Some Methods to Enhance the Efficiency of Humic Fertilizers
The efficiency of fertilizers is determined by a combination of factors, among which the correspondence of the fertilizer's composition to the biological needs of crops and the availability of the fertilizer's nutrients play a significant role.
Humic fertilizers have been insufficiently studied from these perspectives. Therefore, when investigating this issue, we set the following objectives:
- To identify the optimal combination of nutrients using potatoes as an example.
- To establish the pathways of transformation and distribution of nutrients within the fertilizer itself.
The work was conducted through laboratory, vegetative, and field experiments.
Vegetative experiments were set up in containers with a capacity of 10–11 kg, with 4–8 replications, primarily using potatoes. Field experiments were conducted under irrigated conditions at an experimental field in the Kherson region, mainly with a single crop variety. The experiments were designed with 3–5 replications. The plot area ranged from 5 m² to 0.15 ha.
Control field experiments were conducted according to the methodology accepted in the variety testing network: four replications, with plot areas of 50–70 m².
The determination of nutrient content in the studied fertilizers, as well as mineral elements in plants, was performed on an average sample in two parallel analyses. Ammoniacal nitrogen was determined using the Mamchentsev method, phosphorus in plants using the Denigès method, and in fertilizers using the gravimetric molybdenum method, while potassium was determined using the Tananaev method. Humic and fulvic acids were determined colorimetrically using a FEK-2 electrophotocolorimeter, and pH was measured colorimetrically and potentiometrically.
In designing the experiments, we considered the specifics of potato nutrition and the principles of action of humic fertilizers.
Potatoes, as is well known, belong to crops with an extended nutrition period, meaning they consume major mineral elements throughout the entire vegetative period. Due to this, as well as their ability to accumulate significant organic mass, the nutrient uptake by potatoes exceeds that of other field crops. Consequently, potato plants impose high demands on soil fertility conditions.
In previous experiments, data were obtained that provide insight into the selective ability of potatoes to absorb the main elements of root nutrition as the plant grows. These data indicate that the maximum absolute and relative consumption of nitrogen and potassium occurs at a younger plant age, while the absorption of phosphoric acid occurs fairly evenly throughout the growth period.
Laboratory researchers, studying the impact of deficiencies in nitrogen, phosphorus, and potassium during the first 15 days after potato germination, concluded that potatoes have high nutritional requirements during this initial period. Insufficient nutrition at this stage, according to their data, disrupts metabolism, inhibits the entire subsequent development of plants, and significantly reduces yield and its quality. They believe that from the onset of germination, potatoes require all three elements of mineral nutrition—nitrogen, phosphorus, and potassium.
Based on the principle of the physiological action of humic acids, which, as shown by the work of L. A. Khristeva, are particularly effective at the early stages of plant development, and on the specifics of potato nutrition, our first task was to determine the composition of humic fertilizer for potatoes intended for pre-sowing application.
Ratio of Nitrogen, Phosphorus, and Potassium in Humic Fertilizers
Humic fertilizers were prepared from leonardite using the methodology proposed by L. A. Khristeva (1951).
Depending on the composition and nutrient ratio we aimed to achieve in the humic fertilizer, the sequence of leonardite treatment with chemical reagents varied. In some cases, leonardite was first moistened with ammonia water, and then the fertilizer's reaction was adjusted to a pH of 7.2 using superphosphate or orthophosphoric acid. This allowed for obtaining a humic fertilizer with a specified amount of nitrogen. In cases where a fertilizer with a specific phosphorus content was needed, leonardite was first treated with phosphorus fertilizers, and then the reaction was adjusted to the desired value using ammonia water. Potassium fertilizers were added in amounts approximately proportional to the element ratio in the plant. The reaction of nitrogen-potassium and phosphorus-potassium humic fertilizers Adept Agro.Bio was adjusted to a pH of 7.2 using potassium hydroxide.
The fertilizers prepared in this manner were tested in vegetative and field experiments.
