412 THE FERTILITY OF SOILS IN THE TROPICS 



portions of the silts and clay. Consequently, even when 

 adequately drained, root growth is restricted and is 

 mainly confined to the surface. Such soils crack badly 

 in dry weather and the trees suffer severely. 



These observations must be regarded as being general 

 only; hill soils of a clayey type are to be met with, whilst, 

 on the other hand, some low-lying soils are sandy in 

 texture. In the following table are given the percentage 

 results of mechanical analyses of representative samples 

 of the sandier soils, all of which are excellent yielders : 



Coarse sand 

 Fine sand 

 Silt ... 

 Fine silt 

 Clay ... 

 Humus 



No. i is from the Government Experimental Planta- 

 tion at Kuala Lumpur, where trees 12 to 14 years old, 

 numbering now about 90 to the acre, are yielding at the 

 rate of about 9 Ib. per tree per annum. The remainder 

 are all from well-known estates. 



No. 2, on which the trees are n years old, gives 600 Ib. 

 per acre. Nos. 3 and 4, both 9 to 10 year trees, 500 Ib. 

 approximately; and No. 5, where the age is 8 years only, 

 450 Ib. 



It is seen that the proportion of sand to fine silt and 

 clay ranges from 2 : i and over in the first three to i : i 

 in the case of No. 5. 



The sandiest soil under rubber the writer has had as 

 yet occasion to examine contained no more than 71 per 

 cent, of sand to 11*4 per cent, of clay and 6*9 per cent, 

 of fine silt. The yield was poor, but the chemical com- 

 position was poor too, and it would not be safe to regard 

 this degree of sandiness as being one necessarily to be 

 associated with diminished returns. No statement re- 

 garding the limit can therefore be made. 



The texture of typical alluvial clay soils, class No. II, 

 is shown by the following percentage figures. On land 

 of this type 8 year old trees are usually found to yield 

 not more than about 250 Ib. per acre, or 2 Ib. per tree. 



