. PART IV.
A small portion of the shamba with lalang grass has now been
cleared of all rhizomes and is kept in a good state of cultivation in
order to test the value of soil aeration as a means of checking disease.
STARVATION AS A CAUSE OF DISEASE.
Sampson has shown in great detail the importance and role of
certain food substances in the life of the coconut, the chief of which
are nitrogen, potash, phosphoric acid and lime. The plant obtains
these foods from the soil and to a considerable extent from the deeper
layers of the soil; part of these food substances are entirely lost to
the shamba when the crop is removed but part returns to the soil by
the decay of the leaves and other debris. Sampson has shown that
a heavy crop uses up a large amount of food and is followed by a
period of shortage with a consequent small crop, partly due to the
failure of the flowers to set and, partly, to failure to develop properly.
These facts regarding the Madras coconut suggest that one of the
adverse factors in Zanzibar which causes excessive nut fall may be a
lack of the essential food substances, or that these substances though
they may be present in sufficient quantity are not in an available form
for plant food. In this connection it is noteworthy that it is not
uncommon to find unusually good bearers amongst those trees growing
in the yards of Arab houses in the town and which probably have
access to a rich form of manure from drains and cess pits. However
it must not be forgotten that equally good bearers are sometimes to
be found in the shambas remote from any known rich food supply and
in the midst of barren and diseased trees.
As it is possible that excessive nut fall and the occurence of splits
and gummosis may be due or partly due to a shortage of food or of
certain food substances, a few preliminary experiments are being
carried out to test this assumption.
Owing to the fact that analyses were not available of the coconut
soils in 1925 the work has been somewhat handicapped; the only
analyses available at that time were those of several clove shambas.
In these the clove soils are shown to be lacking in sufficient nitrogen
and potash; moreover, it was shown that the soil was acid in reaction.
The coconut is an exhausting crop in as much as a large weight of
fruit is removed annually (average at Marhubi in best part of shamba
187lbs. per tree, per annum); the only enrichment which the soil
receives is the hoed in grasses, the fallen fruit and other debris, in the
case of shambas like Marhubi an infinitesimal amount, as there is
little grass and most of the debris is removed for fuel.
I have been able to find a few records of experiments in manuring
carried out on coconut estates in different parts of the world and of
these the following two reports are of exceptional interest. In the
Annual Report from the Experimental agricultural station at Porto
Rico for 1915 there is an account of manuring experiments which
have been in progress since 1912. It was found that in the first two
years the manure had little effect on the yield of nuts but after that
there was a marked increase in the crop. Trees which had received
a manure containing 6% nitrogen, 89, phosphoric acid, and 129%
potash in the proportion of 10 Ibs. per tree per annum gave a gain of
30 nuts per annum per tree above the control, whilst those receiving
9G lbs. of the same manure gave an increase of 60 nuts per annum

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