1637–present, full-text dissertations 1997–present

 Scopus

Article title, Abstract, and Keywords

( TITLE-ABS-KEY ( soil) AND TITLE-ABS-KEY ( carbon OR "soil OC" OR SOC OR "soil organic C" OR "soil organic carbon" OR "organic matter" OR "soil OM" OR SOM OR "soil organic matter") AND TITLE-ABS-KEY ( biosolid* OR sewage OR sludge OR "sewage sludge" OR biosludge OR milorganite OR "human solid waste" OR "waste amend*"))

All years (1800s–present)

Web of Science from Clarivate Analytics, Core Collection

Topic (titles, authors, abstracts, keywords)

TOPIC: (soil) AND TOPIC: (carbon OR "soil OC" OR SOC OR "soil organic C" OR "soil organic carbon" OR "organic matter" OR "soil OM" OR SOM OR "soil organic matter") AND TOPIC: (biosolid* OR sewage OR sludge OR "sewage sludge" OR biosludge OR milorganite OR "human solid waste" OR "waste amend*")

All years (1900–present)

Search Engines

 Google Scholar search query in Harzing’s Publish or Perish

256-character limit (No field category)

soil (carbon|"soil OC"|SOC|"soil organic C"|"soil organic carbon"|"organic matter"|"soil OM"|SOM|"soil organic matter")(biosolids|sewage|sludge|"sewage sludge"|biosludge|milorganite|"human solid waste"|"waste amendment")

First 1000 results sorted by relevance according to Google Scholar’s algorithm

 Microsoft Academic search query in Harzing’s Publish or Perish

Keywords

soil AND (carbon OR "soil OC" OR SOC OR "soil organic C" OR "soil organic carbon" OR "organic matter" OR "soil OM" OR SOM OR "soil organic matter") AND (biosolids OR sewage OR sludge OR "sewage sludge" OR biosludge OR milorganite OR "human solid waste" OR "waste amendment")

First 1000 results sorted by relevance according to Microsoft Academic’s algorithm