COMMERCIAL FERTILIZERS AND THEIR USE 253 



with nitrate of soda produce luxuriant vines, but only 

 a few small tubers. When a medium dressing is used 

 along with potash and phosphoric acid, a more balanced 

 growth and better yield result. 



Heavy applications of nitrate of soda produce a rank 

 growth of straw, with a low yield of grain. The excess 

 of nitrogen causes the mineral matter to be utilized for 

 straw and leaves only a small amount for grain produc- 

 tion. When applications of commercial fertilizers are 

 too heavy, plants take up unnecessary amounts of food 

 and fail to make good use of it. In fact, crops may be 

 overfed, or fed an unbalanced ration, the same as ani- 

 mals. Hence in the use of fertilizers excessive and un- 

 balanced applications are to be avoided. 



305. Fertilizing Special Crops. - - There are crops 

 which need special help in obtaining some one element, 

 and in using fertilizers the rule should be to help those 

 crops which have the greatest difficulty in obtaining 

 food. When the soil does not show a marked defi- 

 ciency in any one element, light dressings of special 

 purpose manures may be made to the following crops : 



Wheat. Nitrogen first, then phosphoric acid. In 

 the case of some soils, phosphoric acid and potash pro- 

 duce larger yields than nitrogen. 



Barley, oats, and rye require manuring like wheat, but 

 to a less extent. Each crop has a different power of 

 assimilating nitrogen. Wheat requires the most help 

 and barley and rye the least. 



