EFFECT OF DRYING SOILS ON WATER-SOLUBLE CONSTITUENTS 



177 



steamed soils at first showed injury, but later recovered and grew better than i)lants on the 

 unsterilized soil. 



Two soils heated for 2 hours at 2 atmospheres pressure and another for 4 hours (62), were 

 extracted with 5 parts of water to 1 part of soil. Total solids and inorganic matter were in- 

 creased from two to six times by this heating. All other constituents except nitrates were 

 greatly increased by heating. No ammonia was found in any unheated soil and the con- 

 centration of nitrates was decreased by heating in every case. Wheat produced a much 

 larger crop on the heated than on the unheated soil, and the same effect was very evident in 

 the succeeding crop of millet, but wheat seedlings grown in a 1 -1 extract made immediately 

 after steaming, were affected unfavorably. Diluting the extract of steamed soil with distilled 

 water, 3 to 1, improved the growth of seedlings but diluting the extract of untreated soil 

 decreased the growth of seedlings. 



The same writers (62) report that soils whose moisture content was maintained at about 

 25 per cent by adding distilled water, for periods of 56, 82 and 90 days after heating, steadily 

 lost in total water-soluble material so that at the end of 90 days there was but slightly more 



T.\BLE A« 

 Observed and computed conceniration of ?iilrale in successive washings of sand in distilled water 



than one-fourth as much soluble material present as immediately after heating. Nitrates 

 decreased also, but in one soil they seemed to recover in part at the close of the period. 



In a more extended experiment along the same line, soils stood 34 and 39 days after heat- 

 ing. Total solids, inorganic matter and ammonia nitrogen decreased rapidly, while there 

 was a slight increase in nitrates in the same time. 



Fletcher (23) relates that burning organic matter, twigs or manure, or both, greatly 

 increased the yield of crops, but not to so great an extent as did heating the soil directly at 

 200 to 230°F. 



Aitken (1) reports an instance of increased productiveness follo-ning heating of the surface 

 garden soil by a "large and long-continued fire." 



Howard and Howard (36) mention the beneficial effects, noted in parts of India, of expos- 

 ing soil to the strong heat and light of the sun in April and May. 



In soils kept moist for various lengths of time in open pans, Pickering (76) noted that the 

 soluble matter, both organic and inorganic, increased as the temperature was raised from 30 

 to 150''C. The quantity of soluble matter decreased as the time since heating increased, 

 up to 112 days when the last determination was made. In case of the inorganic matter at 



* Letters used for tables derived from the literature. 



