There are few cultivated crops that make less drain upon soil
fertility than cacao, and few drafts upon the land are so easily and
inexpensively returned. From an examination made of detailed analyses
by many authors and covering many regions, it may be broadly stated
that an average crop of cacao in the most-favored districts is about
9 piculs per hectare, and that of the three all-important elements of
nitrogen, phosphoric acid, and potash, a total of slightly more than
4.2 kilograms is removed in each picul of cured seeds harvested. These
37 kilos of plant food that are annually taken from each hectare may
be roughly subdivided as follows:
18 kilos of nitrogen,
10 kilos of potash,
9 kilos of phosphoric acid.
On this basis, after the plantation is in full bearing, we would have
to make good with standard fertilizers each year for each hectare
about 220 kilos of nitrate of soda, or, if the plantation was shaded
with leguminous trees, only one-half that amount, or 110 kilos. Of
potash salts, say the sulphate, only one-half that amount, or 55
kilos, if the plantation was unshaded. If, however, it was shaded,
as the leguminous trees are all heavy feeders of potash, we would
have to double the amount and use 110 kilos.
In any case, as fixed nitrogen always represents a cost quite double
that of potash, from an economical standpoint the planter is still
the gainer who supplies potash to the shade trees. There still remains
phosphoric acid, which, in the form of the best superphosphate of lime,
would require 55 kilos for unshaded orchards, and about 70 if dap-dap,
Pionciana, or any leguminous tree was grown in the orchard. These
three ingredients may be thoroughly incorporated and used as a top
dressing and lightly harrowed in about each tree.
If the commercial nitrates can not be readily obtained, then
recourse must be had to the sparing use of farm manures. Until the
bearing age these may be used freely, but after that with caution and
discrimination. Although I have seen trees here that have been bearing
continuously for twenty-two years, I have been unable to find so much
as one that to the knowledge of the oldest resident has ever been
fertilized in any way, yet, notwithstanding our lack of knowledge of
local conditions, it seems perfectly safe to predicate that liberal
manuring with stable manure or highly ammoniated fertilizers would
insure a rank, succulent growth that is always prejudicial to the best
and heaviest fruit production. In this I am opposed to Professor Hart,
[6] who seems to think that stable manures are those only that may
be used with a free hand.
We have many safe ways of applying nitrogen through the medium of
various catch crops of pulse or beans, with the certainty that we
can never overload the soil with more than the adjacent tree roots
can take up and thoroughly assimilate. When the time comes that the
orchard so shades the ground that crops can no longer be grown between
the rows, then, in preference to stable manures I would recommend
cotton-seed cake or "poonac," the latter being always obtainable in
this Archipelago.
While the most desirable form in which potash can be applied is in
the form of the sulphate, excellent results have been had with the
use of Kainit or Stassfurth salts, and as a still more available
substitute, wood ashes is suggested. When forest lands are near,
the underbrush may be cut and burned in a clearing or wherever it
may be done without detriment to the standing timber, and the ashes
scattered in the orchard before they have been leached by rains. The
remaining essential of phosphoric acid in the form of superphosphates
will for some years to come necessarily be the subject of direct
importation. In the cheap form of phosphate slag it is reported to
have been used with great success in both Grenada and British Guiana,
and would be well worthy of trial here.
Lands very rich in humus, as some of our forest valleys are,
undoubtedly carry ample nitrogenous elements of fertility to maintain
the trees at a high standard of growth for many years, but provision
is indispensable for a regular supply of potash and phosphoric acid
as soon as the trees come into heavy bearing. It is to them and not
to the nitrogen that we look for the formation of strong, stocky,
well-ripened wood capable of fruit bearing and for fruit that shall
be sound, highly flavored, and well matured.
The bearing life of such a tree will surely be healthfully prolonged
for many years beyond one constantly driven with highly stimulating
foods, and in the end amply repay the grower for the vigilance,
toil, and original expenditure of money necessary to maintaining a
well-grown and well-appointed cacao plantation.