72 



TABLE III. Nitrifying Efficiency of a Number of Virgin Sails of 



Various Textures. 



There are some very striking differences to be noted in the foregoing 

 table and, indeed, so noticeable are they that one might readily assume 

 them to result in a large degree from soil texture. The results are from 

 virgin soils, it will be recalled, and ammonium sulphate had been added to 

 each sufficient to supply all the nitrogen necessary for conversion into 

 nitrates. It would seem, therefore, that the nitrifiers were much less de- 

 veloped in certain soil types than in others. The open sandy soils are 

 strikingly low, the loam and clay loam are as impressively high, and in the 

 heavier clays again a falling off is evident. This latter decrease cannot be 

 attributed to denitrification, since the control conditions of the experiment 

 would scarcely admit this process. A condition which brought the averages 

 of the sandy soils so low was due to some of the soils failing completely to 

 nitrify and this was seldom true of the soils of heavier texture. Yet the 

 failure of the former soils to produce nitrates was probably due to their lack 

 of organic matter rather than to any inherent physical condition. The 

 great majority of them are to be regarded as poor soils, low in humus, and 

 deficient in those qualities which would develop a vigorous bacterial flora of 

 any kind. Were these soils to be subjected to a well directed system of 

 organic manuring they would, in all probability, as some of our own experi- 

 ments indicate, assume a high place in nitrifying efficiency. 



The heavy clay soils also are somewhat low in their nitrifying power. 

 That aeration is essential to nitrification is too well demonstrated to question 

 and these virgin clay soils had not the advantage of that condition to stimu- 

 late their nitrifying powers. The inhibiting effect of texture could likely 

 be ameliorated by proper cultivation and there are indeed so many instances 

 of this that it is probable that the undesirable condition may usually be 

 overcome. Considering the natural powers of clay soils to nitrify, the re- 

 sults just cited show that, like extremely open sandy soils, the process is 

 not so vigorous as in some of the other soil types. 



The most satisfactory condition for nitrification, as exemplified by the 

 results from this work, is that which is afforded by soils of the loam and clay 



