WHEN TO IRRIGATE 





181 



Winter Irrigation. On lands with sufficient depth of fairly re- 

 tentive soil, the grower may artificially supplement a scanty rainfall 

 by thoroughly soaking the land by winter irrigation and then by 

 careful summer cultivation he will be able to conserve enough 

 water in the soil to. carry deciduous fruit trees or vines through 

 bearing and autumn bud formation without further water supply. 

 But there are other situations in which no amount of winter irri- 

 gation nor rainfall will suffice for these ends. There are foothill 

 orchard areas in which the winter rainfall is two or three times 

 as great as in the valley situations where fruit is successfully 

 grown without irrigation, and yet water must be applied in summer 

 on those foot-hills or the fruit would be unmarketable and the trees 

 in distress. The forty or more inches of rainfall falling on a shallow 

 soil underlaid by a sloping bed-rock in some cases nearly sluices 

 the cultivated soil from its foothold, and yet the oversaturation in 

 winter avails nothing for summer growth, because most diligent 

 cultivation can not retain moisture enough in shallow soil thus 

 situated to sustain bearing trees in good crops of full-sized fruit. 

 The same is true of valley soils underlaid by hard-pan. In such 

 cases winter irrigation could add nothing but distress to the soil 

 oversoaked by rainfall, and summer irrigation, well-timed and ade- 

 quate, is the secret of success in the orchard. The same conclusion, 

 although for very different reasons, must hold for soils underlaid 

 by gravel or sand, and thus too rapidly dried by leaching. 



But even this generalization must be accepted only for sirua- 

 tions endowed with conditions which justify it. There may be 

 sloping hills with shallow soil where winter rainfall does not 

 amount to saturation". Then winter irrigation to supply such irri- 

 gation is desirable, and then, too, summer irrigation in proper 

 amount and at proper intervals, will also be demanded. Among the 

 foot-hills, also, there may be localities with depth of retentive 

 soil in which water enough can be applied in winter to carry trees 

 through the year. Thus we come again to the only safe generaliza- 

 tion which can be made, and that is, that everywhere water must be 

 adequate to the demands of the tree at the time it is needed, and 

 whether it can best be applied in summer or winter, or both, or 

 whether it is not necessary to make any artificial application at all, 

 depends upon existing conditions which the grower must ascertain 

 and to which his policy and practice must conform. It is a fact, 

 however, that all soils, which under good cultivation are fairly 

 retentive, winter irrigation, when water is most abundant, and 

 usually carries most sediment, can be made to go far toward mak- 

 ing summer irrigation unnecessary for all deciduous fruits. 



As to winter irrigation, practice varies, some relying upon a 

 single heavy flooding by using checks on contour lines, by which, 

 perhaps, a foot in depth or more of water is allowed to soak into the 

 soil; others use the same method of application in winter as in 



