156 Report S.A.A. Advancement of Science. 



As examples of the commercial lime obtainable, the following 

 may be cited : — 



In some districts limestones do not occur, and I have had 

 correspondence with farmers who were anxious to procure lime for 

 agricultural purposes locally, so as to avoid the cost of transport 

 from a distance. Several substances suspected to be rich in lime 

 have been sent to me, but on examination these minerals have been 

 found to be almost free from that constituent. 



The ashes of certain trees have been found to be very rich in 

 lime, and might be used for agricultural purposes when available. 

 Thus a tree from Mozambique was found to yield about 6 per cent, 

 of ash, of which about two-thirds consisted of lime. Another sample, 

 the ash of a tree known as " Mopani," growing in the Tati Conces- 

 sions country, was found to contain over 55 per cent, of lime, a 

 considerable portion of which existed as carbonate. 



4. — Potash. 



As already stated, it is on comparatively few of our soils that 

 potash manures are required. 



Probably wood ashes are the most readily available natural 

 source of potash, especially the ash of twigs, brushwood, etc. 



Should imported manures be used, preference should be given to 

 sulphate of potash. On no account is it advisable to use the lower- 

 priced Kainite, which is open to the objections of involving a much 

 greater cost in transport for the same quantity of potash, and to being 

 contaminated with large quantities of saline matter, which is not only 

 useless, but may prove very harmful. 



In conclusion, I would emphasise the importance of utilising as 

 fully as possible the natural manurial resources of the country, and 

 thus avoiding the expense which is involved in the purchase of 

 imported manures. Indeed, so high are the prices of the latter, 

 when the cost of transport is included, that it is often a matter of 

 difficultv to know whether one is justified in recommending their use, 

 and whether the undoubted increase in yield which would follow their 

 application would pav for their cost. 



Greater attention should be paid by the farmers to the preserva- 

 tion and restoration to the land, of all the waste products of the 

 farm, the use of green manuring, and all means by which the much- 

 needed combined nitrogen, phosphates, and lime may be conveyed to 

 the soil. 



