64 SUCCESSFUL FARMING 



Vegetation and Alkali. — In the irrigation districts of the semi-arid 

 regions of the United States the character. of vegetation often enables 

 one to determine at a glance whether or not the soils are too alkaline for 

 the production of staple crops. This fact is taken advantage of and serves 

 as a great aid to the soil expert in the mapping of alkali soils. The pre- 

 dominance of sage hushes and rabbit's foot indicates freedom from alkali, 

 •while such plants as grease wood, mutton sass and salt grasses show a1 

 once that the soils are highly impregnated with alkali salts. 



Color of Soils Related to Fertility. — Another index to soil fertility is 

 the color of the soil. It cannot always be explained just why a certain 

 color is indicative of fertility or otherwise, but there seems to be a com- 

 paratively consistent relationship between color and degree of fertility. 

 Nearly all black soils are fertile, while those that are of an ashy hue or 

 have a yellowish cast are generally poor. The chocolate-colored soils, the 

 red soils and those of a brown color are, as a rule, fairly fertile. The 

 farmer, as well as the soil expert, soon learns that color is a good index 

 relative to soil fertility. 



It is wise, however, to look further than merely on the surface of 

 the soil or the character of the vegetation. Subsoil is also very important 

 in connection with fertility. There are regions where the surface soil is 

 black and where the subsoil immediately beneath is of a light-colored, tena- 

 cious clay, so nearly hardpan that the soils are not productive for any con- 

 siderable range of general farm crops, although they may be well adapted 

 to grass. 



Maintenance of Fertility.— Soils are permanent. They constitute the 

 most important asset of the nation. Their maintenance through rational 

 systems of farming is essential. Nature has made for increased soil fer- 

 tility, but unfortunately the occupation of the soil by man has often 

 resulted in soil robbery and a decline in productivity. This serious fault 

 should be remedied. 



Fertility Lost by Plant Removal. — Loss of soil fertility by plant 

 removal is legitimate. Such loss must ultimately be replaced, either by 

 the return of the residues of crops thus removed in the form of unused 

 portions or by-products and the excreta of the animals that consume the 

 crops, or by the purchase of the different elements in commercial fer- 

 tilizers. In rational systems of farming the removal of plant food through 

 the removal of crops is not to be considered undesirable, and such removal 

 should result in sufficient profits to enable the soil loss to be replaced at a 

 cost less than the profits received through thfc crops grown. In the pre- 

 ceding chapter we found that of the mineral elements potassium and phos- 

 phorus are the only ones likely to become exhausted to such a degree as 

 to necessitate replacement. As a matter of fact, potash occurs in large 

 quantities in most soils, and the problem of the future seems to be largely 

 the adoption of methods that will bring about its availability. Many 

 soils, however, contain phosphorus in such small amounts that in a short 



