132 THE ROTHAMSTED EXPERIMENTS. 



nearly corresponds with the amount removed in the crop, 

 which was 101 lb. It may at any rate safely be concluded 

 that most, if not the whole, of the nitrogen of the Vicia 

 crops, had been taken up as nitric acid. 



But, as the Vicia crops had removed much more in the 

 preceding years than the Trifolium crops, so also would their 

 crop -residue be greater; and in fact much more nitrogen 

 must have been taken up by the plants each year than the 

 figures show — and the larger the crop-residue, the larger 

 would be the amount of nitric acid for each succeeding crop. 

 But the crop of 1883 was also large, and it would leave 

 a correspondingly large nitrogenous crop - residue ; leaving, 

 therefore, a large amount of the nitrogen assimilated to be 

 otherwise accounted for than by previous crop-residue. 



Lastly in reference to these experiments, it is seen that at 

 each of the twelve depths, the Vicia soils with growth, con- 

 tained much less nitric acid than the Trifolium soil without 

 growth ; and the difference is much the greatest in the upper 

 four or five depths, within which the Vicia throws out by far 

 the larger proportion of its feeding roots ; but the deficiency 

 is quite distinct below this depth. The supposition is that, 

 under the influence of the growth, water had been brought 

 up from below, and with it nitric acid. In fact, determina- 

 tions showed that, down to the depth of 108 inches, the Vicia 

 soils contained less water than the Trifolium soil, in amount 

 corresponding to between 6 and 7 inches of rain, or to be- 

 tween 600 and 700 tons of water per acre. 



Further ex- Experiments of the same kind were again made in 1885. 



penments. Trifolium repens was again selected as the weak and super- 

 ficially rooting plant, Mclilotus leucantha as a deeper and 

 stronger rooting one, and the Medicago saliva as a still deeper 

 and still stronger rooting plant. Samples of soil were taken 

 at the end of July and the beginning of August, from two 

 places on each plot, and in each case as before, to twelve 

 depths of 9 inches each, or to a total depth of 108 inches, or 

 9 feet. It will suffice to quote the results for the Trifolium 

 repens and the Medicago saliva plots. They are given in 

 Table 44. 



It is seen that there was much less nitrogen as nitric acid 

 in the Trifolium repens soil in 1885, after the removal of 97 

 lb. in the crops, than in 1883 (see Table 43, p. 130), when 

 there had been no crop. The deficiency is the greatest in the 

 two upper layers ; but it extends to the fifth depth, repre- 

 senting the range of the direct and indirect action of the 

 superficial roots. Below this point there is, however, even 

 more than in 1883 ; due, doubtless, in part to percolation 

 from above during the two preceding seasons without growth,. 



