70 



SOILS AND THEIR USES 



Enough lime must be present to help produce valuable chemical 

 changes in the soil. Plant food of various kinds must be present. 

 This may be either in solution or in particles to become valuable 

 at a later time. 



Such an ideal soil is one which every good gardener or farmer 

 will strive to produce and maintain. The methods of soil improve- 

 ment discussed in Chapter IX are used by man in his efforts to 

 produce or maintain such ideal soils. 



Organic matter in the decayed or decaying form in the soil 

 is called humus. The amount of it present in a given soil is to a 

 very great extent the measure of the value of that soil. It deter- 

 mines its moisture-holding powers, the amount and activity of 

 the bacteria present, and the condition of the soil with respect to 





Fio. 58. A quiet lily-pond where the feeding stream is depositing its heavy load of 

 soil. As the soil fills in more plants will grow, until the place becomes a level field, suitable 

 for growing crops. 



ventilation and drainage. Humus is also one of the chief sources 

 of nitrogen and other plant food. 



Under natural conditions humus is produced in soils by the 

 death and decay of insects, worms, grasses, leaves, twigs and 

 trunks of trees, and other natural growth (Fig. 58). As these 

 substances decay they are readily incorporated with the soil 

 through the action of water and other natural agencies. 



A sample of soil from the woods is usually black because of the 

 humus present. Such soil is phenomenally rich. Under agri- 

 cultural conditions the grower tries to imitate nature in the pro- 

 duction of such qualities in farm soils. 



There are other forces in nature, such as erosion and the blow- 

 ing by wind, which tend to remove the surface layer of the earth 



