MANURING AND FERTILIZING 41 



The farmer needs to realize that the soil on his fields 

 to-day is not the same as that of last year. Soil is 

 changing. The subsoil of yesterday is the soil of 

 to-day. Although the amount removed by crops is so 

 small that it is a negligable quantity, that removed by 

 washing and by the wind is enormous. The muddy 

 stream, the bars at the mouths of rivers, the move- 

 ment of soils by the wind, and even the dust-cloud 

 raised when harrowing, show that far more plant-food 

 is removed in these ways than in crops, and to check 

 these leaks is of more importance than to try to make 

 up the loss by the addition of plant-food. The main- 

 tenance of a satisfactory amount of organic matter in 

 the soil in a proper condition may usually be accom- 

 plished by a judicious rotation of crops, manuring, and 

 liming. 



' ' The old method has been to feed crops with com- 

 mercial fertilizers, the new agriculture looks to nature 

 for its sources of plant-food. These sources are (i) 

 the large stores of unavailable plant-food in all soils, 

 (2) the unlimited stores of nitrogen present in the 

 air." 1 Research has revealed the fact that soil or- 

 ganisms can take plant-food from both of the above 

 sources and furnish it to growing crops, and that a 

 fertile .soil is one in which these processes are going on 

 at the highest rate, and that it is necessary to stimu- 

 late these biological activities. Humus is a food for 

 these organisms. L,ime is essential for maintaining the 

 soil in a slightly alkaline condition, and for fixing 

 some of the compounds formed in the soil; and drain- 



Dei. Bui 66, p. 14. 



