AGRICULTURAL CHEMISTRY OF CACAO 187 



of the important elements of plant food present in the soil, 

 requires for the yearly production of young shoots, leaves, 

 and fruit not less than 138 lb. of nitrogen, 64 lb. of phos- 

 phoric anhydride, 94 lb. of potash, 104 lb. of lime, and 

 31 lb. of magnesia per acre. Under careful conditions of 

 agricultural practice, however, of this great annual drain 

 upon the soil, but 8*7 lb. of nitrogen, 4*5 of phosphoric 

 anhydride, 3"7 lb. of potash, 1'4 lb. of lime, and 1 lb. of 

 magnesia are necessarily removed from it, the remainder 

 becoming more or less available again for plant food by 

 the decomposition of the fallen leaves, pruning, and husks 

 upon the land. Of the (in round numbers) 130 lb. of 

 nitrogen returned to the soil a considerable proportion, 

 possibly 20 to 30 per cent, may be lost during the decom- 

 position of the vegetable matter, but where the trees ^re 

 shaded by the nitrogen-collecting bois immortel or oronoque 

 trees (Erythina velutina and E. umbrosa which are used on 

 the islands, or E. glauca which is used in Guiana) doubtless 

 much of the amount thus lost is recouped to the soil. 



These considerations lead to the conclusion that a good 

 cacao 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 rapidly rendering again available the 

 large quantities of manurial matter returned to it in the 

 forms of prunings, leaves, fallen and broken pods. It 

 must, in addition, be one in which the course of nitrification 

 readily takes place ; in other words, a fairly rich friable 

 and well-drained soil is of prime importance for the 

 successful production of cacao. 



The samples from Grenada, St. Vincent, and Demerara 

 were personally selected, while those from Trinidad and 

 Nicaragua were given to us and described as very fertile 

 cacao soils by J. H. Hart, Esq., F.L.S. With the exception 

 of the Surinam, Demerara, and Trinidad samples, all are of 

 soils arising from the degradation of lavas and volcanic 

 cUbris, rich in soda lime felspars. As a rule, these fertile 

 cacao soils are fairly rich in nitrogen, and contain a 



