SOURCES OF SOIL HEAT 



149 



duced in the soil is not great, and soon ceases ; it may, 

 however, have a distinct effect in hastening the germination 

 of seeds, and must aid in protecting a spring-sown crop from 

 the effects of frost. The deficiency in temperature observed 

 in the last five days of the experiment in the case of the 

 soils receiving the smallest dressings of manure is attributed 

 by Georgeson to the cooling effect of the larger amount of 

 water held by the manured soils (see p. 72). As the result 

 of adding farmyard manure to a soil is in nearly every case 

 to increase the amount of water retained near the surface, 

 it would appear that the after effect of the manure is rather 

 to cool than to warm the land. 



TABLE XXV 



INFLUENCE OF FAKMYAKD MANURE ON TEMPERATURE OF 



SOIL 



