104 FERTILIZERS 



It has not yet been in use long enough for its qualities to be 



tested, but it has this to recommend it, that it is relatively cheap. 



Among phosphoric acid feriilizers are bone meal, rock phos- 

 phate, and basic slag. Bone meal is an old favorite among 

 fertilizer users. Within recent years basic slag, or Thomas phos- 

 phate powder, a by-product produced in the manufacture of 

 steel, has been used a great deal by orchard men. It has the 

 advantage of carrying a considerable percentage of lime, but this 

 has been reduced recently by changes in the manufacturing 

 process. Acid phosphates or superphosphates are made from 

 both bone and rock phosphates by treating them with sulfuric 

 acid. This takes up a part of the lime, rendering the phosphoric 

 acid more available. The superphosphates are specially useful 

 with young trees where the roots are extending rapidly. They 

 are the only form in which phosphoric acid should be applied 

 to orchards in sod, since in such orchards one must depend on 

 the fertilizer dissolving and being washed into the soil. 



Two forms of potash are in common use, the muriate and the 

 sulfate, the latter coming in both high and low grade. Probably 

 the muriate is more generally used than any other form at the 

 present time. It has the great advantage of being cheaper than 

 sulfate, but it also has a tendency to render the soil acid by 

 taking out the lime. This latter tendency can be overcome of 

 course by adding lime, but that means one more thing to look 

 after. The low grade sulfate carries about half the amount of 

 actual potash that the high grade does, but it also has a large 

 amount of magnesia, which many consider an advantage. There 

 is the same objection to it that there is to any low grade fer- 

 tilizer, viz., that it costs more per unit of plant food to transport 

 it and to handle it in the orchard. It is perhaps best to use the 

 high grade sulfate altogether until such time as it may be shown 

 that some other form is better. 



There is no very definite experimental data to show that lime 

 is beneficial to orchard trees, but there is a very general impres- 

 sion among orchard men that it is an excellent plan to apply lime 

 to orchards. So far as this idea has any real backing, it prob- 

 ably rests on the fact that limestone districts in fruit regions 



