PEAT–MINERAL GRANULAR FERTILIZERS

S. I. Smolyaninov, N. E. Sagachenko, E. F. Prokhoda

(Presented by the Scientific-Methodological Seminar of the Faculty of Chemical Technology)

Among all possible variants of using peat as a fertilizer, a special place is occupied by the 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, preparation technology, and effectiveness [1, 2, 3].

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

The known methods for producing peat–mineral granular fertilizers are based on granulation of dry, finely ground peat with obligatory repeated moistening.

The strength of the granules obtained is insignificant. At present there is no industrial method for producing strong, sufficiently transportable organo-mineral granular fertilizers.

We have carried out a study to develop such a method for producing peat–mineral granular fertilizers.

For the work, peat from the Tagan deposit of Tomsk Oblast was taken; it had a working moisture content of 85%, ash content on a dry basis of 8.5%, nitrogen content on combustible mass of 2.7%, and degree of decomposition of 32%. The peat was lowland, sedge–hypnum peat.

The following were used as mineral components: superphosphate, ammonium nitrate, potassium salt.

At this stage we did not set ourselves the task of finding the best formulations from the agrochemical point of view, and the composition of the organo-mineral granules was determined:

a) by the ratio of the principal mineral components, using as an example the soils of one of the agricultural enterprises of Tomsk Oblast;

b) by the total amount of components applied per hectare of arable land, proceeding from the need to apply the full dose of mineral components, a sufficient amount of the organic part, and depending on the method of fertilizer application—for example, taking into account the possibility of using seed drills for row application of fertilizers. According to our calculation, per hectare of the above-mentioned soil it is necessary to apply: ammoni-

ammonium nitrate—150 kg, superphosphate—134 kg, potassium salt 68.3 kg (total 352.3 kg).

Four batches of fertilizers were prepared (Table 1). The wide range of ratios of the mineral and organic parts in the granules was intended to show the maximum permissible content of the former components. Thus, when 25% of mineral components are added to raw peat—

Table 1

Composition of peat-mineral granules, %

components (composition 3), the granules in the air-dry state (with a peat moisture content of 33%) will contain up to 60% mineral part. About 600 kg/ha of granules of this composition must be applied; in this case the full dose of mineral components is supplied.

The proposed method for producing granulated peat-mineral fertilizers is as follows. Raw peat with an initial moisture content of 75–85% (this moisture content is natural when peat is extracted by excavator or layer-surface methods; overdrying of the peat and subsequent addition of water have an adverse effect) is subjected to mechanical processing (rubbing) in machines of the hammer-crusher type of the TEMП excavator (or another type), and in screw rubbing machines of the meat-grinder type. Mineral components are added to the processed peat mass with thorough mixing and in the required dosage. Depending on its initial moisture content, the resulting mixture can be formed either into large bricks (of the machine-formed peat type), or 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, for example flue gases. After drying to a moisture content of 20–40%, the formed pieces acquire the necessary strength and can be used directly or after crushing and screening into the required fractions.

The most important factors of the technological regime are:

1. 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 74%, the strength of the granules increases by a factor of 2–3 (Fig. 1, curves 3, 4).

1. Degree of processing of the peat (Fig. 1, 2). Processing of peat consists in grinding and mixing the peat mass. This factor has a substantial influence on the strength of peat-mineral granules. Peat that has not undergone mechanical rubbing cannot yield strong granules; even a very slight increase in the degree of processing increases the strength of the granules severalfold.

From the standpoint of reducing fertilizer production costs, the degree of peat processing may be taken as minimal; in this case the crushing resistance will be no less than 100 bar.

Fig. 1. Dependence of granule abrasion on the degree of peat processing at different contents of mineral components and different initial peat moisture contents. 1—peat moisture content, 84%; content of mineral admixtures in raw peat, 25%; 2—the same, 20%; 3—the same, 15%; 4—peat moisture content, 74.6%; mineral components, 15%.

3. Amount of mineral components added to peat. This method permits wide variation in the ratios between peat and mineral components. In general, when the content of the latter is increased, the strength of the granules decreases somewhat. For example, the crushing resistance of granules at an average degree of processing, when the content of mineral components is increased from 15 to 25% (Fig. 2) (calculated for peat with a moisture content of 85%), decreased from 220 to 190–200 bar. Thus, a practically unlimited amount 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 both in physical properties and in chemical composition. The only limitation for insoluble or sparingly water-soluble components is the degree of grinding, which, in order to ensure uniform distribution, should preferably be less than 1 mm. As the degree of grinding of insoluble mineral components is increased, the strength of the granules increases.

Fig. 2. Dependence of granule crushing resistance on the degree of peat processing at different contents of mineral components (initial peat moisture content, 84%); 1—content of mineral admixtures, 20%; 2—the same, 15%; 3—the same, 25%.

Granules obtained by this method have good moisture absorption and swelling capacity (Tables 2 and 3), reaching, in 48 hours in an atmosphere saturated with water vapor at room temperature, 75 and 110%, respectively. In addition, which is an unquestionably positive quality of the granules, their strength in the swollen state remains sufficiently high. Thus, with the full availability

Table 2

Swelling capacity of peat-mineral granules (increase in volume, in % of the initial value) as a function of the time of contact with water (experiments 1, 3, 4) or with its vapor (experiment 2)

of the mineral components to plants, they will not be washed out of the soil at all.

The proposed method differs from all others in that it yields very strong granules and makes it possible to organize industrial production of this type of fertilizer; moreover, the technology may be based on currently existing methods of peat extraction.

Table 3

Moisture absorption of peat-mineral granules (increase in weight, in % of the initial value) as a function of the time of contact with water (experiments 1, 3, 4) or with its vapor (experiment 2)

The strength of the granules is so high that they can be applied to the soil by the most varied methods and, in addition, transported over long distances.

The compositions may be highly diverse, including components of micronutrient fertilizers and bacterial additives.

The agrochemical effectiveness of granulated peat-mineral fertilizers was tested by the seed science laboratory of the Siberian Botanical Garden at Tomsk State University. The growth vigor 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); peat-mineral granulated fertilizers (with an equal dose of mineral components). Growth vigor, as a percentage relative to the control: for the second variant—125%, for peat-mineral granulated fertilizers—138%.

High effectiveness was also shown by granules prepared according to the formulation of the Novosibirsk Agricultural Institute.

This institute conducted field tests of this type of fertilizer on the “Tomsky” state farm when applied under corn. The increase in yield of green mass from plots of 100 m² was 29.6%, as against 3.8% when the mineral components were applied broadcast.

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

Conclusions

1. A method is proposed for obtaining strong peat-mineral granulated fertilizers.

2. The optimal conditions ensuring maximum granule strength have been identified (initial moisture content of the peat and degree of its processing, quantity of mineral components).

3. Preliminary tests of granulated peat-mineral fertilizers have shown their high agrochemical and economic effectiveness.

References

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

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

3. L. I. Slavyu-Lyubitskaya, O. E. Fatunzhikh. The significance and use of peat in agriculture. Publishing House of the Academy of Sciences of the USSR, Moscow—Leningrad, 39–76, 1957.

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

5. V. U. Pchelkin. The significance of granulated fertilizers in increasing yield. Moscow, 3–19, 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. Gosstopyekhizdat, 1963.