42O THE FERTILITY OF SOILS IN THE TROPICS 



access to it can a cover crop be grown. No suitable 

 plant that will grow in the shade has as yet been found. 

 The seed should be sown at the commencement of the 

 wet season, in September or October, and the crop dug 

 in deeply about the following February. A second sow- 

 ing might be possible in May, but one crop a year should 

 be sufficient. Repeating this for three seasons, or as long 

 as the shade is not too dense, will result in a large 

 quantity of humus being incorporated with the soil, ren- 

 dering it lighter and more pervious, beside increasing 

 the nitrogen content. 



A suggestion that seems well worth a trial is to dig 

 narrow trenches 3 ft. deep between the trees, and to 

 bury cow-dung or, as this is rarely obtainable, a green 

 manure, preferably together with some basic slag, in 

 them, finally lightly replacing the soil. These places, 

 to which the young rootlets will rapidly be attracted, 

 will serve as ventilating shafts, and should have a bene- 

 ficial effect on the health of the tree. 



Another serious question is that of the prevention of 

 wash. It is no uncommon sight to see numerous deep 

 furrows cut by the rain water running down the sides 

 of hills planted with rubber, from which the surface 

 soil is obviously being rapidly washed away. Here again 

 a cover crop will prove of great value, but the best pre- 

 ventive undoubtedly is to terrace the land. The high 

 cost is the argument used against this operation, but those 

 who have carried it out hold the opinion that this will 

 be adequately compensated for by the greater rate with 

 which the coolies will be able to tap when the trees come 

 into bearing. 



CHOICE OF LAND. 



In the course of travelling, the writer has made a few 

 observations on the relationship of forest growth to the 

 nature of the soil, which may here be recorded. 



On deep soils of good texture that is, containing a 

 fair proportion of sand the jungle trees have trunks 

 round at the base, like the Hevea tree, and attaining 

 3 ft. to 4 ft. in diameter. On the other hand, where 

 the soil is clayey and the trees shallow-rooted, the but- 



