176 A. F. GUSTAFSON 



Schulze (91) noticed mjurious effects from sterilization at 100 to 125*C. for 1 hour, in the 

 early stages of growth, but later these plants became more vigorous and produced a larger 

 crop, except peas and mustard on one soil. 



Darbishire and Russell (16) heated soil at 90 to 95°C. and obtained very marked increases; 

 the wheat yield (grain), from heated soil was 3.5 times as great as from unhealed, and spinach, 

 tomato and verbena, gave over four times the yield on the heated soil. The second crop, 

 and even the third in one case, showed the same influence, though there was no increase in 

 legumes. Heating to higher temperatures somewhat intensified the effect. 



Koch and Luken (55) heated a poor sandy soil in an autoclave for 2 hours under pressure 

 of two atmospheres. This almost doubled the total soluble solids, quadrupled the soluble 

 organic matter, but increased the soluble inorganic material only slightly. Even though 

 heated and unhealed soils were fertilized alike, the heated one produced the larger crop of 

 oats. Injurious effects following heating were noticeable, but with crops seeded later in the 

 season this influence was not great. 



Rahn (81) made an e.xtensive study of the effect of drying on soils. After drying at room 

 temperature, he secured markedly increased bacterial activity, the difference being greater 

 in heav>'-, rich soils, and increased growth of mustard. 



Pickering (74) heated a soil at 200 C. for 2 hours, finding that 2 year-old apple trees 

 made 63 per cent more growth, produced 48 per cent more leaves containing 52 per cent 

 more dry matter than did similar trees in untreated soil. Heating in a moist condition in- 

 creased the soluble matter, both organic and mineral, more than when heated in the dry 

 condition. Heating soil at 100 C. in a closed vessel (75) increased total soluble matter 25 

 per cent in one case and 107 per cent in another, and in 11 soils an average increase from 

 0.052 to 0t360 per cent of soluble organic matter and from 0.111 to 0.475 percent of total 

 soluble matter was secured. 



Gedroitz (25) found that sterilization brought about an increase in the solubility and 

 assimilability of nutritive substances. 



Russell and Hutchinson (86) report that heating soil at 98°C, increased the j'ield of rye 

 60 per cent and buckwheat 31 per cent. 



Mann (64) gives a brief account of the "Rab" system of rice growing, viz., "burning a 

 mass of branches of trees or cow dung on the land" where rice is to be seeded. He states 

 that it is an almost universal practice on the trap and laterite soils of western India and is 

 considered essential to rice culture there. The surface soil is heated sufiiciently to change 

 tlie bacterial flora, increase the soluble organic matter and improve the physical condition 

 of the soil. 



King (46) treated sand repeatedly with disulfonic acid to free it from all traces of nitric 

 acid and organic matter, then charged it with potassium nitrate, which, after a time, was 

 drained away. After the sand dried, 50 gm. were washed mth 100 cc. of distilled water, the 

 mass was stirred continuously for 3 minutes, the solution drained from the sand and the 

 nitric acid determined. This was repeated until ten washings in all had been made. Table A 

 gives the results of these determinations. 



After the tenth washing the sand was treated with disulfonic acid, as is the residue in an 

 ordinary nitrate determination, and was shown to contain 0.8 mgm. of nitrates, or nearly 

 three times the amount recovered in the second washing, more than one-fourth as much as 

 recovered in the first washing. 



King reasoned from this that each sand grain "appropriated to itself" a film of water with 

 potassium nitrate in solution and this film adhered to the particle so closely that in stirring 

 after adding 100 cc. of distilled water the nitrate was given up by diffusion only and not by 

 forming a mechanical mixture of the distilled water with the film. 



Lyon and Bizzell (61) found that steaming for 2 to 4 hours under 2 atmospheres pressure 

 increased water-soluble ammonia, organic nitrogen, nitrites and total soluble matter, but 

 lessened the amount of nitrates. On standing 56 to 90 days after heating, there was a de- 

 crease in these soluble materials, except nitrates which remained constant. Wheat grown in 



