I40 PHOSPHATIC FERTILISERS [chap. 



by other sources of phosphoric acid and under diverse 

 conditions of soil, has not yet been worked out, 

 but there can be little doubt but that it explains why 

 a phosphatic manuring has such a valuable effect in 

 establishing the plant, even if the gross yield is not 

 ultimately much enhanced. 



It may also go to explain the extraordinary results 

 of quite small dressings of phosphoric acid upon soils in 

 Southern Australia, where a manuring with half a 

 cwt. per acre or even less of superphosphate has been 

 found sometimes to double the yield of cereals. On 

 analysis the soils are not rich, but they show no such 

 signal deficiency in phosphoric acid as would account 

 for the action of the manure ; it seems much more 

 likely that in a semi-arid country where the whole 

 success of the crop depends on the roots getting quickly 

 down to the cooler and moister subsoil, the stimulating 

 action of the phosphoric acid upon the young roots 

 becomes of the greatest value. In this connection it 

 may be noted that the two crops which most respond to 

 phosphatic manuring, turnips and barley, are both 

 possessed of shallow roots, confined to a comparatively 

 limited layer of soil ; whereas, under ordinary farming 

 conditions, wheat responds very little to phosphoric acid 

 and mangolds hardly at all, both being deep-rooted 

 plants. But even for mangolds farmers are accustomed 

 to use superphosphate, because they have found by 

 experience it is of great assistance in securing a plant. 



It has sometimes been stated that phosphoric acid is 

 associated with the assimilation of nitrogen by the 

 plant, and particularly with its migration from the stem 

 or roots into the seed, the opinion being probably 

 founded on the fact that the nucleo-proteins, so char- 

 acteristic of the reproductive parts of plants, contain 

 phosphorus. This opinion is not, however, borne out 



