CALIFORNIA SOIL CHARACTERS 27 



with which the red loam of the placer mines of the Sierra Nevada 

 foothills is re-covered with the natural forest growth of the region, 

 etc., are examples familiar to the residents but surprising to new- 

 comers, who are accustomed to dread the upturning of the subsoil as 

 likely to deprive them of remunerative crops for several years, until 

 the "raw" subsoil has had time to be "vitalized" by the fallowing effect 

 of the atmosphere, and to acquire the needful amounts of humus or 

 vegetable mold. Thus the surface soil, which in the humid regions 

 supplies the bulk of the nourishment, becomes here of minor impor- 

 tance, serving chiefly as a mulch to prevent waste of moisture; while 

 the active process of nutrition occurs in the deeper portion of the soil 

 stratum, whose composition, as well as condition of disintegration and 

 aeration, is substantially the same as above. The second foot is rarely 

 found to differ materially from the first, even as to humus content; 

 for the latter, being almost exclusively derived from the humification 

 of roots, the leaves and herbage on the surface being mostly oxidized 

 away under the intense heat and abundant aeration of summer; it 

 not uncommonly happens in very porous soils that the first six inches 

 of surface soil are poorer in humus than the second foot. 



Practical Results of Lightness and Depth. The "lightness" and 

 previousness of the prevailing soils of the arid region permit of the 

 penetration of roots to depths which in the humid region are inac- 

 cessible to them on account of the dense subsoils, which prevent the 

 needful access of air. This deep penetration enables even annual plants 

 to avail themselves directly of the stores of moisture in the substrata, 

 at depths which in the humid region are scarcely reached save by the 

 tap-roots of some perennials and trees; while the latter themselves 

 reach depth never approached by them in the region of summer rains. 

 Professor Hilgard has personally found the ends of the roots of 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 four- 

 teen feet in loams. Such depth of rooting, when conservation of mois- 

 ture is secured by proper surface cultivation, enables deciduous fruit 

 trees to grow thrifty and bear fine fruit through six months of drouth 

 while as many week's 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 soi\s have also made possible 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 ingre- 

 dients are markedly greater in the arid than in the humid soils, wherever 

 their derivation is at all generalized. Among the agriculturally impor- 

 tant ingredients contained in larger average amounts in the arid soils 



