430 Journal of the Department op Agriculture. 



Alexandria district, while the same soil transported to Middelbnrg 

 still yields excellent returns of that crop. Factors such as diseases 

 and insect pests do not, however, come within the province of the 

 chemist; it is therefore proposed not to deal with them further than 

 drawing attention to them. 



Among harmful chemical factors are the conditions known as 

 soil acidity and " bralc." Both conditions are capable of entirelj- 

 preventing the growth of normal crops, no matter how favourable 

 ntlior factors may be. 



The brak condition of soil is not at all likely to be met with in 

 the area under consideration, so that subject need not be pursued 

 further. Acidity of the soil, on the other hand, is likely to be very 

 prevalent. Reference to all of the analyses recorded in this report 

 will show that out of thirteen samples all, except two, are acid to 

 litmus, viz., they turn blue litmus paper red. 



Now the principal function of carbonates in the soil is to prevent 

 the development of the acid condition, a condition which is not only 

 harmful in a direct manner to cultivated plants, but also indirectly 

 in that it prevents the normal activities of certain soil organisms 

 whose function it is to prepare food for assimilation l)y the plant 

 roots. 



Owing to the importance of carbonates just indicated, it is usual 

 to estimate the quantity present when analysing a sample of soil. 

 Of all the samples, No. 616 alone is well supplied with carbonates. 



Fortunately, it is a simple matter to correct a soil for acidity. 

 This is best done by adding an appropriate quantity of ground lime- 

 stone. So great have been the immediate oenefits following such 

 applications that they have been repeated in some cases too often, 

 as witness the old saying: — 



"Lime and lime without manure 



Will make both land and farmer poor." 



Light. — Crops cannot be grown in the dark, because sunlight is 

 necessary to the utilization by the plant of the food (carbondioxide) 

 it obtains from the atmosphere. The farmer makes use of this fact 

 when he grows a crop of teff grass to smother weeds. The teff grows 

 so quickly that it soon shuts off the sunlight from the slower growing 

 weeds. 



Temperature. — The importance of temperature in crop produc- 

 tion is perhaps too often overlooked. Everyone knows that if the 

 weather is too cold there is no growth, and that certain crops may be 

 killed by frost. So also if the weather is too hot growth comes to a 

 standstill ; but not in all cases, because some crops like hot weather 

 best. The fact is that the temperature requirements of crops vary 

 considerably. 



Potatoes, for instance, require cool weather and a cool soil foi 

 best results : wlieat likes cold weather at the start and a cool soil ; 

 thereafter it needs hot weather for ripening. 



Maize, kaffir corn, pumpkins, melons, and cotton are crops for 

 which hot weather is essential. The first-mentioned crops thrive in 

 the cool climate of Witkop ; the last-mentioned are either not grown 

 at all or do badly. 



It "should be evident that if the temperature conditions are not 

 right, the crop .yield cannot be good, no matter how favourable the 

 other factors may be. 



