Productiveness of Soils 97 



cation of lime may be due to the establishment of bal- 

 ance between the calcium and magnesium as just men- 

 tioned; to the effect on insoluble potassium or phos- 

 phorus compounds (f 90) ; to a mechanical effect on the 

 texture of the soil (f 73) ; to the effect of lime in taking 

 up an excess of acid in soils (f 141); or in neutralizing 

 some forms of alkali. 



140. The Mechanical Condition of the soil may be the 

 cause of unsatisfactory crops. Some crops, like wheat, do 

 best with a settled sub-surface soil, while beets, potatoes 

 and many other crops do best with a very loose soil. 



141. Sour, or Acid, Soils are very unfavorable to some 

 crops. Many soils are slightly acid, as will be found when 

 tested with litmus paper. They differ greatly in the 

 degree of sourness. Very acid soils are not favorable 

 for alfalfa, cotton, etc.; but, for corn and small grains, no 

 rule has yet been suggested. Soils that contain injurious 

 amounts of acid are found in swamps or in sandy uplands. 



14 la. To Test Soils for Acid, use a small slip of litmus paper, 

 secured from the druggist. Place the paper against the moist soil, 

 and the color after some minutes will change. If blue, the soil is 

 alkaline; if red, it is acid. 



141^. Alkali Salts in a soil may be the cause of un- 

 productiveness. There are several kinds of very soluble 

 salts that accumulate in the surface soils, most fre- 

 quently in regions of low rainfall. Often the dwarfing 

 effect of alkali salts is confined to a low place, a wet- 

 weather seep, or other place where a quantity of soil- 

 water is evaporated. These salts are formed in all soils, 

 but where the rainfall is abundant they are washed out 

 of the soil by percolating water. If the rain is all evapo- 

 rated from the surface, it will cause an accumulation of 

 these salts to such an extent that injury to the plant 

 results. Lime is often beneficial on such soils. 



