426 



Biochemical Studies of Heated Soils 



[Mar. 



TABLE 3. EXPERIMENT I. STARTED MAY 5, I9II 



Growth, in Millimeters, of Lupin Seedlings in Soil Extracts 



Note. For analytic data pertaining to these extracts see page 419 (Table 2). 



The appearance and growth of the lupins in the unheated soil 

 extract and the 90 soil extract were apparently normal in every- 

 way. However, in the extracts of the 120 and 170 soils the 

 opposite was true. The white roots very rapidly became brownish 

 in color and the formation of secondary roots was almost entirely 

 prevented. Such lupins looked like similar ones acted upon by toxic 

 though minute amounts of copper. The results of another typical 

 experiment upon the effects of the soil extracts are given below. 



TABLE 4. EXPERIMENT II. STARTED APRIL J, I9II 



Growth, in Millimeters, of Lupin Seedlings in Soil Extracts 



Note. Whenever the extracts of heated soils were to be preserved for 

 analysis or seedling studies, it was found necessary to seal them in glass- 

 stoppered bottles while boiling hot. 



A glance at the results of our seedling experiments (Tables 3 

 and 4) shows that, with slight exceptions due to experimental 

 errors, the soils heated to temperatures in the vicinity of 120 to 

 170 C. contain substances soluble in water which exert a strong in- 

 hibitory effect upon lupin seedlings grown in such solutions. The re- 

 sults of our oat culture work are in harmony with the idea, which 

 Lyon also held, that strong heating produces soluble material harm- 

 ful to green plants. The fact that extracts used for the seedling 

 studies, and the extracts from the oat culture soils, were analyzed 

 and found to have quantitative relations depending on the intensity 

 of the heat, seems to indicate that the causes are to be found in 

 chemical changes rather than changes in the soil flora, and so on. 



