456 



Reading-Course for Farmers. 



3. Drainage increases the depth of root penetration. The 

 greater the area through which the roots are spread, the larger is the 

 reservoir of food and moisture they have available. It is even more 

 important that they penetrate deep than that they spread far later- 

 ally, because the benefit is proportionately greater. Poor or partial 

 drainage forces the roots to develop near the surface where they are 

 quickly subject to local changes. 



Fig. 376. — A traction ditching machine in operation on clay loam soil at the New 



York State College of Agriculture. 



4. Drainage increases the available moisture. By causing im- 

 provement of the tilth of the soil, it increases its capacity to hold 

 capillary moisture. Therefore, drainage is good for both dry and 

 wet weather. 



5. Drainage warms the soil, and thereby not only hastens growth 

 but also gives a longer crop season. Water requires more heat to 

 warm it a given amount than does soil. In addition and more 

 important, it requires several hundred times more heat to evaporate 

 water than is required to increase the temperature of the same 

 volume of water a moderate amount. 



6. Drainage increases the supply of available plant-food, parti- 

 cularly nitrogen. 



