Nutrient Distribution in Humic Fertilizers in Relation to Their Fractional Composition
The composition and ratio of mineral substances can determine the degree of suitability of humic fertilizers for application to a particular crop. It should be noted, however, that the characterization of the various forms of humic fertilizers mentioned was based on the analysis of average samples.
At the same time, it is known that leonardite, from which these fertilizers are currently prepared, is not homogeneous in mechanical composition, but represents an organic mass consisting of peat particles of various diameters.
Fractional Composition of Leonardite
Table 20. Fractional Composition of Leonardite
| Leonardite quality index by fraction | Particle size, mm | Average leonardite sample | ||||||
|---|---|---|---|---|---|---|---|---|
| 10–7 | 7–6 | 5–3 | 3–2 | 2–1 | 1–0.5 | <0.5 | ||
| Fraction composition, % | 3.9 | 7.3 | 17.6 | 26.7 | 23.5 | 11.3 | 9.7 | 100.0 |
| Absorption capacity by methylene blue, % | 1.8 | 1.8 | 2.5 | 3.5 | 3.9 | 5.3 | 5.9 | 3.8 |
| Ash content, % | 19.9 | 20.7 | 20.2 | 20.6 | 19.9 | 20.5 | 32.9 | 21.5 |
Since the machines used for the application of ammonia water and loose mineral components do not produce additional significant fragmentation of the initial raw material, the finished humic fertilizer will not differ from the initial state in terms of fractional composition.
At the same time, as can be seen from Table 20, the fractional composition should have a significant impact on the quality of the fertilizer, since, depending on the greater or lesser content of particles with high cation exchange capacity, the distribution of mineral substances in the finished fertilizer will change. Therefore, we set ourselves the task of clarifying the nature of the distribution of mineral components in the leonardite mass during its treatment with chemicals.
In addition, since the result of such treatment was supposed to be the production of qualitatively different fractions, it was necessary to determine the optimal granule sizes both in terms of nutrient content and their impact on the plant.
Preparation and Analysis of Potassium Humate
To solve these problems, two types of potassium humate were prepared:
- First type: leonardite was treated with ammonia water, and then excess ammonia was neutralized with superphosphate to a pH of 7.2.
- Second type: instead of superphosphate, excess ammonia was neutralized with orthophosphoric acid, pre-diluted in water for more complete wetting of the mass.
Thus, the use of superphosphate and orthophosphoric acid made it possible to compare the effectiveness of treating leonardite with phosphorus in liquid form.
After preparation, the fertilizers were separated into fractions, and average samples were analyzed. Nitrogen and phosphorus were determined in a 0.5 N H₂SO₄ extract. Humic and fulvic acids were extracted cold.
Table 21. Nutrient Content in Potassium Humate by Fractions (in %)
| Analysis name | Potassium humate, neutralized with superphosphate | Potassium humate, neutralized with P₂O₅ | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Average sample | Fractions, mm | Average sample | Fractions, mm | ||||||||||||||
| 7–10 | 5–7 | 3–5 | 2–3 | 1–2 | 0.5–1 | <0.5 | 7–10 | 5–7 | 3–5 | 2–3 | 1–2 | 0.5–1 | <0.5 | ||||
| N | 1.23 | 0.87 | 1.13 | 1.27 | 1.40 | 1.42 | 1.24 | 1.06 | 1.54 | 1.10 | 1.38 | 1.47 | 1.60 | 1.56 | 1.72 | 1.86 | |
| P₂O₅ | 3.27 | 1.25 | 1.68 | 2.21 | 3.04 | 3.91 | 5.36 | 5.15 | 2.94 | 1.50 | 2.03 | 2.74 | 3.23 | 3.19 | 3.09 | 3.58 | |
| P₂O₅:N ratio | 2.6 | 1.4 | 1.5 | 1.7 | 2.2 | 2.7 | 4.3 | 4.8 | 1.9 | 1.4 | 1.5 | 1.8 | 2.0 | 2.0 | 1.8 | 1.9 | |
| Humic acid, soluble in 0.01 N KOH | 0.37 | 0.27 | 0.32 | 0.22 | 0.21 | 0.10 | 0.04 | 1.38 | 0.62 | 0.89 | 1.16 | 1.41 | 1.59 | 1.96 | 1.87 | ||
| Humic acid, soluble in 0.1 N KOH | 7.45 | 7.76 | 8.86 | 7.51 | 7.32 | 4.60 | 0.78 | 16.02 | 15.37 | 14.74 | 18.10 | 16.72 | 16.59 | 16.70 | 12.96 | ||
| Moisture | 22.1 | 37.4 | 41.9 | 44.8 | 46.7 | 45.6 | 38.3 | 44.0 | 18.4 | 25.6 | 44.4 | 47.5 | 48.7 | 40.6 | 25.9 | ||
| Aqueous extract pH | 6.5 | 6.7 | 6.9 | 7.0 | 7.1 | 7.2 | 7.0 | 7.0 | 6.6 | 6.7 | 6.8 | 6.9 | 7.1 | 7.2 | 7.4 | ||
As the analysis shows, the qualitative composition of leonardite fractions is heterogeneous, and regardless of the neutralization method, most of the introduced nitrogen and phosphorus accumulates in the smaller peat granules of 5 mm and less.
