SOIL WATER AND SOIL AIR 25 



but this is not likely to occur, especially when the soil is 

 well aerated. 



How the air is supplied. Any operation that will provide 

 soil spaces, which allow air to enter the soil readily, will keep 

 the soil well supplied with air. As a rule, sandy soils present 

 no difficulty, because the large soil spaces between the parti- 

 cles allow air to enter freely. On the other hand, heavy soils, 

 such as clay and clay loam, having small spaces between the 

 particles, need some modification. By producing a granular 

 condition in the upper part of the soil, the spaces will be 

 enlarged enough to allow air an easier access. If good drainage 

 is provided, the water passing into the drain will be replaced 

 by air. Granulation and drainage are important for other 

 reasons, some of which have been given; others will be 

 considered later. 



