34 RESULTS OF EXPERIMENTS AT ROTHAMSTED, 



there is more than twice as much nitrogen as nitric acid in the 

 Trifolium repens, as in the Wheat fallow soil ; in the second and third 

 3 depths, there is more than 3 times ; and in the fourth 3, more than 4 

 times as much. Hence it is -obvious, that any loss by drainage would 

 be much the greater from the Trifolium plot, so that the difference 

 between the two plots was probably greater than the figures show. 



In the case of both plots the actual amount of nitrogen as nitric 

 acid is the greatest near the surface, indicating more active nitrification ; 

 and the greater amount in the Trifolium soil is doubtless due to more 

 nitrogenous crop-residue from the Leguminous than from the Grami- 

 neous crop. Indeed, as Table XV. (p. 32) shows, about 74 Ibs. of 

 nitrogen had been removed in the Trifolium repens crops, and only 18 

 Ibs. in the Wheat, in 1882, and none from either in 1883, the year of 

 soil sampling ; and the crop-residue of the Trifolium repens would 

 contain much more nitrogen than that of the Wheat. But it is not 

 probable that the excess of nitric acid in the Trifolium soil, together 

 with the larger amount lost by drainage, could be entirely due to the 

 nitrification of recent crop-residue. Some found in the lower layers is, 

 however, doubtless due to washing down from the surface. But as, 

 notwithstanding much more nitrogen had been removed in the crops 

 from the Leguminous than from the Gramineous crop land during the 

 preceding 30 years, the surface-soil of the Leguminous plot remained 

 slightly richer in nitrogen, it is obvious that the whole of the nitrogen 

 of the nitric acid could not have had its origin in the surface-soil. 

 If, therefore, it did not come from the atmosphere, it has been 

 derived from the sub-soil. 



The indication is, that nitrification is more active under the 

 influence of Leguminous than of Gramineous growth and crop-residue. 

 There would not only be more nitrogenous matter for nitrification, but 

 it would seem that the development of the nitrifying organisms is the 

 more favoured. Part of the result may, therefore, be due to the 

 passage downwards of the organisms, and the nitrification of the organic 

 nitrogen of the sub-soil. 



An alternative is, that the soil and the sub-soil may still be the 

 source of the nitrogen, but that the plants may take up, at any rate 

 part, as ammonia, or as organic nitrogen. To this point I shall recur 

 presently. 



Comparing the amounts of nitrogen as nitric acid in the Vicia sativa 

 soils, with those in the Trifolium repens soil, it is to be observed, that 

 whilst from the Trifolium repens soil only 164 Ibs. of nitrogen had been 

 removed per acre in the crops of the five years to 1882 inclusive, 366 

 Ibs. had been removed in the Vicia crops to the same date. Then, 

 whilst none was removed in crops from the Trifolium plot in 1883, 101 

 Ibs. were removed in the Vicia crops just before soil-sampling. Under 

 these circumstances, one of the Vicia soils contains 81*5 Ibs., and the 

 other 91 Ibs., less nitrogen as nitric acid per acre, than the Trifolium 

 repens soil. 



Of course we cannot know exactly how much was at the disposal of 



