WHEN TO DRAIN LANDS 75 



perience shallow-rooting plants have dwindled over tile lines while 

 those midway between the lines were growing rapidly. 



Conditions Determining Recourse to Under drainage. It may 

 be well to specify a few of the conditions which should determine 

 whether underdrainage should be provided in land under considera- 

 tion for vegetable growing. Of course the claim already alluded 

 to, that any piece of soil selected for gardening must be first under- 

 drained, is an exaggeration anywhere in the world probably, because 

 there are areas of naturally well-drained soil everywhere. Enough 

 has been said of California garden soils to show that the most of 

 them are of this character and that no probable amount of rainfall 

 would injure them. The exception has also been sufficiently char- 

 acterized in the chapter on soils. 



To reach assurance for or against underdrainage in particular 

 cases one has to consider the soil, the rainfall, the character of the 

 root growth to be ministered to, the growing season of the crop and 

 the practice of irrigation. 



The mere amount of rainfall is so intimately related to soil 

 texture, depth, subsoil, slope and exposure that, considered alone, 

 it affords no guide whatever to the need of artificial drainage. 

 There are many situations receiving an annual rainfall of forty to 

 sixty inches which not only do not need underdrainage but, on the 

 other hand, irrigation must be employed as early as May to supply 

 the requirements of shallow-rooting plants. These are either coarse, 

 leachy soils or else shallow loams lying upon sloping and porous 

 bed-rock. Leaving these out of consideration it is doubtful whether 

 any land, even of quite retentive character, receiving a rainfall of 

 not more than twenty-five inches, distributed as California rainfall 

 usually is, needs underdrainage for garden purposes. Of course 

 this claim clearly presupposes that the land in question does not 

 receive any considerable amount of water by overflow or underflow 

 by seepage from higher land. Any such rainfall as noted can prob- 

 ably be controlled by such surface use or surface release as have 

 already been described, or by such early and deep cultivation as the 

 garden should receive, there can be stored in the soil the moderate 

 residuum remaining from the amount of rainfall indicated, and 

 under favorable circumstances a greater rainfall can be thus dis- 

 posed of. 



Deep rooting plants like fruit trees will of course be injured 

 by saturation of the subsoil which would not injure garden vege- 



