40 



were, however, slightly the heavier, which vrould indicate that, for 

 comparison, the percentage of nitrogen given for the latter date is 

 perhaps somewhat too low. Still, it is obvious that, as in the case of 

 the "wheat land, so also in that of the barley land, there is, with the 

 decline in the yield of nitrogen in the crop at the same time a decline 

 in the stock of the nitrogen in the soil. 



Nitrogen in the Soils of the Experimental Boot-crop Plots. 



The next results relate to the land upon which root-crops — com- 

 mon turnips, swedes, sugar-beet, and mangel-wurzel (with the 

 exception of the interpolation of three years of barley without 

 manure) have been grown for forty years in succession, 1843-1882 

 inclusive. Samples of the soil have only been taken once, namely, 

 in April, 1870; that is, after the experiment had been continued 

 twenty-seven years. At that time 35 plots were sampled, and four 

 samples were taken from each plot, each 6 by 6 inches area, and to 

 a depth of 3 times 9, or 27 inches. 



The following table shows the percentage of nitrogen in the surface 

 soil of the continuously unmanured plot, and of three plots with 

 mineral manure alone : — 



Table XII, — Barnfield Root-crop Land. 



Nitrogen, j)er cent, in dry Mould, first 9 inches. 



[Root-crops (except barley three years) 40 years in succession, 1843-1882 inclusive.] 



Description of Manure. 



1870. 



Plot 3. — Unmanured 



Plot 4. — Mixed mineral manure. . . . 

 Plot 5. — Superphospliate alone .... 

 Plot 6. — Supcrph'isphate and potash 



Mean of plots 4, 5, G. . . . 



Per cent. 

 -0852 



-0934 

 -0888 

 -0807 



-0896 



Having only taken samples once, we have, of course, no means of 

 comparing the condition of the land as to its percentage of nitrogen 

 at different periods. The point to b" observed in the results given in 

 the table is, that each of these four plots, which have received no nitro- 

 genous manure, shows, after twenty-seven years of experiment (twenty- 

 four years roots and three years barley), a lower percentage of nitrogen 



