AGRONOMIC ORES (EN: agronomic ores, fertilising ores; DE: agronomische Erze; FR: minerais agronomiques; ES: fertilizantes minerales; RU: агрономические руды) are the natural mineral formations, which are the raw materials for the production of the mineral fertilizers or are used for the improvement of the soil for the agronomic objectives.
The term "agronomic ores" has been proposed by the soviet scientist Ya.V.Samoilov (1921). The potassium salts and the phosphate ores belong to the agronomic ores, which are used for the production of the major components of the mineral fertilizers, namely phosphorus, potassium and nitrogen. They used extensively in the past times the natural sodium nitrate as the nitrogenous mineral fertilizer. In the 20th century, after the mastering of the synthesis of ammonia from the nitrogen of the air, the atmospheric nitrogen is serving as the raw material for the production of the nitrogenous fertilizers. Many types of the mineral fertilizers, especially phosphorus ones, are produced with the usage of the significant quantities of the sulfuric acid; sulfur in some form or another (most often in the form of the sulfate ion) is the constituent of the mineral fertilizers, and is introduced together with them into the soil, causing on it the agrochemical impact, which is beneficial for the plants. In accordance with this fact, Samoilov also attributed to the agronomic ores sulfur (see Sulphur ores), iron pyrite, and other raw materials, which are used for the production of the sulfuric acid, which is used for the production of the mineral fertilizers. In addition to nitrogen, phosphorus and potassium, there are essential for the life of the plants the boron, copper, manganese, molybdenum, and other elements, which have been named as the trace elements in the agricultural chemistry, while the substances, which are containing them, and are specially introduced into the soil, have been named as the microfertilizers.
Another important group of the agronomic ores are the mineral formations, which are introduced into the soil in the natural form without the technological processing (except for the grinding). There belong to this group the phosphorites, which are ground into the phosphorite flour, raw potassium salts, various carbonate rocks, which are used for the liming of the soils, and the gypsum for their gypsuming. There are suitable only the certain types of the phosphorites for the production of the phosphorite flour (nodular, granular, weathering crust), which distinguish themselves by the increased content of carbonate as the constituent of the tricalcium phosphate (carbonate-fluorapatites (kurskites)). The content of the P2O5 in the phosphorite flour varies from 19% to 30% according to the grades. The liming is used on the acidic soils with the pH of 6.0-5.5 and lower; such are the soils sod-podzolic, ultisols (red clay soils), and others. They use the limestone flour as the lime fertilizers, which is ground as finely as possible (70% of the particles less than 0.25 millimetres), and obtained during the grinding of the limestone, chalk, which are containing not less than 85% of CaCO3, marl, dolomite, as well as the natural loose calcareous rocks (calcareous tufa, lake lime, etc.). The liming supports the slightly acidic reaction of the soil for 10-12 years. The gypsuming is performed on the strongly saline soils and solonetzes, which are characterized by the alkaline reaction. During the introduction of the gypsum, the sodium, which is absorbed by the soil, is replaced by the calcium, and the alkaline reaction is eliminated, the physical-chemical and biological properties of the soil improve. They are using the finely ground gypsum for the gypsuming, as well as the loose clay-gypsum. The influence of the gypsuming manifests itself for 8-10 years.
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