NITRIFICATION 131 



which is carried to a depth of 60 inches is lost to the growing 

 plant, for in work at the Utah Experiment Station the Senior 

 author and co-workers have found in the spring a nitrate belt as 

 low as the seventh and eighth foot-section. These nitrates had 

 been carried to this depth by the winter and spring water. It 

 was noted that later in the season as the water was brought to the 

 surface by capillarity the nitrates also returned, and by June, July 

 or August, depending upon the crop grown upon the soil and 

 the quantity of irrigation water applied, the nitrate belt which 

 in the spring was in the seventh and eighth foot-section had 

 reached the surface foot-section. Moreover, the deep-rooted 

 plants of the arid regions probably feed from lower depths than 

 do the shallow-rooted plants of the humid regions. 



The practical conclusion to be reached from these results is 

 that the method of reducing the loss by leaching is by growing 

 plants, the roots of which may absorb the plant-food as rapidly 

 as it is made available. 



The loss of nitric nitrogen from irrigated soil may be pre- 

 vented by the judicious use of irrigation water. Experiments at 

 the Utah Station, covering a period of fourteen years, have dem- 

 onstrated that the application of 15 or 20 inches of irrigation 

 water, distributed thruout the season, to deep soil causes little, if 

 any, loss of nitric nitrogen from such a soil, whereas applica- 

 tions of from 25 to 37.5 inches similarly distributed cause con- 

 siderable dimunition in the crop yield. This decrease in crop 

 yield due to excessive quantities of water, up until the soil be- 

 comes water-logged, is largely due to the rapid washing of the 

 nitric nitrogen beyond the feeding area of the plant roots. 



