Chapter 25

COMMERCIAL FERTILIZERS

THE RAW MATERIALS

Next to the soil itself, the farmer's most important sources of plant food are the farm manures. But most farms do not produce these in sufficient quantities to keep up the plant food side of fertility. Therefore the farmer must resort to other sources of plant food to supplement the farm manures.

There is a large class of materials called Commercial Fertilizers, which, if judiciously used, will aid in maintaining the fertility of the farm with economy.

We learned in a previous chapter that the plant foods, nitrogen, phosphoric acid, potash and lime, are apt to be found wanting in sufficient available quantities to supply the needs of profitable crops. We learned also that lime is useful in improving the texture of the soil and in making other plant foods available. Now the commercial fertilizers are used to supply the soil with these four substances and they may be classified according to the substance furnished as follows:

Sources of nitrogen, " " phosphoric acid, " " potash, " " lime.

SOURCES OF NITROGEN

Nitrogen is the most expensive of plant foods to buy, therefore special attention should be given to producing it on the farm by means of barn manures and legumes plowed under.

The principal commercial sources of nitrogen are: Nitrate of soda, sulphate of ammonia, dried blood, tankage, dry ground fish, cotton-seed meal.

_Nitrate of Soda_ or Chile saltpetre containing 15.5 per cent. of nitrogen, is found in large deposits in the rainless regions of western South America. In the crude state as it comes from the mine it contains common salt and earthy matter as impurities. To remove these impurities the crude nitrate is put into tanks of warm water. The nitrate dissolves and the salt and earthy matter settle to the bottom of the tank. The water with the nitrate in solution is then drawn off into other tanks from which the water is evaporated, leaving the nitrate, a coarse, dirty looking salt which is packed in three-hundred-pound bags and shipped.

Plants that take their nitrogen from the soil take it in the form of nitrate. Hence nitrate of soda, which is very soluble in water, is immediately available to plants and is one of the most directly useful nitrogen fertilizers. It is used for quick results and should be applied only to land that has a crop or is to be immediately planted, otherwise it is liable to be lost by leaching.

_Sulphate of Ammonia_ contains 20 per cent. of nitrogen. It is a white salt, finer and cleaner looking than the nitrate. It is a by-product of the gas works and coke ovens. The nitrogen in it is quite readily available.

_Dried Blood_ contains 8 to 12 per cent. of nitrogen. This is blood collected in slaughter-houses and dried by steam or hot air. It decays rapidly in the soil and is a quick acting nitrogen fertilizer.

_Tankage_ contains 4 to 8 per cent. of nitrogen and 7 to 20 per cent. of phosphoric acid. Slaughter-house waste, such as meat and bone scrap, are boiled or steamed to extract the fat. The settlings are dried and ground and sold as tankage. It is much slower in its action than dried blood and supplies the crop with both nitrogen and phosphoric acid.

_Dried Fish Scrap_ is a by-product of the fish oil factories and the fish canning factories. It contains 7 to 9 per cent. of nitrogen and 6 to 8 per cent. of phosphoric acid. It undergoes nitrification readily and is a quick acting organic source of nitrogen and phosphoric acid.

_Cotton-seed Meal_ contains 7 per cent. of nitrogen, about 2.5 phosphoric acid, and 1.5 per cent. of potash. It is a product of the cotton oil factories and is obtained by grinding the cotton seed cake from which the oil has been pressed. It is a most valuable source of nitrogen for the South.

The nitrogen in the dried blood, tankage, fish scrap and cotton-seed meal, being organic nitrogen, must be changed by the process of nitrification to nitric acid or nitrate before it is available. They are therefore better materials to use for a more gradual and continuous feeding of crops than the nitrate of soda or sulphate of ammonia.

Scrap leather, wool waste, horn and hoof shavings are rich in nitrogen but they decay so slowly that they make poor fertilizers. They are used by fertilizer manufacturers in making cheap mixed fertilizers.

SOURCES OF PHOSPHORIC ACID

The principal commercial sources of phosphoric acid are:

Phosphate Rocks. Bones. Fish scrap. Phosphate slag.

The _Phosphate Rocks_ are found in shallow mines in North and South Carolina, Georgia, Florida and Tennessee, and also as pebbles in the river beds. They are the fossil remains of animals. After being dug from the mines the rock is kiln dried and then ground to a very fine powder called "floats" which is used on the soil. The phosphoric acid in the floats is insoluble and becomes available only as the phosphate decays. This is too slow for most plants so it is treated with oil of vitriol or sulphuric acid to make it available. The phosphoric acid in the ground rock is combined with lime, forming a phosphate of lime which is insoluble. When treated with the oil of vitriol or sulphuric acid, the sulphuric acid takes lime from the phosphate and forms sulphate of lime or gypsum. The phosphoric acid is left combined with the smallest possible amount of lime and is soluble in water. It is then called soluble or water soluble phosphoric acid.

Now if this soluble form remains unused it begins to take on lime again and turns back toward its original insoluble form. After a time it gets to such a state that it is no longer soluble in water but is soluble in weak acids. It is then said to be reverted phosphoric acid. Reverted phosphoric acid is also called citrate soluble phosphoric acid, because in testing fertilizers the chemists use ammonium citrate to determine the amount of reverted phosphoric acid.

This form still continues to take on lime and by and by gets back to the original insoluble form called insoluble phosphoric acid.

The soluble phosphoric acid and reverted phosphoric acid are available to plant roots. The insoluble form is not.

