THE POTATO 429 



them open and friable; in other words, to better 

 the mechanical condition. 



These heavy clay loam soils are among the rich- 

 est known in agriculture. This is because they 

 have been made of the finer particles that have 

 been washed out of hills and mountains over a 

 large area. The valleys in which such soils are 

 usually found are really the cream of an entire 

 watershed. A soil that is easier to handle may be 

 very much less rich, because the finer soil particles 

 are held apart by coarse sand of little or no fer- 

 tility, or by large quantities of decayed vegetable 

 matter. 



For this reason about the only problem con- 

 nected with potato growing on the heavier lands 

 in the Sacramento Valley, is to add sufficient vege- 

 table matter to the soil to hold apart the fine soil 

 particles and make it more loose, open, friable and 

 easily worked. 



This can be done by growing alfalfa for several 

 years, filling the soil and subsoil with roots and 

 when it is plowed up turn under a big crop of the 

 green alfalfa to further add to the vegetable con- 

 tent. 



Another way would be to grow and turn under 

 successive crops of peas, vetch, or other cover 

 crops. 



The addition of large quantities of animal ma- 

 nures is another way to loosen up heavy lands. 



In Scotland, one large potato farmer has hauled 

 sand onto heavy clay land to a depth of five inches, 

 incorporating this and large quantities of stable 

 manure into the soil. 



On a small, intensely cultivated farm in the 

 Sacramento Valley, where large quantities of 

 animal manures are returned to the soil, and alfalfa 



