86 Practical Farming 



saltpeter. Wood ashes, especially those from the hard 

 woods, contain a considerable percentage of potash and a 

 large percentage of Hme, and are of value as a source of 

 potash. As an ingredient in a fertihzer, potash is of less 

 importance on many soils than phosphoric acid or nitro- 

 gen, because of its greater abundance in clay soils and 

 because less of it is removed in the crops than of nitrogen 

 or phosphorus. Nevertheless it is important that a suffi- 

 cient supply be at hand in the soil in an available form; 

 and sandy or peaty soils are generally deficient in potash. 

 Manufacturers of commercial fertilizers have as a rule 

 given too much prominence to phosphoric acid in their 

 mixtures and too Httle to potash, especially for use on such 

 crops as largely select potash. In the economy of the 

 plant it has been fully shown that phosphoric acid does 

 not have its full effect unless there is a due supply of potash 

 present, and on the other hand potash will not give the 

 best results in the growth of the plant unless there is also 

 a due percentage of phosphoric acid available. The inter- 

 dependence of these can be easily understood when we 

 realize that the office of potash in the plant is to favor 

 the formation of starch and that of phosphoric acid is the 

 conveyance of the formed material to points where it is 

 needed in the construction of new cell walls. Starch, 

 which we have seen is the starting point of materials for 

 building, and the storage form of plant food, cannot be 

 abundantly made for phosphoric acid to convey to the 

 grain as plant food, unless sufficient potash be available. 

 Though the combination in which potash is applied to 

 the soil may be perfectly soluble in the soil water, the 

 absorptive power of a good loamy or clay soil is such 



