STUDIES ON STEAM STERILIZATION OF SOILS: I. SOME EFFECTS ON PHYSICAL, CHEMICAL, AND BIOLOGICAL PROPERTIES

Abstract

Effects of steam sterilization and recontamination with original soil, on certain physical, chemical, and biological properties of four Alberta soils were investigated. The soils were Edmonton black loam, Vegreville black fine sandy loam, Gros Ventre brown loam, and Fallis gray silt loam. Certain physical properties were affected by steam sterilization as follows: (1) capillary rise of moisture was greatly retarded in all four soils following sterilization; (2) the percentages of the different separates as determined by ordinary mechanical analysis were not changed significantly by sterilization; (3) water-holding capacity and moisture content at the 'sticky point' were slightly reduced, and, in three of the soils, shrinkage was slightly increased by sterilization, but these effects were of uncertain significance; (4) the pH values of these soils were not changed appreciably by sterilization. The following chemical changes were produced by steam sterilization: (1) water-soluble phosphate was generally greatly increased and water soluble sulphate somewhat increased by sterilization. Easily soluble phosphorus (soluble at pH 3) was increased by about one-third in the two black soils rich in organic matter, but not in the other soils; (2) ammonia accumulated rapidly in the sterilized recontaminated black and brown soils for four to six weeks, and then returned to normal in 8 to 12 weeks. Ammonia accumulated less rapidly and to a smaller degree in the gray soil; (3) nitrification was suppressed for about 6 to 10 weeks in the sterilized recontaminated soils, but was later more active in these soils than in the unsterilized (especially in the black soils rich in organic matter).