APPENDIX A 129 



for the development of the fungus Pyronema. The growth of oats was 

 slightly accelerated in soils heated at low temperatures (90°-120° C), 

 but above this temperature growth was retarded, the retardation in- 

 creasing with the temperature to which the soUs had been heated. 



The water extract of soil heated to 120° C. was yeUow in color, due 

 largely to charred organic material. The color was deeper in extracts 

 of son which had been heated to stiU higher temperatures. Both the 

 inorganic and the organic extractions were increased about ninefold 

 by heating soU to 170° C. for two hours. Soils that were heated until 

 they were unfavorable for the growth of oats were nevertheless very 

 favorable for the growth of Pyronema. 



Moist heat produces much the same effect upon soUs as dry heat, 

 provided the temperature goes high enough. 



By steam heating, the physical, chemical, and physiological prop- 

 erties of soils are more or less altered. The chemical changes consist 

 mainly in an increase in soluble matter in the heated soils. This is 

 partly of an inorganic nature, but the largest increase is in the 

 organic matter rendered soluble. Ammonia may be formed from the 

 reduction of nitrates to nitrites and ammonia, but it is especially 

 formed from the decomposition of organic compounds. Large amounts 

 of nitrogenous matter are made soluble and apparently more available 

 for plant use. Carbon dioxide is also produced in large quantities. 



Pfeiifer and Francke '^ steamed soil at 1 atmosphere pressure for 

 three hours and found a consequent increase in dry weight of plant 

 growth and nitrogen content over the unheated. Deherain and 

 De Moussy'' prevented nitrification in soils by heating them at 

 120° C. in an autoclave, although the sterilized soil, when inoculated 

 with a portion of the unsterilized soil, produced more nitric nitrogen 

 than the unsterilized soil. 



Students of this problem sooner or later find that an improvement 

 due to heating soils is often preceded by a marked injury to plant 

 growth. The heat, although it increases the quantity of water- 

 soluble plant nutrients, seems to produce substances which are poison- 

 ous to plants. According to the amount of this poison and the 

 sensitiveness of the plants to it, a positive or a negative acceleration 

 of plant growth is produced. The results appear to vary in different 

 soils. The addition of calcium carbonate to the soil before sterilizar 

 tion prevents, almost if not entirely, the formation of poisonous 

 substances. 



1 Landw. Versuchsst. 46 : 117. 1896. ^ Ann. Agron. 22 : 305. 1896. 



