PHYSICAL PROPERTIES OF SOILS 



109 



tested various seeds at several temperatures and found the lowest 

 temperature at which germination took place was as follows : 

 Alfalfa, beets, barley, beans, red clover, oats, peas, turnips, wheat 32-40 F. 



Indian corn, carrots, sorghum, sunflower, timothy 40-51 F. 



Cucumbers, melons 60-65 F. 



The time required for germination decreases as the temperature 

 rises, until the optimum temperature is reached. For example, 

 corn required 11% days to germinate at 50, 3>4 days at 60, and 

 3 days at 65 F. While the sunflower seeds required 25 days at 

 51, at 60 they required only 3 days to germinate. 



The growth of the plant also depends upon the temperature to 

 which it is subjected. Between the extremes of heat and cold 

 fatal to plants, is an optimum temperature, varying for different 

 plants, at which the maximum growth takes place. For example, 

 Bialablocki 1 grew rye, barley, and wheat 20 days at different soil 

 temperatures, and determined the dry matter produced, with the 

 following results : 



WEIGHT OF PLANTS GROWN AT DIFFERENT TEMPERATURES. 



In this experiment, 20 was the most favorable temperature for 

 rye, 25 for barley, and 30 for wheat. The wheat plant grown 

 at 30 is three times as large as that at 8 C. 



The temperature of the soil has a direct influence not only upon 

 the plant, but upon processes in the soil, especially those relative 

 to the preparation of soil nitrogen for plant food. 



Factors which Influence Soil Temperature. The temperature 

 of the soil varies to a certain extent with that of the air, but the 

 1 Jahresber f. Agr. Chem., 1870-72, p. 190. 



