The smoke in the center right is from burning excrement. The foul smoke spoiled our air on calm days. I was assigned this detail often and I think of it and sandbag filling as my contribution to the war.
In a base camp, Vietnamese were hired for this work and paid $5 per day. Vietnamese were not allowed in our firebase so the duty fell to someone in disfavor with our leaders. The anti-malaria pills we took each day caused diarrhea so we were not burning many solids. Read the full story. https://vietnamsoldier.com/burning-shit-a-how-to-dispose-of-waste-instructional/