30 Soil Classification. 
distress and loss of fruit to surface-rooting trees on the shallow 
soils of the humid region. 
Richness —The foregoing conditions are rendered the more 
significant and effective through the third characteristic of soils 
formed in arid climates. The average aggregate amounts of 
piant-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 cal- 
careous 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 difference 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 considerably less 
than in the humid soils; but the total nitrogen percentage 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 wondertul variety, accord- 
ing to their geographical occurrence, would lead beyond the 
limitations of a treatise upon the practise of fruit growing. 
Rather let an attempt be nade to designate certain grades of soil 
with brief characterization 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 pre- 
‘dominantly 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 defective- 
ness. 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 culti- 
vation, 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 
