98 



CONSERVATION AND IMPROVEMENT OF SOIL 



Chemical changes are often much increased by tillage. The 

 more rapidly chemical changes are going on in the soil the more 

 rapidly plant food is liberated, as most of the changes tend to 

 liberate plant food, or make it available for use by plants. 



The stirring of soil by plows or other implements exposes new 

 surfaces to the sun, air and other weather influences (Fig. 73). 

 Obnoxious gases, such as carbon dioxide, may readily escape. 

 Nitrogen and oxygen may become combined with chemicals in the 

 soil. Particles of lime, phosphorus, or other valuable materials 

 may be brought in contact with each other and with other acids, 



Fio. 73. A spring-tooth harrow is well suited to such a rough soil as this. No other harrow 

 would do good work among the rocks. (New Jersey Station.) 



alkalies or other compounds, resulting in changes which are usually 

 beneficial. 



Plowing is often the best means of incorporating new materials 

 with the soil, such as green manure, barnyard manure and others. 

 The subsequent actions of these are of a chemical nature, and will 

 of course improve the soil chemically as well as physically. 



The physical changes in soils produced by tillage are of several 

 kinds. The plow loosens and shears the soil. As the common 

 mold board bends the furrow-slice the particles are moved among 

 each other and past each other so that each comes in contact 

 with new parts. A field plowed with a very abrupt mold board 

 "shears" the soil more than a long mold board with gradual slope. 

 The latter is more commonly used in turning over sod. 



