Soil Temperatures. 



213 



given the best soil temperatures and the lowest and high- 

 est temperatures at which certain seeds have been observed 

 to germinate. 



The two important facts fixed by these data are: (1) 

 The soil temperatures at which the seeds of most cultivated 

 crops germinate best, lie between 70 and 100 F., wiih 

 an average of about 85 F. (2) The soil temperatures 

 below which germination does not take place are between 

 41 and 54 F. From these it is clear that seeding should 

 not begin until the thermometer will show the temperature 

 of the soil at the depth of planting, well up toward 70 

 F. during the warmest portion of the day. These state- 

 ments should not be understood as advising against the 

 sowing of clover seed early in the spring, while the frost 

 is yet on the ground, under conditions where it might not 

 be possible to get a stand otherwise. 



256. Observed Soil Temperatures The temperatures 

 which the soil does attain at different depths during the 

 different months of the growing season will be of inter- 

 est in connection with the statements made in the last two 

 sections. In the two tables which follow are given the 

 mean seasonal variations of soil temperature at two sta- 

 tions, one in this country and the other in Europe. 

 14 



