"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?
"I can tell you it is correctly named," Percy replied. "Hydrated means watered, and an investment in hydrated lime is properly classed with other watered investments. If you prefer to use hydrated lime I would suggest that you buy fresh burned lump lime and do the hydrating yourself, which only requires that you add eighteen pounds of water to each fifty-six pounds of quick lime; in other words, that you slack the lime by adding water in the proper proportion. Both quick lime and hydrated lime are known as caustic lime. Webster says that the word caustic means 'capable of destroying the texture of anything or eating away its substance by chemical action.'
"This definition is correct for caustic lime, as you can easily determine by keeping your hand in a bucket of slacked lime a few minutes. Caustic lime eats away the organic matter of the soil. In an experiment conducted by the Pennsylvania Experiment Station, during a period of sixteen years, eight tons of hydrated lime destroyed organic matter equivalent to thirty-seven tons of farm manure, as compared with the use of equivalent applications of ground limestone; and, as an average of the sixteen years, every ton of caustic lime applied liberated seven dollars' worth of organic nitrogen, as compared with ground limestone. That this much liberated nitrogen was essentially wasted and lost is evidenced by the fact that larger crops were produced where ground limestone was used than where burned lime was applied.
"The limestone must be quarried whether used for grinding or for burning, and the grinding can be done for twenty-five cents a ton where a large equipment with powerful machinery is used and where cheap fuel is provided, as near the coal mining districts. It need not be very finely ground. If ground to pass a sieve with twelve meshes to the linear inch, it is very satisfactory, provided that all of the fine dust produced in the grinding is included in the product. You see the soil acids are slightly soluble and they attack the limestone particles and are thus themselves destroyed or neutralized. If, however, you ever wish to use raw rock phosphate, insist upon its being sufficiently fine-ground that at least ninety per cent. of it will pass through a sieve with ten thousand meshes to the square inch, this being no finer than is required for the basic slag phosphate, of which several million tons are now being used each year in the European countries. Like the raw rock phosphate, the slag gives the best results only when used in connection with plenty of decaying organic matter."
"That reminds me," said Mr. West, "of what one of the fertilizer agents said about raw phosphate. He said the use of raw phosphate with farm manure reminded him of 'stone soup,' which was made by putting a clean round stone in the kettle with some water. Pepper and salt were added, then some potatoes and other vegetables, a piece of butter and a few scraps of meat. 'Stone soup,' thus made, was a very satisfactory soup. He said that in practically all of the tests of raw phosphate conducted by the various State Experiment Stations, manure has been used as a means of supplying organic matter to liberate the phosphorus from the raw rock, but in such large quantity as to be entirely impracticable for the average farmer to use on his own fields; and his opinion was that the entire benefit was due to the manure. He had a little booklet entitled 'Available or Unavailable Plant Food—Which?' published by the National Fertilizer Association, and said I could get a copy by addressing the Secretary at Nashville, Tennessee."
"Fortunately," said Percy, "this is not a question of opinion but one of fact; and it has been discovered that the fertilizer agents who are long on opinions and short on facts prefer to sell four tons of complete fertilizer for $80, or even two tons of acid phosphate for $30, rather than to sell one ton of raw phosphate, containing the same amount of phosphorus, for $7.50. In the manufacture of acidulated fertilizers, one ton of raw phosphate, containing about two hundred and fifty pounds of the element phosphorus, is mixed with one ton of sulfuric acid to make two tons of acid phosphate; and, as a rule, these two tons of acid phosphate are mixed with two tons of filler to make four tons of complete fertilizer. A favorite filler is dried peat, which is taken from some of the peat bogs, as at Manito, Illinois, and shipped in train loads to the fertilizer factories. The peat is not considered worth hauling onto the land in Illinois, even where the farmers can get it for nothing; but it contains some organic nitrogen, and, by the addition of a little potassium salt, the agent is enabled to call the product a 'complete' fertilizer.
"Experiments with the use of raw rock phosphate have been conducted by the State Agricultural Experiment Stations over periods of twelve years in Maryland, eleven years in Rhode Island, twenty-one years (in two series) in Massachusetts, fourteen years (in two series) in Maine, twelve years in Pennsylvania, thirteen years in Ohio, four years in Indiana, and from four to six years on a dozen different experiment fields in different parts of Illinois.
"I have here some quotations taken from the directors of several of these experiment stations which fairly represent the opinions which they have expressed concerning their own investigations. Thus the Maryland director says: