75 



susceptible to similar agencies of depression or stimulation. Apparently 

 the two processes have little in common, for in 50 percent of the soils ex- 

 hibiting an unusual power in the one process that same soil showed peculiar 

 indifference to the other. Yet despite these results the authors are reluctant 

 to assume such a position. It is at variance with the principles which are 

 believed to regulate both nitrification and nitrogen fixation. It would be 

 safer to ascribe such contradictions as those above to untrustworthiness of 

 method than to conclude that two processes so intricately connected with 

 soil fertility are unrelated. Perhaps in the great majority of our present 

 cultivated soils, receiving as they do no especial treatment which would tend 

 to develop either process, that neither proceeds with such vigor as would 

 present opportiinities for noting a relationship between the two. But soils 

 which are unusual in their fertility, which have been intensely cultivated 

 with reference to promoting those processes which govern productivity in 

 the great majority of these we necessarily expect a vigorous nitrifying and 

 nitrogen fixing flora which are closely related in their activities. 



Referring once more to Table I the results from the nitrate accumulation 

 tests are to be observed. These tests were made by keeping 400 grams of 

 soil in glass fruit jars in the incubator room for six months at 28 C. and 18 

 percent moisture content. No nitrogen was added to the jars and the figures 

 represent the conversion of original organic nitrogen into nitrates. Only 

 one jar was set up for each soil. The results of these tests are summarized 

 in Table VI in the manner of those in which ammonium sulphate was used. 



TABLE VI. Giving the Comparative Accumulation of Nitrates in Certain 

 Virgin and Cultivated Soils. 



Number of pairs in which cultivated soils excelled 



Number of pairs in which virgin soils excelled 19 



Number of pairs in which no nitrification took place 



Total increase in nitrates by cultivated soil 



Total increase in nitrates by virgin soil 



Average increase where cultivated soils excelled 2.8 



Average increase where virgin soils excelled 



In two of the pairs of soil the .nitrates were the same- and in one the 

 analysis was lost. 



The distinction in the nitrifying power of virgin and cultivated soils 

 is not present here to the degree noted in the foregoing tests. The number 

 of pairs in which the virgin soil excelled is the same as where the cultivated 

 soil was highest ; the total quantity of nitrate formed is slightly more in 

 the cultivated soils than in the virgin ; and the average increase is somewhat 

 higher when induced by the former than when taking place in virgin soils. 

 This condition of equality in nitrifying power of the two types of soils is 

 probably due to the superior quantities of nitrogen originally present in the 



