COMMERCIAL FERTILIZERS 207 



usually due to deficiency of humus and available 

 nitrogen. If the nitrogen were supplied, improved 

 cultivation together with the chemical action of the 

 humus on the soil would generally furnish the avail- 

 able potash and phosphoric acid, but instead of pro- 

 viding the one element needed, others which may 

 already be present in the soil in liberal amounts, are 

 often supplied at an unnecessary expense. Another 

 abuse of fertilizers is their application to the wrong 

 crop. A heavy application of potash fertilizer to a 

 wheat crop grown on a clay soil, or an application of 

 nitrate of soda on land seeded to clover, or of land 

 plaster to flax grown on a limestone soil, would be 

 a waste of money. 



280. Judicious Use of Fertilizers. In order to 

 make the best use of commercial fertilizers, both 

 the soil and the crop must be carefully considered. 

 All crops do not possess the same power of assimilat- 

 ing food ; turnips, for example, have very restricted 

 powers of phosphate assimilation, hence they require 

 phosphate manures. Wheat requires help in obtain- 

 ing its nitrogen. In some soils a wheat crop may 

 starve for want of nitrogen, while an adjoining corn 

 crop will scarcely feel its need. Wheat has strong 

 power of assimilating potash, while clover has less. 

 Hence in the use of fertilizers the power of the plant 

 to obtain its food must be considered. A light appli- 

 cation of either a special purpose or a complete fertili- 

 zer at the time of seeding is often advantageous, as 

 it encourages plant growth by supplying food at the 



