THE AGRICULTURAL CHEMISTRY OF CACAO. 79 



From the.se figures it appears that the cacao tree whilst 

 storing up in the plant itself relatively large proportions of the 

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

 the yearly productions of young shoots, leaves and fruit not less 

 than 138 Ibs. of nitrogen, 64 Ibs. of phosphoric anhydride, 94 Ibs. 

 of potash, 104 Ibs. of lime and 31 Ibs. of magnesia. Under 

 careful conditions of agricultural practice, however, of this great 

 annual drain upon the soil but 8*7 Ibs. of nitrogen, 4'5 Ibs. of 

 phosphoric anhydride, 3*7 Ibs. of potash, 14 Ibs. of lime and 1 Ib. 

 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 Ibs. of nitrogen returned 

 to the soil a considerable proportion, possibly 20 to 30 per cent, 

 may be lost during the decomposition of the vegetable matter, 

 but where the trees are shaded by the nitrogen collecting Bois 

 Immortel or Oronoque trees (Erythina velutina and E. urnbrosa 

 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 pruning^, 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 of prime importance 

 or the successful production of cacao. 



