PHOSPHORUS AS A SOIL PRESERVER 91 



plemented by that returned in manure and crop residues, 

 for the production of crops for at least thousands of 

 years." 



Then he sounds this warning note to American land 

 owners : 



"If the supply of phosphorus in the soil is steadily 

 decreased in the future in accordance with the present 

 most common farm practice, then poverty is the only 

 future for the people who till the common prairie lands 

 of Illinois. And this does not refer to the far distant 

 future only, for the turning point is already past on many 

 Illinois lands." 



Average barn manure carries 10 to 15 pounds nitrogen, 

 5 to 9 pounds phosphoric acid and 10 to 15 pounds potash 

 to the ton. This plant food is in a fairly soluble condi- 

 tion, and is readily taken up by the plant. For market 

 gardening purposes it may be balanced and supplemented 

 by suitable fertilizers in case the yield is not up to ex- 

 pectations. In soggy spots slacked lime should be used. 

 Where the crops are light on land that has had barnyard 

 manure and good cultivation it is well to try phosphorus. 



Nitrogen is free as air, and potassium is abundant in 

 nearly all of the soils. Both nitrogen and potassium re- 

 main in the straw and the stalks, and in the farm manure 

 to a considerable extent. 



Phosphorus, on the contrary, is present in nearly all 

 soils in limited amounts and it is being continually re- 

 moved from the land. 



While it is true that some forms of soil bacteria prefer 

 to live in the absence of free oxygen, the large mass of 

 soil organisms can only carry out their life processes in 

 the presence of a plentiful supply of oxygen. Every 

 phase of soil management therefore which affects in any 

 degree the amount of air supplied to the soil is a regulator 

 of the bacterial activities in the soil. Among these im- 

 portant phases of soil management are tillage, includ- 



