SOIL CONSERVATION 411 



content. Any organic material which decays will accomplish the 

 same thing. Many commercial fertilizers are made from guano, 



There is an interdependence between green plants and animals. Animals can make use of 

 the oxygen excreted by green plants. These in turn, can make use of carbon dioxide, water, 

 and possibly urea excreted by animals. 



bird waste. Refuse from abattoirs, and meat and fish canneries, 

 or specially prepared mixtures of chemical compounds, may be 

 purchased and plowed into the soil. The land may be allowed 

 to lie fallow, that is, unused for a season or so. Certain minerals 

 in the ground may break down in fallow fields and thus restore 

 the usable mineral elements. A leguminous crop, such as peas, 

 beans, or alfalfa, may be planted, allowed to grow, and marketed. 

 At the same time, nitrates are restored to the soil in which they grow. 

 Soil conservation. If the soil is kept in good condition, nitrates, 

 sulphates, and phosphates are constantly renewed as they are 

 removed. The passage, use, and return of these materials consti- 

 tute a cycle as shown in the diagram. Were it not for the action 

 of bacteria in the soil, all vegetation on the earth would cease. 

 Soil fertility is primarily a bacterial activity. Bacteria are com- 

 monly thought of as being particularly injurious. In reality, the 

 beneficial effects of bacteria far outweigh the injurious effects in 

 many ways. 



QUESTIONS AND SUGGESTIONS 



1. Using the following topics, make out a tabular outline of the 

 relation of bacteria to food preparation. 



A. Name of bacterium. 



B. Material attacked, 



