178 A. F. GUSTAFSON 



100°C., however, there was an increase at both 44 and 112 days. WTien the soils were kept in 

 sealed flasks there was an increase after 10 days in every case except that of inorganic matter 

 at US^C. When stored in sealed flasks for 43 days, the soils heated at 100 and 125°C. showed 

 «li]^ht increase of soluble matter. WTien stored for 1 16 days there was a gain in the amount of 

 soluble organic matter at the above temperatures but a loss in tlie quantity of soluble in- 

 organic matter. Storing in light or darkness made no appreciable difference. In the case 

 of the soil that had been heated at 125° there was no difference in organic matter whether 

 stored at 15° or 5°, but that was a rather marked increase of inorganic matter for the lower 

 temperature. 



Pickering (77) secured increased growth of grasses and non-grasses (except in a preliminary 

 experiment with the latter) when planted in soils previously heated. The amount of growth 

 increased as higher temperatures were used. This increased growth correlates fairly closely 

 with increase in soluble material, both organic and inorganic, resulting from heating. 



Hall (26) says, in speaking of effect of sterilization of soil, "Approximately, the crop 

 becomes doubled if the soil has been first heated to a temperature of 70 to 100°C. for 2 hours," 

 while volatile antiseptics bring "about an increase of 30 per cent or more." 



Russell (85) discusses briefly the beneficial effects of sterilization by heat and antiseptics, 

 and assigns killing of the larger soil organisms which destroy the beneficial ones, as the 

 explanation of the effect of this treatment. 



Dyer (20) states that commercial vegetable growlers near London partially sterilize their 

 greenhouse soils with steam and if they use the ordinary amount of nitrogenous fertilizer the 

 plants grow so rank as to "spoil their bearing capacity." 



Seaver and Clark (92) heated soils from New York, Massachusetts and North Dakota. 

 They found that the soluble matter in extracts of heated soils was generally six to ten times 

 as great as that from the same soil not heated. The increase varied somewhat with the 

 organic content of the soil, the temperature to which it was heated, and the period of heating. 



Hinson and Jenkms (31) state that tobacco plants in steamed soils start quicker and 

 grow faster than in unheated soil. They think this accelerated growth due to warming the 

 soil, possible solvent action of the steam on the plant-food, but surely, in part, to change in 

 the "microbe life in the soil." 



In Kentucky, it is a common practice among tobacco growers to heat or bum the soil of the 

 tobacco beds to kill weed seeds and disease. 



Nagoaka (69) reports a material increase in solubility of phosphorus in dilute acids after 

 heating the soil. He found autoclave heating had greater effect on solubility than other 

 methods. 



Peterson (72) heated wavellite and found that it increased the quantity of phosphorus 

 soluble in 0.2 N nitric acid from 4.12 per cent of the total phosphorus, in unheated material, 

 to 54.9 per cent in wavellite heated to 160°C., 49.0 per cent at 200°, and 98.7 per cent at 

 240°C. He noted little effect on soil at*100°C. but at 200°, after a five-hour treatment, there 

 was a marked increase in solubility of phosphorus. 



Ritter (83) exj)erimented along the same lines as Rahn and found that drying increased 

 bacterial activity, and with less effect on light than on heavy soils. 



Fischer (22) comments on the work of Rahn and Ritter, but holds the chemical factor 

 more important than the bacterial. He attaches much importance to oxidation since drying 

 increases the amount of nitrates, even though it kills nitrifying organisms; also credits colloids 

 and surface tension with playing important rdles. 



Schreiner and Lathrop (90) in studying the chemistry of steam-heated soils made 1 to 4 

 extracts. Many organic compounds were found in heated soil that were not isolated from 

 fresh soil. Dihydro.xystearic acid was increased when present in the fresh soil and produced 

 when not present. Seedlings were grown in the extracts for 10- and 15-day periods; extracts 

 from heated soil depressed growths. Heating increased acidity. 



Skalskii (94) found that sterilizing with chloroform and with heat increased the yield of 

 crops by converting phosphoric acid and nitrogen into available forms. 



