THE FERTILITY OF SOILS IN THE TROPICS 



417 



ages of trees, etc., their yielding capacity is equal, and 

 is the maximum attainable. 



When differences of yield do exist they may be ascribed 

 either to different cultivation policies or to variations in 

 the degree of drainage. 



It is not improbable that in all these soils the amounts 

 of the various plant foods present are greater than the 

 tree requires for the development of its maximum pro- 

 ductivity. 



More light on the relation of soils to yield can be 

 obtained from a study of some inland soils, percentage 

 analyses of which are given in the following tables : 



Mechanical Analyses. 



SERIES I. GOOD SOILS. 



3 



Nil 



83-9 

 4-5 



Nil 



2'I 

 II'I 

 I2'2 



1-6 



5 



Nil 



70-0 



4 '9 



9'4 



14-0 



17 



Nil 

 72;3 



5'3 



2'0 



7 



29-4 

 38-2 



37 

 7*8 



19*3 

 1-6 



SERIES II. POOR SOILS. 



Except for No. 2 in Series II, all these soils are seen 

 to be of good texture, and no distinction between the 

 "good" and the "poor" can be drawn. No. 3 of 

 the " good " list, for instance, contains less clay than 

 Nos. i and 3 of the "poor," which might otherwise 

 have had their infertility attributed to lack of this sub- 

 stance. 



Recourse to chemical considerations must therefore 

 be made to find an explanation for the differences. 



The percentage results of chemical analyses are given 

 in the next table : 



2? 



