12 Dr. Bernard Dyer. Chemical Study of the Phosphoric 



soluble phosphoric acid, however, appear to afford a striking index 

 to the relative phosphatic fertility of the soils. In the subsoils, the 

 irregularities and variations in the natural and original phosphoric acid 

 of the subsoils themselves are such that the total percentage tells us 

 nothing; while the citric acid results frequently show striking and 

 consistent differences, and are also of considerable interest when 

 studied in connection with the problems of root-range and subsoil- 

 feeding, which are discussed in examining the results of the individual 

 plots. In the surface soils, the average ratio of phosphoric acid, on 

 the plots manured with superphosphate and ammonium salts, with and 

 without various additions of alkaline salts, to that in plots not manured 

 Avith phosphates for fifty years, was T65 : 1, while the citric acid 

 soluble phosphoric acid ratio for the same groups was 5-46 : 1. On 

 the two dunged plots the ratio of total phosphoric acid to that of the 

 plots not phosphatically manured is 1*78 : 1 and 1*36 : 1 respectively; 

 while the corresponding ratios for citric acid soluble phosphoric acid 

 are 6-83 : 1 and 3*91 : 1. f 



The probable limit denoting phosphatic deficiency for cereals seems 

 to be, as deduced from this investigation, between O01 per cent, and 

 0*03 per cent, of citric acid soluble phosphoric acid in the surface soil. 

 That is to say, a percentage as low as 0*01 seems to denote an impera- 

 tive necessity for phosphatic manure, while as much as 0'03 would 

 seem to indicate that there is no such immediate necessity. For root- 

 crops — more especially turnips — the limit would probably be higher. 



The results, generally, show that by far the greater proportion of 

 unconsumed manurial phosphoric acid, though originally water-soluble, 

 is accumulated in the surface or first 9 inches, but that in the case of 

 dung there is considerable descent into the second and third 9 inches, 

 and that, in the case of superphosphate accompanied by constant 

 dressings of potassium, sodium and magnesium salts without nitrogen 

 (full supply and small utilisation), there is evidence of a tangible 

 descent into the second and even the third 9 inches. In the case of 

 the chemically manured plots, not only is the greater part of the 

 calculated accumulation found by analysis in the surface soil, but a 

 large proportion of it is found in a condition in which it dissolves in a 

 weak solution of citric acicl. This reagent also enables us to trace 

 qualitatively the descent alluded to in the subsoils. Potassium, sodium, 

 and magnesium salts have a distinct influence in the retention of the 

 phosphoric acid in a less fixed and presumably more available condi- 

 tion, the effect increasing as the saline applications are greater. 



The superabundance of phosphoric acid estimated to have been 

 supplied in dung for fifty years is less satisfactorily accounted for 

 than is that on the chemically manured plots ; and even allowing for 

 the difficulty of accurately estimating the phosphoric acid in the dung, 

 it seems probable that there has been a considerably greater descent 



