Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/533

Rh MANURE 509 largely into the composition of recent and fossil bones, coprolites, and guano, and of a variety of [ihosphatic minerals, such as Norwegian and Canadian apatite, Sombrero and Curagoa rock phosphate, South Carolina phosphate, Spanish and Portuguese phosphorite, etc. These and other phosphatic materials are now used largely in the manufacture of superphosphate and other artificial manures. Phosphate of lime is so sparingly soluble in pure water that, for all practical purposes, it may be considered to be insoluble in water ; it is, however, attacked by the natural agencies at work in the soil, and rendered available as plant food. According to the more or less porous condition of the phosphatic manuring materials, phosphate of lime is rendered more or less readily assimilable. Thus, while bone dust and guano, on account of their porous condi tion, may be used with good effect as suppliers of phosphoric acid to the soil, others, such as hard and crystalline Canadian or Norwegian apatite, produce but little or no result when used as manures merely in a powdered state. It was in 1840 that Liebig suggested the treatment of bones with sulphuric acid in order to make their action more rapid. This treatment of bones b/ acid converts the phosphate of lime into a soluble lime suit called superphosphate, or, speaking chemically, trans forms the original tribasic phosphate of lime into the mono- calcic phosphate, sulphate of lime being at the same time produced. Following on this, Mr (now Sir) John Lawes treated mineral phosphates similarly with sulphuric acid, and with results which led to the establishment of a new industry, the manufacture of superphosphate and other artificial manures. The yearly importation of phosphatic minerals, etc., into England for this manufacture alone exceeds 500,000 tons. The acid or soluble phosphate of lime in superphosphate, when applied to the soil, is first dissolved by the rain, and equally distributed in a portion of the soil, in which it must be precipitated and rendered insoluble before it can Ir-i assimilated by the plant. It is this intimate distribu tion and subsequent precipitation in a most finely divided state that would seem to constitute the beneficial effects of superphosphate, and its superiority over undissolved phosphates. It supplies at once phosphoric acid, lime, and sulphuric acid to the soil, and is much used in con junction with nitrogenous materials. Superphosphates are manufactured of various strengths, the percentage of tribasic phosphate of lime, rendered soluble by acid, being taken as the basis of valuation. 3. Potash. The next to rank after phosphoric acid as a valuable constituent of manures is potash. It enters largely into the composition of all crops, especially root crops. Sanely soils, as a rule, are poor in potash, for which reason they are benefited to a greater extent by the application of potash salts than most clay soils, which con tain sufficient potash to meet the requirements of farm crops. In clay soils potash mainly occurs in the form of insoluble silicate of potash together with other silicates. 13y autumn cultivation, subsoiling, and similar means of facilitating the free access of the air to clay-land potash is gradually liberated from the insoluble silicates and is rendered available as plant food. Lime also seems to be an important agent in the liberation of potash. Potash also occurs in farmyard manure, urine, all excrements, in oil cakes, and largely in wood ashes. Most potash salts are very soluble in water ; this explains their greater abundance in the liquid than the solid excre ments of animals. On this account it is a matter of importance, in making farmyard manure, to preserve the urine, and not lose the benefit of the potash salts it con tains. On most soils in a good agricultural condition the addition of potash manures produces little or no effect, but on poor sandy soils or worn-out pasture land the use of potash salts, in conjunction with superphosphate, dis solved bones, and guano, is followed by most beneficial results. Potash salts as an addition to manures for potatoes have been found advantageous, while their effect on pasture seems to be to improve the quality of the herbage rather than to increase the yield of grass per acre. 4. Soda. Most soils contain in abundance all the soda that farm crops require. &quot;With the exception of chloride of sodium (common salt), which occasionally is applied with more or less benefit to light sandy soils, and of nitrate of soda, which is employed as a nitro genous manure, soda salts are not used for manuring purposes. 5. Lime. Lime is essential for the production of healthy crops. Experience has shown that, when a soil is deficient in lime, farm yard manure, Peruvian guano, and other manures, though used in abundance, produce comparatively but little effect. Again, on poor sandy soils, lime, marl, or chalk not unfrequently produces better crops than farmyard or expensive artificial manures. Lime not only supplies an essential constituent of plants, but also prevents the loss by drainage of fertilizing matters such as potash, ammonia, and phosphoric acid. One of the functions of lime in the soil is to combine with the acids of the potash and ammoniacal salts of guano and of farmyard and other manures, and -to liberate potash and ammonia, which are retained in the land, while the inexpensive lime salts pass into the land drainage. Lime is used in agriculture in the form of quicklime, chalk (carbonate of lime)*, gypsum (sulphate of lime), marl, and shell- sand. Foi 1 liming purposes gas-lime also is frequently employed, and, if well exposed to the air before being put on the land, may be used with safety and advantage. 6. Magnesia. Magnesia is of but slight importance in manures ; it occurs with potash in kainite and other potash salts, and the sulphate is sometimes used in making up artificial manures, but apparently without benefit. 7. Silica. Silica is a constituent of the ashes of all plants, and occurs specially in large proportion in the straw of cereal crops. All soils contain such an abundance of silica that no necessity exists of supplying it artificially. 8. Chlorine, Sulphuric Acid, and Oxide of Iron. These ash constituents are of little practical importance, inasmuch as most soils contain a sufficiency of them to meet the requirements of the crops usually cultivated on the farm. It may be observed, how ever, that chlorine has been found to be essential to plant life, and that iron is necessary for imparting to plants their green colour. 9. Organic Matter or Humus. The importance of organic matter in manures was formerly much exaggerated. It has been con clusively proved that the carbon of which the bulk of the dry sub stance of all agricultural produce consists is derived from the carbonic acid of the atmosphere, and not from humus of the soil or the non-nitrogenous organic matters supplied in the manure. The organic matters present in dung in the shape of more or less decomposed or rotten straw exert a beneficial effect by improving the physical condition of both light and heavy land. Farmyard Manure. Farmyard manure is composed of the urine and solid excrements of animals collected in the stalls or yards, together with the straw used as litter. Its TABLE IV. The Composition of Farmyard Rotted Dung from Horses, Cows, and Pigs, in 100 parts. Water V.r-J-J Soluble 1 organic matter 3 &quot;1 Soluble inorganic matter (ash) Soluble silica 254 Phosphate of lime 3K2 lime 117 Magnesia 047 Potasli Soda Chloride of sodium Sulphuric acid Carbonic acid and loss. 44 (i 023 037 100 Insoluble - organic matter Insoluble inorganic matter (ash) Soluble silica 1-424 Insoluble silica 1-010 Oxides of iron and alumina with phosphates 947 (Containing phosphoric acid -274, equal to bone earth -573.) Lime 1-G7 Magnesia 091 Potash -045 Soda OSS Sulphuric acid 003 Carbonic acid and loss 1 295 1-47 12-82 1 Containing -297 of nitrogen, equal to -36 of ammonia. 2 Containing -309 of nitrogen, equal to 375 of ammonia. containing ammonia in free state, 04C; in form of salts, 057. The whole manure