FERTILIZERS 259 



Barnyard Manure. - Where a sufficient amount of 

 barnyard manure is obtainable at a reasonable price, it 

 may be profitably utilized in the orchard. Barnyard 

 manure is a complete fertilizer and acts in two ways, 

 directly by adding plant food, and indirectly by adding 

 humus to the soil. Rank-growing trees should not be 

 fertilized with barnyard manure, but where the trees are 

 weak and the foliage is yellow, it proves most beneficial. 

 It may be applied to the orchard at almost any season of 

 the year, but most advantageously in early spring, when 

 there will be less waste by leaching and washing. Its 

 effect upon orchard trees is more lasting than that of com- 

 mercial fertilizers. A good dressing of it once every two 

 or three years is sufficient. 



Commercial Fertilizers. - The function of commercial 

 fertilizers is to supply the kinds of plant food that are de- 

 ficient in the soil and that are necessary for producing 

 profitable crops. Nitrogen, phosphoric acid, and potash 

 are called the essential fertilizers because they are the ones 

 that are likely to be present in but limited amounts in the 

 soil. 



Nitrogenous fertilizers promote a vigorous growth of 

 both twigs and foliage. Nitrate of soda is used when it 

 is desirable to apply a fertilizer whose nitrogen is quickly 

 available. It should be applied only when the trees can 

 take it up immediately, as it is very soluble in water and 

 hence apt to leach away. Sulphate of ammonia has much 

 the same value and effect as nitrate of soda. Cottonseed 

 meal, dried blood, tankage, and fish scrap are used more in 

 producing crops that have a long growing season, since the 

 nitrogen which they contain is more slowly available. 



Phosphoric acid promotes fruit production and the 



