216 The Principles of Friuit-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 
