NITRIFICATION 127 



organic matter probably due to the poor aeration, however, when 

 growing in the soil they are benefited by it. 



Altho they produce acids they will not tolerate an acid me- 

 dium. The nitrous acid as rapidly as formed is converted into a 

 nitrite by the bases of the soil, whereas the nitric acid is quickly 

 changed into a nitrate in which form it may accumulate. Dur- 

 ing this neutralization of the acids, some phosphorus, potassium, 

 and other plant food is rendered available. The magnitude of 

 this change varies with diiferent soils. It is low in a calcareous 

 soil and high in some containing only small quantities of car- 

 bonates. Inasmuch as acids inhibit the growth of these organ- 

 isms we find their activities increased in acid soils when quick- 

 lime or limestone are added. Even large quantities of the latter 

 may be present in a soil without interfering with nitrification, 

 as we obtain rapid nitrification in the Greenville (Logan, Utah) 

 Experimental Farm which contains about 40 per cent of calcium 

 and magnesium carbonate. 



Crop and Fallow. — Even as early as 1855 the work at Rot- 

 hamsted had demonstrated that the beneficial eilects of fallow 

 lie in the increase brought about in the available nitrogen com- 

 pounds of the soil. Deherain and Demoussy's work indicated 

 that there is a larger production of nitrates in fallow than in 

 cropped soils. In humid districts fallowing is often looked upon 

 as an extreme form of soil robbery for it promotes the activity 

 of soil organisms, and some workers have recorded a loss in fal- 

 low plats of 85.5 pounds per acre of nitrogen. This often ex- 

 ceeds the quantity removed by a crop. But these results do not 

 hold in an arid climate nor during dry seasons, for here bare fal- 

 low may not necessitate this loss and much is to be gained by 

 its practice. 



Work carried on at the Utah Experiment Station and extend- 

 ing over a number of years showed that the fallow soil contains 

 considerably more nitrates in the summer and fall than do most 

 cropped soils. This gain is carried over into the next spring, and 

 hence furnishes a ready supply of nitrogen for the growing plant. 



