CHEMISTRY AND CROPS. 165 



We have now considered chemistry as an indicator of soil 

 fertility. It is also extremely valuable in pointing out causes of 

 sterility other than those which depend on an insufficiency of 

 plant food materials. For example, in certain parts of this coun- 

 try the periods of drought are so extensive and the amount of 

 rainfall so slight that the total products of weathering remain 

 in the soil, and frequently attain to sufficient dimensions to give 

 rise to the condition known as "brak," viz., the visible occur- 

 rence of saline matter in the soil. Such excessive quantities of 

 soluble salts are very deleterious to the growth of ordinary 

 crops, and for certain crops very much smaller Quantities of 

 saline compounds than are indicated by their visibility would be 

 fatal or inhibitory. Little has been done towards the investiga- 

 tion of these, our richest soils, but in America and India much 

 work has been acomplished. The subject is a larg'e one, and 

 cannot be discussed here ; therefore I would refer anv who desire 

 information on this subject to the writings of Hilgard and to the 

 bulletins of the United States Bureau of Soils. IMay I urge upon 

 you who, because of your climatic conditions, have little or no 

 interest in this special branch of agricultural chemistrv that the 

 study of saline soils, if it does nothing else, will certainly broaden 

 your view of the chemical reactions that must occur in soils of 

 humid lands. Particularly applicable to this country are the 

 writings of Juritz* and Steadf bearing on this subject. 

 These would probably be profitably perused before the other pub- 

 lications mentioned. Some recent work, too, by Osterhout 

 (California) is also important to students of this subject. He 

 has shown that salts are mutually antagonistic in their effects 

 upon plants, which opens up the possibility of treating "brak" 

 lands bv approoriate additions of requisite salts. Enough has 

 been said to indicate how indispensable is the help of the chemist 

 if we are to bring our rich "brak" lands under economical and 

 profitable cultivation. 



That many other advantages would accrue from a system- 

 atic and thorough chemical investigation of our soils is very pos- 

 sible. Take for example our stock diseases and our insect pests. 

 It is important to know whether soil composition has any in- 

 fluence in these directions. Long ago Juritz suggested that the 

 prevalence of lamziekte in certain districts of the Cape Colony 

 was closely connected with a notorious deficiency of lime and 

 phosphates in the soil. Ingle has laid stress on the abnormal 

 ratio of lime to phosphoric acid in the general diet of our stall- 

 fed animals. Of late writers have urged that white bread, with 

 its lack of phosphates, has a predisposing effect as regards tuber- 

 culosis in man. Dogs have been fed on phosphorus deficient 

 rations, and have become unhealthy and ill-developed. Further, 

 it is known that certain inorganic elements inhibit while others 

 again promote phagocytosis. Finally, we feed bones to our 

 cattle, which crave for them, while we ourselves consume tonics 

 consisting largely of p hosphorus and other inorganic elements. 



* "Soils of Cape Colony." 'pp. 1,72-187: also Eeport of the Robertson 



Irrigation Congress, 1900, pp.. 64-70. 

 I Trans. Phil. Soc, O.R.C., 1908 ; also Reports of Director of Agriculture, O.R.C., 



1907-8 and 1908-9. 



