WHEN IS IRRIGATION DESIRABLE \ft\ 



But owing to local conditions of soil and climate, the rainfall, no 

 matter how large, may not always be relied upon to carry the trees 

 through the dry season. The fact is that the soil is not capable either 

 of receiving the heavy rainfall or of long retaining such portions as 

 actually enter it. There is, then, a considerable part of the rainfall 

 which is worse than worthless, because it does injury by soil wash- 

 ing and soil leaching, and places where extremely heavy rainfall 

 occurs may be actually worse off than other places with less rain- 

 fall. Some localities of large rainfall lead in amounts of water sup- 

 plied by irrigation. The converse is also true, for some localities of 

 light rainfall report success with deciduous fruit trees with a mini- 

 mum amount of irrigation water. 



Deciduous Fruits. Without making too much of individual re- 

 ports there appear instances enough to warrant the conclusion that 

 the deciduous fruit tree can winter successfully with a small mois- 

 ture 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 mois- 

 ture 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 deter- 

 mination of what is an adequate supply by reference to local con- 

 ditions, but as an estimate of necessary rainfall has been made at 20 

 inches, it is evident that adequate 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 before 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 con- 

 servation, 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 favor- 

 able 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 indicating soils lacking retentiveness, 

 either through shallowness or coarseness, or either of these accom- 

 panied 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 evaporation from their leaf surfaces, they must 

 always be provided with moisture or ill will result to tree or fruit. 



