Florida Agricultural Experiment Stations


pressed as pounds per acre, the highest rates were usually found
in groves with trees closely planted.
 While the majority of the groves under study used chemical
fertilizer exclusively, approximately one in every five groves
added some form of organic nitrogen, usually with the summer
application. Most of the groves in that group used 25 percent
organic nitrogen and a small number of groves used 40 percent
organic nitrogen in summer applications. In 12 groves some
form of organic nitrogen (usually 25 percent) was mixed in
all the fertilizer applications. In 1955 single applications of
sludge, tobacco stems or cyanamid were applied to 10 of the
groves in place of the summer fertilizer applications. Among
the inorganic nitrogenous compounds used in separate applica-
tions, sodium nitrate was most commonly used (50 groves). It
was followed closely by calcium nitrate (43 groves). Thirteen
groves used ammonium nitrate in separate applications. Po-
tassium nitrate was used as a single compound in 29 of the
groves one time or another during the three-year period. The
distribution of groves in relation to the amount of applied nitro-
gen is summarized in Table 7.
 Wide variations in the use of phosphorus were observed from
grove to grove. Approximately 14 percent of the groves did not
receive any phosphorus between 1953 and 1955. The other 86
percent were fertilized with amounts varying from 0.1 to 3.8
pounds of P20O per tree per year, or from 9 to 233 pounds per
acre (Table 7).
 The quantity of potassium used in different groves ranged
from 0.72 to 4.80 pounds per tree, or 72 to 310 pounds per acre.
Analysis of various data accumulated from the survey indicated
that results concerning potassium can be interpreted only on the
basis of its usage in relation to the quantity of nitrogen applied
and the nitrogen-potassium ratio used in the fertilizer. The dis-
tribution of groves using various quantities of nitrogen and
potassium is shown in Table 6.
 More potassium than nitrogen was used in 20 percent of the
groves, while another 27 percent of the groves received equal
quantities of both. In general, less nitrogen was applied to
groves receiving higher rates of potassium and vice versa, al-
though there are exceptions. Also, nearly half of the groves
under study received more potassium than the present recom-
mended rates (12).