236 SOIL ACIDITY AND LIMING 



infested with sheep sorrel, horsetail rush (Fig, 150), common 

 plantain, paintbrush, corn spurry and wood horsetail are usually 

 acid. The fields become infested with such weeds because the 

 soil conditions are unfavorable to the clover or alfalfa. 



Conversely, soils on which alfalfa, sweet clover and the June- 

 berry grow are usually not acid. Marsh lands, or other low soils, 

 which become thinly coated with a white substance invariably are 

 not acid (Fig. 151). This white substance in humid climates is 

 usually mild alkali. 



FIQ. 151. This marsh soil is not acid because it becomes coated with a thin, white coating 



of mild alkali. 



Low Wet Lands Not Necessarily Acid. It is commonly 

 believed that all low, wet soils are sour. In a general sense, there 

 is no relation, whatever, between wet lands and acidity. In 

 sections in which both acid and non-acid soils occur, the low soils 

 are the least acid or not sour at all; either because of seepage which 

 brings carbonate of lime and other substances to the surface, or 

 because carbonate of lime is washed down from the surrounding 

 uplands, as in a limestone country. 



Acidity is rarely found in soils or valleys which are frequently 

 flooded by streams coming from limestone regions. 



Peat and muck soils surrounded by high, limestone soils are 



