ON THE GROWTH OF LEGUMINOUS CROPS. 35 



the plants at the commencement of growth ; but if there had only been 

 as much as in the case of the Trifolium plot, it is seen that the 

 deficiency in the Vicia soils nearly corresponds with the amount 

 removed in the crop, which was 101 Ibs. 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, there- 

 fore, 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 12 depths, the Vicia soils with growth, contained much less nitric 

 acid than the Trifolium soil without growth ; and the difference is 

 much the greatest in the upper 4 or 5 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 being 

 that, under the influence of the growth, water had been brought up 

 from below, and with it nitric acid. In fact, the determinations 

 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 between 600 and 700 tons of water per 

 acre. 



Experiments of the same kind were again made in 1885. Trifolium 

 repens was again selected as the weak and superficially rooting plant, 

 Melilotus 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 2 places on each plot, and, in each case, as before, to 12 

 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 XVII. (p. 36). 



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

 Trifolium soil in 1885, after the removal of 97 Ibs. in the crops, than 

 in 1883 (see Table XVI, p. 33), when there had been no crop. The 

 deficiency is the greatest in the two upper layers, but it extends to the 

 fifth depth, representing 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, and possibly in part to 

 percolation of the nitrifying organisms, and the nitrification of the 

 nitrogen of the sub-soil. 



Let us now compare the results relating to the Medicago saliva with 

 those relating to the Trifolium repens soils. 



