46 



CONSERVATION OF THE SOIL 



2. After a heavy summer rain the water of a small stream 

 contained 1 Ib. of sediment for every 500 gal. of water. If 

 the rainfall was 1 in., the area of the basin drained 4 sq. mi., 

 and the amount of water that ran off 1 of all that fell, how 

 much soil did the rain carry away ? 



3. After a heavy rain the water of a small stream that 

 drained a meadow contained 1 Ib. of sediment for every 

 2000 gal. of water. If the rainfall was 2 in., and 1 of all the 

 water that fell ran off, how much soil was carried away from 

 a 40-acre meadow ? 



4. If the water running from a piece of land that has 

 been planted with corn contained 1 Ib. of sediment for 

 every 250 gal. of water, how much soil was carried away 

 from a 40-acre cornfield after a 2-inch rainfall, J of the 

 water running off ? 



TAX UPON THE SOIL BY DIFFERENT CROPS 



53. Nitrogen, phosphoric acid, and potash are the most 

 important plant foods contained in the soil. They are ex- 

 tracted from the soil in different proportions by different 

 crops. Clover, cowpeas, and a few other crops draw their 

 nitrogen from the air and thus save the soil. 



54. The table below will give some idea of the amount of 

 plant food removed from the soil in growing certain crops. 



