TRANSACTIONS OF SECTION B. 525 



quale when available nitrofjen was also supplied. So far as the root crops are con- 

 cerned, the yield of nitrofren, thoiiorh it declined very much, was greater at first, and 

 on the average, than in the case of the cereals. As to the leg-uminosfe, which re- 

 quire so much nitrogen from somewhere, it is to be observed that on ordinary arable 

 land the yield has not been maintained under any conditions of manuring ; and the 

 decline was nearly as marked with mineral manures as without any manure. Com- 

 pared with the growth of the leguminosse on arable land, the remarkable result with 

 the o-arden clover would seem clearly to indicate that the question was one of soil, 

 and not of atmospheric supply. And the fact that all the other crops will yield 

 full agricultural results even on ordinary arable land, when proper manures are 

 applied, is surely very strong evidence that it is with them, too, a question of soil, 

 and not of atmospheric supply. 



But we have other evidence leading to the same conclusion. Unfortunately 

 Ave have not reliable samples of the soil of the difierent experimental fields taken at 

 the commencement of each series of experiments, and subsequently at stated inter- 

 vals. We have, nevertheless, in some cases, evidence sufiicient to show whether or 

 not the nitrogen of the soil has suffered diminution by the continuous growth of the 

 crop without nitrogenous manure. 



Thus, we have determined the nitrogen in the soil of the continuously unmanured 

 wheat plot at several successive periods, and the results prove that a gradual reduc- 

 tion in the nitrogen of the soil is going on ; and, so far as we are able to form a judg- 

 ment on the point, the diminution is approximately equal to the nitrogen taken out 

 in crops ; and the amount estimated to be received in the annual rainfall is approxi- 

 mately balanced by the amount lost by the land as nitrates in the drainage water. 



In the case of the continuous root-crop soil, on which the decline in the yield of 

 nitrogen in the crop was so marked, the percentage of nitrogen, after the experiment 

 had been continued for twenty-se\en years, was found to be lower where no nitrogen 

 had been applied than in any other arable land on the farm which has been 

 examined. 



In the case of the experiments on the mixed herbage of grass land, the soil of 

 the plot which, under the influence of a mixed mineral manure, including potass, 

 had yielded such a large amount of leguminous herbage and such a large amoimt of 

 nitrogen, showed, after twenty years, a considerably lower percentage of nitrogen 

 than that of any other plot in the series. 



Lastly, determinations of nitrogen in the garden soil which has yielded so much 

 nitrogen in clover, made in samples collected in the fourth and the twentj'-sixth 

 years of the twenty-seven of the experiments, show a ^erj^ large diminution in the 

 percentage of nitrogen. The diminution, to the depth of 9 inches only, represents 

 approximately three-fourths as much as the amount estimated to be taken out in 

 the clover during the intervening period ; and the indication is, that there has been 

 a considerable reduction in the lower depths also. It is to be supposed, however, 

 that there would be loss in other ways than by the crop alone. 



I vrould ask. Have we not in these facts — that full amounts of the different crops 

 can be grown, provided proper soil-conditions are supplied ; that without nitrogenous 

 manure the yield of nitrogen in the crop rapidly declines ; and that, coincidently 

 with this, there is a decline in the percentage of nitrogen in the soil — have we not 

 in these facts cumulative e\"idence pointing to the soil, rather than to the atmosphere, 

 as the source of the nitrogen of our crops ? 



In reference to this point, I may mention that the ordinary arable soil at Rotham- 

 sted may be estimated to contain about 3000 lbs. of nitrogen per acre in the first 

 1) inches of depth, about 1700 lbs. in the second 9 inches and about 1500 lbs. in 

 the third 9 inches — or a total of alx)ut 6200 lbs. per acre to the depth of 27 

 inches. 



In this connection, it is of interest to state that a sample of Oxford clay, obtained 

 in the sub-Wealden exploration boring, at a depth of between 600 and 600 feet 

 (and which was kindly given to me by the President of the Association, Professor 

 Ramsay, some years ago), showed, on analysis at Rothamsted, approximately the 

 same percentage of nitrogen as the subsoil at Rothamsted taken to tlie depth of 

 sihont 4 feet only. 



