SOILS 153 
tilizers may be used to supply the deficiency, but in ordinary 
farming they are too expensive. (2) The nitrogen may have 
been carried away in drainage waters. Especially in sandy 
soils, the rain water as it sinks in carries with it the soluble 
matter, and the nitrogen compounds are the most readily 
dissolved of all the plant foods. (3) In some regions the 
land is impoverished because the richest surface soil is gradu- 
ally carried away by wind or by running water from rains. 
APPARATUS TO TEST THE CAPACITY OF SoILs TO Hotp WATER 
There are sections where more fertility is lost in this way 
than is used up by crops. (4) Unproductiveness may result 
from bad physical condition caused by bad tillage, especially 
cultivation when the land is too wet. (5) The most prev- 
alent and most fundamental cause of unproductiveness is 
the exhaustion of humus. That implies these specific faults: 
(a) The soil no longer holds the moisture supply so well as 
it did formerly. (6) It is less porous and otherwise less 
favorable to root growth, and it “‘ bakes ” more easily. (c) De- 
