“The mere presence of such an amount of phosphoric acid in a soil, however, by no means proves its sufficiency for the production of so many crops of wheat; for, in the first place, it can not be shown that the whole of the phosphoric acid found by analysis, occurs in the soil in a readily available combination; and, in the second place, it is quite certain that the root-fibres of the wheat-plant can not reach and pick up, so to speak, every particle of phosphoric acid, even supposing it to occur in the soil in a form most conducive to ‘ready assimilation by the plant.’ “The calculation is not given in proof of a conclusion which would be manifestly absurd, but simply as an illustration of the enormous quantity in an acre of soil six inches deep, of a constituent forming the smaller proportions of the whole weight of an acre of soil of that limited depth. It shows the existence of a practically unlimited amount of the most important mineral constituents of plants, and clearly points out the propriety of rendering available to plants, the natural resources of the soil in plant-food; to draw, in fact, up the mineral wealth of the soil, by thoroughly working the land, and not leaving it unutilized as so much dead capital.” “Good,” said the Deacon, “that is the right doctrine.” “The roots,” continues Dr. Vœlcker, “from one square foot of soil were cleaned as much as possible, dried completely at 212°, and in that state weighed 240 grains. An acre consequently contained 1,493½ lbs. of dried clover-roots. “The clover-roots contained, dried at 212° Fahr., Organic matter* 81.33 Mineral matter,† (ash) 18.67 ------ 100.00 ====== * Yielding nitrogen 1.635 Equal to ammonia 1.985 † Including insoluble silicious matter, (clay and sand) 11.67 “Accordingly the clover-roots in an acre of land furnished 24½ lbs. of nitrogen. We have thus: Lbs. of nitrogen In the six inches of surface soil 3,350 In large clover-roots 24½ In second six inches of soil 1,875 --------- Total amount of nitrogen in one acre of soil 12 inches deep 5,249½ Equal to ammonia 6,374½ =========