30 CALIFORNIA FRUITS: HOW TO GROW TTIKAI 



food ingredients are markedly greater in the arid than in the humid 

 soils, wherever their derivation is at all generalized. Among the 

 agriculturally important ingredients contained in larger average 

 amounts in the arid soils than in the humid, lime stands foremost; 

 its percentage in soils not derived from calcareous formations being 

 from twelve to fourteen times greater in the arid than in the humid 

 soils. Magnesia follows lime in this respect, but the average differ- 

 ence is only about half as great. The average content of potash 

 in the arid soils exceeds that in the humid in about the proportion 

 of one to three or four. But no such constant difference exists in 

 respect to phosphoric acid. As regards humus, and the nitrogen 

 of which it is the carrier and reservoir, its amount is usually con- 

 siderably less than in the humid soils; but the total nitrogen per- 

 centage does not differ widely, because the humus of arid soils 

 contains, on the average, from three to five times as much nitrogen 

 as is found in the humus of humid soils, and therefore, the supply 

 of soil nitrogen is very nearly the same in both regions, while 

 from several causes, the humus-nitrogen of arid soils is more 

 available to plants. 



CLASSIFICATION OF CALIFORNIA SOILS 



Any attempt to classify the soils of California upon scientific 

 lines or even to describe them in their wonderful variety, according 

 to their geographical occurrence, would lead beyond the limitations 

 of a treatise upon the practice of fruit growing. Rather let an 

 attempt bt made to designate certain grades of soil with brief 

 characterizacion of their leading features as they are related to the 

 growth of fruits. By such a course it may be made to appear that 

 though the soils of the State are predominantly light, deep and rich 

 and thus eminently fitted for fruit growing, there are many degrees 

 in the possession of these characters or any of them, in local soils, 

 and upon this individual manifestation they rate all the way from 

 perfection to defectiveness. Let a classification proceed then upon 

 a descending scale. 



Light, Deep Loams. Admixture of clay with enough coarse 

 materials to secure permeability to air and water, ease in cultiva- 

 tion, deep root penetration and free drainage of surplus water, 

 produces soil of the highest adaptability to the growth of fruit trees 

 and vines. These soils are popularly known as loams. They are 

 designated as sandy loams, medium loams and clay loams, accord- 

 ing to the proportion of clay commingled with the sand or coarse 

 materials. 



Professor Hilgard has devised the following nomenclature of 

 soils based upon their content of clay : Sandy soils, less than 5 

 per cent of clay ; sandy loams, from 5 to 10 per cent ; ordinary or 



