I! 



54 



The actual amount of leguminous herbage produced, however, is 

 not sufficient to account for nearly the whole of the increased yield 

 of nitrogen in the produce of the plot. The fact is that, besides a 

 porportionally very large increase in the growth of leguminous her- 

 bage, there has been a gradually increasing amount of gramineous 

 produce developed ; far beyond what would be anticipated from the 

 extremely limited effect of such manures on gramineous crops grown 

 separately on arable land. How far this result may be due to an 

 increased tendency of the grasses to form stem, and to ripen, under 

 such conditions ; — how far to more active nitriBcation induced under 

 the influence of the mineral manure in the much more highly nitro- 

 genous gi'ass-land than in the poorer arable soil, and so yielding a 

 direct supply to the Gi-amineoe of the mixed herbage ; — or how far to 

 an increased supply in a condition available for the grasses as the 

 result of a previously increased growth of the Legumiuosse, may be 

 a question. But it is of interest to note that the gramineous species 

 that are developed are among the most superficially rooting of the 

 grasses found on the experimental plots. 



Before leaving the subject of these experiments on the mixed 

 herbage of grass land, it may be well to call attention to the fact that, 

 on the assumption that the whole of the nitrogen of the herbage, 

 beyond the small amount of already combined nitrogen coTjtributed by 

 rain and condensation from the atraosphe*"e, is derived from the soil, 

 we have to conclude that about 25 pounds per acre per annum have 

 been yielded by the soil of the unmanured plot, and nearly an addi- 

 tional 25 pounds, or in all about 50 pounds, from the mineral- 

 manured plot. It was estimated that, in the case of the continuous 

 wheat experiments, about 20 pounds of nitrogen had been annually 

 obtained in the crop, and a minimum of 12 pounds lost by drainage ; 

 in all 32 pounds. It cannot fail to be observed how closely this 

 amount corresponds with the annual yield of nitrogen (83 pounds) in 

 the unmanured mixed herbage. With the richer grass-land, tliough less 

 aerated than arable land, it might be expected there would be some 

 increased activity of nitrification, even in the unmanured soil ; and 

 there may be some loss by drainage. But, with a mixed herbage of 

 some 50 species, of very varying habit of growth, and with the 

 possession of the soil all the year round, it is only what would be 

 expected that there would be more of the available nitrogen taken up 

 by the crop, and less lost by drainage, than with the cereal grown sepa- 

 rately on arable land, and occupying the soil for only a very limited 

 period of the year. 



We conclude, then, that the results relating to the two mixed 



