28 J. H. Gilbert— Points in connection with Vegetation. 



conclusion that this increased assimilation is at the expense of 

 the nitrogen existing at any rate in the upper layers of the soil. 

 In fact, such initiative results as we have relating to the nitro- 

 gen in the soil of the experimental bean field, would rather 

 lead to the conclusion that tin' better the crop has grown, and 

 the more nitrogen it has assimilated, the riclier rather than the 

 poorer in nitrogen (as indicated by the soda-lime method) has 

 the surface soil become. To this point, however, we shall have 

 to recur presently ; but in the meantime let us first refer to the 

 yield of nitrogen in other cases in which leguminous crops have 

 been interpolated with others. 



It is, indeed, well known that the growth and removal of a 

 highly nitrogenous leguminous crop is one of the best possible 

 preparations for the growth of a gramineous corn crop, which 

 characteristically requires nitrogenous manuring. A striking 

 illustration of this apparent anomaly is ail'orded in the results 

 next in order recorded in Table III. 



After the growth of six corn crops in succession by artificial 

 manures alone, barley was grown without manure in 1873 on 

 one portion of the same land; and on another portion cl-vcr 

 was grown. It is calculated that there were taken off in the 

 barley 37*3 lbs. of nitrogen, and in the three cuttings of clover 

 151-3 lbs. Yet, in the next year, 1874, barley succeeding the 

 bariev gave 3wl lbs., and barley sueceeding'the clover gave 

 69<4 U^. of nitrogen; or 30-3 lbs. more after the removal of 

 151-3 lbs. in clover than after the removal of 373 lbs. in barley. 

 Nor was this remarkable result to be explained by either acci- 

 dent or -Tror. For, determinations of nitrogen in four separately 

 t , .ken samples of the soil, in the mixture of the four, and in the 

 mixture of six others, taken from each plot, and at different 

 depths, all concurred in showing an appreciably higher percent- 

 age of nitrogen, especially in the surface soil, nine inches deep, 

 of the land from which the clover had been removed than in 

 that from which the barley had been taken ; and this was so, 

 although, in every case, all visible vegetable debris had been 

 carefully picked out. Here, then, the surface soil at any rate 

 was positively enriched in nitrogen (determinable by soda lime) 

 by the growth and removal of a very highly nitrogenous crop. 

 It may be mentioned that Dr. Voelcker has obtained results of 

 a similar character. 



The results next to be considered are those obtained in an 

 actual tour-course rotation of crops — namely, turnips, barley, 

 clover or beans, and wheat. The experiments have been con- 

 ducted through seven such courses ; that is to say, over a period 

 of twenty-eight years. One portion of the land, the results 

 relating to which are given in the table, has been entirely 

 unmanured during the whole of that period, and the other has 



