ORCHARD SOILS 135 



presence of considerable percentage of organic material and 

 this is usually associated with a rich soil. 



The Porters black loam of Virginia and the Phoenix adobe 

 clay of Medford, Oregon, are examples of black soils espe- 

 cially valuable for fruit-growing. Most fruit soils are not so 

 dark in color. A reddish or yellowish soil usually indicates 

 the presence of a large amount of oxidized iron. Some of 

 the clays are very red as also are some of the soils derived 

 from sandstone formation. Some of these are rich and 

 productive, but ordinarily the red color would not indicate 

 a well aerated and rich soil. 



119. Limestone soils. — ^The question as to whether lime- 

 stone soils are preferable for fruit is frequently raised. In 

 order to form an opinion, the function of lime in the soil may 

 be briefly reviewed. 



The function of lime in the soil is two-fold: (1) to 

 prevent "sourness" and neutralize the aluminum com- 

 pounds; and (2) to flocculate clay soils and tend to hold to- 

 gether the sandy ones. Lime is looked on as a soil "im- 

 prover" but it is of course a plant-food, for it is present in 

 the ash of all plants and has a definite function to perform. 

 However, it is rarely necessary to apply it for that purpose 

 since all soils contain some calcium oxide. The exact per- 

 centage of lime necessaiy varies with the nature of the soil 

 and hence is relative. "The greater the clay percentage 

 in a soil, the more lime carbonate it must contain in order 

 to possess the advantages of a calcareous soil ; and that while 

 in sandy lands lime growth may follow the presence of only 

 .10 per cent of lime, in heavy clay soils not less than about 

 .6 percent should be present to bring about the same re- 

 sult." ^ 



The adaptation of plants to soils is a well-known phenom- 

 enon and one which has frequently guided the agricultur- 

 1 Hilgard, E. W. Soils, p. 369. New York. 1906. 



