“It is worthy of notice, that nitrogenous manures, which have such a marked and beneficial effect upon wheat, do no good, but in certain combinations, in some seasons, do positive harm to clover. Thus, Messrs. Lawes and Gilbert, in a series of experiments on the growth of red-clover, by different manures, obtained 14 tons of fresh green produce, equal to about three and three-fourths tons of clover hay, from the unmanured portion of the experimental field; and where sulphates of potash, soda, and magnesia, or sulphate of potash and superphosphate of lime were employed, 17 to 18 tons, (equal to from about four and one-half to nearly five tons of hay), were obtained. When salts of ammonia were added to the mineral manures, the produce of clover-hay was, upon the whole, less than where the mineral manures were used alone. The wheat, grown after the clover, on the unmanured plot, gave, however, 29½ bushels of corn, whilst in the adjoining field, where wheat was grown after wheat, without manure, only 15½ bushels of corn per acre were obtained. Messrs. Lawes and Gilbert notice especially, that in the clover-crop of the preceding year, very much larger quantities, both of mineral matters and of nitrogen, were taken from the land, than were removed in the unmanured wheat-crop in the same year, in the adjoining field. Notwithstanding this, the soil from which the clover had been taken, was in a condition to yield 14 bushels more wheat, per acre, than that upon which wheat had been previously grown; the yield of wheat, after clover, in these experiments, being fully equal to that in another field, where large quantities of manure were used. “Taking all these circumstances into account, is there not presumptive evidence, that, notwithstanding the removal of a large amount of nitrogen in the clover-hay, an abundant store of available nitrogen is left in the soil, and also that in its relations towards nitrogen in the soil, clover differs essentially from wheat? The results of our experience in the growth of the two crops, appear to indicate that, whereas the growth of the wheat rapidly exhausts the land of its available nitrogen, that of clover, on the contrary, tends somehow or other to accumulate nitrogen within the soil itself. If this can be shown to be the case, an intelligible explanation of the fact that clover is so useful as a preparatory crop for wheat, will be found in the circumstance, that, during the growth of clover, nitrogenous food, for which wheat is particularly grateful, is either stored up or rendered available in the soil.