686 eepoet — 1884. 



The total combined nitrogen brought to the earth annually in measured 

 aqueous deposits — snow, rain, &c. — has been found to be only 6 - 12 kilos per 

 hectare. 



An acid solution and a moist, acid, porous soil have been found to absorb, for the 

 period of these experiments (seventy-two days in April, May, and June), combined 

 nitrogen at the rate of some 10 kilos per hectare. The amount of nitrogen acquired 

 from the atmosphere in the one of these experiments, in which the conditions were 

 most nearly normal, was at the rate of 137 kilos per hectare, twice as much as the 

 total nitrogen contained in grain and straw of a wheat crop oi thirty bushels, and 

 more than the total nitrogen of three tons of clover hay. 



4. On some points in the Composition of Soils, with results illustrating the 

 Sources of Fertility of Manitoba Prairie Soils. By Sir John B. Lawes, 

 Bart., F'.R.S., and Dr. J. H. Gilbert, F.B.S. 



This paper was a continuation of one given by the authors at the meeting of 

 the American Association, held at Montreal two years previously, entitled: 

 'Determinations of nitrogen in the soils of some of the experimental fields at 

 Rothamsted, and the bearing of the results on the question of the sources of the 

 nitrogen of our crops.' The first part of the present paper consisted of a rSsumS 

 ■of the previous one. 



It was shown that when crops were grown year after year on the same land 

 without nitrogenous manure, the produce, and the yield of nitrogen, declined in a 

 verv marked degree. This was the case even when a full mineral manure was 

 applied ; and it was the case not only with cereals and with root-crops, but also 

 with Leyuminosce. Further, with this great decline in the annual yield of nitrogen 

 of these Very various descriptions of plant, when grown without artificial nitrogenous 

 supply, there was also a marked decline in the stock of nitrogen in the soil. Thus a 

 :soil-source, of at any rate some, of the nitrogen of the crops was indicated. Other 

 •evidence was also adduced clearly pointing to the same conclusion. 



Next, determinations of the amounts of nitrogen as nitric acid, in soils of 

 known history as to manuring and cropping, and to a considerable depth, showed 

 that the amount of nitrogen in the soil in that form was much less after the 

 growth of a crop than under corresponding conditions without a crop. It was 

 hence concluded that nitrogen had been taken up by the plant as nitric acid. In 

 the case of gramineous crops, and some others, the evidence pointed to the conclu- 

 sion that most, if not the whole, of the nitrogen was so taken up from the soil. It 

 was also clear that some, at any rate, of the nitrogen of Leyuminosx. had the 

 same source, and the results were in favour of the supposition that in some of the 

 cases the whole of it might be so accounted for. Still it was admitted that, in 

 some cases, this seemed very doubtful. 



The conditions and the results of a large number of new experiments were 

 next described. It was found that there was very much more nitrogen as nitric 

 acid, in soils and sub-soils, down to the depth of 108 inches, where leguminous 

 than where gramineous plants had grown. The results pointed to the conclusion 

 that under the influence of leguminous growth and crop-residue, especially in the 

 case of strong and deep-rooted plants, the conditions were more favourable for the 

 development and distribution of the nitrifying organism ; and, if this view were 

 confirmed, an important step would be gained towards the more complete explana- 

 tion of the sources of the nitrogen of the Leyuminosa which assimilate a very large 

 quantity of nitrosren, inducing, as above supposed, the nitrification of the nitrogen 

 of the subsoil, which may thus become the source of the nitrogen of such crops. 

 An alternative obviously was, that the plants might still take up nitrogen from the 

 subsoil, but as organic nitrogen, and not as nitric acid. There was, however, no 

 direct experimental evidence in favour of such a view, whilst some physiological 

 considerations, which were discussed, seemed to be against it. Again, results 

 showed that the soil and subsoil contained less nitrogen as nitric acid after the 

 orowth of good crops of vicia srtt int. than where the more shallow-rooted trifolium 

 repens had failed to grow. This was further evidence that the Lryuminoscc took up 



