WATER-REQUIREMENTS OF DIFFERENT TREES 157 



converse is also true, for some localities of light rainfall report success 

 with deciduous fruit trees with a minimum amount of irrigation water. 



Deciduous Fruits. Without making too much of individual 

 reports there appear instances enough to warrant the conclusion that 

 the deciduous fruit tree can winter successfully with a small moisture 

 supply and is, in fact, in less danger from lack of moisture than from 

 over-supply at this time of the year. If there be enough moisture to 

 prevent injury from evaporation, the tree will start good growth as the 

 season advances and continue it if irrigation is given promptly and in 

 sufficient quantity. There must always be a determination of what is 

 an adequate supply by reference to local conditions, but as an estimate 

 of necessary rainfall has been made at 20 inches, it is evident that ade- 

 quate irrigation may be very much less than that. The rainfall of 20 

 inches is distributed through six or seven months. Some of it consists 

 of light rains, with long, dry intervals, where there is slight penetration 

 and quick evaporation. Some of it is lost by run off and by drainage. 

 It is not surprising, then, that some growers having deep valley loams 

 to render their irrigation effective, report success with deciduous trees 

 with 8 or 10 inches of water applied just at the time of the tree's 

 greatest needs and used, no doubt, with maximum efficiency. It seems 

 to be a warranted deduction, from all data known to the writer, that 

 10 inches of water, applied at the right time to soils of good depth and 

 fair retentiveness, and accompanied by good tillage for conservation, is 

 an adequate supply for five months of growth and fruiting even when 

 the rainfall is only about enough to prevent drying out during the 

 winter season. Some growers report use of less than this. Certainly 

 less will do for young trees under favorable conditions, and some of 

 the least amounts are reported from the newly planted regions. As 

 the trees advance in age and bearing, larger amounts will be required. 

 Instances of greatest frequency of application may be taken as indicat- 

 ing soils lacking retentiveness, either through shallowness or coarse- 

 ness, or either of these accompanied by extreme summer heat and 

 aridity. 



Citrus Fruits. As these trees are evergreens, and as their habit 

 is to make their chief fruit growth in the autumn after the work of the 

 deciduous tree has been finished for the season, the irrigation season 

 for them is much longer. As they are, in fact, almost always active 

 and sustaining uninterrupted evaporation from their leaf surfaces, 

 they must always be provided with moisture or ill will result to tree 

 or fruit. They thus require more water than do deciduous trees. 

 There is the same relation between irrigation and rainfall with 

 citrus, as with deciduous fruit trees, but the degree of relation is 

 different. Many trials have shown that it is practically impossible 

 to grow satisfactory citrus fruits without irrigation, unless there be 

 underflow, and this is attended by the usual difficulties of high 

 ground water and undesirable. There is no combination of heavy 

 rainfall, or winter irrigation, and soil retentiveness which will sup- 

 ply the summer and autumn thirst of the orange or lemon in Cali- 

 fornia. Irrigation, too, must be maintained both summer and win- 

 ter wherever the rainfall is not well distributed and adequate. In 



