THE FERTILITY OF SOILS IN THE TROPICS 419 



Manuring coconut trees with salt is a very common 

 practice amongst most Eastern races, and probably 

 originated in the observation that trees planted by the 

 sea so often do well. Although salt is not a necessity 

 many inland plantations to which it is never applied give 

 high yields it is undoubtedly in many cases beneficial. 

 Probably its action is to increase the amount of ''avail- 

 able " potash in the soil. 



A much-disputed point amongst the coconut cultiva- 

 tors is whether to clean weed or to allow grass to grow. 

 The writer's observations have led him to the conclusion 

 that the latter practice is unsound; probably on account 

 of the formation of toxins, as demonstrated at Woburn 

 and other places. On the other hand, clean weeding has 

 its disadvantages the soil gets baked and loses its humus 

 more quickly, and on slopes loss results from wash. 



A better practice would be to grow a leguminous cover 

 crop, to be fed to cattle or turned in at the commence- 

 ment of the dry season. The coconut tree suffers 

 severely in times of drought and a timely mulch may 

 have an effect of great importance on the ensuing season's 

 yield. A feature about a coconut plantation is that the 

 growing of such a crop is at all times possible. With 

 rubber, on the other hand, after about the fourth year 

 the shade is too dense to permit of anything being inter- 

 planted. 



SOIL AMELIORATION. 



In the case of both cultivations the least suitable soils, 

 and the ones most difficult to deal with are the heavy 

 clays that have been described. 



Liming is one method of treatment for the purpose 

 of flocculating the clay particles and thus lightening the 

 soil, making it more porous. Lime, however, is very 

 expensive in Malaya, costing nearly 2 per ton; for 

 the above purpose a large quantity is required, and alto- 

 gether it is doubtful whether the results would justify 

 the expenditure. 



The other method of improving such a soil is by 

 green manuring. This must, however, be started early, 

 when the trees are young, as only when light has free 



