28 CALIFORNIA FRUITS I HOW TO GROW THEM 



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 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 re- 

 gards 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 there- 

 fore, 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. . 



Practical Lessons from the Constitution of Our Soils. The ex- 

 traordinary depth of our soils, which reveals a favorable physical, 

 chemical and biological nature, teaches the importance and essential 

 nature of: (1) deep tillage; (2) deep incorporation of manures and 

 fertilizers; (3) deep irrigation. It is clear that if we can make condi- 

 tions just as congenial for the roots of plants in the lower layers of 

 the soil as in the upper, there is but one course left open to us, namely : 

 taking advantage of the opportunities afforded us by nature, if we 

 would maintain the fertility of our soils. To do this we must en- 

 courage the deep rooting of our trees, and nothing in the line of soil 

 management can accomplish the desired end so well as making available 

 to the roots in the deeper soil layers, air, plant food and water by the 

 methods above enumerated. 



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 be made 

 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 predominantly light, deep and rich and thus eminently fitted for 

 fruit growing, there are many degrees in the possession of these char- 

 acters or any of them, in local soils, and upon this individual manifesta- 

 tion 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 cultivation, 

 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 rae popularly known as loams. They are designated as 

 sandy loams, medium loams and clay loams, according to the propor- 

 tion of clay commingled with the sand or coarse materials. 



