1922.] 



Phosphatic Fertilisers. 



285 



proved as successful as superphosphate for turnips, or as basic 

 slag for grass. Steamed bone flour, being very finely ground, 

 has proved useful in dry situations: and bone-meal has yjwn 

 tolerably good results for potatoes and for other crops at Ro'- 

 hamsted and at Saxmundham, but at Cockle Park and Ah irdeec 

 it did not come out well. There is a belief among certain farmers 

 that dissolved bones are better for the land than superphosphate, 

 but no clear evidence has ever been obtainable in spite of much 

 search for definite instances. On the whole we must conclude 

 that dissolved bones are more popular than they deserve to be. 



Superphosphate. — Superphosphate is by far the most widely 

 used of all artificial fertilisers. It is made by treating mineral 

 phosphates with sulphuric acid, and is sometimes therefore re- 

 garded as an " acid " fertiliser, but this is incorrect; well made 

 superphosphate has no acidifying effect on the soil. But it is 

 also important to avoid another common error — the assumption 

 that the " lime " referred to in the full name " superphosphate 

 of lime." behaves like lime in the soil and so obviates the neces- 

 sity for periodical applications of true lime or limestone. Super- 

 phosphate contains 7\o true lime, and the fact that it is being 

 applied regularly to land does not in the least reduce the neces- 

 sity for periodical applications of lime. What superphosphate 

 does contain besides calcium phosphate is gypsum, and so much 

 of this is present that the practice of using gypsum as a fertiliser, 

 which at one time was common, is no longer recommended. 



Superphosphate is usually sold on its content of water-soluble 

 phosphate, but this is expressed in terms of tricalcic phosphate, 

 thereby facilitating comparison with other phosphatic fertilisers. 

 Thus, when a superphosphate is guaranteed " 30 per cent, 

 soluble" it does not mean, as is often supposed, that 30percent 

 of the manure is soluble in water, or that 30 per cent, of the 

 phosphate is rendered soluble, hut that the water-soluble phos- 

 phate in 100 lb. of the manure contains as much phosphorus (the 

 thing the farmer really wants) as does 30 lb. of tricalcic 

 phosphate. 



For Roots. — The most profitable use of superphosphate is on 

 potatoes and on roots. For potatoes it is in practically all condi- 

 tions the best phosphatic fertiliser wo have, and dressings of 1. 

 6 or even 8 cwt. per acre are often given according to the yield 

 obtainable. In the north (Durham. Northumberland. S.W. 

 Scotland), it has been recommended to use a certain amount of 

 basic slag (2 to 8 cwt.) in partial replacement of the super- 

 phosphate. It is not desirable to replace too much, however. 



