IMPORTANCE OF DRAINAGE 189 



defective in this respect. The evil has resulted from excessive rainfall 

 and excessive irrigation, either direct or by underflow 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 overloaded 

 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 watersoaked. 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 attention to the needs of vines and 

 trees in this regard. 



The following summary of drainage needs, and the advantage of 

 providing drainage when needed, is made by Professor Hilgard : 



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 advantage, 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 irri- 

 gated 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 prevent the pene- 

 tration and healthy life of the roots in the depths of the soil mass. If by inten- 

 tional or careless over-irrigation, or by leakage from the ditches, the water 

 level is allowed to rise within a few feet of the surface, the wonderfully pro- 

 ductive 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 exhausted, and copious artificial fertilization is required 

 to maintain profitable 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. 



2. It prevents, or at least limits definitely, the shallowing of the soil caused 

 by high-lying ground water, resulting in the need of early and copious fertiliza- 



