AGRICULTURAL CHEMISTRY OF CACAO 213 



35"7 per cent, of iron and alumina are shown by Harrison 

 as occurring in a Grenada soil, the proportions being 18-6 

 per cent, iron and 17'1 per cent, alumina. In one of 

 Harrison's " poor soils " as much as 49-2 per cent, of iron 

 and alumina was found, the same sample containing 12-8 

 per cent, of organic matter, which is a higher percentage 

 than any in the Trinidad soil. In all his " good soils " 

 the percentage of organic matter and combined water is 

 high, with the exception of the two samples from St. Vincent 

 and Trinidad, while the analyses made in the Trinidad 

 Laboratory show a much lower percentage of organic 

 matter, given in the table as " loss by ignition." ^ 



Professor Harrison concisely states that K'nesWl" ^' "^ 



A good caoao soil should be one capable of yielding to the tree in the course 

 of years a somewhat high proportion of the important constituents of plant- 

 food without exhaustion, and also capable of rendering again available the 

 large quantities of manurial matter which return to it. . . . And it must be 

 one in which nitrification readily takes place. 



In discussing questions of the exhaustion of soils, Sec, 

 it should not remain unnoticed that in tropical countries 

 a factor is present which the writer has termed " the 

 incidental increment of plant food." This factor is, 

 however, in general disregarded. 



Soils are found, for instance, to contain a certain con- 

 stituent in definite quantity. The trees are said to require 

 a certain quantity of such constituent year by year, and 

 the popular argument follows that when the total is used up 

 the land becomes " exhausted." Well, it has been found, 

 say, that they require a certain amount of phosphoric acid ; 

 the land when examined is proved to contain an amount 

 that would last for ten years. The ten years pass, and 

 according to analysis the land should be exhausted, but 

 good crops continue from year to year, and have continued 

 for half a century to do so, on land supposed to contain 

 only a ten years' supply. It is one of the strong arguments 

 of the manure merchants that " what is annually taken 

 away exhausts, and must be artificially supplied." In our 

 case it is not supplied artificially, but apparently naturally, 

 and by methods which are not yet fully understood, and 



