ON THE GROWTH OF LEGUMINOUS CROPS. 59 



comparatively small and declining amounts of nitrogen in the produce, 

 there has, coincidently, been a considerable reduction in the amount of 

 nitrogen in the surface-soil. There has, in fact, not been compensation 

 from the free nitrogen of the air, or at any rate not at all in amount 

 corresponding to the annual losses. 



Lastly, Grass-land which, under the influence of a full mineral 

 manure, including potash, but without any supply of nitrogen for more 

 than thirty years, has grown crops containing rather large amounts of 

 comparatively superficially rooting leguminous herbage, which has been 

 succeeded by increased amounts of gramineous herbage, and has, under 

 those conditions, yielded about the same amount of nitrogen per acre 

 as M. Berthelot assumes to be the average produce of a meadow, but it 

 has done so, only with coincident great reduction in the nitrogen of the 

 surface-soil. 



Whether, therefore, we consider the facts of agriculture generally, 

 or confine attention to special cases under known experimental 

 conditions, the evidence does not favour the supposition that a balance 

 is maintained by the restoration of nitrogen from the large store of it 

 existing in the free state in the atmosphere. Further, our original 

 soil-supplies of nitrogen are, as a rule, due to the accumulations by 

 natural vegetation, with little or no removal, over long periods of time. 

 Or, as in the case of many deep subsoils, the nitrogen is partly due to 

 animal remains, intermixed with the mineral deposits. The agricul- 

 tural production of the present age is, in fact, so far as its nitrogen is 

 concerned, largely dependent on previous accumulations ; and, as in the 

 case of the use of coal for fuel, there is not coincident and corresponding 

 restoration, so in that of the use or waste of the combined nitrogen of 

 the soil, there is not evidence of coincident and corresponding 

 restoration of nitrogen from the free to the combined state. 



In the case of agricultural production for sale, without restoration 

 by manure from external sources, a very important condition of the 

 maintenance of the amount of nitrogen in the surface-soil, or of the 

 diminished exhaustion of it, is the growth of plants of various range 

 and character of roots, and especially of leguminous crops. Such 

 plants, by their crop-residue, enrich the surface-soil in nitrogen. It is, 

 as a rule, those of the most powerful root-development that take up the 

 most nitrogen from somewhere ; and this fact points to a sub-soil 

 source. But, independently of this, which obviously may be held to be 

 only evidence of the necessity of obtaining water and mineral matters 

 from below, in amount commensurate with the capability of acquiring 

 nitrogen, direct experimental evidence can leave no doubt that such 

 plants do obtain at any rate much of their nitrogen from the sub-soil. 

 The question arises whether or not the whole of the nitrogen of our 

 crops comes from combined nitrogen, in the soil and sub-soil, in manure, 

 and in rain, &c., or whether part of it is in some way derived from the 

 free nitrogen of the atmosphere 1 Cumulative evidence points to the 

 conclusion that, in the case of our gramineous, our cruciferous, our 

 chenopodiaceous, and our solaneous crops, free nitrogen is not the 