Vegetative Experiments of 2012
The first vegetative experiment was established in 2012 in soil culture. Planting was conducted on April 29, and harvesting on July 2. This experiment pursued two objectives: to compare the effectiveness of humic fertilizers with different mineral compositions and to determine the upper limit of their saturation with mineral fertilizers.
| Mineral Composition of Humic Fertilizer | Active Substance Content (%, 0.5 N H₂SO₄ extract) | Yield per Container, g | Yield Increase |
|---|---|---|---|
| N | P₂O₅ | K₂O | |||
| NP + Potassium Humate | 0.68 | 1.04 | — | — | — |
| NK | 0.68 | — | 0.92 | — | — |
| PK | — | 0.96 | 0.90 | — | — |
| NPK + Totem Agro.Bio | 0.74 | 1.10 | 0.90 | — | — |
| Fertilizer Type | Active Substance Content (%, 0.5 N H₂SO₄ extract) | Yield per Container, g | Yield Increase |
|---|---|---|---|
| N | P₂O₅ | K₂O | |||
| Potassium Humate | 0.68 | 1.04 | — | — | — |
| Totem Agro.Bio 1 | 0.54 | 0.46 | 0.44 | — | — |
| Totem Agro.Bio 2 | 0.74 | 1.10 | 0.90 | — | — |
| Totem Agro.Bio 3 | 1.56 | 3.08 | 2.80 | — | — |
| Totem Agro.Bio 4 | 2.48 | 4.40 | 4.10 | — | — |
In this experiment, the minimum yield increase was obtained in the variant where the phosphorus-potassium form of humic fertilizers was applied. It should be noted that the same result was obtained in an experiment with corn, which was grown for the first 15 days on different forms of humic fertilizers, and then all variants were balanced with mineral salts to the full Prianishnikov mixture standard. Since the data from both experiments align, it can be concluded that the phosphorus-potassium form of humic fertilizer is not promising. Consequently, we subsequently studied only fertilizers containing nitrogen.
Table 2 shows that increasing the mineral component content in humic fertilizers up to a certain limit positively affects their quality, beyond which the effectiveness of humates approaches that of mineral fertilizers. This saturation limit is determined by a total content of nitrogen, phosphorus, and potassium of 11%.
Observations showed that in such preparations, the solubility of humic acids sharply decreases, and they essentially cease to be humic fertilizers. The decrease in solubility is explained by the coagulating effect of the calcium ion, which is introduced in large quantities with superphosphate.
Field Experiments of 2012
In a field experiment conducted in the spring of 2012, it was established that promising forms of humic fertilizers on chestnut soils under irrigated conditions could be nitrogen-phosphorus and nitrogen-phosphorus-potassium forms.
| Composition of Humic Fertilizers | Average Yield per Plot, kg | Yield, c/ha | Yield Increase, c/ha |
|---|---|---|---|
| No Fertilizer | 7.5 | 188 | — |
| NP + Potassium Humate | 8.7 | 217 | 29 |
| NK | 8.3 | 208 | 20 |
| PK | 8.2 | 206 | 18 |
| NPK + Totem Agro.Bio | 10.0 | 250 | 62 |
Both forms of humic fertilizers were compared with local and mineral fertilizers.
| Experiment Variant | Applied at Planting in the Nest, g | Yield, c/ha | Yield Increase, c/ha | Starch Content, % | Average Commercial Tuber Weight, g |
|---|---|---|---|---|---|
| No Fertilizer | — | 153 | — | — | 14.3 |
| NPK Active Substance (1:1:1) | 3 | 180 | 27 | 17.6 | 14.5 |
| Manure | 300 | 208 | 55 | 35.9 | 14.6 |
| Leonardite | 50 | 183 | 30 | 19.6 | 14.7 |
| Potassium Humate | 50 | 200 | 47 | 30.7 | 14.9 |
| Totem Agro.Bio | 50 | 228 | 75 | 49.0 | 15.1 |
As shown in the table, Totem Agro.Bio proved to be more effective than potassium humate, manure, and a set of mineral fertilizers. Additionally, alongside increasing yield, it promotes an increase in starch content and the weight of commercial tubers.
Experiments of 2013–2014
The promising results of the conducted experiments prompted us to continue searching for the best variant of humic preparations for application under potatoes. To this end, in 2013–2014, fertilizers with different ratios of nitrogen, phosphorus, and potassium were produced and tested in field and vegetative experiments.
