RULING CHARACTERS OF CALIFORNIA SOILS 



27 



grape-vines at a depth of twenty-three feet, in a gravelly clay-loam ; 

 from ten to fifteen feet are ordinary depths reached by the root 

 system of fruit trees. Even the roots of cereals have been found 

 to penetrate to a depth of twelve feet in California sandy alluvial 

 soils and to fourteen feet in loams. Such depth of rooting, when 

 conservative of moisture is secured by proper surface cultivation, 

 enables deciduous fruit trees to grow thriftily and bear fine fruit 

 through six months of drouth while as many weeks of drouth may 

 bring distress and loss of fruit to surface-rooting trees on the shallow 

 soils of the humid region. Recent investigations at the California 

 Agricultural Experiment Station have also disclosed that the good 

 physical and chemical conditions of the deeper layers of our soils 

 have also made possble the penetration from the surface layers, of 

 various forms of micro-organisms upon which we are dependent not 

 only for a solution of the insoluble plant food, but for the addition 

 of nitrogen to the soil from the atmosphere. 



Richness. The foregoing conditions are rendered the more sig- 

 nificant and effective through the third characteristic of soils formed 

 in arid climates. The average aggregate amounts of plant-food in- 

 gredients are markedly greater in the arid than in the humid soils, 

 wherever their derivation is at all generalized. Among the agricul- 

 turally important ingredients contained in larger average amounts 

 in the arid soils than in the humid, lime stands foremost; its per- 

 centage 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 regards organic matter, and the nitrogen of 

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

 ably less than in the humid soils ; but the total nitrogen percentage 

 does not differ widely, because the organic matter of arid soils con- 

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

 in humid soils, and, therefore, the supply of soil nitrogen is very 

 nearly the same in both regions, while from several causes, the nitro- 

 gen 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 con- 

 ditions 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 encourage 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. 



