STUDIES ON STEAM STERILIZATION OF SOILS: II. SOME FACTORS AFFECTING MINIMUM STERILIZATION REQUIREMENTS

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Abstract
For steam sterilization of 50-gm. to 1000-gm. samples of three Alberta loam soils and a peat, the required length of treatment increased with the weight and depth of sample. The peat and black soils, high in organic matter, required longer treatments than the brown or gray soils, low in organic matter. However, identical depths of different air-dry soils were found to reach 120 °C. in the same time. Moistening large samples prior to autoclaving greatly reduced the time required to reach 120 °C. and to obtain sterility, but had no similar effect on small samples. A moisture content of 75% water holding capacity was optimum, reducing the 180 min. required to reach 120 °C. in 6 in. of air-dry peat to 80 min. Autoclaving samples in a moist condition, however, resulted in larger increases in base exchangeable ammonia than autoclaving in an air-dry condition. Generally, minimum single treatments at 15 p.s.i. gauge produced less ammonia than at 12 p.s.i. gauge and single treatments produced less ammonia than intermittent treatments. A slight reduction in nitrate on autoclaving was observed.
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