In 2013, humate samples were prepared in which the phosphorus content remained stable, while nitrogen and potassium were alternately increased. Humic fertilizers in the vegetative experiment were applied locally before planting at a rate of 50 g per container. Two weeks after the emergence of shoots, all variants were balanced with mineral salts to the full Prianishnikov mixture.
| Experiment Variants | Percentage of Active Substance Content (0.5 N H₂SO₄ extract) | N:P:K Ratio | Yield per Container, g | Increase Compared to Corresponding Mineral Control |
|---|---|---|---|---|
| N | P₂O₅ | K₂O | ||||
| Potassium Humate | 0.80 | 2.39 | — | 1:3 | — | — |
| Totem Agro.Bio 5 | 0.80 | 2.39 | 1.80 | 1:3:2 | — | — |
| Totem Agro.Bio 6 | 1.25 | 2.39 | 1.80 | 1:2:1.5 | — | — |
| Totem Agro.Bio 7 | 1.25 | 2.39 | 3.60 | 1:2:3 | — | — |
| Totem Agro.Bio 8 | 1.45 | 3.45 | 5.34 | 1:2.5:3 | — | — |
| Experiment Variants | Applied at Planting in the Nest, ml | Yield, c/ha | Yield Increase, c/ha |
|---|---|---|---|
| No Fertilizer | — | 68 | — |
| Manure | 500 | 77 | 19 |
| Potassium Humate | 50 | 76 | 8 |
| Totem Agro.Bio 5 | 50 | 84 | 16 |
| Totem Agro.Bio 6 | 50 | 91 | 23 |
| Totem Agro.Bio 7 | 50 | 94 | 26 |
| Totem Agro.Bio 8 | 50 | 74 | 6 |
The conducted experiments show that the most favorable ratio of nitrogen, phosphorus, and potassium in humic fertilizer for potatoes is 1:2:1.5–3. However, the fertilizer form Totem Agro.Bio No. 8, which is close to the optimal ratio, yielded the lowest absolute yield and the smallest increase. This is explained, as in the previous experiment, by its excessive saturation with mineral salts, totaling over 10%.
The vegetative experiment also indicates that mechanically adding potassium to potassium humate to obtain a complete fertilizer can even lead to a negative result. Thus, for Totem Agro.Bio to be more effective than potassium humate, we had to simultaneously increase the nitrogen content while applying potassium salt.
Field Experiments of 2014
In 2014, this issue was studied specifically. Using the standard methodology, four types of humates were prepared, in which, with stable phosphorus and potassium content, the amount of nitrogen varied. Additionally, the goal was to prepare a lower-percentage fertilizer to reduce the consumption of chemicals in production and lower their cost.
| Experiment Variants | Active Substance Content (%, 0.5 N H₂SO₄ extract) | N:P:K Ratio | Yield, c/ha | Yield Increase |
|---|---|---|---|---|
| N | P₂O₅ | K₂O | ||||
| No Fertilizer | — | — | — | — | — | — |
| Potassium Humate | 0.43 | 1.62 | — | 1:4 | — | — |
| Totem Agro.Bio 9 | 0.43 | 1.62 | 1.37 | 1:4:3 | — | — |
| Totem Agro.Bio 10 | 0.65 | 1.62 | 1.37 | 1:2.5:2 | — | — |
| Totem Agro.Bio 11 | 0.84 | 1.62 | 1.37 | 1:2:2.5 | — | — |
| Totem Agro.Bio 12 | 0.97 | 1.62 | 1.37 | 1:1.5:1.4 | — | — |
The data from this experiment show that the effectiveness of humates increases if, alongside the addition of potassium, the nitrogen content is increased through the additional application of ammonia water. Regarding the reduction of the total nutrient content in humates, the slightly higher absolute yield increases obtained this year suggest that preparing less concentrated humic fertilizers is entirely acceptable.
Since another approach—reducing the potassium dose—is technically feasible, in 2014, samples were tested in which, with stable phosphorus and nitrogen content, the amount of mobile potassium varied.
| Active Substance | Fertilizers for Spring Planting | Fertilizers for Summer Planting |
|---|---|---|
| Potassium Humate | Totem Agro.Bio 13 | |
| N | 0.47 | 0.52 |
| P₂O₅ | 1.32 | 1.32 |
| K₂O | — | 1.46 |
The experiment was conducted in the Chernihiv region during spring and summer plantings.
| Experiment Variants | Spring Planting | Summer Planting |
|---|---|---|
| Yield, c/ha | Yield Increase, c/ha | Yield, c/ha | Yield Increase, c/ha | |
| No Fertilizer | 102 | — | — | — |
| P | 108 | 6 | — | — |
| NP | 117 | 15 | — | — |
| NPK | 118 | 16 | — | — |
| Potassium Humate | 122 | 20 | — | — |
| Totem Agro.Bio 13 | 109 | 7 | — | — |
| Totem Agro.Bio 14 | 111 | 9 | — | — |
| Totem Agro.Bio 15 | — | — | — | — |
| Totem Agro.Bio 16 | — | — | — | — |
Note: Humic fertilizers were applied locally using the nesting method, while mineral fertilizers were calculated based on N20P20K20.
