186 CHEMICAL FERTILIZERS 



Table 22, p. 187. In the experiments recorded in the Table, 

 manure was applied equally on all plots at the rate of about 

 12 tons per acre. Sulphate of ammonia and 30 % potash 

 manure salts were applied equally to all plots except No. i, 

 at the rate of J cwt. per acre. An equal amount of phos- 

 phoric acid, approximating 50 pounds of )$ per acre, 

 was given to each of the plots excepting plot No. i. From 

 plots 8-1 1 one-third of the phosphoric acid only was obtained 

 from superphosphate, whilst two-thirds were obtained from 

 one of the other phosphatic manures, which were in all cases 

 of a very much lower order of solubility than superphosphate. 

 As is to be expected in field experiments, the individual 

 trials showed great variation. In some cases this was 

 due to the fact that the soil was already in such a high con- 

 dition that a full crop was obtained without the use of 

 artificial manure, whilst in other cases the entire absence of 

 artificial manure resulted in hardly any crop at all. It is 

 important to recognize that for a real trial of the relative 

 value of soluble and insoluble phosphates, the experiments 

 should have been conducted throughout an entire rotation, 

 which adds much to the difficulties of experimental trials. It 

 should be noted that the present test of only one crop in the 

 rotation would be unfairly disadvantageous to the insoluble 

 manures. It may be taken for granted that if there is any 

 difference between a soluble and an insoluble fertilizer, the 

 soluble fertilizer will produce its best results in the first year, 

 and, therefore, one may safely assume that the results for 

 the whole rotation would have been more in favour of the 

 insoluble phosphates than the experiments on one crop in 

 the rotation were. The general result of the experiments 

 is to show that the average benefit of superphosphate is only 

 slightly greater than that of insoluble phosphates. It will 

 be noted that the amount of phosphate is by no means 

 extravagant ; it would therefore be wrong to assume that 

 the reason, why the insoluble phosphates appear to be as good 

 as the soluble ones, was that one-third of the dressing of 

 phosphates was sufficient. The only conclusion one can draw 

 from these experiments is that soluble phosphate is some- 



