52 THE IRRIGATION AGE. 



but in the last two years there has been considerable loss from its be- 

 ing empty like the reservoirs above ground. You have all seen how 

 a piece of dry uncultivated ground will sap the moisture from several 

 feet of an adjoining irrigated piece. No matter how wet you may 

 make the latter or how well you may cultivate it, several feet of it 

 along the dry piece will be too dry in a very few days. 



When you try to cultivate a layer of two or three feet upon the 

 top of an ash heap you have a difficult and dangerous task. The dry 

 stuff below will sap the moisture even more quickly than the air and 

 the sun will sap it from above. The latter you may prevent to a great 

 extent by cultivation. But the downward sapping of the moisture 

 you cannot prevent. If anything fails from neglect of watering at 

 just the right time it is almost impossible to restore it to w T here it 

 would have been, and, if the top layer is very thin, a very few hours 

 reduce the plant from prosperity to failure. 



Quite the reverse is the case when the subsoil is filled with moist- 

 ure as far as the principles of good drainage allow. It will take a 

 long neglect to injure plants or trees, and if they fail it will be but 

 slightly at first. It w r ill take several days and often weeks for them 

 to fail so far that the damage cannot be repaired quite fully by irri- 

 gation of the top soil. 



The amount of water required to keep the subsoil in this right 

 condition is much greater than is commonly supposed. Ordinary irri- 

 gation is rarely sufficient even though 'continued through the year. 

 It takes a large rainfall each year to do it, and if that fails then that 

 amount should be put in with winter irrigation. One inch of rain 

 wets dry ground about ten inches if it all goes in. But twenty inches 

 of rain will not wet two hundred inches or anything like it. At least 

 one-half is lost in run off and evaporation from the surface. And one 

 inch does not make ten inches of soil as wet as it should be for the 

 best results. For safety the subsoil should be kept damp down 10 

 fifteen feet and even more. Where the drainage is good enough to 

 make the land safe for fruit trees there is little danger of getting in 

 too much. And all that can be put m, up to the point of safe drain- 

 age, is an insurance policy of more or less value in all short years. 



Ordinary winter irrigation is not enough for this. On most soils 

 in winters like the last two at least a foot and a half in depth of water 

 should be put in. This would take for ten acres thirty inches, twelve 

 days run, if it all went in. But it could not be put into most soils in 

 twelve continuous days or anything like it. Six irrigations of two 

 days' run would be much nearer what is needed and some time should! 

 elapse between them. Three years ago with sixteen inches of rain in 

 Los Angeles I found many places during the spring and summer 

 where the proof was positive that the water had uot gom> down over 

 four feet and many more where it had not penetrated over five feet. 

 The ground below was all dry as a chip from the lack of rain in the 



