SOIL MANAGEMENT. 55' 



vice-versa . Under favourable conditions legumes can make 

 normal grofwth in soil completely devoid of available nitrogen. 

 These crops are of particular value for improvement of soils 

 low in nitrogen, as they tend to correct the deficiency in this 

 respect. The total nitrogen content of legumes is generally 

 much higher than that of non-legumes, consequently they are 

 of greater nutritive value as stock feed. 



(2) Non-legimies. — These take their nitrogen directly 

 from the soil's supply, and therefore do not enrich the soil in 

 this respect. 



The principal crops grown in South Africa for green- 

 manuring are : — 



Legumes. — Cowpeas, velvet beans, soy beans, and lupines, 

 are all summer annuals adapted to parts of the Transvaal, 

 Orange Free State, Natal, and Cape Province. Field peas 

 and vetches are winter annuals used chiefly in the South- 

 West Cape, but also under irrigation in other parts of the 

 Union. 



Lucerne residues provide some green manure when the 

 crop is ploughed down after it ceases to give profitable yields. 



Non-legumes. — Buckwheat, a summer annual, is one of 

 the best known. INTustard is often grown as a green manure. 



The aftermath of certain hay and pasture crops frequently 

 supplies a certain amount of green manure. Towards the end 

 of the season teff grass will often make a growth insufficient 

 for hay, but of appreciable value as green manure. Eye and 

 oats are frequently grown for grazing, and after this they may 

 make a fair growth, which is sometimes ploughed under. 



Although not strictly green manures, the residues of 

 certain crops when ploughed down contribute to no small 

 extent to the humus control of the soil, e.g., the straW of 

 headed wheat. 



The turning in also of a heavy growth of weeds provides 

 a certain amount of green manure. 



The Ploughing Down of Green Manures. — This should 

 be done when conditions are such that rapid decomposition will 

 be ensured. If the crop is in a succulent condition, the pre- 

 vailing temperature high, and the soil reasonably moist, 

 humification will be certain and quick. If the soil is too dry at 

 the time when ploughing takes place, its consequent loose, 

 open condition may cause excessive evaporation of soil 

 moisture, especially in semi-arid parts. Again, if the crop is 

 ploughed under when very mature, and consequently in a hard. 



