Page:Popular Science Monthly Volume 22.djvu/102

92 in the annual rain-fall is approximately balanced by the amount lost by the land, as nitrates in the drainage-water."

Where the great decrease in the yield of nitrogen was observed, in the case of the root-crops which were grown for thirty-one years in succession, the soil at the end of twenty-seven years was found to contain a smaller percentage of nitrogen than any other arable land of the farm.

In the experiments on the mixed herbage of permanent grass-land, "the soil of the plot which, under the influence of a mixed mineral manure, including potash, had yielded such a large amount of leguminous herbage, and such a large amount of nitrogen, showed, after twenty years, a considerably lower percentage of nitrogen than that of any other plot in the series."

The soil of the garden-plot, which gave so large a yield of clover over a period of twenty-seven years, was analyzed at the end of twenty-six years, and Dr. Gilbert remarks, in regard to the loss of the nitrogen of the soil, that "the diminution, to the depth of nine inches only, represents, approximately, three fourths as much as the amount estimated to be taken in the clover in the intervening period; and the indication is, that there has been a considerable reduction in the lower depths also."

When nitrogenous manures were applied in the form of ammonia salts or nitrate of soda there was little or no decrease in the nitrogen of the soil, and in some cases there was an actual gain; but the loss from drainage was much greater, and it increased with each increment of the manures applied under the same conditions. On plots receiving 43, 86, and 129 pounds, respectively, of nitrogen in the form of ammonia salts, mostly applied in the autumn, the estimated loss of nitrogen by drainage was 19, 31, and 42·4 pounds; "and with 86 pounds of nitrogen applied without, or with different mineral manures, the estimated loss ranged from 31 pounds with the most liberal manure to 43-2 pounds with the ammonium salts continuously used alone."

The nitrogen of barn-yard manure, which from its comparative insolubility is more slowly available for purposes of plant-growth, was not lost by drainage to the same extent as the chemical manures, and there were decided indications of considerable accumulations of it in the soil. The nitrogen applied in manures is not all accounted for in the amounts removed in the crop, lost by drainage, and stored up in the soil; and it therefore seems probable, in the absence of any other known disposition of it, that the estimated losses by drainage, based on the materials discharged by the tile-drains, are altogether too low. As the drainage-waters, with the substances they hold in solution, pass from the upper to the lower strata of the soil, we can not avoid the conclusion that a large proportion must pass below the level of the drains without entering them. The drains of the experimental wheat fields are nearly twenty-five feet apart, and the underlying chalk at the