The rock phosphates contain from 26 to 35 per cent. of insoluble phosphoric acid. The acid phosphates or dissolved rock phosphates contain from 12 to 16 per cent. of available phosphoric acid and from 1 to 4 per cent. of insoluble.

_Bone Fertilizers._ Bones have long been a valuable and favored source of phosphoric acid. In addition to phosphoric acid they contain some nitrogen which adds to their value. They are organic phosphates and are quite lasting in their effect on the soil as they decay slowly.

The terms "Raw Bone," "Steamed Bone," "Ground Bone," "Bone Meal," "Bone Dust," "Bone Black," "Dissolved Bone," indicate the processes through which the bone has passed in preparation, or the condition of the material as put on the market and used on the soil.

Ground bone, bone meal, bone dust, indicate the mechanical conditions of the bones.

The bones are sometimes ground "raw" just as they come from the slaughter-house or kitchen, or they are sometimes first "steamed" to extract the fat for soap, and the nitrogenous matter for glue.

_Raw Bone._ Analysis: Nitrogen, 2.5 to 4.5 per cent. Available phosphoric acid, 5 to 8 per cent. Insoluble phosphoric acid 15 to 17 per cent.

_Steamed Bone_ contains 1.5 to 2.5 per cent. of nitrogen, 6 to 9 per cent. of available phosphoric acid and 16 to 20 per cent. of insoluble phosphoric acid.

Steamed bone pulverizes much finer than raw bone and decays more rapidly in the soil because the fat has been extracted from it.

_Dissolved Bone._ Ground bone is sometimes treated with sulphuric acid to render the phosphoric acid in it more available. It is then called dissolved bone and contains thirteen to fifteen per cent. of available phosphoric acid and two to three per cent. of nitrogen.

_Dissolved Bone Black._ Bone charcoal is used for refining sugar. It is then turned over to the fertilizer manufacturers who sell it as "Bone Black" or treat it with sulphuric acid and then put it on the market as dissolved bone black.

The bone black contains thirty to thirty-six per cent. of insoluble phosphoric acid.

The dissolved bone black contains 15 to 17 per cent. of available phosphoric acid and 1 to 2 per cent. insoluble.

"_Thomas Slag_," "_Phosphate Slag_," "_Odorless Phosphate_." Phosphorous is an impurity in certain iron ores. In the manufacture of Bessemer steel this is extracted by the use of lime which melts in the furnace, unites with the phosphorous and brings it away in the slag. This slag is ground to a fine powder and used as a fertilizer. It contains 11 to 23 per cent. of phosphoric acid, most of which is available.

_Superphosphate._ The term superphosphate is applied to the phosphates that have been treated with sulphuric acid to make the phosphoric acid available. Dissolved bone, dissolved bone black, and the dissolved phosphate rocks are superphosphates.

_Fish Scrap_, mentioned as a source of nitrogen, is also a valuable source of phosphoric acid, containing 6 to 8 per cent., which is quite readily available owing to the rapid decay of the scrap.

SOURCES OF POTASH

The chief sources of potash used for fertilizers are the potash salts from the potash mines at Stassfurt, Germany, where there is an immense deposit of rock salt and potash salts.

The principal products of these mines used in this country are the crude salts:

_Kainite_, containing 12 per cent. of potash.

_Sylvinite_, containing 16 to 20 per cent. of potash, and the higher grade salts manufactured from the crude salts:

_Muriate of Potash_, containing 50 per cent. potash.

_High grade Sulphate of Potash_, containing 50 per cent. potash.

_Low grade Sulphate of Potash_, containing 25 per cent. potash.

_Wood Ashes_, if well kept and not allowed to get wet and leach, contain 4 to 9 per cent. of potash.

_Cotton Hull Ashes_ contain 20 to 30 per cent, of potash and 7 to 9 per cent. of phosphoric acid.

The potash in all these forms is soluble in water and equally available to plants. The crude salts, kainite and sylvinite, and the muriate contain chlorine and are not considered good for potatoes and tobacco as the chlorine lowers the quality of these products.

In tobacco regions tobacco refuse is a valuable source of potash, the stems are about five per cent. potash.

LIME

_Lime_ is generally supplied to the soil in the form of quicklime made by burning lime stone or shells. Other forms are gypsum or land plaster, gas lime (a refuse from gas works) and marl. Most soils contain sufficient lime for the food requirements of most plants. Some soils, however, are deficient in lime and some crops, particularly the legumes, are benefitted by direct feeding with lime.

Lime is valuable for its effect on the soil properties which constitute fertility.

Physically lime acts on the texture of the soil making clay soils mealy and crumbly, and causing the lighter soils to adhere or stick together more closely.

Chemically, lime decomposes minerals containing potash and other plant foods, thus rendering them available for the use of plants. It also aids the decay of organic matter and sweetens sour soils.

Biologically lime aids the process of nitrification.

The action of lime is greatest in its caustic or unslacked form.

Too much or too frequent liming may injure the soil. It should be carefully tried in a small way, and its action noted, before using it extensively.

A common way of using lime is to place twenty to forty bushels on an acre in heaps of three to five bushels, covering them with soil until the lime slacks to a fine powder. The lime is then spread and harrowed in. Lime tends to hasten the decay of humus. It should not be applied oftener than once in four or five years.

_Gypsum_, a sulphate of lime, is similar to lime in its action on the soil. Its most important effect is the setting free of potash from its compounds.

_Gas lime_ should be used with great care as it contains substances that are poisonous to plant roots. It is best to let it lie exposed to the weather several months before using.

_Marl_ is simply soil containing an amount of lime varying from five to fifty per cent. It has value in the vicinity of marl beds but does not pay to haul very far.