216 EXPERIMENT STATION RECORD. [Vol.41 



accelerated germination on soils not productive of high toxicity on heating or 

 upon heating soils to low temperatures only. 



Growing plants differed markedly in their sensitiveness to the action of 

 heated soils. The similarity of their behavior and of germinating seeds in this 

 respect suggested that the injurious and beneficial substance in both cases may 

 be the same, although toxicity to seed germination did not appear to be always 

 correlated with toxicity to plant growth and vice versa. Sensitiveness of seeda 

 to the toxic agent in germination was also not indicative of the behavior of 

 the same species in its growth on the same soil. The growth of fungi on 

 heated soil was correlated with toxicity to seed germination and plant grmvth 

 on any one soil, the development of Pyronema having been studied in particular. 

 This and other fungi and apparently bacteria also grew best iu soil heated to 

 250°, diminishing in rate and profuseness of growth at lower or higher tem- 

 peratui-es of heating. 



The ammonia content of soil heated to different temperatures was highest 

 on heating to about 250°, and diminished gradually at higher and lower 

 temperatures, this also being true for the concentration of the soil solution. 

 Ammonia content and cencentration of the soil solution were, therefore, 

 roughly correlated with, the degree of toxicity to seed germination and early 

 plant growth and the extent of the beneficial action to late growth of green 

 plants and to growth of lower microorganisms In any one soil, although there 

 was apparently no correlation between these factors when different soils were 

 compai'ed with each other. 



The absorptive capacity of different soils varied greatly, this in turn mark- 

 edly influencing the action of toxic compounds produced in the soil. In water 

 extracts of heated soils, the toxicity to seed germination was more directly 

 proportional to the ammonia content, indicating that the toxicity of the soil 

 was not only determined by the amount of the toxic agent produced by heat- 

 ing but also by the absorptive capacity of the soil for the toxic agent, as 

 well as by a number of other factors the additive and subtractive value of 

 which gave balance of toxicity very difficult to analyze properly. 



The addition of ammonia as such to soil in varying amounts is said to 

 be capable of producing a condition similar in many respects to that pro- 

 duced by heated soils on seed germination and plant growth. It was found 

 that similar "qualitative" reactions can be produced with certain seeds on 

 highly toxic heated soils or their extracts and with certain strengths of am- 

 monia, these reactions not appearing to be reproducible with chemicals other 

 than a.mmonia or ammonium salts. 



It is believed that much of the toxic action in heated soils is due to the 

 ammonia produced and that it exists in heated dry soils largely as ammonium 

 carbonate, which is, however, gradually decomposed under normal growing 

 conditions. All toxic properties in heated soils are not, however, believed 

 to be the same, certain changes termed "chemical" injuries seemingly being 

 due to quite different causes than ordinary retardation. The toxic property 

 was found to be volatile, and to be destroyed or changed to nontoxic com- 

 pounds in soils kept under normal-growing conditions due to the activity of 

 ordinary soil flora, which, however, may apparently at the same time increase 

 the amount of ammonia present. Pyronema confluens has also been shown 

 to be efiicient in both these respects. Reduced toxicity in the presence of in- 

 creased ammonia content in the soil is believed to be explained by the exist- 

 ence of the ammonia in various delicate transition stages rather than as 

 true ammonia due to the activity of soil organisms, these transition prod- 

 ucts being broken down when the ammonia determinations are made. The 



