SOIL 143 



2. If a cubic foot of soil weighs 75 pounds, how 

 many pounds of cultivated soil per square yard? Per 

 square rod ? Per acre ? 



3. Find the number of pounds of nitrogen, potash 

 and phosphoric acid in the cultivated soil per acre for 

 each of the four kinds of soil. 



4. If the soil is cultivated to the depth of eight 

 inches, how many pounds of each of the three fer- 

 tilizing substances per acre in each of the soils given in 

 the table ? 



5. How many pounds of nitrogen, potash and phos- 

 phoric acid are used, annually, per acre, by a crop of 

 20 bu. of wheat? In how many years will one-half of 

 the nitrogen in clay be used up by this crop feeding to 

 the depth of eight inches? 



6. How will this affect future crops ? 



7. Work the same problem for other soils. 



8. Use a 50 bu. corn crop per acre and work prob- 

 lem 7. Also a 60 bu. oat crop. A 120 bu. potato crop. 



LESSON XLVII 

 PLANT FOODS 



While we are waiting for spring to come, when we 

 shall be almost too busy on our farm to read, we shall 

 continue our studies of soils and plant foods. 



Elements of the earth. Chemists have found that 

 all the substances of the world can be separated into 

 about eighty different things. These are called elements. 

 Iron, gold, silver, tin, carbon, sulphur, etc., are elements. 



