32 



RESULTS OF EXPERIMENTS AT ROTHAMSTED, 



about eleven times as much as in the Wheat, and more than thirteen 

 times as much as in the Eed Clover. Indeed, this very deeply, and 

 very powerfully rooting plant, yielded, in its above-ground produce 

 alone, 337 Ibs. of nitrogen in 1884, 270 Ibs. in 1885, 167 Ibs. in 1886, 

 247 Ibs. in 1887, and 161 Ibs. in 1888. 



TABLE XV. 



Estimated yield of Nitrogen per acre, in Ibs., in Wheat alternated with Fallow, 

 and in various Leguminous Crops, without Nitrogenous Manure. 



PRELIMINARY PERIOD. WHEAT AND FALLOW, 27 yrs., 1851-'77. EED CLOVER, &c., 29 yrs., 1849-'77. 



EXPERIMENTAL PERIOD. 



* Eight years only, 1878-'85. 



Not only have these large amounts of nitrogen been removed in the 

 above-ground produce, but determinations of nitrogen in the surface- 

 soils of the Vetch plot in 1 883, 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 has gained rather than 

 lost nitrogen, due to the accumulation of nitrogenous crop-residue. 

 Here again, then, it is obvious, that the original source of the nitrogen 

 of the crops has not been the surface-soil. It must have been derived 

 either from the atmosphere or from the sub-soil. 



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 12 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 



