318 MAN'S USE AND CONSERVATION OF SOILS 



or bean crop is harvested, the roots are plowed under to 



enrich the soil. 



Animals like moles and gophers plow their holes through 



the soil, mixing up the particles and making the soil porous, 



so that the water can readily get in to aid in breaking up and 



decomposing the soil 

 particles. These 

 holes also provide 

 openings through 

 which plant roots 

 and soil organisms 

 can obtain the oxy- 

 gen and dissolved 

 food they need. 

 Ants each year move 

 vast quantities of 

 fine material to the 

 surface, and in some 

 places change the 

 surface soil in a few 

 years. 



Angleworms, the 

 most important ani- 

 mal soil builders, 



BACTERIAL NODULES ON BEAN ROOTS chaimel the Soil wlth 



their burrows, thus 



providing ready-made openings for the growing roots and 

 by increasing the porosity of the soil aid in its ventilation 

 and drainage. They swallow the soil as they make their 

 burrows, in order to get the decaying vegetable matter for 

 food, and they grind it fine as it passes through their 

 bodies. Every year they bring to the surface great quan- 



