152 PHOSPHATIC FERTILISERS [chap. 



England, the popular opinion seems to be founded on 

 a misapprehension. It has probably arisen from the 

 fact that on the poor sandy grass pastures basic slag 

 never shows the extraordinary effect it does on the 

 poor clay pastures. This is due, not to the ineffective- 

 ness of the phosphoric acid in the basic slag, but to the 

 lack in the sandy soil of both potash and of humus to be 

 set in action by the lime contributed by the basic slag. 

 The great outburst of white clover which often follows 

 the application of basic slag to a clay pasture is 

 mainly promoted by the potash liberated from the soil. 

 As a source of phosphoric acid for tillage land basic 

 slag is probably little less effective on a light than a 

 heavy soil, but it should be applied early and well 

 worked in. 



On such light land, however, there is a very general 

 preference for some of the forms of insoluble phosphate 

 that are found by experience to be readily attacked 

 by the soil water and available to the plant ; phosphatic 

 guano, steamed bone flour, basic superphosphate, and 

 precipitated phosphate are all of the type that is valu- 

 able on such soils. Very effective phosphatic fertilisers 

 for light soils deficient in carbonate of lime, and there- 

 fore requiring a neutral manure, may be made by mix- 

 ing about two parts of superphosphate with one of 

 steamed bone flour, phosphatic guano, bone meal, or 

 basic slag itself. If the mixture be left in a heap for a 

 time in the manure shed the superphosphate will react 

 with the tri-calcium phosphate of the bone or guano 

 to produce a di-calcium or precipitated phosphate ; and 

 though the mass cakes a little when the reaction is 

 complete, it can easily be broken down into the original 

 fine powder. This is probably the cheapest way of 

 obtaining an easily available neutral phosphate for use 

 on light arable land where superphosphate is unsuitable 



