"There are three general methods for applying biosolids to forests: 1) spray irrigation with either a set system or a traveling gun, 2) spray application by an

"There are three general methods for applying biosolids to forests: 1) spray irrigation with either a set system or a traveling gun, 2) spray application by an application vehicle with a spray cannon, and 3) application by a throw-spreader or manure-type spreader. In the Pacific Northwest, the most common methods for forest applications are the throw-spreader or a vehicle-mounted cannon. Table 7.7 lists these application methods, their range, relative costs, advantages and disadvantages, and their suitability for biosolids of different solids contents." https://fortress.wa.gov/ecy/publications/documents/9380.pdf https://fortress.wa.gov/ecy/publications/documents/9380.pdf It was the top item of the first google search for "biosolids washington forest". Here's pictures if you're interested. https://www2.gov.bc.ca/assets/gov/environment/natural-resource-stewardship/land-based-investment/forests-for-tomorrow/forest_fert_presentation_feb2011_final.pdf https://www2.gov.bc.ca/assets/gov/environment/natural-resour... Here's another article from 20 years ago about the practice: http://thewatchers.us/wef/PacNW.pdf http://thewatchers.us/wef/PacNW.pdf