SOIL MANAGEMENT. 49 



(3) It gives rise to soluble bicarbonate of lime in the soil, 

 which flocculates clay, thus greatly facilitating granulation. 

 Therefore, the addition of lime greatly improves the mechanical 

 condition of soils that are inclined to be " heavy." 



(4) In cases, probably rare, where the soil not only lacks 

 free lime, but is also markedly deficient in other compounds 

 of calcium, addition of lime may have a beneficial effect by 

 virtue of the plant food element calcium which it furnishes in 

 readily available form. In this respect it acts as a 

 direct " fertiUser." 



Of greatest importance are the effects of lime as related 

 to soil activity and mechanical condition, and from the point 

 of view of these functions it is termed a soil " amendment." 



Agricultural experience in Europe and America shows 

 that the presence of free lime commonly plays a controlling 

 part in soil fertility, and it has frequently been found that acid 

 soils of low fertility become highly productive after lime has 

 been added. 



Under South African soil and climatic conditions, how- 

 ever, it should be stated that, except in the case of a few crops, 

 such as sugar cane and certain legumes, practical experience 

 has not clearly estabhshed the genuine necessity of a sufficient 

 supply of free lime in the soil. On the score of economy, 

 therefore, the advisability of liming soils for field crops in 

 South Africa, with the exceptions already noted, is still 

 problematical, although there is no doubt as to the beneficial 

 effect of lime upon the mechanical condition of heavy soils. 

 On some acid soils, however, where transport facilities are 

 reasonable, and lime easily and cheaply obtainable, liming 

 will, no doubt, be found to be lucrative; more particularly on 

 soils that are naturally rich in humus, or have recently 

 received large applications of organic matter in the form of 

 manure or green-manure. 



Lime may be applied to the soil in the mild form of finely- 

 ground hmestone, commonly known as " agricultural lime," 

 or in the more energetic caustic form of slaked lime. The 

 former is generally to be preferred, because the energetic action 

 of slaked lime is liable to cause excessive decomposition of 

 organic matter, leading to rapid depletion in this respect. In 

 the case of heavy soils, where the mechanical effect is chiefly 

 sought after, slaked lime will cause more rapid improvement. 



In general, lime should be applied early, by spreading 

 over the ploughed soil and then harrowing it in. 



