CHAPTER VIII 

 FERTILIZERS 



It frequently happens that soils lose their ability to 

 raise good crops. They no longer continue to produce the 

 high yields which are characteristic of soils functioning 

 properly in accordance with the facts stated in the last two 

 chapters. This failure in fertility may be due to several 

 causes: Poor drainage, exceptionally bad climatic con- 

 ditions, insufficient water, poor seed, bad physical condition, 

 presence of fungous diseases, not enough organic matter, 

 and lack of available plant food. Most of the conditions 

 can be remedied by the farmer. The climatic factor is one 

 not to be controlled except that a dry condition may be 

 overcome by irrigation where a source of water is con- 

 venient and it is possible to ditch the land. All other factors 

 can be supplied. In this discussion of the chemical phase 

 of soil fertility only one factor can be considered, namely, 

 the supply of plant food, available or total. 



146. Plant Food in the Soil. — When it is a question of 

 unavailable plant food, attention to such things as cultiva- 

 tion and the supply of organic matter will frequently remedy 

 the deficiency; but where these factors are insufficient, or 

 where plant foods are actually lacking, then it becomes 

 necessary to add them to the soil. 



From Table III, p. 114, showing the number of pounds of 

 nitrogen, phosphoric acid, and potash removed from an acre 

 by various crops, it can readily be seen that there is a steady 

 drain on the reserve food supply in the soil, and no compensa- 

 tive natural return. In the case of nitrogen there is an addi- 

 tion of possibly 40 to 60 pounds of nitrogen in the roots and 

 stubble of one legume crop. This is in excess of the amount 

 removed from the soil and illustrates very forcibly the 



