192 CALIFORNIA FRUITS: HOW TO GROW THEM 



excessive rainfall and excessive irrigation, either direct or by under- 

 flow from adjacent irrigations. In some places this latter movement 

 of water has brought alkali to assist in the ruin of the trees and 

 vines. The cure is drainage to sufficient depth and with good outlet 

 for the drainage water. 



Information on the construction of under-drains is too available 

 through other sources to call for its presentation in this connection.* 



Drainage and Irrigation. A special importance attaches to com- 

 plete and systematic drainage in connection with irrigation. There 

 is pressing need of such provision where the soil has become over- 

 loaded by seepage water from irrigation ditches, and it is well that 

 people in such situations are waking up to the need of coupling 

 drainage outlets with their irrigation inlets. Another matter closely 

 allied to this is the action of alkali on soils thus artificially water- 

 soaked. This has been made the subject of a special publication, to 

 which allusion has already been made in Chapter III. Drainage is 

 plainly essential, both in individual farms and in districts where the 

 water level is rising too high, and the striking statements given 

 below by Professor Hilgard should incite all to give immediate at- 

 tention to the needs of vines and trees in this regard : 



In the valleys and plains of the arid irrigation countries the soils are pre- 

 dominantly of a light, sandy or silty nature, easily penetrated to great depths 

 by water and air. With these the roots of plants also reach to such depths, 

 drawing therefrom not only moisture, but also plant food, which in these 

 soils is, as a rule, very abundant. The plants of the arid region thus are 

 enabled to utilize nearly as many feet of soil mass as in the regions of 

 summer rains inches would be drawn upon; and it is evident that this advan- 

 tage, which postpones for a long time the need of fertilization, should not 

 be lightly thrown away. Each farm in the arid region has several similar 

 ones underground, which with proper management can be fully utilized. 



But this presupposes that the water, air and roots can all penetrate under 

 irrigated culture as they do in the natural condition. It means that the 

 ground water level shall not be allowed to rise to such an extent as to pre- 

 vent the penetration and healthy life of the roots in the depths of the soil 

 mass. If by intentional or careless over-irrigation, or by the leakage from 

 the ditches, the water level is allowed to rise within a few feet of the sur- 

 face, the wonderfully productive lands of the arid valleys are reduced to 

 the same condition as are those of the humid countries; a shallow layer 

 of surface soil, within which alone the roots can exercise their functions 

 of plant nutrition. The natural result is that this layer soon becomes ex- 

 hausted, and copious artificial fertilization is required to maintain prolific 

 production. 



And even this is the most favorable case. When, in addition, the upward 

 movement of the soil water carries with it the entire mass of salts of various 

 kinds which exist in all arid soils, and brings them within reach of surface 

 evaporation, these "alkali" salts impregnate the soil to such an extent as to 

 render the cultivation of many crops unprofitable, or sometimes altogether 

 impossible. 



Summarizing the advantages of systematic land draining it may be said 

 that: 



1. It prevents the drowning out of the deeper roots of plants by the rise 

 or fluctuations of the ground water, by which the vineyards and orchards are 

 so frequently rendered unprofitable. 



*"Farm Drainage Methods" by W. W. Weir. Circular 174 of University of California 

 Experiment Station, Berkeley, Calif. 



