PEAT-MINERAL GRANULATED FERTILIZERS

S. I. Smolyaninov, N. E. Sagachenko

Agrochemical science considers it most appropriate to apply mineral fertilizers together with organic ones.

Of all possible variants for using peat as fertilizer, a special place is occupied by so-called peat-mineral fertilizers, i.e., fertilizers consisting of peat and various mineral components. There are several types of peat-mineral fertilizers. They differ from one another in composition, manufacturing technology, and effectiveness [1, 2, 3, 7].

From the standpoint of a number of questions directly connected with agrochemistry, the production of complete peat-mineral granulated fertilizers is of great importance [4, 5, 6].

Organo-mineral granules are a mixture of organic fertilizer with a mineral fertilizer or with several mineral fertilizers, including microfertilizers and other special additives. Organo-mineral granulated fertilizers have a number of advantages over other fertilizers.

1. Organo-mineral granules, when applied to the soil, improve its structure.

2. When granulated fertilizers are applied to the soil, nutrient foci are created: the granules contain hundreds of times more nutrients than are found in places where fertilizers were not applied. That is, the farther from the granule, the fewer the nutrients. Such a differing concentration of nutrient elements is of very great importance for increasing the yield of agricultural crops, because around organo-mineral granules there is a significant intensification of the growth and development of microflora.

The concentration of nutrients created around granules provides the most favorable conditions for the growth and development of agricultural crops, since each of them extracts the elements it needs from those concentrations of nutrients that best correspond to its biological requirements.

1. Being contained in granules, mineral fertilizers are protected from leaching into deep soil layers: the contact surface is reduced; phosphoric acid, for example, is converted to a lesser extent into insoluble compounds—aluminum and iron phosphates.

2. In granulated form, mineral fertilizers possess significant advantages over the same powdery fertilizers: they do not cake, and therefore they can be evenly distri-

distributed over the field. In the form of granules, the fertilizers can be applied together with seeds by seed drills.

1. The organic portion of the granules improves the water–air regime of the soil.

The agrochemical effectiveness of organo-mineral granulated fertilizers has been shown in works of the Academy of Sciences of the BSSR, the All-Union Institute of Fertilizers, and the Novosibirsk Agricultural Institute [4, 5, 6].

At present there is no industrial method for producing strong, sufficiently transportable organo-mineral granulated fertilizers. We have carried out a study aimed at developing such a method for obtaining peat-mineral granulated fertilizers.

To create granules of increased strength, the colloidal properties of raw peat (not subjected to preliminary drying) were used. For the work, peat from the Tagan deposit in Tomsk Oblast was taken; the degree of decomposition was 32%; the peat was lowland, sedge–hypnum peat.

Superphosphate, ammonium nitrate, urea, ammonium sulfate, ammonia water, potassium salt, potassium chloride, and others were used as mineral components. The proposed method for producing granulated peat-mineral fertilizers is as follows.

Raw peat with an initial moisture content of 70–85% is subjected to mechanical processing (attrition) in screw attritors. Mineral components, in the required dosage, are added to the processed peat mass with thorough mixing. The resulting mixture can be formed into granules of such a size that, after drying and shrinkage, they will give the required grain size. The wet formed pieces are dried naturally or with the aid of some heat carrier. After drying to a moisture content of 20–30%, the formed pieces acquire the necessary strength and can be used.

The most important factors of the technological regime are:

1. The initial moisture content of the peat. The fundamental difference between the proposed method and all others is the use of the colloidal binding properties of peat, which is an irreversible colloid; therefore excessive overdrying, even if the loss of water is compensated by its subsequent addition, leads to a deterioration in the mechanical strength of the granules. With a decrease in the initial moisture content from 84 to 70%, the strength of the granules increases by a factor of 2–3. At an initial moisture content of about 70%, it is possible to obtain granules directly of the required size by rolling the peat mass extruded from the forming machine in the form of jets of comparatively small diameter in a drum granulator.

2. The degree of processing of the peat. This factor has a substantial influence on the strength of peat-mineral granules. Peat not subjected to mechanical attrition cannot give strong granules; even a very slight increase in the degree of processing increases the strength of the granules severalfold. Thus, at a degree of processing of peat corresponding to that which usually occurs in the excavator method of peat extraction, the crushing resistance of the granules is about 100–150 bar; when the degree of processing is increased threefold, the crushing resistance of peat-mineral granules rises to 300 bar. From the standpoint of reducing production costs for peat-mineral fertilizers, the degree of processing of the peat may be taken as minimal. In this case the crushing resistance will be not less than 100 bar.

3. The amount of mineral components added to the peat. This method permits a wide variation in the ratios between peat and mineral components.

As the content of the latter increases, the strength of the granules decreases somewhat. For example, the crushing resistance of granules at an average degree of processing, with an increase in the content of mineral components from 15 to 25% (calculated for peat with a moisture content of 85%), decreased from 220 to 190–200 bar. Thus, a practically unlimited quantity of mineral components may be added, and the upper limit is determined only by agrochemical requirements.

