Lawn Bonitation Value as a Function of Glycine-Complexed Iron Formulation Application

Abstract

The research carried out at the Experimental Station of the University of Agriculture in Krakow aimed to assess the utility value of the turf of a lawn sown with the “Super Trawnik” lawn mixture. The experimental factor was spraying the turf with an amino acid preparation in the form of the AMINO ULTRA Fe-20 fertilizer in three doses: 0.3, 0.5, and 0.7 dm³·ha⁻¹. The iron in the tested preparation is complexed with glycine, a natural plant transporter of microelements. A total of 60 g (variant I), 100 g (variant II), and 140 g (variant III) Fe·ha^–1 were applied accordingly. The assessment of the examined features was performed based on a nine-point scale. The highest aesthetic and functional values were characteristic of the grass in sites with the highest dose of complexed iron (variant III). The applied fertilization reduced the occurrence of plant diseases. Compared to the plants from the control groups, infestation with snow mold was 14% lower, and the occurrence of brown leaf blotch was lower by 16%. Satisfactory results were also obtained at the sites where the preparation was applied at a dose of 0.5 dm³·ha⁻¹ (variant II). At these sites, a higher, more favorably assessed compactness and higher resistance to snow mold and brown leaf spots were found compared to the plants from the control groups. The major finding of this work is that applying a higher dose of foliar iron fertilizer complexed with glycine allows one to obtain a high-quality lawn in terms of visual and functional features.

1. Introduction

Grass species intended for lawn use should be characterized by high aesthetic values, uniform turf cover, and slow regrowth after mowing [1,2]. One of the essential features of lawn evaluation is the overall aesthetic aspect [3,4]. The assessment of this feature’s value and that of the regrowth rate constitute decisive factors for qualifying a variety of lawn grasses. The assessment of the general aspect is highly correlated with other traits, such as the turf, regrowth rate, or leaf perfection [4,5].

One of the many factors significantly influencing the appearance of a lawn is its degree of fertilization with macro- and microelements. An essential nutrient for all organisms is iron (Fe) [6]. Iron plays a vital role in plants, and it participates in many physiological processes, including its role as an activator of the biosynthesis of chlorophyll and many proteins [7,8,9]. In addition, it affects the proper growth and development of plants and ensures better crop quality parameters.

In the case of lawn grasses, iron primarily affects a lawn’s uniform and intense green color [10]. Iron deficiency leads to a reduction in the content of chlorophyll, a pigment that gives the grass its green color. Therefore, iron deficiency manifests as chlorotic symptoms (yellowing), which negatively affect a lawn’s visual qualities. Additionally, iron deficiency can make a lawn less frost-resistant and more dehydrated in winter. It may be necessary to apply the essential minor nutrient Fe to turfgrass growing in soils with less than 2 ½ ppm of extractable Fe [11]. An iron preparation used on a lawn is also an effective way to eliminate moss from the turf. The preparation not only eliminates the moss problem but also prevents its occurrence in the future.

Iron deficiency in plants may result from the element’s deficiency in the soil; alternatively, although the Fe content in the soil may be high, the available form of Fe²⁺ may be low. This is because a large part of it is associated with soil components [7,12], creating insoluble Fe³⁺ bonds. Especially high pH soils are usually poor in the available form of Fe²⁺ [8]. Iron availability is also lower in heavy, compact, and poorly permeable soils. Unfavorable humidity conditions, such as heavy rainfall or excessive watering, can also contribute to iron chlorosis on a lawn. Therefore, when there are unfavorable conditions for plant growth, and during the critical stages of this process, it becomes advisable to use appropriate macro- and microelements. The application of foliar iron (Fe) sprays is a standard method of correcting an Fe deficiency in crops [13]. Hence, this study aimed to evaluate the effect of the foliar application of glycine-complexed iron on the utility value of lawn turf under high pH and heavy soil conditions.

