The forms in which combined nitrogen is available to most agricultural plants are nitrates, ammonium salts and certain organic com pounds. Of the latter the simpler compounds, like urea, appear to be most readily taken up by plants. Decomposition is therefore a necessary process for most of the organic fertilizers be fore their nitrogen becomes available, and their usefulness is, in general, proportional to the readiness with which aerobic decomposition proceeds, or to the proportion of available com pounds which they contain in their original con dition. Guano, for instance, apparently, con tains much nitrogen that is available without further decomposition. Dried blood quickly decomposes and soon forms available sub stances. In fact, it produces results more quickly than any other form of organic nitrogen.
Dried meat contains a high percentage of nitrogen, but does not decompose so readily as dried blood, and is not so desirable a form of nitrogen. Hoof meal while high in nitrogen, decomposes slowly, being less active than dried blood. Ground fish is an excellent form of nitrogen, and is as readily available as blood but has a lower nitrogen content. Tankage is highly variable in composition, and the con centrated tankage being more finely ground, undergoes more readily the decomposition nec essary for the utilization of the nitrogen. Crushed tankage contains from 3 to 12 Rer Cent of phosphoric acid, in addition to its nitrogen. Leather meal and wool-and-hair waste when untreated are in such a tough and undecom posable condition that they may remain in the soil for years without losing their structure. • They are therefore not to be recommended as fertilizers.
Phosphate Fertilizers.— By the term phos phate fertilizers is meant those substances that are used for manures chiefly because of the phosphorus they contain. The phosphorus is generally present in the form of a phosphate of lime, iron and alumina mixed with other substances. Some of these phosphates also contain organic matter, in which case they generally carry some nitrogen, which adds something to their value as fertilizers. Phos phates associated with organic matter decom pose more quickly in the soil than purely mineral phosphates, and are therefore more readily available fertilizers.
The bones of animals have been for a great many years an im portant form of phosphate manure. bones were used entirely in the raw either ground or unground. In the gr a dition they are a more quickly acting fertilizer. Raw bones contain about 22 per cent phosphoric acid and 4 per cent nitrogen. The phosphoric
acid is in the form of tricalcium phosphate.
At the present time most of the bone used as manure is first boiled or steamed. This frees it from fat and nitrogenous matter both of which are used in other ways. Steamed bone is a more valuable fertilizer than raw bone, as the fat in the latter retards decom position and also because the steamed bone is in a better mechanical condition. The form of the phosphoric acid is the same as in the raw bone and varies from 28 to 30 per cent, while the nitrogen is reduced to about 1V2 per cent. Bone tankage, which has already been spoken of as a nitrogen fertilizer, contains from 7 per cent to 9 per cent phosphoric acid, largely in the form of tricalcium phosphate. All of these bone-phosphates are slow-acting fertilizers and should he used finely ground and for the per manent benefit of the soil rather than as direct plant-food material.
Mineral Phosphates.— There are many natural deposits of mineral phosphates scattered over the earth, some of the most important of which are in America. The phosphorus in all of these is in the form of tricalcium phosphate, but the materials associated with it vary greatly.
Coprolites are concretionary nodules found in the chalk or other deposits in the south of England and in France, the name having been given them on the assumption that they con sisted of fossilized animal excrement. They contain 25 to 30 per cent of phosphoric acid, the other constituents being calcium carbonate and silica.
Apatite is found in large quantities in the provinces of Quebec and Ontario, Canada. It occurs chiefly in crystalline form. The calcium phosphate of which it is composed is in one form associated with calcium fluoride and in the other with calcium chloride. The Canadian apatite contains about 40 per cent phosphoric acid, being richer in this ingredient than that found elsewhere. Phosphorite is another name for apatite, but is chiefly applied to the impure amorphous form.
South Carolina phosphate occurs in the form of lumps from the size of a pebble to a mass weighing a ton. These are distributed through a deposit varying from 1 to 20 feet in thick ness, which occurs both on the land and in the river beds. It contains from 26 to 28 per cent of phosphoric acid and but a very small amount of iron and aluminum. As these substances interfere with the manufacture of superphos phates from the rock, their presence is very un desirable, rock containing more than 3 to 6 per cent being unsuitable.