THE CULTIVATION OF COCOA 167 



shall contain these latter elements to a certain percent- 

 age, but also, if they are to be of use to the plants, that 

 they shall be present in an available form. 



For instance, the soil may contain potassium com- 

 pounds which are of no use to the plants, as the latter 

 are unable to absorb them ; while there are other potas- 

 sium compounds which can readily be absorbed by the 

 roots, and are therefore called " available plant -food." 

 The non-available compounds are also called " dormant 

 plant-food," a name which indicates that these com- 

 pounds can by certain influences be " awakened," i.e. 

 changed into available compounds. The elements nitro- 

 gen, potassium, phosphorus and lime must thus be 

 present in the soil to a certain quantity in order to 

 provide sufficient food for the cocoa tree, and they must 

 be present in the form of available compounds. 



The first purpose of manuring is, therefore, to add to 

 the soil those elements of which available compounds 

 are present in smaller quantities than the plant requires 

 in order to produce the highest yield. 



The question now becomes : " How can we find out 

 what is needed ? " and the answer is, only by giving the 

 soil larger and smaller quantities of nitrogen, phosphorus, 

 potassium and lime compounds, and seeing whether any 

 increase in the yield is obtained. There was a time, 

 however, when it was expected that chemical analysis 

 of a soil would tell us which elements, and what amount 

 of each, had to be supplied by manure in order to obtain 

 the highest return, and that it would no longer be 

 necessary to carry out manuring experiments, which 

 sometimes require several years to give a clear result. 

 The analysis of soils has, however, not been so useful 

 as was anticipated, for the reason that chemists have 

 not succeeded in discovering a method for ascertaining 

 the quantity of available compounds of nitrogen, phos- 

 phorus and lime present in a soil. The absolute quantity 

 of these elements can be very accurately determined, but 

 as long as it is uncertain what part of the total quantity 

 found is available and what part dormant plant-food, 



