THE WATER REQUIREMENTS OF FRUIT PLANTS 7 



That the first presented figures are probably representative for many 

 tree fruits is suggested by their close agreement with the 9 acre-inches 

 estimate of Hilgard^^ as the water requirement of 15-year old orange 

 trees in southern California and the 4,500 gallons per tree estimate of 

 Duggar43 as the requirement of a 30-year old apple tree. It is interesting 

 to note that a 12-inch summer rainfall has been estimated as sufficient for 

 the actual water consumption of 100-year old beech trees standing about 

 200 to the acre.^^ Data presented in Table 6 show that the variation in 

 the water requirements of individual crops often exceeds the difference 

 of 200 assumed in the case of the peach orchard. This emphasizes the 

 point that it is frequently a matter of much practical importance to 

 provide the tree with as nearly optimum nutritive conditions as possible, 

 to secure the economical use of water if for no other reason. 



Total Amounts Required for Plants and to Compensate for Evaporation 

 Run-off and Seepage. — It should be noted that in the last paragraph when 

 7 to 11 acre-inches of water was mentioned, as approximately the amount 

 required to mature a peach crop of a certain size, reference was made 

 only to the water actually taken up and used by the plant. As is well 

 known, a considerable percentage of the water that reaches the land as 

 rain or snow or through the irrigation channel is made unavailable by 

 run-off, evaporation and seepage. The exact percentages removed in 

 these ways vary greatly, depending on the seasonal distribution of the 

 rainfall, the topography, the character of soil and subsoil, the atmos- 

 pheric humidity and other factors. It has been estimated that in the 

 forest, where conditions are more favorable than in most fruit plantations 

 for the reduction of run-off and evaporation, probably not more than 35 

 per cent, of the precipitation actually becomes available for tree growth. '^ 

 In orchard practice then, it is doubtful if much more than one-third of 

 the natural precipitation or irrigation water can be considered to be 

 utihzed by the trees, and under poor methods of soil management or in 

 soils of poor water-absorbing and water holding capacity the percentage 

 may be much lower. 



In the light of what has been said it obviously would be impracticable 

 to attempt the construction of a table showing the rainfall requirements of 

 different fruit crops, such as strawberries, cherries, apples and olives, for 

 there are too many contributing factors to be evaluated, but the general 

 principles that have been given should be capable of interpretation and 

 intelligent application to many concrete practical problems as they arise 

 in orchard management. For instance, with a fairly accurate knowledge 

 of the mean and minimum rainfall of a particular location and its seasonal 

 distribution, and after a first hand study of soil conditions as they relate 

 to moisture, it should not be difficult to determine more or less accurately 

 the practicability of growing a certain fruit crop without irrigation 

 facilities, or to determine the relative importance of certain moisture 



