32 SOILS 



before they have had time to germinate if the 

 temperature of the soil is below 45 ; the colder the 

 soil, the slower the seeds germinate. Only after the 

 soil has reached a temperature of 65 to 70 do most 

 crops grow well in it. The soil temperature that is 

 considered most favourable for the germination of 

 barley has been determined by experiment to be 61 

 to 70 F.; of clover, 77 to 100 F.; of pumpkins, 

 100 F.; of tomatoes, 100 F. 



The growth of a crop after germination is in- 

 fluenceu fully as much by the temperature of the 

 soil as is the sprouting of the seeds. The farmer 

 knows that certain crops, as onions, barley, turnips, 

 parsnips, peas and potatoes, are "cool plants"; 

 they can be sown early when the ground is cold, 

 ana thrive in the coolness of spring. Others, as 

 corn, tomatoes, melons and squashes, are "hot 

 plants"; seeds of these do not sprout well if sown 

 very early, and the plants do not begin to grow 

 satisfactorily until there have been summer days 

 to warm the soil thoroughly and deeply. 



The Temperature of Different Soils. The tem- 

 perature of a soil depends upon many factors, most 

 of which are beyond the control of the farmer, but 

 some of them ne can regulate by comparatively 

 simple means. The temperature of every soil 

 vanes widely with the season, and from day to 

 night. The surface soil becomes warm on a hot 

 day and cools several degrees at night, but this 

 fluctuation rarely extends below two and one- 

 half feet. At a depth of thirty feet the soil tem- 

 perature changes little if any throughout the year, 

 even in the Northern States. Much also depends 

 upon the materials of which the soil is composed. 

 The coarser it is, the warmer it gets, and the better 

 it holds the heat; hence gravelly and sandy 



