

How wild 

 grass 

 improved 

 the soil 

 on the 

 plains 



Leaching 



What 

 water 

 removes 



40 Nature-Study Agriculture 



the water, and it prevented heavy rains from washing 

 the nourishment from the soil. Second, as the roots 

 decayed to make room for new ones, an abundance of 

 humus was formed. (Exp. i.) It is this humus that 

 gives the characteristic dark color to prairie soil. Third, 

 the grass, most of which was burned away each year, was 

 not altogether lost, for the mineral food material that it 

 had taken for growth was returned to the soil in the form 

 of ashes. 



The loss of fertility in cultivated soil. Cultivated 

 soil is more exposed to the action of rain than is land 

 that is covered with sod. The more soluble substances 

 in cultivated soil go into solution and are carried away. 

 This process is called " leaching." If we should mix 

 a pound of sugar or salt with the surface soil on a very 

 small area, a few heavy rains would be sufficient to 

 remove it almost entirely. A pound of marble dust or 

 other insoluble substance would, on the contrary, 

 remain for years. Certain plant foods, as compounds 

 containing nitrogen, are as soluble as salt and sugar, 

 and for that reason they leach out of the soil very 

 readily, especially when no crop is growing to absorb 

 and hold them. 



To find out what element of the soil's strength and 

 how much of it is being wasted, it is necessary to col- 

 lect samples of the drainage water and evaporate it 

 completely. Although this water may be perfectly 

 clear and colorless before evaporation, some solid ma- 

 terial will remain. (Exp. 2.) This residue may be 

 examined chemically to see of what it is composed. By 

 examining the water of the Mississippi it has been found 



