382 MISCELLANEOUS FARM SUBJECTS 



The conclusion seems justified that, although differences in 

 the dissolved salt content, or in the concentration and composition 

 of the soil moisture, may 'be a factor in the yield as well as quality 

 of a crop, it does not appear to be a major one in determining or 

 controlling the wide variations observed in crop yields on different 

 soils. It appears further that practically all soils contain sufficient 

 plant food for good crop yield, that this supply will be indefinitely 

 maintained, and that this actual yield of plants adapted to the soil 

 depends mainly, undetf favorable climatic conditions, upofn the 

 cultural methods and suitable crop rotation, a conclusion strictly 

 in accord with the experience of good farm practice in all coun- 

 tries, and that a chemical analysis of a soil, even by these extremely 

 delicate and sensitive methods, will in itself give no indication of 

 the fertility of this soil or of the probable yield of a crop, and it 

 seems probable that this can only be determined, if at all, by physi- 

 cal methods, as it lies in the domain of soil physics. 



The Color of Soils. It is recognized that soil colors are not 

 pure colors, but at best are shades and tints. Thus, the material by 

 which soils ordinarily considered as red are colored is ferric oxide, 

 which is never a pure red, for it varies from dark brown to yellow- 

 ish, and when in the soil it is further tinted and shaded by other 

 materials. 



In soils it is possible to find almost any conceivable color, from 

 the white beach sand to the black mucks of the swamp. Soils gen- 

 erally fall into one of three color groups; white, red and black. 

 Whitish or gray soils are not generally of much agricultural value 

 for general field crops, though sometimes of very great value for 

 special purposes. In humid climates such a color indicates im- 

 mediately that the soil lacks organic matter. In general it has 

 a very high content of silica and alumina and very small content 

 of iron or other colored oxides and organic matter. In arid re- 

 gions the so-called alkali sometimes accumulates in white spots, 

 frequently inhibiting the growth of plants. Occasionally a high 

 content of gypsum gives some soils or arid regions a white or light- 

 gray appearance. 



Yellowish soils are very common, although a truly yellow soil 

 is rather rare. It is generally considered that they owe their color 

 to small amounts of ferric oxide, more or less hydrated. Black soils 

 are universally esteemed highly. They are characterized by a high 

 percentage of organic matter and frequently a comparatively high 

 percentage of lime. The color is thought to be due to the forma- 

 tion of black humus bodies by the interaction between decaying 

 organic compounds and the lime or other bases in the soil. 



In the cotton States red soils are much in favor for agricultural 

 purposes. In the States south of Pennsylvania and east of the 

 Mississippi Kiver there are many occurrences of soils of a bright red 

 color. In the cotton States it is common to find intermingled with 

 these bright red colors, yellow, brown, blue and green in the same 

 bank. 



