ACID SOILS 85 



ing the scrapings away and dumping them where they 

 can do no damage. 



When preparing an * alkali ' spot for a crop, deep 

 plowing should be practiced, so as to open up the soil 

 and remove the excess of alkaline matter from the 

 surface. Where manure, particularly horse manure, 

 can be obtained these spots should be manured very 

 heavily. The horse manure, when it decomposes, fur- 

 nishes acid products, which combine with the alkaline 

 salts. The manure also prevents rapid surface evapora- 

 tion. Oats are about the safest grain crop to seed on 

 an < alkali ' spot because the oat plant is capable of 

 thriving in an alkaline soil where many other grain 

 crops fail. 



'Alkali' soils are usually deficient in available 

 nitrogen. The organism which 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, nitri- 

 fication cannot take place. After thorough drainage and 

 preparation 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. 



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

 alkaline matter, humic acids are formed from the 

 decay of animal and vegetable substances. 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 the blue litmus 

 paper which changes to red in the presence of free 



