THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 437 



clover-yielding capabilities of the land. On the other hand, it should be particularly 

 observed that, after taking 20G - Slbs. of Nitrogen from an acre of land in the clover- 

 crop of the first year, the wheat-crop of the second or succeeding year, compared with 

 that of the same season in the adjoining experimental wheat-field where the crop is 

 grown year after year on the same land, was about double that obtained from the plot 

 which had there been unmanured for a series of consecutive years, and fully equal to that 

 from a plot which had for the same period received annually a dressing of farm-yard 

 manure. It should be added that, after failing to get any crop of clover at all in 1853 

 and in 1854, and getting a very poor one in 1855, the land was allowed to lie fallow 

 for two years; that after this, in 1S58, there was obtained an over-luxuriant and laid 

 crop of barley, more than twice as great as the average annual produce of eight years 

 of the successive growth of the crop without manure in the same field; yet, after 

 resowing with clover in the spring of 1859, and getting a small cutting in the autumn 

 of the same year, the plant has again died off during the winter of 1859-GO. This was 

 the case notwithstanding that it was a perennial variety that was last sown. 



Again, eight consecutive crops of turnips (four "White Globe" and four "Swedish") 

 gave an average annual yield, per acre, of about 40 lbs. of Nitrogen, without the supply 

 of any in the manure. In the case of these turnips, however, the land received annually 

 certain "mineral" manures. In fact, turnips grown year after year without manure of 

 any kind, yielded, after a few years, only a few hundred-weights of produce per acre ; 

 but the percentage of Nitrogen in these diminutive unmanured turnips was very un- 

 usually high. It will be observed that the average annual yield of Nitrogen per acre, 

 in the turnips grown by mineral manures (containing no Nitrogen), was considerably 

 more than that in the unmanured Cereal grain-crops. And, in connexion with this 

 point, it is worthy of remark, that, on barley, without manure, succeeding on the land 

 from which these eight mineral-manured turnip-crops had been taken, the produce 

 was only about three-fourths as much as that obtained, in the same season, where 

 barley was grown for the second year in succession without manure, in another field ; 

 and it was only about three-fifths as much as that obtained, also in the same season, 

 where barley was grown as the second crop of the second course, in a series of entirely 

 unmanured four-course Rotation-crops. 



It may be mentioned that, in the case of the purely Graminaceous crops, there has 

 been but veiy little gain in the annual yield of Nitrogen per acre by the use of mineral 

 or non-nitrogenous manures. But in the case of the Leguminous crops, as in that of the 

 root-crops just referred to, there has been much more Nitrogen harvested over a given 

 area, within a given time, when mineral manures were employed, than when no manure 

 at all was used. 



It has thus far been seen, then, that the Leguminous crops yield much more Nitrogen 

 over a given area than the Graminaceous ones, and, further, that the amount of Nitro- 

 gen harvested in the former is increased considerably by the use of " mineral " manures, 

 whilst that in the latter is so in a very limited degree. It is, nevertheless, a well-known 

 agricultural fact, that the growth of the Leguminous crops, which carry o^such a com- 



