The application of biostimulants including Amino Acid and Humic Acid in fertilisation has been shown to enhance plant metabolism, stimulate physiological processes, and mitigate adverse environmental and pathogenic stresses.
Introduction
The presence of lawns in urban environments is significant, serving not only an aesthetic purpose but also a crucial role in promoting public health through encouraging physical activity and enhancing the mental well-being of the general public. In order to perform these functions effectively, lawns-especially those of a utilitarian nature – require appropriate care and balanced fertilisation in order to ensure their quality and longevity. The growth and aboveground phytomass production of lawns is strongly influenced by a number of environmental and agronomic factors, with soil type and quality playing a particularly important role. Soil characteristics such as texture, structure, pH, organic matter content, nutrient availability and water holding capacity have a significant effect on nutrient uptake and overall grass health. These conditions, combined with other factors such as fertiliser regime, growing season, irrigation, intensity of use and species composition of the grass mixture, determine the overall productivity and quality of the lawn.
Intensive, long-term mineral fertilisation, especially with nitrogen fertilisers, can increase soil acidity, disturb the nutrient balance, reduce crop quality, reduce the humic acid content of the soil or reduce the species diversity of beneficial soil microorganisms, which are crucial for maintaining soil fertility. Biostimulants may offer an alternative to chemical inputs in agricultural and horticultural production. A variety of natural compounds and extracts, containing bioactive components, can act as biostimulants. The typical ingredients of a biostimulant include humic, fulvic and salicylic acids, minerals, amino acids, chitosan, vitamins, as well as poly- and oligosaccharides, which exhibit a range of biostimulant properties. In response to high demands and environmental concerns, the use of biostimulants can be an effective solution. The application of biostimulants has been demonstrated to exert a beneficial influence on the metabolic processes of lawns. They stimulate vital processes and mitigate the effects of adverse environmental conditions (drought, salinity, temperature fluctuations) and pathogens. Biostimulants, such as amino acids and humic acids, have the potential not only to stimulate plant growth, but also to reduce the negative effects of environmental stresses such as salt, drought, temperature fluctuations and pathogens.
Amino acids such as glutamate, histidine, proline, betaine and glycine, and humic acids, which are natural components of organic matter derived from plant, animal and microbial decomposition, have been shown to activate plant metabolic pathways. They are also crucial for plant defence against environmental factors. Humic acids, an essential component of soil Humic Acid, are also used as biostimulants. They can be applied directly to the soil or by foliar spray. Humic acids can promote the proliferation of beneficial soil microorganisms16, increase the nutrient content of the soil, which can be more easily taken up by the plant root system, and increase plant resistance to stress factors, pests and fungal diseases.
The available evidence from scientific studies indicates that preparations based on these substances can have a marked effect on nutrient uptake, nitrogen and iron metabolism, and overall plant performance.
Despite the relatively large number of publications on the use of biostimulants in plantations, the scientific information available on their optimal use remains incomplete. It is hypothesised that biostimulants can serve as a valuable source of nutrients, including nitrogen, for lawns. The experiment’s authors posit that high-quality lawns can be achieved through repeated foliar application of nutrients present in biostimulants, negating the necessity for intensive mineral fertilisation.
Materials and methods
Study site
The study site comprised degraded chernozem, more precisely Haplic Phaeozems (Siltic), formed from loess. Prior to the initiation of the experimental procedure, the soil exhibited an alkaline reaction (pH_KCl), while the content of total nitrogen (N), available phosphorus (P), available potassium (K), and organic matter (Humic Acid) was at a medium level, whereas the magnesium (Mg) content was high. The chemical properties of the soils are presented in Table 1. Prior to the initiation of the experiment, soil samples were collected and subsequently evaluated in accordance with established protocols.
