124 



Indiana University Studies 



soils and the roots of certain plants form the home of species of 

 bacteria that have the power to take up the nitrogen from the 

 air and give it up in the form of nitrates to the soil. In this form 

 it is known to be one of the most important of plant foods. Along 

 with these discoveries it became known that these organisms 

 thrive better in normal or slightly alkaline soils, and that when a 

 soil becomes markedly sour or acid, their development is arrested 

 and in fact a point is quickly reached where they cease to live. 

 The scientists discovered the fact that these microscopic organ- 

 isms live in tubercles upon the roots of various members of the 

 family of plants known as legumes (clover, peas, soy beans, 

 cowpeas, etc.). These tubercles can be easily seen on the roots 

 of these plants, varying in size with the different kinds of plants; 

 but the organisms themselves are far too small to be visible to 

 the naked eye. As the nitrates are formed the plant draws upon 

 them for its own food, but when the crops are harvested and the 

 roots remain behind or when the crop is ploughed under, nitrates 

 remain in the soil and increase its fertility. A chief reason for the 

 use of lime or limestone upon the land is to neutralize the acids 

 that may be present in the soil. These acids are always present 

 to a greater or less degree, since they result from the decay of any 

 form of organic matter. The most common acids present in 

 soils are carbonic acid and nitric acid, as well as the various 

 organic acids, such as lactic acid, acetic acid, etc. The reaction 

 between these acids and a base or basic salt gives a salt, and 

 leaves the soil free of acid. To supply this base, quicklime is 

 often used, but it is now known that finely ground limestone 

 will serve as well in reducing the acidity of the soil, and is far 

 less destructive of the organic matter contained in the soil. 



The burning of limestone into lime is a process of driving 

 off the carbon dioxide contained in the calcium carbonate of which 

 the hmestone is formed, and takes place according to the fol- 

 lowing reaction: 



CaCOs = CaO + CO2 



In other words, the calcium carbonate is broken up into calcium 

 oxide, which is the quicklime, and carbon dioxide, which is driven 

 off as a gas. The calcium oxide thus formed reacts with the 

 waters of the soil, and slaked lime or calcium hydroxide is formed 

 according to the following reaction: 



CaO + H2O = Ca (OH) 2 



