THE KINDS OF SOILS 259 



One of the best ways of improving the quahty of a clay 

 soil is to work into it a considerable amount of organic 

 matter. When this decays, the particles of humus be- 

 come thoroughly mixed with the soil particles, holding 

 them apart and furnishing a porous material that absorbs 

 water readily and also gives it up readily to plant roots. 

 The practice of applying barnyard manures, of plowing 

 under green crops, or of working in fallen leaves is an 

 excellent method of adding organic matter to the soil. 

 By a constant repetition of such practice, clay soils may 

 be brought into admirable condition for crop production. 



Clay soils may be greatly improved by the liberal 

 appHcation of some form of agricultural lime. Finely 

 ground limestone appears to be one of the best forms 

 in which to apply this substance. The improvement 

 brought about is to be explained in several ways. Lime 

 has a direct action upo n the particles of clay, causing 

 them to break apart and thus increasing the air spaces 

 between the particles. This is often called the floccu- 

 lating action of lime. 



The presence of lime also hastens the decay of organic 

 matter and apparently renders the soil more favorable 

 to the nitrogen-gathering bacteria which live in the roots 

 of clover, alfalfa, and other legumes. The lime neu- 

 tralizes many acid substances in the soil and directly or 

 indirectly helps to prevent the growth of various organ- 

 isms which injure the roots of plants. 



The application of lime is especially desirable before 

 sowing any leguminous crop. It also helps the growth 

 of many other farm and garden crops, but it has an in- 

 jurious effect upon potatoes, strawberries, and a few 

 other fruits and vegetables. 



