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It is well known that Liebig lias favored what is termed the " Mineral Manure Theory," while the late Prof. Norton held different views, and believed in nitrogenized manures, that is, manure produced by decayed vegetable or animal substances. In England two farmers, Messrs. Lawes and Gilbert^ have been experimenting to test the two kinds of fertilizers. Their experiments have extended over a number of years, and have been on quite' a large scale. They took a field at the close of a lour years' rotation, when the manures added at the commencement of the course were exhausted. On this ground they have cultivated wheat for ten years under various circumstances. One plot remained un-manured, and the produce of this served as a standard and starting point for comparison during the whole period. Thus, if its yield in IB45 was seventeen bushels peracre,the improvement over this in an adjoining plot^ otherwise the same, was set down to the advantage of whatever manure had been employed. Such a system of cropping, continued for so long a time, affords results that are worthy of much confidence. The first year's comparative practice was with various approved mfneral manures alone. It was found that, with the addition of large quantities of these, the increase of product over the unmanured plot, was but trifling. In the next year the same character of mineral manures was employed, but with the addition in several cases of ammoniacal or nitrogenous substances; in all of these the effect was quite marked, the yield increasing to 10,12, and 14 bushels above the unmanured plot This, in short, was the character of all the results; sometimes ammoniacal manures alone were added, and then the increase was several times more than by mineral manures alone. One experiment was very striking. Four hundred weight per acre of Liebig's special mineral manure for wheat was applied to a plot and produced an increase of but about two or three bushels; upon this same plot^ in the next year, a purely amtnoniacal manure gave an increase ot ten or twelve bushels. To make the experiment still more conclusive, no mantrre was added to this plot for the next crop, and the yeld then fell again almost to the original standard.
