Improving the Chemical Nature of the Soil 91 



meal, for instance, must be converted into a soluble 

 salt before it can be absorbed. This change is complex 

 and is brought about by certain kinds of bacteria in 

 the soil. 



128. How to Promote Nitrification. Since the amount 

 of nitrate nitrogen in the soil affects the yield of crops, 

 particularly grain and forage crops, the question is often 

 asked, "Can the farmer promote the growth of the nitri- 

 fying bacteria in his soils?" The answer is "yes." These 

 bacteria are most active when the soil is loose, so that 

 air can enter. These bacteria use large amounts of oxy- 

 gen in making the nitrates, hence deep cultivation is 

 the first essential to promote their activity. They do not 

 grow in strongly acid soils. (See further in any ency- 

 clopedia, under "Saltpeter.") Nitrification is most active 

 during the summer when the temperature is high. It 

 ceases when the temperature of the soil falls below 

 50 Fahr. 



129. De-nitrification is the destruction of nitrates. 

 This is due to another class of bacteria, but, fortunately, 

 the soil conditions that favor nitrification tend to retard 

 de-nitrification. De-nitrification takes place in a serious 

 degree, sometimes, when manure is not properly cared 

 for; as when it becomes too dry, or when so wet that air 

 is excluded. The same is true for the soils of the fields. 



130. How the Soil Loses Nitrogen. The complex 

 nitrogen compounds are usually converted into nitrates 

 and absorbed by growing plants. If not absorbed, they 

 may be destroyed by the de-nitrifying bacteria, or leached 

 from the soil by percolating waters. They are quite 

 soluble and, therefore, easily washed from the soil, par- 

 ticularly so from fallow soils through the winter months. 

 The practice of leaving our cotton and corn fields fallow 