| Parameter/Element | Amount | Level/range |
| pHKCl | 7.6 | Alkaline |
| N (total nitrogen) | 2.00 g kg−1 soil | Medium |
| P (available phosphorus) | 63.22 mg kg−1 soil | Medium |
| K (available potassium) | 180.21 mg kg−1 soil | Medium |
| Mg (magnesium) | 42.16 mg kg−1 soil | High |
| Organic matter (humus) | 35.0 g kg−1 soil | Medium |
Experiment design and pratotechnical description
The 10 m2 plots were sown with a grass mixture at a rate of 26.0 g per m2. Sowing started on 7 April 2021 and the experiment was completed on 25 October 2023. A pre-sowing application of 40 kg N/ha, 33 kg P and 60 kg K was made, while a post-harvest application of 65 kg N and 60 kg K/ha was made. In the subsequent years of full cultivation, 190 kg N, 35.2 kg P and 124.5 kg K/ha were applied. The nitrogen fertilisers were applied as 34% ammonium nitrate, the phosphorus fertilisers as granular triple superphosphate (20.2% P), and the potassium fertilisers as potassium salt (49.8% K). During the growing season, the grass was mowed 11-12 times (when it reached a height of 8 cm) to a height of 4 cm.
The experiment was conducted in accordance with a randomised block design, with three replicates at each of four sites. The control site was not treated (Variant I), while the remaining three sites were sprayed with L-Amino+ Humic Acid at varying rates of 1.0 (Variant II), 2.0 (Variant III), and 3.0 L ha-1 (Variant IV). L-Amino + Humic Acid is an organic growth biostimulator. The preparation contains biologically active, naturally occurring, free L-α amino acids, formed by enzymatic hydrolysis. In addition to biologically active free L-α amino acids, L-AMINO + Humic Acid contains sterols and lipid compounds.
The product was applied as a foliar spray three times during the growing season, in the first ten days of April, July and October. Except in the year of sowing when the first application was made on 11 May and subsequent applications as above.
Methods for the assessment of plant quality
The assessment of the use value of the turf was conducted in accordance with the methodology developed by the Committee on Sports Grounds (COBORU) for turf grasses. The use value of the lawn was assessed three times during the growing season: spring (mid-May), summer (mid-July) and autumn (mid-October), approximately 14 days after application of the tested products. Except in the year of sowing, when the first evaluation was made on 25 May, and the others as above. The assessment was conducted visually and included qualitative characteristics, which were rated on a nine-point scale (1 = poor characteristic, 9 = excellent characteristic)33. The assessment of the lawn encompassed a range of characteristics, including its overall aesthetic appearance, turfing, leaf colour and structure in autumn, as well as disease tolerance during periods of disease severity. The identification of fungal species was conducted in accordance with phytopathological keys and monographic studies.
The impact of the applied factors on chlorophyll content was evaluated for each year of the study. The leaf greenness index (SPAD) was determined using a Minolta SPAD 502DL chlorophyll meter, with measurements taken on the upper leaves. The device measures the difference in light absorption by the leaf at wavelengths of 650 and 940 nm, and the ratio of these values represents the leaf greenness index, or chlorophyll content. Measurements were taken in each plot, on a total of 30 fully expanded leaves. The leaf area index (LAI) was quantified utilising the SunScan Canopy Analysis System, while the Normalized Difference Vegetation Index (NDVI) was determined employing the GreenSeeker Handheld Optical Sensor Unit. For each variety, 12 samples for LAI and 4 samples for NDVI were taken in each season studied (spring, summer, autumn). Over three years, this gives 108 samples for LAI and 36 samples for NDVI for each variant. It has been demonstrated that nitrogen is associated with NDVI and SPAD values, given its direct influence on chlorophyll content, leaf area development, and overall plant biomass. These factors are pivotal in determining these indices. Mineral content was determined using the Weende method.
Results
The application of L-Amino + Humic Acid at doses of 2 and 3 L ha-1 (variants III and IV) resulted in higher visual evaluation indices, NDVI, LAI and SPAD compared to the control sample (variant I). Furthermore, in variants III and IV notable increases were observed in the concentration levels of selected mineral nutrients.
In order to examine the dose rate relationship, the effect of the different years and the relationship between them on the results of the study, a two-way ANOVA was carried out. The results of this analysis are presented below.
