The inventive developments disclosed in this application include the following features and combinations thereof: extracting oil from spent bleaching earths for animal feed; using earths and acid water as soil amendment/fertilizer; efficient extraction of substances valuable to plants, animals, and humans from plant, animal, and fish oil soapstock, especially using the "interphase" emulsion from soapstock acidulation; use of "black paste" from oil refining as fertilizer component (nutrient source); use of interphase from agricultural oil refining, especially refining of non-degummed oils, as animal feed; use of "oil refining by-products to fertilizers" process and/or KOH refining in conjunction with "Miscella"-type hexane refining or "Zenith" process refining; fertilizers containing silica/silicates from by-products of agricultural oil refining; use of higher-sodium oil refining by-products as fertilizer for sodium-tolerant plants; using by-products of sugar beet refining as nutrient source; agriculturally useful potassium soaps from oil refining; products of the refining of non-degummed agricultural oils having useful biocidal or other biological properties; the use, as a feed additive, of potassium soapstock from the caustic refining of agricultural oils using a potassium caustic (KOH), especially with non-degummed oils, which has unexpected advantages over the use of soapstock from sodium caustic (NaOH) refining, especially from degummed oils.