10 BULLETIN 462, IT. S. DEPAETMENT OF AGEICULTTJBE. 



in 1910 and twice in 1911, these irrigations coming in April and 

 May. There was no irrigation in 1912, and the chart shows that 

 probably none was needed. The years 1913 and 1914 were very 

 well supplied with rainfall, although irrigation should have been 

 practiced in the late spring of both years, and probably would have 

 been if the engine had been in repair. The spring of 1913 was very 

 dry in some parts of the State and was the cause of much loss through 

 dropping of the newly formed fruit. 



From a study of the records of the Florida State Horticultural 

 Society, 1 it seems that there was considerable loss from drought in 

 citrus groves in 1892-93 and 1893-94, and again in 1897-98. The 

 proceedings of this society for the years 1895-96 and 1898-99 seem 

 to be barren of discussion regarding irrigation affairs, but interest 

 was again aroused during the long drought of 1906-7 and has con- 

 tinued to the present time, although the last three seasons have been 

 favorable in some sections. A study of the rainfall charts makes 

 apparent the reason for the ebb and flow of interest in irrigation. 



Judging from the data in hand and a study of the rainfall charts, 

 it would seem fair to estimate that about half the years (from 10 to 



11 years in the last 22) are deficient in rainfall to such an extent as 

 to make irrigation of citrus groves profitable. The Hypoluxo chart 

 shows that the number of years in which irrigation was required is 

 less than this average, probably varying from 5 to 7 in the last 22 ; 

 in other words, 20 to 35 per cent of the years would call for irriga- 

 tion. On the other hand, the number of years when irrigation was 

 necessary is not of main consideration. The important points are 

 how badly the trees need water when the dry years appear, and how 

 much damage a drought causes, not only in immediate loss of fruit, 

 but in permanent harm to the tree. These questions are answered in 

 several ways, but nearly all answers agree that such years as 1897-98, 

 1906-7, and 1909-10 severely shock the health of the tree, and there 

 is no doubt that irrigation at these times would insure a good 

 crop of fruit when prices are high because of the lack of high-grade 

 products. 



RELATION OF SOIL TYPES TO IRRIGATION. 



The relation of soil types to irrigation probably ranks second in 

 importance to rainfall in determining irrigation needs. The writer 

 has made a number of soil-moisture tests which bear directly on the 

 needs of irrigation, but before discussing this subject it would be 

 well to outline briefly the general types of soils as popularly known. 



It is estimated by the State geologist, E. IT. Sellards, that 75 per 

 cent of the State originally was covered with pine forests. This 



1 Annual Proceedings of Florida State Horticultural Society. 



