LEGUMINOUS CHOPS. 129 



clover 22 lb., in the white clover 47 lb., in the vetch 75 lb., 

 in the Bokhara clover 64 lb., and in the lucerne the enormous 

 amount of 160 lb., of nitrogen per acre per annum. 



Again, if we take the total yields of nitrogen over the 

 experimental periods, we have — in the wheat 163 lb., in the 

 red clover 112 lb., in the white clover 283 lb., in the vetch 

 1051 lb., in the Bokhara clover 702 lb., and in the lucerne 

 1916 lb. ; that is, in the lucerne about twelve times as much 

 as in the wheat, nearly twice as much as in the vetch, and 

 very much more than in either of the other Leguminosse. 

 Indeed, this very deeply and very powerfully rooting-plant 

 yielded, in its above-ground produce alone, 337 lb. of nitrogen 

 in 1884, 270 lb. in 1885, 1G7 lb. in 1886, 247 lb. in 1887, 

 and an average of 146 lb. over the next four years. 



Not only have these large amounts of nitrogen been Soil en- 

 removed in the above-ground produce, but determinations of n ^ d in 

 nitrogen in the soils of the vetch plot in 1883, and of the 

 white clover, the Bokhara clover, and the lucerne plots, in 

 1885, have shown, as in the case of the clover after the 

 beans, that the surface - soil had gained rather than lost 

 nitrogen, due to the accumulation of nitrogenous crop- 

 residue. Here again, then, it is obvious that the original Nitrogen 

 source of the nitrogen of the crops has not been the surface- f ro J n ' ?, Ae 



^iCOSOZC 07* 



soil itself. It must have been derived either from the the atmo- 

 atmosphere or from the subsoil. sphere. 



The next results will throw some light on this point. 

 Thus, having made initiative experiments of the same kind 

 some years previously, in July 1883 samples of soil were 

 taken to the depth of twelve times 9 inches, or 108 inches in 

 all, on the wheat-fallow plot, on the white clover plot, and 

 on two of the vetch plots, for the determination of the 

 amount of nitrogen existing as nitric acid at each depth. 

 Table 43 (p. 130) summarises the results. 



The first point to notice is that at each depth, from the 

 first to the twelfth, the Trifolium repens soil contained much 

 more nitrogen as nitric acid than the wheat-fallow soil ; and 

 as the figures at the bottom of the table show, whilst to the 

 total depth of 108 inches, or 9 feet, the wheat-fallow soil 

 was estimated to contain only 52.4 lb. of nitrogen as nitric 

 acid per acre, the Trifolium repens soil — that is, the legu- 

 minous plant soil — contained to the same depth 145.7 lb. 



Now, independently of the fact that the leguminous plant Nitrogen 

 plots had received mineral manures and the wheat-land had ) nsoll . a f te ^ 



r -, . pp .,,. .. leguminous 



not, the characteristic difference in the history of the two crops, 

 plots was, that the one had from time to time grown a legu- 

 minous crop, and the other had not ; and the one which had 

 grown leguminous crops contained, to the depth of 9 feet, 

 VOL. VII. I 



