SOIL MANAGEMENT, 51 



Nitrogen and humus go hand-in-hand and proper atten- 

 tion to the humus supply will in part or completely solve the 

 nitrogen problem. The best methods of supplying humus and 

 nitrogen are : — 



(1) By crop rotation, including a green manure; prefer- 

 ably leguminous. {See next section.) Where practicable, the 

 residues (straw, etc.) of other crops should also be returned to 

 the soil. 



(2) By the use of animal manures, either by feeding 

 crops to stock on the land or by applying stable and kraal 

 manure. 



A ton of fresh stable manure, consisting of cattle and 

 horse excrements, together with more or less straw, etc., con- 

 tains as a rough average about 10 pounds nitrogen, 5 pounds, 

 phosphoric oxide, and 10 pounds potash. Partly decomposed 

 kraal manure is generally richer if kept under proper con- 

 ditions. 



In feeding crops to stock, under average conditions, it is 

 said that about one-third of the total dry matter of the feed, 

 about three-fourths of the total nitrogen and phosphoric oxide, 

 and practically all the potash, are recovered in the excrements, 

 liquid and sohd. On this basis, for every ton of dry feed con- 

 sumed, rather more than a ton of fresh manure is produced, 

 assuming the latter to contain 75 per cent, water. 



To summarise the foregoing, the principal facts that 

 should be noted, and made use of in regard to the mainten- 

 ance of fertility, are as follow : — 



{a) The beneficial effects of the rotation of crops as 

 opposed to the single crop system. 



(b) That most South African soils are deficient in humus, 

 and in many cases present cropping methods are causing 

 further rapid depletion of the soil's supply, resulting in nitro- 

 gen deficiency, poor mechanical condition, and decreased 

 availability of other plant foods. Provision must be made for 

 maintaining the humus supply, as already described. 



(c) That proper maintenance of the humus supply will 

 in large part, and under best conditions, wholly maintain a 

 sufficiency of nitrogen in the soil. In no other way can 

 nitrogen be maintained so economically. The nitrogen alone 

 in one ton of average kraal or stable manure, at current 

 market prices, is worth over ten shillings. 



{d) That practically all South African soils are deficient 

 in phosphoric oxide. Therefore, regular and adequate applica- 

 tions of commercial phosphatic fertilisers, such as super- 

 phosphate bone dust or basic slag, are absolutely essential. 



