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 1 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 



