252 SOILS AND PLANT LIFE 



188. How Acid Soil affects Clovers. — Under the sys- 

 tem of fanning generally practiced in the United States, 

 the soil gradually becomes acid, or sour. We can not, 

 of course, perceive this change in the soil with our senses ; 

 and since it comes so slowly, and its effect on cereal crops 

 is not readily seen, it may remain unsuspected for a 

 considerable time, sometimes even for several years. 



The clovers generally are singularly sensitive to this 

 acid condition of the soil; and often the first indication 

 we have of it is their feeble and uncertain growth in 

 fields where it seems that they should thrive. 



The truth is that it is impossible to grow red clover, 

 sweet clover, alfalfa, or certain other legimies success- 

 fully in an acid soil. How long they can survive in it 

 even depends chiefly upon how strongly acid the soil 

 may be. Thus if the acidity is only very slight, the young 

 clover plants may be only somewhat weakened, rather 

 than killed ; and the crop may even mature, though the 

 growth will not be vigorous. If, however, a little more 

 acid is present, the little plants Asdll grow still more weakly ; 

 and because of this weakened state, they readily succumb 

 to unfavorable climatic conditions, such as drouth, or 

 perhaps extreme cold, later, in which case the failure is 

 commonly attributed to drouth or winterkilling as the 

 sole cause. It is merely a matter, then, of the degree of 

 acidity as to what the effect upon the clovers will be; 

 and if the soil is strongly acid, we find, just as we should 

 expect, that the little plants usually die soon after the 

 germination of the seed. 



It is not at all difficult to detect acidity in the soil. 

 If a shp of blue litmus paper, such as we used in Exer- 

 cise 28, is placed in a cup of acid soil which has been 

 made wet with soft water, it will gradually change in 

 color, becoming tinged with pink. Let us make some 



