80 CROP GROWING AND CROP FEEDING 



Experiments that have been long and carefully conducted by the Ehode 

 Island Agricultural Experiment Station, have shown that the sweetening of 

 an acid soil by the application of lime is not always an advantage, since there 

 are some plants that seem to prefer the acid soil, or rather some that are more 

 exempt from disease in such a soil. On the Irish potato crop, for instance, 

 it was found that liming brought about conditions that were favorable to 

 the fungus that causes scab in the potato, and while the resulting crop may be 

 larger the market value was reduced by reason of the scab. Acidity in the 

 soil is detrimental, it appears, to the lower forms of plant life rather than to 

 green plants. Many people have jumped to the conclusion that their land 

 has become infested with sheep sorrel because of its acidity. The fact is that 

 while this is usually the case it by no means follows that the sheep sorrel gets 

 its acid from the soil. The sheep sorrel is one of the plants that can abide 

 the presence of free oxalic acid, while this acid is formed in other plants, the 

 plant at once makes a combination of it with lime or potash and locates it 

 in crystals insoluble in the sap at ordinary temperatures, and thus renders 

 it harmless. The oxalic acid in the sheep sorrel, like other vegetable acids, 

 is the result of the assimilation of carbon from the air, and it does not come 

 from the soil. But sheep sorrel will grow in a soil too acid to allow the suc- 

 cess of clover, and hence it is the common complaint that we cannot get clover 

 on account of the sheep sorrel. An application of lime will bring about con- 

 ditions favorable to the clover and enable it to smother out the sheep sorrel. 

 Not that the liming kills the sheep sorrel, but that it enables the clover to 

 grow and overcome it. Anyone can readily test the condition of his soil by 

 getting a piece of blue litmus paper from a drug store, and burying it over 

 night in the damp soil. If, on taking it up, it is found to have turned to a 

 pink color it is evidence that the soil is in an acid condition, and as our most 

 valuable crops Jhrive best in a soil of a feebly alkaline nature, an application 

 of lime to such soils will usually be beneficial. While most legumes, and 

 especially red clover, are greatly benefited by an application of freshly water 

 slaked lime, there is one important legume which is not thus helped. The 

 cow pea, the greatest legume for the Southern farmer, is positively damaged 

 by a dressing of lime. Hence one reason why the cow pea will thrive on a 

 soil too acid to permit the growth of clover. It seems probable, too, that the 

 microbes that exist on the roots of the pea, and enable it to get the free nitro- 

 gen from the air, are better able to exist in an acid soil than those of the clo- 

 ver ; for it is well known now that each legume has its own particular microbe, 

 and that some of them may be inimical to those of other legumes, and it is 

 rare to find one species of legume doing its best immediately after the removal 

 of another of the same order from the land. This is only another reason for 



