48 



i 



Nitrogen as Nitric Acid in other Soils and Subsoils. 



It will be some furtlicr aid in judging of tho possibility or pro- 

 bability that the nitric acid in the soil and subsoil may be an adequate 

 source of tho nitrogen of the LeguminoscB, if wo quote a few results 

 indicating the amount of nitric acid found in some other soils under 

 known conditions. 



In the first place, three soil drain-gauges, one with 20, ono with 40, 

 and one with GO inches depth of soil, in its natural state of consolida- 

 tion, and each of one-thousandth of an acre area, have been under 

 experiment for between eleven and twelve years. No manure has been 

 applied to these soils, nor have they gi'own any crop, from the com- 

 mencement. The drainage has been regularly collected and measured ; 

 and for nearly the whole of the last five years the nitric acid has 

 been determined in monthly average samples of the drainage waters. 

 Taking the result of the three gauges, for four harvest-years (Sep- 

 tember 1, 1877, to August 31, 1881), these soils, which had been 

 about six years without any manure at the commencement of the 

 period under consideration, have lost by drainage an average of nearly 

 43 pounds of nitrogen as nitric acid per acre per annum, of which 

 perhaps not much more than 5 pounds would be duo to rain and con- 

 densation of combined nitrogen from the atmosphere. In fact, about 

 35 pounds, or perhaps more, would appear to have been annually due 

 to the nitrification of the nitrogenous matter of these unmanured soils. 

 It has to be borne in mind, however, that tho blocks of soil having 

 access of air from below as well as from above, the nitrification may 

 have been freer than it would be in soil in its ordinary condition. 



Again, in some of the samples of soil taken from the plots in the 

 experimental wheat field, in October 18G5, and in many of those taken 

 in October 1881, that is in each case about two months after the 

 removal of the crop, the nitric acid has been determined. 



In the case of one plot sampled in 18G5, which had received 

 annually mixed mineral manure and ammonium salts, determinations 

 made in 186G (by Br. Pugli's method), showed nearly 76 pounds of 

 nitrogen as nitric acid per acre to tho depth of 27 inches. As, how- 

 ever, these soils had been stored in a rather moist condition, it is 

 possible that nitrification may have taken place after the collection, 

 and that the results are so far somewhat too high. 



The following table (XVl) gives an abstract of the results of the 

 determinations of nitrogen as nitric acid in the 1881 samples of the 

 experimental wheat field soils : — 



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