How to Increase the Produce of the Soil ¹

Abstract

IN this pamphlet Prof. Wagner distinctly asserts the power of leguminous cultivated plants, such as peas, beans, vetches, lupines, and clovers, to use the free nitrogen of the air for purples of nutrition. As this conclusion is distinctly at issue with the opinions of the Rothamsted school, it revives a question of deep interest, the answer to which has varied with our knowledge from time to time. In the earlier days of agricultural chemistry the “mineral theory” of plant nutrition was in the ascendant. According to this theory the mineral, earthy, or ash constituents were taken from the soil, while the gaseous, combustible or organic portions of the plant were derived from the air. As knowledge progressed, this somewhat bold and sweeping generalization required to be modified, and the most usually received view (in this country, at least) for some time past has been that of the absorption of mineral matter and nitrates from the soil, and of carbonaceous matter from the air, and to a limited extent from the soil in the form of carbonic acid gas in solution. It has been urged that proof is entirely wanting of the alleged power of plants to take free or combined nitrogen from the atmosphere, while the intense effect of nitric nitrogen upon growing crops, when added to the soil, has amply proved that the soil is a source of nitrogen, and, according to received views, the chief or only source of nitrogen to growing crops. The results obtained by Sir John Lawes, Dr. Gilbert, and Mr. Warrington at Rothamsted, upon the cultivation of red and Bokhara clover, have been considered as proving that the source of nitrogen in these plants was not the atmosphere, but the soil and the subsoil, the plants having been found to send down their roots some fifty-four inches in depth into sections of the soil which, although out of reach of most cultivated plants, were able to yield sufficient nitrogen for the uses of these nitrogen-loving plants. Collectors of nitrogen these plants are allowed to be by all, but at Rothamsted the collection is considered to be carried on in the deeper layers of the soil, and not to extend above ground. Prof. Paul Wagner declares that cultivated plants may be properly divided into nitrogen collectors and nitrogen consumers, or as we might put it, into nitrogen savers and nitrogen wasters. In the first class are arranged the various members of the Leguminosæ already named. At a certain stage of their development these plants acquire the power of taking all their nitrogen from the air. They thus become a means of securing fertilizing matter from a free source, and are therefore profitable. In the second class are placed the cereals, grains, turnips, flax, &c.. all of which are able to take next to nothing from the store of nitrogen in the air, but which waste the nitrogen of the soil, and must take from it, in the form of nitrates, all the nitrogen they contain. In the pamphlet under notice no proof is adduced for these views, but reference is made to the detailed investigations carried out by the author. Hellriegle, and E. von Wolff. These views must be considered as reactionary and startling, and as diametrically opposed to the current of opinion in this country for some years past.