Sails 63 



their best growth; their action is practically discon- 

 tinued when the air supply is reduced greatly. 



SOIL HEAT 



The temperature of the soil is important because of its 

 influence on the germination of seeds and on the growth of 

 plants, and also because of its effect on chemical changes 

 and bacterial action in the soil. When a soil is cold, life 

 in it is dormant and chemical action is reduced. The 

 earlier a soil is warmed in spring and the later it is kept 

 warm in fall, the longer is the growing season. This is 

 very important for sugar-beets, since there is not time 

 during a short season to store large quantities of sugar. 



Soil heat is derived largely from the sun, the rays of 

 which are most effective when striking perpendicularly. 

 A south slope, therefore, is considerably warmer than one 

 facing the north. A sandy soil is also warmer than a 

 clay. On account of the high specific heat of water, a 

 wet soil is much slower to warm up in spring than a well- 

 drained soil. The high evaporation from a wet soil also 

 reduces the temperature. Such factors as colors, specific 

 heat, and tillage play an important r61e in regulating soil 

 temperature. 



ORGANIC MATTER 



The chemical, physical, and biological conditions of the 

 soil are greatly influenced by organic matter because it 

 reacts favorably on the tilth, the water-holding capacity, 

 and the temperature of the soil. Through its decay, or- 

 ganic matter increases the availability of mineral matter 



