v.] RELATIVE VALUE OF VARIOUS PHOSPHATES 147 



It will be seen that the phosphates have produced a 

 greater effect upon Swedes and barley than upon the 

 deeper rooting and more slowly growing mangolds and 

 wheat, but that on the whole the three fertilisers are 

 equally valuable as sources of phosphoric acid on the 

 Rothamsted soil. The soil of the Little Hoos field, in 

 which the experiment is being conducted, contains a 



Table XXXIX.— Relative Yield from various Phosphates 

 (Rothamsted). Unmanured = 100. 



reasonable working quantity of carbonate of lime; it 

 is also fairly heavy and cool, so that it retains sufficient 

 moisture to give the phosphates of basic slag and bone 

 meal an opportunity of coming into solution. 



Without attempting any detailed review of the 

 numerous experiments upon phosphatic fertilisers, we 

 may yet draw certain general conclusions from them. 



On nearly all normal soils superphosphate is the 

 most effective phosphatic fertiliser when equal amounts 

 of phosphoric acid are compared. The exceptions are 

 the light sands and gravels very deficient in carbonate 

 of lime, peaty soils where the humus is of the sour acid 

 type and all other soils that have developed an acid 

 reaction. On the peaty soils of the fen country 

 superphosphate is the fertiliser most valued, but 

 there the humus is of the " mild " type, consisting 



