PRESIDENT S ADDRESS. 9 



and a small portion of i)hosphoric acid and are a vaAiabjt tertilisei 

 but this manure can of course only be got in small quantities. In 

 South Africa most manure merchants make up mixtures suitable 

 for different crops, such as mealie and tobacco fertilisers, and as 

 they are already mixed the farmer is saved the trouble of doing so. 



I have dealt with the several chemicals which it is necessary to 

 have in the soil in order to fully sustain plant life. I should now 

 like to say a word regarding chemicals which are in the soil and 

 which have a deleterious effect on plants and which, therefore, have 

 to be got rid of if jwssible. One which is ver}^ common in South 

 Africa and which is doing an immensity of harm is what is called 

 " black brak," or scientifically called a deposit of sodium carbonate. 



In a large portion of South Africa the undergroiuid waters, which 

 are raised to the surface through the agency of fountains, sj^-ings 

 or by pumps, are for the most part impregnated with mineral 

 compounds, es])ecially sodium salts, derived from the soils and 

 rocks in which the waters are stored ; these sodium salts are also 

 present in conserved water, but not quite to the same extent ; 

 when such water is used for irrigation eventually the liquid jiortion 

 is either consumed by the plants, soaks into the ground or 

 evaporates, but the sodium salts remain on the surface of the soil 

 and by degrees accumulate to such an extent that the soil becomes 

 sterile, and in many instances the only bit of ground on the farm 

 upon which water can be carried becomes useless. One per cent, 

 of sodium carbonate in the soil renders it absolutely sterile. The 

 principal preventative or remedy for this state of affairs is to 

 properly irrigate and drain the land. It may surprise some of my 

 listeners to know that in Egyjjt, where irrigation is carried to a 

 fine art, there has been nearly as much expenditure upon the 

 drainage of the ground as there has been in building canals and 

 furrows to convey the w^ater to the ground, and when fresh irriga- 

 tion works are under consideration both sides of the question 

 receive equal attention. By a proper system of irrigation and 

 drainage the sodium salts can usually be taken away. This can be 

 accelerated by occasionally gi\'ing the ground a reall}/ good soaking. 

 If sodium • carbonates are present to any great extent the 

 method of applying gypsum should also be combined with 

 flooding or soaking with water. This method of counteracting 

 black brak is, I think. ])articularly suited to the case of small 

 farmers in this country, who find that their little patch of irrigated 

 land is gradually becoming unjiroductive and perhaps white with 

 brak salts. It is remedied by the application of j^owdered gypsum to 

 the infected spot. Gypsum is a soft chalky white mineral and is 

 abundant in many of the western and southern parts of this Colony 

 — in fact, I have reason to believe that the Bloemfontein-Kimberley 

 Railway cuts through one or two large beds of it, so that if it was 

 worked it ought to be obtained very cheaply. G.ypsum. together 

 with sodium carbonate, forms calcium carbonate, which is highly 

 beneficial to plant life. 



The salts to which I have referred move up and down, descending 

 as the moisture gets into the ground, ascending as the ground dries 

 up, and at thej^end of a dry season practically the entire mass of the 



