"Decaying or active organic matter is one of the great factors in the liberation of plant food, and undoubtedly the extension or distribution of the root system of the growing plant is another very potent factor. If the root surfaces come in contact with one per cent. of the total surface of the soil particles in the plowed soil, then we might conceive of a relationship whereby one per cent. of the phosphorus in that soil would be dissolved or liberated from the insoluble minerals and thus become available as food for the growing crop. We know that the rate of liberation varies greatly, with different soils and seasons, and crops also differ in their power to assist themselves in the extraction of mineral plant food from the soil. The presence of limestone encourages the development of certain soil organisms which tend to hasten some decomposition process. But, all things considered, it may be said, speaking very generally, that the equivalent of about one per cent. of the total phosphorus contained in the plowed soil does become available for the crops under average conditions. On this basis one hundred and sixty pounds of phosphorus would furnish about one and one-half pounds for the crops during one season. But in such a soil the phosphorus still remaining may be the most difficultly soluble, and the supply of decaying organic matter may be extremely low, so that possibly less than one pound per acre would become available, and this would meet the needs of less than four hundred pounds per acre of clover hay. Furthermore, the supply grows less and less with every crop removed. "With your ordinary soil, carrying twelve hundred and seventy pounds of phosphorus, perhaps you may be able by a liberal use of decaying organic matter to liberate ten or fifteen pounds of phosphorus, or sufficient for a crop of forty to sixty bushels of corn; and, with a subsoil richer in phosphorus than the surface, and with more or less of the partially depleted surface removed by erosion year by year, the supply of phosphorus is thus permanently provided for unless the bed rock is brought too near the surface. It is doubtful if the direct addition of phosphorus to your sloping lands will ever be necessary or profitable. Certainly such addition is not advisable until you have brought the land to as high a state of fertility as is practicable by means of limestone, legumes, and manure." "That seems clearly to be the case with most of the land now under cultivation on this farm," said Mr. West "Can you tell me anything about this hydrated lime?