THE CONTENTS OP THE SOIL 21 



friable soil rich in vegetable matter, the original 

 basis of which is sand ; a clay loam is one simi- 

 larly ameliorated, the basis of which is clay. 

 "Worn-out" lands usually suffer more from 

 lack of humus than from lack of actual plant- 

 food, and this explains why the application of 

 stable -manure is so efficacious. 



34. There are three general ways in which 

 humus is obtained in farm -practice : (1) By 

 means of the vegetable matter which is left on 

 or in the ground after the crop is removed (as 

 roots, stubble, sod, garden refuse) ; (2) by 

 means of crops grown and plowed under for 

 that particular purpose (green-manuring) ; (3) by 

 means of direct applications to the land (as com- 

 post and stable -manure). The deeper and more 

 extensive the root -system of any plant, the 

 greater, in general, is its value as an ameliorator 

 of soil, both because it itself exerts a more wide- 

 spread influence (30), and because when it de- 

 cays it extends the ameliorating effects of humus 

 to greater depths. 



35. Aside from these varied component ele- 

 ments, fertile soil is inhabited by countless num- 

 bers of microscopic organisms, which are peculiar 

 to it, and without which its various chemical 

 activities can not proceed. These germs con- 

 tribute to the breaking down of the soil particles 

 and to the decay of the organic materials, and 



