EFFECT OF DRYING SOILS ON WATER-SOLUBLE CONSTITUENTS 183 



cent and 25 per cent in the moist soil. When the volatile antiseptics are applied with heat 

 (82°C.) and pressure, the amount of soluble solids in moist soil is increased 25 per cent. 



Christensen (10) noted that air-dry soil had its power to liberate acid from calcium acetate 

 considerably increased as compared with that of fresh moist soil. 



Koch (54) determined the effect of sterilization on the concentration of the soil solution 

 by means of the freezing-point method. Concentration was increased more in the heavy 

 soils. Steaming was more effective than sterilizing with formalin. Using formalin 1:50 

 and steaming at 10 pounds pressure increased the concentration of the soil solution more 

 than any other metliod used, in fact to three times the original concentration. In Sassafras 

 and Penn loams it was increased, respectively, 0.24 and 0.3 atmospheres. Sterilization by 

 the so-caUed "commercial" methods increased the concentration of the soil solution, varying 

 with soil and method of sterilization. Heating with steam at 10 pounds pressure for 1 hour 

 increased tlie concentration of the soil solution 0.56 atmosphere in a loam soil; with a Norfolk 

 sand tlie increase was but one-fourth as great. 



Stewart (96) studied water extracts of thirteen soils, of two distinct types both planted and 

 fallow, finding as did King (44) that "poor" soils yielded extracts containing solids less sol- 

 uble than solids in extracts from "rich" soils. 



Hartwell and Pember (28) while investigating the effect of aluminum on barley and rye, 

 compared unheated acid soil with samples heated at 100, 260, 360, and 420°C. The lime 

 requirement was markedly reduced by heating and the reduction increased somewhat with 

 the temperature. The weight of green tops of rye was reduced by heating except that 

 heating at 420°C. caused no difference in yield. The yield of green barley tops was decreased 

 at both 100 and 260°C. but increased at both of the higher temperatures. 



Potter and Snyder (80) state that "the amount of ammonia was increased by all the heat 

 treatments, the higher temperatures to which the soils were heated giving in general greater 

 increases;" also that dry heating at 100°C. did not materially affect nitrates, but at 10 pounds 

 pressure in an autoclave for 9 hours, nitrates were markedly increased while a temperature 

 of 200°C. caused an almost total disappearance of nitrates. 



Johnson (39) heated soil at 250°C. The yield of tobacco was increased 571 per cent 

 on muck, 473 per cent on Waukesha silt loam, 150 per cent on clay, 96 per cent on fine sandy 

 loam and 62 per cent on virgin sandy loam. A single heating gave a larger yield than did 

 heating two to eight times at 115°C. He found, also, enormous increases in concentration 

 of the soil extract, as shown by freezing-point determinations. Heating at 250°C. caused 

 the highest concentration. 



He classifies under eight heads the published theories explaining the effect of sterilizing 

 soils on plant growth, three of which have some bearing on the problem in hand; (a) "Modi- 

 fied organic compounds" as already mentioned from Schreiner and Lathrop (90). {b) 

 "Modified inorganic soil compounds." This theory is supported by many investigations 

 which show that an increase in inorganic plant nutrients occurs on heating soUs. (c) "Physi- 

 cal theories." The author says the physical "theories are not subscribed to by any author 

 in particular at the present time, although it was quite generally believed at one time that 

 aU the benefit derived from burning the soil was due to purely physical changes. Some of 

 the physical factors which play a part in soil fertility are, however, coming to be regarded 

 as very influential in conjunction with chemical factors." 



Beaumont (3) showed that drying soil caused a decrease in the amount going into suspen- 

 sion in distilled water or 4 per cent ammonia. Oven-drying soils and then putting them under 

 water logged conditions increased the quantity of iron compounds soluble in dilute hydro- 

 chloric acid. He states, also, that "sterilization checked the formation of this easily soluble 

 colloidal material." 



Noyes (70) while working with adsorption of different radicals by soils and decaying leaves 

 detected no adsorption of nitrates. He holds "nitrates are completely recovered from soil 

 in one extraction by water, and nitrates added to soil are completely recovered in addition 

 to those present in the soil." He noted also that the lime requirement of a residual limestone 

 soil was higher when not heated than when evaporation is carried on in the usual way. 



