52 PRINCIPLES OF FARM PRACTICE 



naturally deficient in potash, it is necessary to make up this 

 deficiency. The form of potash used makes little difference. 

 The one selected may depend upon the form most easily and 

 cheaply obtained. In some instances wood ashes, containing 

 about five per cent of potash, might prove to be more eco- 

 nomical than the expensive muriate or sulfate of potash. 



If manure is used its composition should be taken into 

 account. The proportion of nitrogen, phosphoric acid, and 

 potash in manure, expressed as a complete fertilizer, is about 

 10-5-10. This should be balanced by the addition of sufficient 

 phosphoric acid and potash to make the proportion some- 

 thing like 3-8-2. The amount of each ingredient to be added 

 in order to secure this proportion may be easily calculated 

 by the use of simple arithmetic. 



Clay soils. We have seen that clay soils, because of 

 their fine particles, have a great capacity for holding capillary 

 water. Due to the same formation they also possess another 

 valuable quality solubility. For this reason they are 

 regarded as rich soils. Material in a finely divided condition 

 presents a larger surface for contact with water than a coarse 

 material like sand. Consequently, such material is much 

 more soluble. The effect of the size of particles on solubility 

 is shown by comparing the rate at which powdered sugar is 

 dissolved with that of sugar in lumps. Sugar in the former 

 condition dissolves much more rapidly than in the latter. 

 Even glass, which under ordinary conditions is regarded as 

 insoluble, if made into very fine powder, will dissolve to some 

 extent in water. 



To offset these two valuable attributes of clay, there are 

 several disadvantages which must be overcome as far as 

 possible. Clay is hard to handle. It is sticky when wet and 

 hard when dry. There is a very short period during which 



