34 IRRIGATION FARMING. 



Utterly impossible to exhaust the soil irrigated with 

 such water. Aside from this there is the humus com- 

 ing in the form of leaf mold and decayed vegetable 

 matter, which is considered the most valuable element 

 of all in improving the natural soils of the west. 



Manure on Irrigated Soil. — After being assured 

 that a great surplus of fertilizing ingredients is yearly 

 deposited on the land by the irrigating waters, the 

 reader might conclude that the application of barn-yard 

 manure would be quite superfluous. It has, however, 

 been conclusively proven in pradlice that even in the 

 case of wheat, which may remove only half the 

 nitrogen yearly deposited by some rivers, the crop is 

 very considerably increased when the land receives a 

 moderate dressing of barn-yard manure every three or 

 four years, while it is often impossible to successfully 

 raise vegetables unless barn-yard manure is freely em- 

 ployed. It is claimed by some that these good effedls 

 are due to the improved mechanical condition of the soil 

 and its increased power for holding moisture, and 

 doubtless these fadls may have something to do with 

 the result, but it is probable that the real explanation 

 is to be found in the action of soil ferments. Nitrogen 

 may exist in the soil even in excess and yet not be in 

 a form available for plants to feed upon. The same 

 may be said of other fertilizers. 



It has been demonstrated that nitrogen in the soil 

 is reduced to nitric acid by means of living bacteria, 

 which are multiplied by fermentation, and this occurs 

 most rapidly in decomposing barn-yard manure. How 

 bacteria perform this useful work is not fully under- 

 stood, but it has long been noticed that a dressing of 



