122 VENTILATION OF THE SOIL. 



that a system of cultivation was based upon it, and 

 the effects were remarkable, even without the 

 addition of the least manure. Before drainage has 

 taken place, this is impossible, as the ground is so 

 wet that the more it is worked the closer it becomes ; 

 but when it is dry it crumbles in handling. 



The j^^'evetition of injuiy from drought, which we 

 have already commented upon, is another benefit 

 which arises from draining. 



The jwiver of absorbing moisture. The dry and 

 friable soil is better prepared to drink in the dews 

 of the night, and thus is partially compensated for 

 what it has lost during the day by evaporation. 

 This is a potent source of fertility, for the air is 

 freighted with fertilizing gases, which the soil im- 

 bibes with the water. 



The ventilation of the soil is also accomplished by 

 drainage. The earth contains substances which 

 require the oxygen of the atmosphere to decompose 

 and prepare them to become the food of plants. 

 While the soil is filled with stagnant water, decom- 

 position is arrested ; but when the air takes its 

 place, it progresses rapidly. This decomposition is 

 slow combustion, and therefore generates heat, which 

 increases the warmth of the earth in the spring, at 

 which time it is so desirable. 



It j^e^'^iit'S the ivarm, earli/ shoivers to enter the soil 

 and aid decomposition, by augmenting the heat of 

 the ground. 



