34 



therefore, the percentages of nitrogen as actually determined in the 

 166;') samples, and we assume the weight of dry mould (9 inches deep) 

 represented by the samples to be 2,300,000 pounds per acre. But, in 

 the case of the 1881 samples, we assume that one-tenth of the heavier 

 weight had the composition determined iu the second 9 inches (it 

 would be very slightly higher), and the percentage in the remaining 

 nine-tenths, representing 2,300,000 pounds of surface soil, is raised by 

 calculation accordingly. 



The following table (IX, p. 35) gives for the surface soils (9 inches 

 deep), of the unmanured plot, and the nine artificially manured plots, 

 sampled in 1805, the actually determined percentages of nitrogen in 

 the dry mould ; and for the 1881 samples from the same plots, it gives 

 both the actually determined percentages, and the corrected percentages 

 calculated as above described. The table also shows the amount of 

 nitrogen per acre, reckoning 2,300,000 pounds of dry mould, calculated 

 for 1805 according to the actually determined percentages, and for 

 1881 according to the corrected percentages. The quantities per acre 

 more ( + ), or less ( — ), in 1881 than in 1805 are also given. Lastly, 

 for each period, there are given the quantities more or less on each of 

 the other plots than on plot 5a, which received the mineral manure 

 alone. 



As already said, in 1865 the land had grown twenty-two crops of 

 wheat in succession, and in 1881 thirty-eight crops. Plot 3 had been 

 unmanured from the commencement. Plot lOci received mineral 

 manure in the first year, but the ammonium salts alone each year 

 since. The remaining plots were somewhat variously manured during 

 the first eight of the thirty-eight years ; but (excepting plot 16) each 

 has been manured every year for the last thirty of the thirty-eight 

 years, as described in the table. 



It will be observed that, for every plot, the actual determinations 

 show a lower percentage of nitrogen in 1881 than in 1865, The cor- 

 rected percentages for 1881 are, of course, all rather higher than the 

 actual determinations ; and they, in some cases, show a higher, and in 

 others a lower, percentage than in 1865. Nevertheless, it cannot fail 

 to be noted that the relation of plot to plot is essentially accordant at 

 the two periods. 



The significance of the results will, however, be rendered the more 

 appai'ent on an examination of the calculated quantities per acre. It 

 is obvious that absolute accuracy cannot be claimed for such figures, 

 but the general accordance of the indications at the two periods is 

 such as to leave no doubt of their import. 



Keeping in view the special object of this communication, which 