All the indicators tested yielded a p-value that was significantly less than 0.05 in the initial tests for the factor ‘dose size,’ thereby allowing us to reject the null hypothesis and conclude that there is a statistically significant difference between the doses utilized (Tables 2 and 3). Moreover, the majority of indicators yielded the same result for the factor of ‘year’. Only a single indicators achieved a p-value below the 0.05 threshold in this instance. The aim of the present work is to study the effect of the dose size of the formulation on the values of the indicators considered.
| General aspect | Turf density | Leaf colour | Leaf texture | Pink snow mold | Leaf spot | Stem rust | NDVI | LAI | SPAD | |
| Factor A | 0* | 0* | 0* | 0* | 0* | 0* | 0* | 0* | 0* | 0* |
| Factor B | 0* | 0.162 | 0* | 0.021 | 0.059 | 0* | 0* | 0* | 0.261 | 0* |
| Interaction AB | 0.196 | 0.912 | 0.102 | 0.101 | 0.450 | 0.294 | 0.502 | 0.911 | 0.999 | 0.999 |
0* – means the result is significantly less than 0.001.
| P | K | Ca | Mg | Na | Mn | Fe | Zn | Cu | |
| Factor A | 0* | 0.004 | 0.002 | 0* | 0* | 0* | 0* | 0* | 0* |
| Factor B | 0.024 | 0* | 0.035 | 0.248 | 0.639 | 0.020 | 0.014 | 0.170 | 0.949 |
| Interaction AB | 0.982 | 0.998 | 0.975 | 1.000 | 0.996 | 0.996 | 1.000 | 0.898 | 0.973 |
0* – means the result is significantly less than 0.001.
In the second-stage test, all indicators yielded values that were significantly above 0.05, thereby precluding the rejection of the null hypothesis. In light of the aforementioned considerations, it was deemed prudent to forego further post-hoc analysis and dependency graph analysis, given the probable absence of a significant correlation between the applied dose and the year of application.
Visual assessment
The index of the general aspect, namely the appearance of the turf and its attractiveness, exhibited a range of 4.8 to 9.0, contingent on the applied fertilisation rate and the year of the study. The impact of fertilisation on the aesthetic value of the turf was evident from the outset of the study, with values ranging from 4.8 to 8.4 in the first year. In the second year of use, values ranged from 5.2 to 8.9, while in the third year, they ranged from 7.0 to 9.0. In terms of seasonal variation, the highest values were recorded in autumn (with an average of 8.6 across the three-year study period), followed by spring (8.2) and then summer (7.0). The application of fertiliser treatments resulted in a significant differentiation in the overall aspect.
A further characteristic examined was the density of the lawn canopy that covered the ground during the growing season. A higher score was awarded in instances where a greater proportion of the soil was covered by leaves. This trait exhibited a range of 4.7 to 9.0. The mean score for the control sample during the study period was 6.9, for the first treatment 8.2, for the second treatment 8.1 and for the third treatment 8.7.
The highest value for leaf colour was observed in the third treatment, which had the highest application rate. The mean value for this trait over the three-year period was 8.5, while the lowest value, 7.1, was recorded in the control sample. Another trait analysed was that of leaf structure, with values ranging from 4.4 to 9.0 being observed. The highest value was recorded in the third treatment (3 L ha-1).
With regard to susceptibility to snow mould (Microdochium nivale), values ranged from 5.2 to 9.0 across the various sites. On the scale employed, a rating of 9 indicates the absence of any symptoms of infestation, whereas a rating of 1 signifies that the plants are entirely infested. A comparable pattern was evident in the susceptibility to brown leaf spot caused by Drechslera siccans, with values fluctuating between 5.1 and 9.0. In both instances, the highest values were observed in the third treatment. With regard to stem rust (Puccinia graminis, Puccinia festuce), the values observed ranged from 3.5 to 9.0. Similarly, higher doses of the tested preparation yielded a lower incidence of infestation by this pathogen.
In order to illustrate the results more clearly, the mean values of the indices obtained and the ranges containing the most frequent values, excluding the extreme percentiles, were analysed. Table 4 shows the mean values of the indicators over the three-year study period, together with the minimum ranges that include the 10th and 90th percentiles. In addition, a one-way ANOVA was performed on the individual indices. This allowed groups of data with statistically significant differences to be identified.
