THE CHEMICAL COMPOSITION OF SOILS IOI 



gen. The organism whicK carries on the work of 

 changing the humus nitrogen to available forms cannot 

 thrive in a strong alkaline solution. In many of these 

 soils, as demonstrated in the laboratory, nitrification 

 cannot take place. After thorough drainage and prepa- 

 ration for a crop, a few loads of good soil from a fertile 

 field sprinkled on alkali spots will do much to encourage 

 nitrification, by introducing the nitrifying organisms. 



For a more extended account of the cause of alkali 

 soils, and methods for improving them, the student is 

 referred to Hilgard's "Soils." 





 110. Acid Soils. When a soil is deficient in active 



alkali, and there is an excess of organic material, humic 

 acid is formed from the decay of the animal and vege- 

 table matter. Acid soils are readily detected by the 

 reaction which they give with sensitive litmus paper. 

 In making the test the moistened soil is pressed against 

 blue litmus paper, which changes to red in the presence 

 of free acids. Acid soils are made productive by using 

 lime and other alkaline material to neutralize the humic 

 acid before applying farm and other manures. Acid soils 

 are not suitable for the production of clover and legumes. 

 Experiments by Wheeler at the Rhode Island Ex- 

 periment Station indicate that there are large areas 

 of acid soils in the eastern states which are much 

 improved when treated with air-slaked lime. 30 There 

 is great difference in the power of plants to live in 

 acid soils. Some agricultural crops as legumes are par- 



