Fertility of some Colonial Soils. 11 



the general public and the farming community more particularly, 

 a keener sense of their importance and value, is most pro- 

 nounced; hence my reason for laying before you figures which 

 might otherwise have been well deferred until they had attained to 

 greater completeness. 



In all the analytical results which follow the method of analysis 

 adopted has been the extraction of the soil at the ordinary tempera- 

 ture with hydrochloric acid of 1-115 specific gravity for five days, 

 and the determination of inorganic constituents in the solution 

 so obtained/'' This method was very fully detailed in my previous 

 paper, and I still regard it as, of all extraction methods, the most 

 satisfactory for quantitatively gauging the reserve stock of plant food 

 in soils. 



Although the figures arrived at by this method from various soils 

 of similar type are in very close agreement amongst themselves, it 

 must not be supposed that the reserve stock of plant food is a 

 sharply defined item in any soil — one that can be determined with 

 the rigid accuracy generally associated with chemical operations. It 

 must be clearly understood that the methods of determining plant 

 food in soils have an element of arbitrariness about them which 

 causes the results obtained by their means to be more or less 

 empirical. At the same time it must never be forgotten that all this 

 can be true without in the least detracting from the great value of 

 the information thus gained. 



Just here one or two figures may be given to indicate how plant- 

 food constituents in different degrees of availability are to be found 

 in one and the same soil. The following, taken from Bulletin No. 41 

 of the Minnesota Agricultural Experiment Station, shows that a very 

 considerable proportion of the plant-food constituents present 

 may be in forms not available for plants : — 



Phosphoric 

 Lime. Potash. Oxide, 



„,, . ., (Grade II 2-44 -54 -38 



Wheat soil i„ ., ^„ „^ ^ ^„ 



(Grade III -36 248 — 



-TT , ., (Grade II -48 -21 '12 



Heavy clay soil {^^^^^j^^ .,6 g..^ .Qg 



Grass and grain soil ^-f"; f. .T. f. 



^ I Grade III -35 1*45 -05 



It will be noticed that in the clay soil as much as 96 per cent, of 

 the total potash is in a form unavailable for plants. 



Similar results have been arrived at in our own laboratory. For 

 instance, three soils from farms in the George Division (Uitkyk and 



* For the determination of phosphoric oxide the soil was extracted by boiling 

 with nitric and sulphuric acids. 