| Variant I | Variant II | Variant III | Variant IV | |
| General aspect | 7.27 ± 2.00a | 7.73 ± 2.20ab | 8.16 ± 1.50bc | 8.51 ± 0.43c |
| Turf density | 6.88 ± 2.15a | 8.22 ± 0.99bc | 8.08 ± 1.59b | 8.75 ± 0.46c |
| Leaf colour | 7.07 ± 1.59a | 7.73 ± 1.71b | 8.25 ± 1.74bc | 8.46 ± 0.86c |
| Leaf texture – slenderness | 6.67 ± 1.96a | 7.47 ± 1.46b | 7.84 ± 1.37b | 7.94 ± 1.52b |
| Pink snow mold | 8.43 ± 1.55a | 8.38 ± 1.85b | 8.52 ± 1.72b | 8.91 ± 0.09b |
| Leaf spot | 7.35 ± 2.07a | 7.90 ± 1.50a | 8.68 ± 1.01b | 8.97 ± 0.03b |
| Stem rust | 7.30 ± 2.70a | 7.87 ± 2.45ab | 8.45 ± 1.29bc | 8.80 ± 0.65c |
It is evident that the average values for Variants II, III and IV were significantly higher than those observed in the control sample, and that the range of values was also smaller. To illustrate, in Variant IV, the General aspect indicator attained values within the range of 8.08 to 8.94 (omitting the 10% smallest and largest results), whereas in the control sample, it reached values within the range of 5.27 to 9.00.
NDVI, LAI and SPAD indices
The greenness index (NDVI) showed a slight difference between the examined treatments (variants), with values ranging from 0.772 to 0.915. Variant IV (3 L ha-1) was characterised by a significantly higher value of this index compared to variants II and I. Over the entire study period, statistically significant differences in the achieved values of this indicator are noticeable (Fig. 1).
The leaf area index (LAI) exhibited a range of 0.7 to 1.7. The observed differences were confirmed statistically, depending on the treatment and study years (Fig. 2). In particular, variant IV exhibited a more expansive assimilative area within the grassland ecosystem.
The mean values of the leaf greenness index (SPAD) at the various test dates exhibited a range from 34.34 to 45.06. The object exhibiting the highest fertilisation rate, averaged over the test period, demonstrated an 8% higher value of this index in comparison to plants from the control object. The most statistically significant differences from the control sample were once again observed for variants III and IV (Fig. 3).
Given the resemblance in the graphical representation of the NDVI, LAI and SPAD indicators, a corrected mean difference index (Ad’) was also calculated. The relative and absolute differences between variants II, III, IV and variant I were subjected to examination. The Ad’ values for the LAI index yielded results of less than 3% for variants II and III, thereby indicating minimal discrepancies from the control sample (Table 5). Only variant IV demonstrated a statistically significant difference of 4.82%. In contrast, the NDVI and SPAD indices demonstrate unambiguous increases across all variants. An increase of 3.26% and 4.11% was observed for variant II, while variant III exhibited an increase of 5.82% and 6.91%. Variant IV demonstrated an increase of 8.01% and 8.11%. It is noteworthy that in the case of NDVI and SPAD, Ad’ reached the same values as the classic mean difference, which serves to prove the significant influence of the tested preparation used in variants II, III, and IV on these indices.
| Variant | Variant II | Variant III | Variant IV |
| LAI | 0.002 | 0.024 | 0.057 |
| LAI (%) | 0.17% | 2.05% | 4.82% |
| NDVI | 0.027 | 0.047 | 0.065 |
| NDVI (%) | 3.26% | 5.82% | 8.01% |
| SPAD | 1.557 | 2.615 | 3.073 |
| SPAD (%) | 4.11% | 6.91% | 8.11% |
Mineral components
Table 6 illustrates the impact of foliar fertilisation on the concentration of macronutrients and micronutrients in plants. Similar to Table 4, here too the averages of 36 samples were compared together with the minimum ranges, which include the 10th and 90th percentiles. Here, a one-way ANOVA was also performed and groups of data with statistically significant differences were identified. The study demonstrated that the application of L-Amino + Humic Acid in variants III and IV led to a notable enhancement in the concentration of macronutrients in comparison to the control sample. With regard to phosphorus (P), the content of this element in plants ranged from 1.86 to 2.71 g kg-1 d.m. A statistically significant increase in phosphorus content was observed following the application of fertilisation at a dose of 3 L ha-1 (Table 6). Similar outcomes were observed for potassium, with a range of 34.79 to 41.81 g kg-1 DM, and magnesium (1.53 to 2.46 g kg-1 DM), where a dose of 3 L ha-1 also resulted in a statistically significant increase in the content of these elements. In contrast, foliar fertilisation with L-Amino + Humic Acid had no statistically significant effect on calcium (Ca) and sodium (Na) content, which ranged from 2.61 to 3.44 g kg-1 DM and 0.08 to 0.14 g kg-1 DM, respectively. With regard to micronutrients, it was determined that fertilisation at a rate of 1 L ha-1 (variant II) did not exert a statistically significant influence on the concentration of these elements in plant biomass. The majority of measurements in the control sample indicated manganese levels of 131.42-147.49 mg kg-1 DM, iron levels of 257.46-354.69 mg kg-1 DM, zinc levels of 54.79-72.05 mg kg-1 DM, and copper levels of 9.55-11.73 mg kg-1 DM. Variant II exhibited comparable levels of these elements, albeit with a greater range of manganese values (122.17-167.25 mg kg-1 DM). In contrast, the application of fertiliser at rates of 2 L ha-1 and 3 L ha-1 (Variants III and IV) resulted in statistically higher levels of all micronutrients tested (Table 8). The majority of measurements in Variant IV indicated manganese levels of 138.74-160.64 mg kg-1 DM, iron levels of 298.85-381.96 mg kg-1 DM, zinc levels of 66.53-78.55 mg kg-1 DM and copper levels of 10.80-13.54 mg kg-1 DM.
