THE SOIL STRUCTURE 



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and smoothing harrows are run along the hillsides 

 for the same purpose and with results that are nearly 

 always advantageous to the dry-farmer. Of neces- 

 sity, each man must study his own farm in order to 

 devise methods that will prevent the run-off. 



The structure of soils 



Before examining more closely the possibility of 

 storing water in soils a brief review of the structure 

 of soils is desirable. As previously explained, soil 

 is essentially a mixture of disintegrated rock and 

 the decomposing remains of j^lants. The rock par- 

 ticles which constitute the major portion of soils 

 vary greatly in size. The largest ones are often 500 

 times the sizes of the smallest. The following table 

 shows the limits of sizes and the names used to 

 designate them : — 



It will be observed that it would take 50 of the 

 coarsest sand particles, and 25,000 of the finest silt 