The mineral components added to peat may be highly diverse in both physical and chemical properties. The only limitation for components insoluble or sparingly soluble in water is the degree of grinding, which, to ensure uniform distribution, should preferably be less than 1 mm. As the degree of grinding of insoluble mineral components increases, the strength of the granules increases.

1. Rotation speed of the drum. When the rotation speed of the drum granulator is varied, three regimes of motion of the material being rolled are distinguished [8]: A—rolling; B—cataracting; C—cyclic. Motion of the material in the rolling regime is observed at low drum rotation speeds and is characterized by the mass of material reaching the highest point of the circular portion of the trajectory and subsequently spilling down in a thin layer along the inclined surface formed by the material itself. The particles spilling down have no parabolic portion of the trajectory.

The cataracting regime, which arises at higher drum rotation speeds, is characterized by the presence of three portions in the trajectory of the moving particles: a circular portion, a parabolic portion, and a spilling portion. In this case, after the circular portion of the path, the material separates from the surface of the drum and then moves along an aerial parabolic trajectory. After falling, the material spills down along the inclined surface and again passes to the circular portion.

The cyclic regime of material motion is characterized by the transformation of the trajectories of individual elementary layers into closed curves that do not intersect one another. In this regime there is no spilling portion, and the material passes directly from the parabolic trajectory to the circular one. The cyclic regime of motion appears at a sufficiently high rotation speed.

The motion of the material in the granulator must occur in the rolling regime. The principal condition for granulation is to ensure the possibility of the granules rolling down the inclined surface and to prevent destruction of the granules by excessively large dynamic loads. The degree of filling of the drum is of great importance here. At a high degree of filling, the weakest granules may be destroyed under the action of the overlying layers of great thickness.

Granules obtained by this method have good moisture absorption and swelling capacity, reaching, in 48 hours in an atmosphere saturated with water vapor at room temperature, 75% and 110%, respectively. In addition, in the swollen state the granules do not lose their shape. Thus, with complete availability of the mineral components to plants, they will be only weakly leached from the soil.

The proposed method differs from all others in that it gives very strong granules, eliminates the multistage nature of the production of peat-mineral granulated fertilizers, and makes it possible to organize industrial production of this type of fertilizer; moreover, existing methods of peat extraction may serve as the basis of the technology.

The strength of the granules is so high that they can be applied to the soil by a wide variety of methods and, in addition, transported over long distances. This will make it possible to organize, in areas of peat deposits, large-scale centralized production of fertilizers and to supply consumers with them over great distances. Peat-mineral granulated fertilizers possess high performance qualities. Experiments conducted under storage conditions in sealed containers and in the open showed that, during storage, the granules do not cake and do not break down. In addition, peat-mineral granules satisfactorily withstand sharp fluctuations in ambient humidity and restore their performance properties upon drying.

The agrochemical effectiveness of granulated peat-mineral fertilizers was tested by the seed-testing laboratory of the Siberian Botanical Garden at Tomsk State University. The growth power of seeds of spring wheat “Diamant” was determined by the method of N. V. Prikladov in the following variants: control without fertilizers; loose mineral fertilizers (nitrogen, phosphorus, potassium); and peat-mineral granulated fertilizers (with an equal dose of mineral components). Growth power, as a percentage relative to the control, was: for the second variant—125%; for the peat-mineral granulated fertilizers—138%.

High effectiveness was also shown by granules prepared according to the composition of the Novosibirsk Agricultural Institute. This institute conducted field trials of this type of fertilizer at the “Tomskii” state farm when applying them under corn. The increase in the yield of green mass from the plots amounted to 29.6%, whereas when mineral fertilizers were applied in loose form it was 3.8%.

An approximate assessment of the economic effectiveness of this type of fertilizer, carried out by us taking into account data from the Novosibirsk Agricultural Institute, shows that the costs of fertilizing one hectare of crops are 3–5 times lower than with any other type of fertilizer.

LITERATURE

1. S. A. Tsuprov. For the further expansion of the use of peat resources in agriculture. Peat Industry, No. 1, 1, 1961.

2. S. A. Tsuprov. For the development of extraction and comprehensive use of peat in agriculture. Peat Industry, No. 1, 1, 1962.

3. L. I. Savich-Lyubetskaya, O. E. Fatchikhina. The significance and use of peat in agriculture. Publishing House of the USSR Academy of Sciences, 1957.

4. A. A. Khrapal. A new method for increasing crop yields. Publishing House of Glavsevmorput, 1950.

5. V. U. Pchelkin. The significance of granulated fertilizers in increasing yields. Moscow, 1954.

6. V. S. Boiko. Experience in the use of highly concentrated peat-mineral and peat-bacterial fertilizers under the conditions of certain farms in Western Siberia. Abstracts of reports for the scientific and technical conference on peat. Gostoptekhizdat, 1963.

7. K. I. Chekalov. Preparation and application of organic and organo-mineral fertilizers. Selkhozgiz, 1958.

8. M. B. Frenkel. Laboratory studies of the granulation of cement raw-material mixtures. 1957.