The choice of phosphorus component has a significant impact only on the mobility of humic, fulvic, and ulmic acids in the fertilizer. Thus, superphosphate treatment generally reduces the yield of alkali-soluble humic acids, and the smaller the granule size in the fraction, the greater the reduction. The decrease in humic acid content from larger to smaller fractions occurs in parallel with an increase in their phosphoric acid content and is explained by a greater enrichment of the fine fractions with powdered superphosphate.
In contrast to superphosphate, the use of orthophosphoric acid does not lead to a decrease in the yield of humic acids. On the contrary, in this case, an increase in the content of humic acids in the fractions is observed in parallel with the increase in nitrogen and phosphorus in them.
Microvegetation Experiment
The fractions of the specified types of potassium humate were tested in a microvegetation experiment to determine their effectiveness as sources of mineral nutrition for plants. The experiment was conducted in Koch dishes in a sand culture. The sand sample per vessel was 400 g. 1.5 ml of fertilizer was added per vessel, and 50 barley seeds were sown. 10 days after seedling emergence, the barley was harvested, and the nitrogen and phosphorus content was determined, and then the removal was calculated.
Table 22. Effectiveness of Potassium Humate Fractions as Nutrient Sources (Superphosphate Neutralization) (2016 Microvegetation Experiment, Barley)
| Potassium humate fraction, mm | Dry weight of 50 plants, g | Content, % | Total removal per vessel, mg | Taken from fertilizers per vessel, mg | Introduced per vessel, mg | Utilization of the introduced amount, % | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| N | P₂O₅ | N | P₂O₅ | N | P₂O₅ | N | P₂O₅ | N | P₂O₅ | ||
| Average sample | 0.52 | 4.15 | 0.643 | 21.6 | 3.33 | 9.4 | 2.16 | 18.4 | 49.1 | 50.8 | 4.4 |
| 10–7 | 0.55 | 3.51 | 0.441 | 19.3 | 2.42 | 7.1 | 1.25 | 13.1 | 18.7 | 54.2 | 6.7 |
| 7–5 | 0.54 | 4.48 | 0.536 | 24.2 | 2.91 | 12.0 | 1.74 | 16.9 | 25.2 | 71.0 | 6.9 |
| 5–3 | 0.57 | 5.31 | brak | 30.3 | brak | 18.1 | brak | 19.1 | 33.1 | 94.7 | brak |
| 3–2 | 0.57 | 4.15 | 0.466 | 23.6 | 2.68 | 11.4 | 1.51 | 21.0 | 45.6 | 54.0 | 3.3 |
| 2–1 | 0.56 | 4.15 | 0.625 | 23.2 | 3.47 | 11.0 | 2.30 | 21.3 | 58.6 | 51.6 | 3.9 |
| 1–0.5 | 0.54 | 4.06 | 0.536 | 21.9 | 2.91 | 9.7 | 1.74 | 18.6 | 80.4 | 51.2 | 4.0 |
| <0.5 | 0.54 | 3.71 | 0.682 | 20.0 | 3.67 | 7.8 | 2.50 | 27.9 | 53.7 | 27.9 | 4.6 |
| Without fertilizers | 0.45 | 2.71 | 0.264 | 12.2 | 1.17 | brak | brak | brak | brak | brak | brak |
Analysis of Results
The data obtained in this experiment allow us to conclude that the medium fractions are the most valuable constituent of humate. Granules with a diameter of more than 7 mm are a poor source of both nitrogen and phosphorus for plants, which is why it is absolutely necessary to reject them during fertilizer production.
Most likely, it will be appropriate to do the same with the dust fraction <0.5 mm, which mainly consists of poorly humified leonardite particles and a mineral admixture.
As for the optimal granule sizes, judging by the nitrogen uptake, their effectiveness depends on the form of the phosphorus component. Thus, when using superphosphate, granules of 3–5 mm are preferred, while when preparing fertilizers with orthophosphoric acid, the optimal particle size is in the range of 1–3 mm.
Conclusions
- The studies conducted have shown that the effectiveness of humic fertilizers can be increased by selecting the optimal composition and ratio of mineral components, as well as the appropriate granule size and fertilizer reaction for each crop and crop group.
- Saturation of a humic fertilizer (intended for use during sowing) with mineral components up to a certain limit increases their effectiveness. This limiting saturation is determined by the total content of nitrogen, phosphorus, and potassium of 11%. The effectiveness of more concentrated humic fertilizers approaches the action of mineral salts.
- The addition of potassium to humate to obtain a humic fertilizer with a complete mineral composition, as a rule, should be accompanied by additional enrichment of the fertilizer with ammonia water.
- Of the studied types of preparations, the most effective were those in which one part of nitrogen accounts for 1.5–2 parts of phosphorus and 1.5–3 parts of potassium.
- The content of water-soluble humic acids, soluble in water without heating, in such fertilizers should be in the range of 0.17–0.19 percent.
- In the process of treating leonardite with chemicals in the production of humic fertilizers, the distribution of mineral substances among the leonardite fractions turns out to be uneven. Nitrogen from ammonia water and superphosphate are mainly absorbed by fractions of 5 mm and less.
- The vegetation experiment showed that the medium fractions—1–5 mm are the most valuable constituent part of humates. Granules larger than 7 mm in diameter are a poor source of both nitrogen and phosphorus nutrition for plants, and those smaller than 0.5 mm are a poor source of nitrogen nutrition.