LEGUMINOUS CROPS. 131 



soil is doubtless due to more nitrogenous crop-residue from 

 the leguminous than from the gramineous crop. Indeed, 

 about 74 lb. per acre of nitrogen had been removed in the 

 Trifolium repens crops, and only 18 lb. in the wheat (reckoned 

 on the half-acre in crop) 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 nitri- 

 fication of recent crop -residue. Some found in the lower 

 layers was, 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 Again, 

 slightly richer in nitrosren, it is obvious that the whole of ™h eredid 



i- * i • • • 1 i i ii -i-i-i •• the nitro- 



the nitrogen of the nitric acid could not nave had its origin gen came 

 in the surface-soil. If, therefore, it did not come from the f rom i 

 atmosphere, it has been derived from the subsoil. 



The indication is, that nitrification is more active under Nitrifica- 

 the influence of leguminous than of gramineous growth and ^fZ^qu- 

 crop-residue. There would not only be more nitrogenous minous 

 matter for nitrification, but it would seem that the develop- growth. 

 ment of the nitrifying organisms is the more favoured. 

 Part of the result may, therefore, be due to the passage down- 

 wards of the organisms, and the nitrification of the organic 

 nitrogen of the subsoil. 



An alternative is, that the soil and the subsoil may still Analter- 

 be the source of the nitrogen, but that the plants may take nahve - 

 up, at any rate part, as ammonia or as organic nitrogen. To 

 this point we shall recur presently. 



Comparing the amounts of nitrogen as nitric acid in the Results 

 Vicia saliva soils with those in the Trifolium repens soil, it is ^ches. 

 to be observed that, whilst from the Trifolium repens soil 

 only 164 lb. of nitrogen had been removed per acre in the 

 crops of the five years to 1882 inclusive, 366 lb. 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 lb. were removed in the Vicia crops just before soil- 

 sampling. Under these circumstances one of the Vicia 

 soils contained 81.5 lb., and the other 91 lb., 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 the plants at the commencement of growth ; but 

 if there had only been as much as in the case of the Tri- 

 folium plot, it is seen that the deficiency in the Vicia soils 



