94 



SOILS AND FERTILIZERS 



no. Humic Acid. In the absence of calcium car- 

 bonate or other alkaline compounds, the vegetable 

 matter may produce acid products destructive to the 

 growth of some crops. The acidity in such cases can 

 be readily corrected by the use of lime or wood ashes. 

 Acid soils can be distinguished by their action upon 

 blue litmus paper. A soil may, however, give an acid 

 reaction and contain a fair amount of lime as a silicate. 

 The subject of acid soils and liming is considered in 

 Chapter IX. Studies conducted by the Rhode Island 

 Experiment Station indicate that the areas of acid 

 soils are quite extensive. 



in. Soils in Need of Humus. Sandy and sandy 



Fig. 20. Hunris from old scil. 



Fig. 21. Humis from new soil. 



loam soils that have been cultivated for a number of 

 years to corn, potatoes, and small grains without rota- 

 tion of crops or the use of stable manures, are deficient 

 in humus. Clay soils, as a rule, do not stand in need 

 of humus so much as loam and sandy soils. The me- 



