56 RESULTS OF EXPERIMENTS AT ROTHAMSTED, 



root-range of the crop grown, and to the season, but that in the depths 

 of the sub-soil below this point, the amount is again greater. 



Again, M. Berthelot thinks it probable, though not absolutely 

 established, that there is loss of nitrogen from the plant itself during 

 growth. Long ago, we supposed that there was such loss ; but careful 

 consideration of the evidence relating to the subject has led us to the 

 conclusion that it is not proved, and to believe that it probably does 

 not take place. It may be observed, that when in his vegetation 

 experiments M. Boussingault found a loss of nitrogen, there was 

 coincidently some decaying vegetable matter, such as fallen leaves ; and 

 in somewhat parallel experiments at Rothamsted, no loss of nitrogen 

 was found as a coincident of growth, and in the absence of dead 

 vegetable matter. Indeed, if there were such loss during growth when 

 there was no decay, either in M. Boussingault's experiments or our own, 

 it must have been almost exactly balanced by corresponding gain ; an 

 assumption which is without any proof, but which has nevertheless had 

 its advocates. 



In fact it may be concluded that, under the existing conditions of 

 practical agriculture in temperate climates, the annual loss of combined 

 nitrogen over a given area, by cropping and otherwise, is by no means 

 so great as has been assumed; that the restoration required to 

 compensate the loss is, therefore, correspondingly less ; and further, 

 that the known facts relating to the maintenance or the reduction of 

 the fertility of soils, do not point to the conclusion that such loss 

 as actually does take place, is compensated by such restoration. 



The well known accumulation of nitrogen which takes place in the 

 surface-soil within a few years, when arable land is laid down to grass, 

 is, it may be admitted, not conclusively explained. At the same time, 

 there is abundant experimental evidence pointing to the conclusion 

 that some deep-rooted leguminous plants derive a considerable quantity 

 of nitrogen from the sub-soil ; and there seems no reason to doubt that 

 the deep-rooting plants of the mixed herbage of grass-land, whether 

 leguminous or otherwise, may also avail themselves of sub-soil 

 nitrogen ; and, if so, it is to be supposed that they, like clover for 

 example, will leave nitrogenous crop-residue in the surface-soil, the 

 nitrogen of which has been derived from the sub-soil. In reference to 

 this point it may be observed, that at Rothamsted there is per acre, in 

 soil and sub-soil, to the depth at which the action of some deep-rooted, 

 and large nitrogen-accumulating plants, has been proved, a store of 

 about 20,000 Ibs. of already combined nitrogen. It is true that whilst 

 many other soils and sub-soils will contain as much, or more, many will 

 contain much less. 



It is indeed pretty certain, that at any rate much of the nitrogen 

 gained by the surface-soil of land newly laid down to grass, has its 

 source in the combined nitrogen of the sub-soil. Obviously, however, 

 in view of results showing that leguminous crops may acquire nitrogen 

 brought into combination under' the influence of the symbiotic growth 

 of lower organisms, the question suggests itself whether part of the 



