368 SOILS: pnopmrrim and managmmjejmt 



273. Relation of absorptive capacity to productiveness. 

 — The absorptive capacity of a soil is not so much a 

 measure of its immediate as of its permanent productive- 

 ness. It is well known that a very sandy soil responds 

 quickly to the application of soluble manures, but that 

 the effect is confined mainl}^ to one season ; while a clay 

 soil, although not so quickly responsive to fertilization, 

 shows the effect of the application much more markedly 

 the second or the third year than does the sandy soil. 

 Adsorption, which is largely shown in sandy soil, holds 

 the nutritive material in a very readily available con- 

 dition, while absorption by amorphous compounds 

 renders these substances somewhat less readily available. 

 There are also other reasons why the sandy soil is more 

 responsive. King,^ in working with eight types of soil 

 from different parts of the United States, found that 

 those soils removing the most potassium from solution 

 gave the largest yield of crops. It would not be per- 

 missible, however, to adopt this test as a method for 

 determining productiveness in soil. 



274. Absorption as related to drainage. — The drainage 

 water from cultivated fields in humid regions, and to a 

 less e^ctent in semiarid and arid regions, except where 

 irrigation is practiced, carries off very considerable quan- 

 tities of plant-food material. The loss of this material 

 is due to the operation of the various natural disintegrating 

 agents on the soil mass, and to the application of fertilizing 

 materials in a soluble form. The various absorptive prop- 

 erties stand between the natural solubility of the soil and 

 the tendency to loss in drainage, and hold, in a condition 



^ iiiag, F. H. Influence of Farm Yard Manure upon Yield 

 and upon tlie Water-Soluble Salts of Soils, p. 25. Madison, 

 Wisconsin. 1904. 



