13 



possible preparations for the growth of a cereal crop, which charac- 

 teristically requires nitrogenous manuring. A field which had grown 

 six corn crops in succession, by artificial manures alone, was then 

 divided, and (in 1873) on one half barley, and on the other half 

 clover, vras grown. The barley yielded 37-3 pounds of nitrogen per 

 acre; but the three cuttings of clover yielded 151-3 pounds. In the 

 next year (1874) barley was grown on both portions of the field. 

 Where barley had previously been grown, and had yielded 37-3 pounds 

 of nitrogen per acre, it now yielded 391 pounds; but where the 

 clover had previously been grown, and had yielded 151-3 pounds of 

 nitrogen, the barley succeeding it gave 69-4 pounds, or 80-3 pounds 

 more nitrogen after the removal " 151-3 pounds in clover than after 

 the removal of only 37-3 pounds in barley. It will be seen further on 

 that this result was not in any way accidental. 



Yield of Nitrogen hy a Rotation of Crops. 



The last results recorded in the table relate to the yield of nitrogen 

 in an ordinary four-course rotation of — turnips, barley, clover or 

 beans, and wheat. The average yield per annum is given for seven 

 courses, or for a period of twenty-eight years ; in one case without any 

 manure during the whole of that time, and in the other with super- 

 phosphate of lime alone, applied once every four years, that is, for the 

 turnips commencing each course. 



Here, with a turnip crop, and a leguminous crop, interpolated with 

 two cereal crops, we have, without manure of any kind, an average of 

 36-8 pounds of nitrogen per acre per annum, or very much more than 

 was obtained in either of the cereal crops grown consecutively. With 

 superphosphate of lime alone, which much increased the yield of 

 nitrogen in the turnips, reduced it in the succeeding barley, increased 

 it greatly in the leguminous crops, and slightly in the wheat suc- 

 ceeding them, the average annual yield of nitrogen is increased to 

 45-2 pounds, or to about double that obtained in either wheat or 

 barley grown consecutively by a complete mineral manure. On this 

 point it may be further remarked that in adjoining experiments, in 

 which, instead of a leguminous crop, the land was fallowed in the 

 third year of each course, the total yield of nitrogen in the rotation 

 was very much less. In other words, the removal of the most highly 

 nitrogenous crops of the rotation — clover or beans — was succeeded by 

 a growth of wheat, and an assimilation of nitrogen by it, almost as 

 great as when it succeeded a year of fallow ; that is, a period of some 

 accumulation by rain, &c., and of no removal by crops. 



