53 



alone, to which we have hitherto referred, and to which we confine 

 attention on the present occasion. 



In the nex<- place, that the difference in the condition of the two 

 plots is not merely local is shown by the fact that the determinations 

 on a sample from the unmanured plot taken in 1870 entirely confirm 

 the relative composition shown Ly the samples of 1876. Again, the 

 lower percentage of nitrogen in the 1876 samples of the mineral 

 manured plot is entirely confirmed by the results obtained on samples 

 taken in 1878. Further, of the twenty experimental plots, there is 

 only one other showing so low a percentage as the mineral-manured 

 plot, and that is the one which had received the same mineral manure, 

 but for a shorter series of years. 



We have in fact no doubt whatever that the differences indicated by 

 the figures are real, and dependent on the conditions of manuring and 

 of growth. The reduction is, moreover, very great, amounting to 

 nearly one-tenth of the total quantity of nitrogen, and far beyond 

 the limits of accidental difference in the sampling or the analysis. 



Calculated per acre, the sui'face soil of the mineral-manured plot 

 contained, at the end of the twenty years, 50G pounds less nitrogen than 

 the soil oi the unmanured plot to the same depth, corresponding to an 

 annual reduction of 25"3 pounds of nitrogen per acre per annum. It 

 is, to say the least, a very remarkable coincidence that the in'^reased 

 yield of nitrogen in the crop on the mineral-manured plot which has 

 to be accounted for is 22'6 pounds per acre per annum. 



We do not pretend to claim absolute accuracy for such results, but 

 we ourselves entertain no doubt whatever of their significance and 

 their importance. 



It will be asked — How is it that in the case of the red clover, and 

 the melilotus, it was concluded that, so far as the plants had derived 

 their nitrogen from the soil, it was at any rate mainly from the lower 

 depths, and that here, in the case of the permanent mixed herbage 

 plots, we assume the increased yield of nitrogen to be derived from 

 the surface soil ? 



Under the influence of the mineral manure, a larger proportion 

 and amount of leguminous herbage was developed than on any other 

 p,ot ; but the leguminous plant the most, indeed very prominently, 

 favoured was the Lathyrns p-atensis, which throws out an enormous 

 quantity of root near the surface ; and it is sufficiently established 

 that the potash of artificial manures remains almost exclusively in the 

 superficial layers. On the other hand, the perennial red clover, and 

 the Lotus corniculatus, which have a much more deeply-rooting ten- 

 dency, are comparatively little encouraged. 



D 2 ' 



