IRRIGATION IN FLORIDA. 15 
chart, the soil in the grove was in this condition for the period from 
May 1 to June 9, with the exception of five days from May 12 to 16. 
Other factors affecting the soil moisture which are not shown 
graphically are temperature and wind. February and March were 
cold and the evaporation was small, but April, May, and June were 
excessively hot. Many tests in the West show that the evaporation 
from an open, well-cultivated space is very small. With reference to 
the upper curve, it may, therefore, be assumed that the difference 
between the two curves shows approximately the effect of the groves 
upon evaporation, although the temperature in a grove is somewhat 
less than that in the open. However, the samples were taken as far 
away from the influence of shade as was possible while still well 
within the root area, and the trees were trimmed high, which per- 
mitted a good air current throughout. 
This chart is especially valuable when used in connection with the 
rainfall charts (figs. 1-4) . Taken together they give a clear idea as 
to soil-moisture conditions for the past 22 years, and from them it is 
possible to arrive at a fair average which should apply to the future 
as well as to the past. Space will not permit a thorough study of 
these problems, but from the charts it may be seen that there have 
been many periods in the past when the moisture content of the aver- 
age orange grove has been below the 3 or 4 per cent which seems to 
be necessary for growth. It also may be seen that small amounts of 
rainfall in the warm spring months of April, May, and June are not 
of great importance, since the moisture soon disappears. 
Figure 6 shows the effect of cultivation in a citrus grove. These 
tests were made in representative groves, and the curves show the 
average of a number of tests made at Maitland, Orlando, and Dren- 
nen Station, 4 miles south of Orlando. These borings were made at 
times of drought, most of the tests being made in May and June, 
1914, at a time when the soil was very dry, as is shown in figure 5. 
The cultivated portions were kept in good condition throughout the 
season, a good dust mulch being preserved. The uncultivated por- 
tions were not disturbed at any time through the summer or winter. 
The soil, in some cases, was well packed, and in all cases it was cov- 
ered with a heavy growth of grass and weeds, dead at the time the 
samples were taken. It would have been possible to keep the weeds 
and grass down, but this would not have represented true conditions, 
as grass and weeds grow in abundance where groves are not culti- 
vated. The spaces designated in figure 5 as " open " were outside 
the radius of any tree roots. The curves for the grove show mois- 
ture content for full-grown orange trees. Soils, in all cases, were of 
the high-pine class. 
The results shown by the curves need little comment. It is ap- 
parent that cultivation in the open spaces has had a marked effect 
