216 The Principles of Fruit-growing. 



to buy potash. The commercial article analyzes 50 

 per cent or less of actual potash. Sylvinit is a 

 lower grade of potassium fertilizer. Its value like 

 that of other materials mentioned should be reck- 

 oned upon the amount of potash present. 



Phosphoric acid may be obtained in the form of a 

 high-grade plain superphosphate (like dissolved South 

 Carolina rock), in bone compounds, and Thomas 

 slag. The plain superphosphate contains about 16 

 or 18 per cent of phosphoric acid, and two hun- 

 dred to five hundred pounds per acre is a liberal 

 and very useful dressing for bearing orchards. The 

 bone fertilizers are always valuable. Those which 

 are untreated give up their phosphoric acid slowly, 

 unless they are very finely ground. Dissolved bone 

 gives more immediate results. Thomas or basic slag, 

 which is yet less known to farmers in this country, 

 has given good results in many tests, but it parts 

 with its fertility very slowly. It is yet too early 

 to recommend this material for orchards with full 

 confidence. 



In general, phosphoric acid is probably less im- 

 portant in fruit plantations than potash, although 

 this order is reversed in general farming. Potash 

 should undoubtedly be the leading factor in orchard 

 fertilizers, and nitrogen may be obtained largely, or 

 even wholly, in some cases, by means of tillage and 

 green crops. It will then be seen that the use of 

 combined or " complete " commercial fertilizers may 

 not be economical. The best results are to be ex- 

 pected when the fruit-grower observes closely the 



