Page:Popular Science Monthly Volume 22.djvu/101

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SCIENTIFIC FARMING AT ROTHAMSTED.

and that the soil, under certain conditions, may suffer a loss of nitrogen in this form.

Of the rain falling upon the drain-gauges, the unmanured soil of which, it will he remembered, is in a natural state of consolidation and kept free from vegetation, for a period of ten years, about forty-four per cent has appeared as drainage-water, and about fifty-six per cent has been evaporated. Approximately, two thirds of the evaporation takes place during the summer months, and one third during the winter months.

The annual loss of nitrogen in the drainage-water has been, upon the average, at the rate of 43·7 pounds per acre. This represents, approximately, the loss involved under the conditions of a bare summer fallow.

When the roots of growing plants are distributed through the soil, they take up the nitrogen as it becomes soluble in the process of nitrification, and the loss by drainage is to that extent diminished.

The drainage from the unmanured wheat-plots contained nitrogen at the rate of only from 12·56 to 18·62 pounds per acre each year, and during two seasons of excessive drainage, when every running from the drains was analyzed, "it was estimated that from fifteen to seventeen pounds of nitrogen were lost per acre, per annum, by drainage from plots which had received no nitrogenous manure for many years," and the average for thirty years was from ten to twelve pounds per acre. During its period of active growth, the crop appropriated the nitrogen of the soil, so that there was little or none lost by drainage, and nearly the entire loss took place after harvest, and during the winter and spring months.

The nitrogen lost by drainage on land receiving no nitrogenous manure is therefore considerably more than can reasonably be estimated in the supply from atmospheric sources.

When nitrogenous manures were applied, the loss of nitrogen by drainage was materially increased, and on the average for more than thirty years, and under the most favorable conditions of growth, less than one third of the nitrogen applied as manure was recovered in the increase of the crops, and much less than this when there was a deficiency of potash or phosphoric acid in the soil.

In connection with these facts, relating to the amounts of nitrogen removed in the crops and lost by drainage, and the inadequate supplies of available atmospheric nitrogen for the purposes of plant-growth, it becomes a matter of particular interest to trace the influence of this system of continuous cropping, without nitrogenous manures, upon the nitrogen contained in the soil itself.

The nitrogen in the soil of the unmanured wheat-plots has gradually diminished, and Dr. Gilbert says, "So far as we are able to form a judgment on the point, the diminution is approximately equal to the nitrogen taken out in the crops, and the amount estimated to be re-