2 BULLETIN 31, PORTO RICO EXPERIMENT STATION 
land would be considered excellent for cane growing and is better 
than is ordinarily used for coffee. 
The plats are shaded by leguminous trees, which are uniformly 
planted throughout and kept thinned or replanted as may be required 
to maintain favorable light and shadow. The trees furnish a heavy 
mulch of fallen leaves and twigs and, in effect, may be considered a 
leguminous cover crop. 
Seed from a single Arabian tree of the Padang variety was planted 
in October, 1913, and the resulting seedlings were set in permanent 
place in September, 1914. They failed to thrive, however, owing to 
poor drainage, and many had to be replaced with others from the 
same nursery. Eleven replacements were made later with seedlings 
from a tree of the original planting. These were not included in the 
records of data until 1924, when eight of the trees, then 8 years old, 
apparently equaled companion trees in yield. 
The trees were set in 40 plats of 3 trees each and spaced 6 feet 
apart within the plat and 9 feet between plats. Shallow ditches have 
run lengthwise the plats since 1919. The field was separated into 
5 divisions, each of which contained a check plat, 1 plat which 
received a complete fertilizer — nitrogen, phosphoric acid, and pot- 
ash — 1 plat for each combination of 2 elements, and 1 plat for each 
element alone. Where 1 or 2 elements only were applied the quantity 
of each equaled that of the same element used in the complete fer- 
tilizer. A single definite rate of fertilization was applied to all 
trees within a division. Beginning on the west side of the field, each 
division to the east received twice as much fertilizer as the preceding, 
so that the most eastern or fifth division received 16 times as much 
fertilizer as was given the most western or first division. (See fig. 6.) 
In the discussion the term "group " refers to all trees (15 trees, 
including 1 plat from each division) which received fertilizer identi- 
cal in quality and the term " section " refers to all trees (60 trees, in- 
cluding 4 plats from each division) which received a particular 
element, such as nitrogen, either alone or in combination. The check 
comprised all trees failing to receive any particular element. Nitro- 
gen is indicated by the letter N, phosphoric acid by the letter P, and 
potash by the letter K. 
In the first division complete fertilizer was used at the rate of % 
pound per tree per application, in the second at the rate of y 2 pound, 
in the third at the rate of 1 pound, in the fourth at the rate of 2 
pounds, and in the fifth at the rate of 4 pounds per tree, the single 
elements and combinations of two elements being applied at the same 
rates as in the complete fertilizer. Applications were made semi- 
annually, usually in December and in May. 
Since November, 1917, the fertilizer has been uniformly distributed 
over a square 6 by 6 feet, with the tree in the center. The six appli- 
cations which were made prior to that date were smaller than is noted 
in the diagram, because they were applied to a smaller area. They 
were given at a rate proportionate to the area fertilized, however, the 
trees being too small at first to benefit by the application later given 
the full area. 
The basal formula used was 7 per cent nitrogen, 10.5 per cent phos- 
phoric acid, and 14 per cent potash, thus carrying 1 part nitrogen, 
iy 2 parts phosphoric acid, and 2 parts potash. The materials used 
were ammonium sulphate, superphosphate, and potassium sulphate. 
