LEGUMINOUS CROPS. 123 



were only taken to a depth of 9 inches, so that no compari- 

 son can be made of the condition of the subsoil at the two 

 periods. In 1879, however, the second 9 inches of the gar- 

 den-soil was found to contain a much higher percentage of 

 nitrogen than the first 9 inches of the clover-exhausted arable 

 field, and about three times as high a percentage as the sub- 

 soil of the arable field at the same depth. It cannot be 

 doubted, therefore, that the subsoil of the garden plot has 

 contributed nitrogen to the clover crops. 



Here, then, notwithstanding the very little effect of direct Soil-source 

 nitrogenous manures on either the beans or the clover grow- %^^ 

 ing on the ordinary arable land, there would seem to be very 

 clear evidence of a soil-source of, at any rate much of the 

 enormous amounts of nitrogen assimilated over a given area 

 by the clover growing on the rich garden-soil. 



It may here be observed that, in experiments on the mixed 

 herbage of permanent grass-land, in which the growth of 

 leguminous herbage was much increased by the application 

 of mineral manure containing potash, it was found at the end 

 of 20 years that the amount of nitrogen in the surface-soil 

 had been considerably reduced, compared with that of a plot 

 which had been unmanured, and had yielded very much less 

 leguminous herbage. The conclusion was that, as in the case 

 of the clover growing on the rich garden-soil, the nitrogen of 

 the surface-soil had been a source of, at any rate much of the 

 nitrogen of the increased produce of Leguminosae in the mixed 

 herbage of the grass-land. 



Bed Clover grown after the Beans. 



After the cessation of the experiment with beans in 1878, 

 the land was left fallow for between four and five years, to 

 1882 inclusive, when grass-seeds were sown, but failed. On 

 this land, on which the attempt to grow the leguminous crop, 

 beans, year after year had failed, and been abandoned, barley 

 and clover were sown in the spring of 1883. 



In April 1883, however, before the barley and clover were Exhaustion 

 sown, the surface-soil (free of stones, and reckoned dry) of the °/ y f^ m 

 plot, which had been entirely unmanured during the 32 years 

 of the experiments with the beans, was found to contain 

 0.0993 per cent of nitrogen, that of the mineral-manured plot 

 0.1087 per cent, and that of the plot which had received both 

 the mineral and nitrogenous manure 0.1163 per cent — amounts 

 which show considerable nitrogen exhaustion of the surface- 

 soil. 



Also in 1883, the nitrogen as nitric acid was determined in 

 samples, each of 9 inches of depth, down to a total depth of 



