80 



adding one-fourth percent clay to Norfolk soil there was practically no in- 

 crease in nitrification, yet no deleterious action was noted such as that 

 reported by Pichard. 1 



There are in the above analyses some slight variations in results from 

 pots which received duplicate treatment. This is to be expected when such 

 large quantities of nitrate are being measured. The differences between the 

 pots which received different treatment are so well defined that it is easy 

 to attribute it to the particular treatment each pot received. The variations 

 emphasize, however, the fact that it is unwise to draw conclusions in nitrate 

 tests on extremely small difference especially if large quantities of nitrates 

 are involved. 



The results in this paper are somewhat at variance with those published 

 in the Annual Report of this Station, 1911-12 2 An increase in nitrification 

 was noted therein under the influence of one-fourth sand when added to 

 Albemarle and Appomattox chocolate soils, the former giving with sand a 

 maximum increase over the control of 2.8 mgs. per 100 grams of soil and 

 the latter 7.5 mgs. The experiment which showed these results was started 

 in November, 1911, and no increase from the sand was observed until April 

 of the following year. From that date until September the increase was 

 observed. As the present experiment ran from May to August, 1914, the 

 period of active nitrification was practically the same in both experiments. 

 The variations can only be explained by the difference in time which the 

 two experiments ran, yet admitting this factor the results on this point are 

 somewhat irreconcilable. 



'Compt. rend. (Paris), 109, 1889. pp. 455-447. 

 2 P. 185. 



