FORMS TO USE 103 



Influence of Phosphoric Acid. — The exact part which phos- 

 l)horic acid plays in orchard development seems not to have been 

 so Avell worked out, at least there is less agreement on the sub- 

 ject. It is certainly important in seed development and prob- 

 ably m the ripening of the fruit, and some men have even 

 given it credit for improvements in the color of fruit, though this 

 is not very generally accepted. If it occurs it is probably as a 

 result of the control which this element exerts on the growth of 

 the tree. Maturity and sunlight are certainly the two most 

 important influences in producing color in fruits. "Where phos- 

 phoric acid is applied to orchards it is probably most useful to 

 the cover crop and nia^' generally be best applied wlien that crop 

 is sown. 



Forms to Use. — If we are to use fertilizers we have the choice 

 of several forms of each one. 



For nitrogen we have nitrate of soda, sulfate of ammonia, 

 tankage, cyanamid and nitrate of potash. Nitrate of soda is prob- 

 ably used more than any other form and has the advantage that it 

 is very quickly available. It is also a reasonably cheap form. 



Sulfate of ammonia acts more slowly than the nitrate because 

 it has to be changed in the soil into the nitrate form before it can 

 be used by the plant. It also has a tendency to make the soil 

 sour because it leaves behind the sulfuric acid. Still, it is fairly 

 popular, and if lime is used to take care of the acid, it is good 

 to use in combination where a long season of growth is wanted. 



Tankage is still more slowly available and is usually reason- 

 able in the price per unit. It is used with particular satisfaction 

 on young trees or in any situation where a relatively long period 

 of groAvth is desired. With young trees tankage in combination 

 with nitrate of soda has given veiy much better results than the 

 nitrate alone, even when two applications of the latter were given. 



The nitrate of potash is hardly worth discussing because it is 

 so seldom that one can get it. It carries about the same percent- 

 age of nitrogen as the nitrate of soda and in addition about 

 as much potash as the muriate. It is thus a very high grade 

 fertilizer, the highest that we have. It has the disadvantage 



