FERTILIZERS AND MANURES FOR THE ORCHARD 183 



Table LV 

 amount of mineral plant-food material used to the acre 



(after VAN SLYKE) 



Variety 



Apple. . 

 Peach. . 

 Pear. . . 

 Plum. . 

 Quince . 



Phosphoric 

 acid 



(P^Os) 



lbs. 

 14.0 

 18.0 



7.0 



8.5 

 15.5 



Magnesia 

 (MgO) 



lbs. 

 23 

 35 

 11 

 13 

 19 



150. Fruit-trees essentially different from other crops. — 



It must be recognized in dealing with the fertility problem 

 that fruit-trees are essentially different from other crops 

 because of their greater root area and the fact that a large 

 part of the roots may be found in the subsoil. This means 

 that the soil will support a fruit-tree better than a plant 

 with a restricted root system. Also the orchard occupies 

 the land for many years, and hence the problem is different 

 from that in which a rotation of crops is practiced. The 

 situation is also more complex because of the material that 

 is returned to the soil from the leaves. 



151. Amount of food materials found in plants not a 

 guide. — The relative amounts of the various "essential" 

 elements in the tissues of the plant cannot be taken as an 

 actual guide, because the soil may contain an abundance 

 of the element which would seem to be most necessary to 

 apply. This is particularly conspicuous with regard to pot- 

 ash. According to the data, the tree uses four times as much 

 potash and nitrogen as phosphoric acid. It is usual to find 

 that most fruit soils are relatively rich in potash which ap- 

 pears to become available sufficiently rapidly by good tillage 



