IRRIGATION I3ST FLORIDA. 13 



SOIL-MOISTURE TESTS. 



The writer has made a number of soil-moisture determinations 

 in citrus groves in and near Orlando and in the trucking sections of 

 Sanford and Orlando. These tests were made in the spring of 1913 

 and throughout the season of 1913-14 for the purpose of determining 

 the amount and location of available soil moisture at different times 

 of the year and in the different types of soil. 



Figure 5 represents the percentage of soil moisture x for the differ- 

 ent dates throughout the season 1913-14, and at the same time shows 

 the amounts of rainfall by three-day periods during the season. The 

 tests for this chart were made in a citrus grove in Orlando. The 

 top curve shows the average percentage of soil moisture for the first 

 6 feet of soil in an open, cultivated space that is not affected either by 

 tree roots or by grass. The lower curve shows moisture content 

 among full-grown orange trees, which have grown up from roots 

 since the 1895 freeze. The vertical figures represent soil moisture in 

 percentages and inches of rainfall, given in three-day periods. As an 

 example illustrating the use of the chart, it will be noted that the 

 total rainfall for the period between January 21 and January 24 was 

 3.8 inches. Again, note the effect of this rain on the soil moisture. 

 On January 15 the soil in the grove showed only 3.9 per cent of soil 

 moisture and the open space showed about 5.7 per cent. Immediately 

 after the rain the average moisture content for the two sections was 

 9.5 per cent and 7.8 per cent, respectively, falling to 5 and 5.7 per cent 

 within a few days. It will be noticed that in all cases showing a 

 plentiful rainfall the two curves are close together, but that where 

 the rainfall is deficient the curve representing the soil-moisture con- 

 tent in the grove drops very rapidly. The moisture in the open, root- 

 less space, however, averages considerably higher at all times. The 

 lower curve shows very plainly the effect of tree roots in absorbing 

 the available soil moisture. 



It is not possible to determine the exact percentage of soil moisture 

 needed to keep the trees in good condition, as the citrus tree is very 

 hardy and will not show wilt for a considerable period after the 

 available moisture of the soil has been exhausted. The character of 

 the soil also affects this, as some soils are more retentive of moisture 

 than others. But there can be no doubt that the available supply of 

 moisture is gone when the soil will run from the hand like dry sugar. 

 This condition is found in most of the soils tested after the moisture 

 content has fallen below 3 per cent. Judging from the curves in the 



1 The percentages of moisture referred to in this discussion are based on the ratio of 

 the weight of dried samples to the difference in weight between the wet and dried samples. 

 Each sample represents the moisture content at a certain depth in the grove or garden, 

 and this is taken to be representative of a larger area. 



