C — INVJXriGATTONS INTO THE PHYSICAL COMPOSI- 

 T^ION OF 80ME CAPE COLONY .SOILS.* 



By C)iai:m:s F. Jiimtz, i\I.A., D.Sc, F.T.C. 



TIk^ cuinparatively few scientific in\ estimations tluit liave hitherto 

 been made into the characters of the agricultural soils of the Cape 

 Colony have been devoted all but entirely to the consideration of 

 (juestions pertaining to the chemical nature of the soil, and more 

 particularly to the proportions of plant food present therein. Now, 

 ln>wever important the chemistry of the soil may be, there is a danger 

 of its obscuring the vision to other factors whicli go to make up soil 

 fertility. Chemical analysis alone can never suffice to measure a soil's 

 fertility, and even still less its productiveness. The ferfiHty of the 

 soil depends upon other inherent prcjperties besides the presence of 

 plant food — for instance, its texture and general physical condition ; its 

 productireness is dependent on variable environments and incidental 

 circumstances, such as rainfall, atmospheric temperature, conditions of 

 drainage and methods of cultivation ; in a word, it dejiends largely on 

 factors which are altogether extraneous to the soil itself. Hence a soil 

 well supplied with plant food is not always fertile, and a fertile soil is 

 not necessarily productive : the most fertile soil cannot be productive 

 when climatic conditions are unfavourable, and the methods of culti\a- 

 tion adopted unsuitable. These distinctions i-ecjuire to be well kept in 

 view. Leaving aside, however, the wider subject of crop production, 

 and turning again to the more restricted one of soil fertility, it would 

 Ije well clearly to understand that e\en the chemical aspects thereof 

 are closely connecter! with the soil's mechanical condition. The supply 

 of water which circulates within the soil, and which is there tenaciously 

 retained for plant use, is directl}' dependent upon the state of sub- 

 division of the soil particles, other conditions being equal. The very 

 availability of the plant food constituents, moreo\ er, is regulated by the 

 fineness of division in which they exist in the soil. 



In the niechanical analysis of a soil we aim at determining the 

 relati\e proportions in which the different sizes of soil particles are 

 present. There is, however, a sad lack of uniformity in the nomen- 

 clature by the medium of %\hich these various grades are wont to be 

 designated : it may hence prove profitable to examine into this subject 

 somewhat closely. 



In popular language the generality of soils has for many year.s 

 been divided into sandy soils and clay soils, as though all soils consisted 

 essentially or solely of either sand or clay. For the purposes of rough 

 and ready classification a broad differentiation on these lines may pass ; 

 but when, apart from chemical composition and t)ther modifying cir- 



* Tliis piifier \\;ix lieen soiiiewliat abri(lj;e(l. 



