48 PARA RUBBER. 



excretions may be prevented from accumulating to any injurious 

 extent both by cultivating rotations of crops and by proper 

 tillage. The importance of the latter remedy cannot be too 

 highly estimated in the cultivation of a permanent crop like Para 

 rubber, which, when closely planted, debars the growth of inter- 

 crops. 



MANURING. 



On comparing the analyses of the soil in which Hevea has 

 been growing for thirty years with that which has been under 

 pasture at Heneratgoda, we find that the former has increased 

 its supply of organic matter, nitrogen, and potash, but its lime 

 and magnesia content has decreased. This is not altogether 

 surprising, as it is generally found that lands occupied by trees 

 are yearly enriched by the annual leaf fall. In addition to re- 

 turning to the soil a large proportion of the elements used up in 

 the development of the leaf, part of that obtained by the elabora- 

 tion of the atmospheric carbon dioxide during the processes of 

 assimilation which take place in the leaf is annually deposited. 

 This annual mulching of leaves contains a considerable amount 

 of organic matter which is converted into soluble plant foods by 

 the atmosphere and nitrifying bacteria. 



The soil has been also considerably improved by the various 

 other beneficial agents which operate on lands occupied with 

 thickly planted trees. The network of roots formed by them 

 holds the particles of soil together and checks the rain washing 

 away soluble plant foods. Soil moisture is conserved through 

 being shaded from the sun by the foliage of the trees, and 

 the conditions favouring the development of nitrifying bacteria 

 are ameliorated. 



On rubber estates where these natural soil improving agencies 

 are allowed to proceed unhindered, the principal losses that the 

 soil sustains are the elements consumed in the building up of the 

 stems and branches of the rubber trees and those contained 

 in the bark excised and the latex extracted during tapping 

 operations. 



It will thus be apparent that, providing good land has been 

 selected for the plantation, and there is no excuse for choosing 

 poor land, considering the enormous areas of rich virgin land in 

 the tropics well adapted for rubber cultivation now lying idle, 



