AGRICULTURAL SOILS 



319 



titles of this finely ground soil mixed with the undigested 

 vegetable matter. Darwin estimated that the angleworms 

 in English soil deposited 

 one fifth of an inch of 

 these castings each year 

 over some parts of the 

 surface. This is the 

 finest kind of fertilizer. 

 It is a common saying 

 that the more angle- 

 worms the better the 

 soil. 



ANTHILL 

 ., . OM This soil has been brought from below 



Agricultural Soils. - and piled up by the ants> 



As has already been 



shown, soils differ greatly in fineness, mineral composition, 

 and waterholding capacity. They also differ greatly in the 

 amount of decayed vegetable material or humus in them. 



The humus is a most im- 

 portant soil ingredient. 

 It not only furnishes 

 plant food, but it also 

 increases the capacity of 

 the soil for holding mois- 

 ture and prevents the 

 soil particles from pack- 

 ing together too closely. 

 In sandy soils, since 

 there is usually little hu- 

 mus, the water soon 

 drains out and plants be- 

 come parched. Such soils 



MOLEHILLS 



Showing how these animals burrow up 

 the soil and make it porous. 



