Fertility of some Colonial Soils. 13 



regard to a soil collected on the Government agricultural farm, 

 " Elsenburg," in the Stellenbosch Division : — 



Phosphoric 

 Potash. Oxide. 



Grade I. — Extracted with water Undetermined -0013 



Grade I.— Extracted by Dyer's method 



(citric acid) -017 -0036 



Grade II. — Extracted by standard method -024 '024 



Of course it will be seen that, as everything that water or the 

 weaker organic acids could extract from a soil will also be removed 

 by hydrochloric acid of the standard strength, the second grade of 

 plant food will generally include the first ; in other words, if Grade I. 

 is taken to mean " immediately available " plant food, then Grade II. 

 means "immediately available" plant food plus ''reserve stock." 

 This being the case, it follows that when water or citric acid 

 extract only infinitesimal quantities of plant food from the soil, 

 there may still be a large stock of plant food in reserve, but if only 

 small amounts are extracted by hydrochloric acid there cannot be 

 much plant food of any kind. If, therefore, the hydrochloric acid 

 extraction method indicates the soils of a certain area to be poor, 

 there can be no question that they are poor indeed. 



I pass on from these more or less introductory remarks to another 

 aspect of the subject under consideration. At the time of my 

 former paper the work of the Geological Commission had not 

 advanced to the stage it has now attained, and the results of that 

 work were not available, as they are at present, for the purposes of 

 our own investigation. The geological survey of the Colony cannot 

 but be of great worth to the scientific agriculturist, the more so 

 when supplemented by investigations such as those with which the 

 Government analysts have been engaged ; in fact it is not too much 

 to say that, in great part, they only become thus fully valuable when 

 so supplemented. The detailed and instructive maps issued by the 

 Geological Commission, showing, in very many cases, the boun- 

 daries of the farms surveyed, cover largely the ground traversed by 

 the chemical staff, and are comparable with the maps issued by my 

 own office, in connection with which the endeavour has ever been to 

 mark, as accurately as possible, the farm boundaries and all locali- 

 ties whence samples of soil have been collected. Hence the soils 

 analysed can often be assigned to their proper geological formations, 

 and deductions drawn accordingly. Facilities were thus afforded 

 whereby it became possible to arrange the figures in the subjoined 

 tables in classified lists. 



Before any further reference is made to these figures, the extreme 

 difficulty of obtaining samples of soils typical of definite geological 