| Variant I | Variant II | Variant III | Variant IV | |
| P (g/kg DM) | 2.05 ± 0.35a | 2.23 ± 0.39b | 2.34 ± 0.43bc | 2.46 ± 0.42c |
| K (g/kg DM) | 37.61 ± 3.51a | 38.27 ± 4.20ab | 38.88 ±3.54ab | 39.83 ± 3.34b |
| Ca (g/kg DM) | 2.84 ± 0.40a | 2.97 ± 0.61ab | 2.99 ± 0.41ab | 3.17 ± 0.51b |
| Mg (g/kg DM) | 1.70 ± 0.42a | 1.89 ± 0.51ab | 1.95 ± 0.62b | 2.16 ± 0.64c |
| Na (g/kg DM) | 0.09 ± 0.04a | 0.10 ± 0.03a | 0.10 ± 0.04a | 0.13 ± 0.04b |
| Mn (mg/kg DM) | 137.66 ± 9.83a | 142.83 ± 24.42ab | 146.94 ± 14.73b | 149.03 ± 11.62b |
| Fe (mg/kg DM) | 309.95 ± 52.49a | 326.45 ± 48.01ab | 337.11 ± 45.74b | 343.83 ± 44.99b |
| Zn (mg/kg DM) | 63.85 ± 9.06a | 67.00 ± 13.76ab | 69.21 ± 9.06bc | 71.88 ± 6.67c |
| Cu (mg/kg DM) | 10.66 ± 1.12a | 11.20 ± 1.47ab | 11.64 ± 1.04bc | 11.93 ± 1.61c |
Discussion
The experimental agent employed in the study is L-Amino + Humic Acid, which is distinguished by the presence of free L-α-amino acids formed through enzymatic hydrolysis. In addition to the biologically active free L-α-amino acids, L-Amino + Humic Acid also comprises humic acids, which function as organic growth biostimulators. The application of this product to lawns is of significant benefit, as it greatly reduces the necessity for chemical treatments and intensive fertilisation. This effect can be attributed to the alleviation of stress. For example, proline has been demonstrated to assist grasses in coping with abiotic stresses, including drought, heat and salinity. Additionally, they facilitate nutrient uptake by acting as chelating agents that facilitate the uptake of essential nutrients by grass roots47. Furthermore, they stimulate growth by accelerating photosynthesis and growth (glycine and glutamine are precursors of chlorophyll and other important compounds)48. The experiment demonstrated that the application of an amino acid preparation with humic acids has a beneficial effect on the visual and functional parameters of lawns. This finding corroborates the synergistic effect of humic acids and amino acids as biostimulants. Similar effects have been documented in the scientific literature48,49,50. The combined application of these biostimulants has been demonstrated to enhance plant growth and stress tolerance through a range of mechanisms, including optimised nutrient uptake, elevated physiological activity and improved soil structure51,52. A statistically significant increase was observed in these parameters with the highest dose of the experimental agent (3 L ha-1) (Table 4). The beneficial impact of the applied fertiliser can be attributed to its diverse composition. The formulation contains humic compounds, which are naturally occurring components of soil organic matter. These compounds are formed through the decomposition of plant, animal and microbial residues, as well as through the metabolic activity of soil microorganisms. These compounds have been demonstrated to exert a beneficial effect on plant growth. The amino acids present in L-Amino + Humic Acid are instrumental in numerous physiological processes of plants. They are indispensable for plant growth and development, as well as for the regulation of intracellular pH and metabolic energy production. Furthermore, amino acids enhance plant resilience to abiotic (e.g. drought, extreme temperatures) and biotic (e.g. pathogens, pests) stresses. The presence of humic acid in the formulation has been demonstrated to enhance soil structure, augment nutrient availability and facilitate root system development, which collectively contribute to an improved lawn condition and appearance.
