jan. 22,1917 Effect of Fertilizers on Oranges 129 
From the ultimate analyses of the oranges, Colby found the lowest 
nitrogen content in those samples which had received no nitrogenous 
fertilizer, from which he deduced a lack of nitrogen in the soil. The 
samples not receiving phosphates showed the lowest percentage of 
phosphoric acid, from which the need of a fertilizer of that nature was 
deduced. The percentage of potash was not appreciably affected by 
the presence or absence of fertilizers, showing that potash was not 
deficient in the soil. 
DESCRIPTION OF THE EXPERIMENTAL PLOTS 
The University of California Citrus Experiment Station has maintained 
a continuous fertilizer experiment at Riverside with Citrus trees since 
1907. The experiment is composed of 20 plots, with six trees each of 
Washington Navel oranges, Valencia oranges, Eureka lemons, and Lisbon 
lemons in .each plot. The experiment as laid out consists of four tiers of 
plots from east to west and five from north to south. The ground slopes 
from northwest to southeast. The soil is not entirely uniform, being a 
fairly light sandy loam at the upper end and considerably heavier, with 
a denser subsoil, at the lower end. Pipe lines are run at the head of each 
tier of plots in order to provide for the independent irrigation of each 
plot. The trees of each plot have been managed as uniformly as possible. 
The plan of the experiment provided for the addition of the same 
quantities of the different elements of fertility, from whatever source 
derived. Every plot receiving a nitrogenous fertilizer, for example, has 
received the same quantity of nitrogen. Up to the end of 1914, the total 
amounts applied to each tree had been approximately 6 pounds of 
nitrogen and potash each, and 12 pounds of phosphoric acid. 
EXPERIMENTAL WORK 
A study of the quality and composition of the fruit was first taken up 
with the crop of 1914. In this work a sample of 10 fruits was taken from 
each tree, and a composite of these fruits taken for analysis. Individual * 
records for each tree were thereby obtained. In order to eliminate 
diurnal variations, the sample from one tree of each of the 20 plots was 
picked and analyzed on the same day. In all cases but one the fruit 
from the individual trees of each plot was picked on successive days. 
The Valencia samples of the crop of 1914 were picked on alternate days.* 
The samples were first weighed and the specific gravity of the fruits 
taken by immersing them in jars of alcohol of varying specific gravity 
until the fruit and liquid were in equilibrium, the specific gravity of the 
liquid being taken as that of the fruit. It was then peeled and ground 
through a food chopper. The ground sample was placed in a double 
cheesecloth bag and pressed in a 2-quart fruit press for 20 minutes. The 
peel, material left in the bags, and juice were weighed; and from these fig¬ 
ures the percentage of juice was obtained. All other determinations were 
