SOIL MANAGEMENT. 47 



ing resistance to disease, and assists in the formation of plump, 

 heavy seed; and more particularly of good tubers, roots, bulbs 

 and fruit. 



The most marked deficiency of South African soils as a 

 whole, as shown by chemical analysis, field tests, and practical 

 experience, seems to be in respect of phosphoric oxide. With 

 reference to Transvaal soils, Juritz says : " An average of 100 

 analyses of Transvaal soils out of various parts of 

 the Province, done by the Department of Agriculture, show 

 the average soil to be poor in phosphates, medium in nitrogen 

 and good in potash." Broadly speaking, this generalisation 

 may well be applied to the soils of the other Provinces too. 



Throughout the Union, with rare exceptions, the judicious 

 use of phosphatic fertilisers is necessary and profitable. 



With regard to nitrogen, deficiency, though not so general, 

 is fairly common, and is invariably associated with a de- 

 ficiency of soil humus. In the summer rainfall area nitrate 

 formation in the soil is rapid during the summer, and the need 

 for nitrogen is not so urgently felt by summer crops as by 

 winter crops. In any case, the demands for nitrogen are most 

 economically met by leguminous green-manuring, or by the 

 incorporation of stable or kraal manure with the soil, or by a 

 combination of both. In this way not only is the nitrogen 

 supply increased, but a large quantity of humus is added to the 

 soil, and in the case of animal manures considerable quantities 

 of phosphoric oxide and potash are also added to the soil's 

 supply. 



Potash is usually present in sufficient quantities, and its 

 application is seldom profitable in South Africa, except on 

 certain sandy soils, and possibly on even better supplied soils 

 where potash feeders such as potatoes, tobaccp, etc., are 

 grown. 



Commercial Fertilisers. — The following are a few of the 

 principal commercial fertilisers available to the farmer in 

 South Africa : — 



(1) Nitratf Soda. — Containing about 15 per cent, nitro- 

 gen immediately available to crops. It is soluble in water and 

 apt to be leached out of the soil by heavy rains. For this 

 reason it is usually applied in comparatively small quantities 

 as a top dressing after the crop is up. 



(2) Sulphate of Ammonia. — Containing about 20 per cent, 

 nitrogen, which rapidly becomes available. It is less liable to 

 be leached out of the soil than nitrate of soda. 



