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THE OLIVER PLOW BOOK 



matter, often give off more free nitrogen than is used in 

 forming the nitrates in them. Thus they become 

 depleted on account of too much water and not enough 

 oxygen. Too much oxygen in the soil burns up the 

 fertility and has a tendency to form clods. 



Seeds will not germinate in ground from which oxygen 

 has been completely excluded; neither will growth take 

 place. Water, completely filling pore spaces, excludes 

 oxygen. This is another way of saying that plants drown. 

 The human being drowns because oxygen is excluded 

 from the lungs; so do plants. Compact earth prevents 



This illustration shows a soil that had been covered with water for a 

 long time. The excessive air spaces caused by these cracks are due to 

 the shrinking of the soil particles after the swelling caused by the water. 

 It is easy to see that the cracks penetrate deeply thus causing the air and 

 heat of the sun to evaporate the moisture from a great depth. 



circulation of air and creates a condition fatal to growth, 

 even if the ground contains sufficient moisture. Some 

 authorities claim poisonous gases are formed by this 

 condition. 



While the evil effects of excluding air from the soil 

 are many, it is equally true that too much air is harmful. 

 Air is just as essential in the forming of nitrates as 