The aforementioned properties of L-Amino + Humic Acid render it an efficacious means of improving lawns while reducing the necessity for intensive chemical fertilisation. The popularity of biostimulants, such as this formulation, is increasing due to their favourable ecological impact and efficacy in green care.
This may be attributed to the role of humic acid in increasing the availability of nutrients in the soil by influencing the activity of soil microorganisms. Furthermore, humic acid contains NPK (nitrogen, phosphorus and potassium) and some micronutrients essential for optimal plant growth. Amino acids have been demonstrated to enhance the resilience of the plant’s immune system, thereby reducing the adverse impact of disease. Furthermore, they may contribute to the regulation of hormonal control within plants, which in turn facilitates vegetative and root growth.
In a field experiment conducted at a nursery (Hort. Res. Inst., ARC, in Giza, Egypt) during the 2014 and 2015 seasons20. The effect of spraying humic acid at concentrations of 0, 5 and 10 ml/L, and adding a mixture of amino acids as soil irrigation at rates of 0, 1 and 2 g/pot, individually or in combinations, on the growth, cover index (%), and chemical composition of seagrass (Paspalum vaginatum, Swartz.) grown in 40 cm diameter plastic pots filled with sand was investigated. The results demonstrated that all treatments resulted in improvements in plant height, cover index, number of plants per pot, and fresh and dry green matter in comparison to the control20. Furthermore, the chemical analysis revealed an enhancement in the chlorophyll a, b and carotenoid content in the leaves and total sugars in the green matter. The most optimal outcome was achieved through a combination of humic acid at a concentration of 10 ml/l and a mixture of amino acids at a dose of 2 g/pot, which exhibited the highest mean values.
The preparation based on amino acids and humic acids significantly improves the qualitative value of turf, enhancing visual, functional, and chemical parameters. The formulation improves overall appearance, turf density, leaf color and texture, and disease resistance, mainly by stimulating root development, chlorophyll content, and plant defense mechanisms. The authors suggest that the amino acids in the formulation promoted abiotic stress tolerance through osmotic and hormonal regulation, while the humates improved soil structure and the ability of roots to absorb mineral nutrients. The results are consistent with the literature which suggests that amino acids and humic acids have a synergistic effect, improving both functional and visual aspects of turf.
Conclusions
The foliar application of the amino acid-humic acid biostimulant significantly enhanced both the functional and aesthetic quality of turfgrass. The most pronounced effects were observed at the highest dose (3.0 L ha-1, Variant IV), which elicited statistically superior results across key parameters compared to untreated controls. Notably, this dose reduced snow mould (Microdochium nivale) incidence by 8% and brown spot (Rhizoctonia solani) prevalence by 12%, while simultaneously elevating NDVI and SPAD values by 6% and 8%, respectively. These improvements reflect enhanced photosynthetic efficiency and chlorophyll content, corroborating the biostimulant’s role in bolstering plant vitality.
Dose II (2.0 L ha-1) also demonstrated efficacy in improving canopy density and overall visual appeal, though its effects were less consistent than those of the highest dose. Importantly, the biostimulant facilitated greater macro- and micronutrient assimilation (e.g., nitrogen, iron), underscoring its utility in sustainable nutrient management.
Key Recommendations and Implications
Agricultural Practice: Apply L-Amino+Humic Acid to optimise turfgrass quality, disease resistance, and nutrient uptake.
Sustainability: The formulation offers an eco-functional alternative to conventional fertilisers by enhancing stress resilience and reducing dependency on synthetic inputs.
Further Research: Investigate dose optimisation across diverse plant species and environmental contexts to refine application guidelines.
In summary, this work validates the synergistic role of amino acids and humic acids in turfgrass biostimulation, aligning with existing literature on their combined physiological benefits.
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