WHEN DRAINAGE IS DESIRABLE 63 



accomplished with the plow, first by opening drainage furrows at 

 proper intervals, and this is often all that is needed to dispose of 

 surplus water j second, by ridging with the plow which prepares 

 long seed beds a little above the general surface and at the same 

 time leaves channels for the escape of the water; third, by opening 

 deeper surface-drains to act directly or to receive and speed the 

 departure of the outflow from the open furrows. All of these forms 

 of treatment, selected according to the degree of the need of drain- 

 age, have proved widely satisfactory and have facilitated magnifi- 

 cent winter growth of vegetables upon heavy adobe soils in some 

 of our regions of heaviest winter rains. The action is quicker than 

 underdraining because percolation is notably slow in such soil. It 

 removes the surplus from the surface just at the time its absence 

 is most desirable and it leaves the moisture stored below to rise as 

 the demand for it advances. On the other hand underdrainage, 

 where it is not imperatively demanded by exceptional conditions, has 

 clearly acted too slowly to bring the surface speedily into satis- 

 factory condition and has acted too long in drawing away more 

 water than desirable from below and has +hen continued as a very 

 effective hot-air system for further drying of soil-substance which 

 should have retained more moisture to supply the plant and foster 

 capillary action from still lower layers. In the writer's own ex- 

 perience shallow-rooting plants have dwindled over tile lines while 

 those midway between the lines were growing rapidly. 



Conditions Determining Recourse to Underdrainage. 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 



