34 CALIFORNIA FRUITS: HOW TO GROW THEM 



want of water. Under such circumstances it is possible with three 

 or four feet of good loam above the gravel to maintain profitably the 

 shallower rooted trees by practicing heavy green manuring and con- 

 stant summer cultivation to conserve what moisture the loam retains 

 and by recourse to irrigation, when required. 



Hardpan. It has ferquently been observed that even where 

 hardpan has been blasted prior to tree planting, the evil effects of 

 waterlogging in a rather retentive overlying soil have either killed 

 trees or made them unprofitable. This condition occurs not only on 

 level land, but also on rather steep hillsides where on a priori considera- 

 tions it would never be expected. In such cases drainage gives imme- 

 diate relief and the maintenance of a good humus supply in the soil 

 with constant summer cultivation, will usually insure good moisture 

 conditions. 



"Plow Sole" or "Plow Pan." Constant plowing to the same 

 depth or a failure to break up thoroughly the silty deposits at the 

 bottom of irrigation furrows may in a few seasons produce a hard- 

 ened and difficulty permeable layer of soil known, according to its 

 origin, as plow sole or "irrigation hardpan." This may also be aggra- 

 vated through the treading of stock and fruit pickers. Such hardened 

 soil layers interfere with root development and make for poor aeration 

 and water supply. They must be broken up by plowing or subsoiling. 



Rise of Ground Water. The rise of the water table mainly 

 due to excessive irrigation or the impermeability of one of the under- 

 lying soil layers is a question of the most serious significance and one 

 which the prospective purchaser of land or the owner of cropped land 

 must not lose sight of. For this reason precautions taken in the ex- 

 amination of land for hardpan, irrigation with necessary, but not 

 superfluous, amounts of water and adequate provision for drainage wili 

 not only go far toward making land profitable at the time cropping is 

 commenced, but will prevent troubles for the future through the ac- 

 cumulation of alkali and other baneful physiological effects on plants 

 of a high water table. 



Alkali. The term "alkali" denotes an accumulation of salts, in 

 a limited depth of soil, which may be of such nature and quantity as 

 to render the soil partially or totally unfit for profitable cropping. 

 The term has no necessary reference to the reaction of the soil, as is 

 commonly supposed, therefore, a misnomer, and should not be confused 

 with the term "alkaline," as referred to soil, since the latter denotes 

 merely a "sweet" or favorable condition for the development of most 

 of our crop plants. 



The "Alkali" salts may include common salt, Glauber salt, car- 

 bonate of soda, Epsom salt, the chlorides of calcium and magnesium 

 and more rarelv some others, but for practical purposes we may take 

 the ordinary classification namely that of "black" and "white" alkali 

 as being sufficient for the needs of soil management. By the "black" 

 alkali which is by far the most harmful of the sodium of salts men- 

 tioned, we mean carbonate of soda. It is so called because it dissolves 

 out the humus and forms a black slimy layer on the. surface. Very 



