250 THE RUBBER TREE BOOK 



estates, and is scarce and dear, chemical products may be 

 more economical. Where cattle are kept, every effort should 

 be made to preserve the manure, especially the liquid, as an 

 application gives young plants a splendid start off. 



In many cases manures, and especially expensive manures, 

 might very well be dispensed with on rubber plantations, even 

 where there is a tendency to backward growth. The backward 

 growth does not generally arise from a deficiency in any of the 

 necessary elements of fertility, but may be due solely to the fact 

 that while present they are not in a form readily " available." 

 In most cases the addition of four or five hundredweights per 

 acre of unslaked lime will greatly benefit the soil. This is not 

 so much because lime is a manure, but because it acts on certain 

 chemical elements and transforms them into a form readily 

 available for plant life. 



The beneficial effects of adding lime to the soil are numerous 

 and easily apparent. The lime is of great assistance to the 

 bacteria in converting decaying vegetable remains in the soil 

 into nitrates, the form in which they are immediately " avail- 

 able " for plant food. It has also an action upon the natural 

 silicates present in the soil and liberates from them supplies of 

 potash which the roots of the trees desire. Lime has also a 

 sweetening effect. Where soil is somewhat acid, lime induces 

 an alkaline reaction and thereby promotes high fertility. In 

 the case of heavy clay soil it has the effect of making the soil 

 more easily divisible and coarser, this permitting a freer circula- 

 tion of both water and air, a very marked benefit indeed. As 

 a simple form of manure, and one which at the same time con- 

 tains a proportion of lime, and thus yields special additional 

 benefits, basic slag is often very serviceable. 



Basic slag, which during recent years has come into general 

 demand for purposes of manuring, is a by-product in the manu- 

 facture of steel from pig-iron. The pig-iron contains large 

 quantities of phosphorus which it is necessary to get rid of, and 

 this is effected by blowing air through the molten mass of iron 

 which has been previously mixed with lime. The slag and the 

 lime bricks which line the converter where the smelting takes 

 place are, after the smelting is finished, ground to powder and 

 sold as the phosphatic manure known as basic slag. 



There has been a good deal of discussion as to whether rubber 