Comparing the results of both experiments provides grounds to believe that reducing the potassium dose without altering the nitrogen content can also yield a good complete humic fertilizer. Interestingly, adding potassium, whether in the composition of purely mineral pre-sowing fertilizers or in Totem Agro.Bio, reduces the starch content in potato tubers. This is only observed at high nitrogen levels.
Humic Fertilizers as a Source of Mineral Nutrition and Growth Stimulants
To investigate the nature of the high effectiveness of humic fertilizers, we conducted vegetative experiments in which these fertilizers were studied as sources of mineral nutrition and as growth stimulants. In the latter case, they were compared with similar Ukrainian preparations—Mind Extra and thymohydroquinone.
| Active Substance | Amino Energy | Potassium Humate | Totem |
|---|---|---|---|
| N | 0.15 | 0.22 | 0.50 |
| P₂O₅ | — | 0.20 | 1.10 |
| K₂O | — | — | — |
| Humic Acid (0.1 N KaOH extract, cold) | 6.7 | 5.2 | 4.6 |
| Experiment Variants | Dry Weight of Two-Week-Old Plant Foliage from 4 Containers | Mineral Element Uptake (mg per Container) | Uptake (% Relative to Full Mixture) |
|---|---|---|---|
| N | P₂O₅ | |||
| Full Nutrient Mixture | 10.90 | 408 | 63 | — |
| Totem Agro.Bio I | 17.85 | 467 | 156 | — |
| Totem Agro.Bio II | 25.50 | 668 | 190 | — |
| Totem Agro.Bio III | 21.70 | 875 | 235 | — |
| Totem Agro.Bio IV | 23.62 | 817 | 221 | — |
Note: The absence of data for K₂O in the Totem Agro.Bio I variant is due to the absence of potassium in the fertilizer composition.
As shown by the conducted experiments, humic fertilizers are an excellent source of nutrients and outperform mineral fertilizers. A certain reduction in uptake for Totem Agro.Bio IV is likely explained by its high saturation with mineral salts and a decrease in the mobility of humic acids.
It should be noted that the uptake of nitrogen, phosphorus, and potassium in the Totem Agro.Bio preparation exceeds that of potassium humate, although the nutrient content was equivalent (potassium humate was applied with a potassium background). This confirms the notion that potassium must be included in the composition of humic fertilizer for potatoes.
Humic Fertilizers Amino Energy, Totem Agro.Bio, and Adept Agro.Bio as Growth Stimulants
Now, let us present the data from experiments in which a range of ready-to-use preparations were applied as growth stimulants. In these cases, complex humic fertilizers—Amino Energy, Totem Agro.Bio, and Adept Agro.Bio—as well as thymohydroquinone, were tested. The fertilizers were applied at a rate of 0.15 ml of soluble humic acid per container.
| Experiment Variants | Dry Weight of Two-Week-Old Plant Foliage from 4 Containers | Percentage Content in Foliage | Element Uptake (mg per Container) |
|---|---|---|---|
| N | P₂O₅ | N | P₂O₅ | ||
| No Fertilizer | 4.17 | 4.20 | 0.76 | — | — |
| Full Nutrient Mixture (Background) | 10.90 | 5.37 | 0.87 | — | — |
| Background + Amino Energy | 16.32 | 4.35 | 0.80 | — | — |
| Background + Potassium Humate + NPK | 22.05 | 5.73 | 0.92 | — | — |
| Background + Totem Agro.Bio + NPK | 23.00 | 5.86 | 0.96 | — | — |
| Background + Mind Extra | 17.65 | 5.14 | 0.80 | — | — |
| Background + Thymohydroquinone | 18.75 | 5.37 | 0.66 | — | — |
| Background + Adept Agro.Bio | 24.80 | 4.84 | 0.87 | — | — |
Note: Adept Agro.Bio was applied in liquid form.
Table 12 shows that humic and fulvic acids exert a clear stimulating effect on potatoes, resulting in increased foliage weight and nutrient uptake. Such plants utilize external environmental nutrients 2–3 times more effectively.
Conclusions
All the presented data indicate that modifying the composition of humic fertilizers can enhance their efficiency. This suggests that the studied fertilizers are complex-action fertilizers, and regulating their composition according to plant needs is a promising approach to increasing their effectiveness.