2. Materials and Methods

2.1. Study Site and Soil Conditions

The research was carried out in the years 2020–2021 at Prusy Experimental Station (50°07′ N, 20°05′ E) of the University of Agriculture in Krakow, Poland, on degraded chernozem made from loess (on Haplic Phaeozem (Siltic) soil developed from loess). The chemical properties of the soil were as follows: pH_KCl (soil reaction)-7.6 (determined by the potentiometry method in 1M KCl solution); N (total nitrogen)-2.47 g·kg⁻¹ (d.m., determined by the Kjedahl method); P (available phosphorus)-64.35 mg·kg⁻¹ (d.m., determined by the spectrophotometric method); K (available potassium)-147.23 mg·kg⁻¹ (d.m., determined by the Egner–Riehm method); and Mg (magnesium)-41.12 mg·kg⁻¹ (d.m., determined by the FAES atomic emission spectrometry method). The evaluation of these parameters was performed in accordance with the methodology in [14].

2.2. Experimental Design

The experiment was designed following the agrotechnical recommendations for establishing lawns. The utility value of the “Super Trawnik” lawn mixture was assessed in the experiment. The tested mixture consisted of perennial ryegrass (Lolium perenne L.)—Stadion 12%, perennial ryegrass (Lolium perenne L.)—Poppies 30%, red fescue (Festuca arundinacea Schreb.)—Fawn 20%, red fescue (Festuca rubra L.)—Aniset 25%, and red fescue (Festuca rubra L.)—Reverent 13%. On 10 m² plots, the lawn mixture was sown at a density of 260.0 g·m⁻². The sowing date was April 4, 2020. In the year of sowing, 65 kg N·ha⁻¹, 33 kg P, and 124.5 kg K·ha⁻¹ were used for fertilization, while in the years of full use, 190 kg N ha⁻¹, 35.2 kg P, and 124.5 kg K ha⁻¹ were used. Nitrogen fertilizers were used in the form of 34% (N) ammonium nitrate, phosphorus-triple-granulated superphosphate (20.2% P), and potassium in the form of potassium salt (49.8% K). The experimental factor was spraying the lawn with the amino acid preparation in the form of AMINO ULTRA Fe-20 fertilizer in three doses: 0.3, 0.5, and 0.7 dm³·ha⁻¹. The iron in this preparation was complexed with a natural plant transporter of microelements: glycine. This preparation contained 200 g Fe∙kg⁻¹ (20%). Therefore, doses of 60 g Fe·ha^–1 were applied accordingly (variant I), along with 100 g Fe·ha^–1 (variant II) and 140 (variant III) g Fe·ha^–1.

The evaluated iron fertilizer is a commercial fertilizer produced by INTERMAG sp.z o.o. in Olkusz (Poland). This preparation was applied by foliar absorption three times during the growing season in the first ten days of April, June, and August. On average, the lawns were mowed 10–11 times to a height of 4 cm during the growing season. Mowing was carried out when the plants reached a height of 8 cm. The number of and grass height in mowing procedures were in line with COBORU (Research Centre for Cultivar Testing, Slupia Wielka, Poland) recommendations for “recreational” mixes [15,16].

2.3. Weather Conditions

The weather conditions were generally favorable for the growth and development of lawn grasses. During the growing season (April–September), the precipitation amounted to 385.2 mm in 2020 and 633.0 mm in 2021 (Figure 1). The average air temperatures during the research period were 16.0 °C (2020) and 15.3 °C (2021). During more prolonged periods of drought, irrigation (sprinkling) was applied systematically at 3-day intervals in the amount of about 10 dm⁻³∙m² (rainfall 10 mm) of water at a time.

2.4. Assessment of Lawns

The valorization of the lawn turf was performed based on the valuation method according to [15] and the visual and functional method according to [17]. The values in use included the following parameters: general aspect (Ao), compactness (D), color (C), overwintering (O), and susceptibility to diseases (SD). In assessing lawn grass infestation, keys and graphic scales were used. The results of the observations were determined on a 9-point scale, in which individual numbers indicate the conventional level of intensity of a given phenomenon. The number 9 means the best grade, and the number 1 means the worst [15]. A similar methodology was used to assess disease susceptibility (snow mold—Microdochium nivale and brown leaf spot—Drechslera siccans). Lawns were not infected with pathogens. The diseases appeared on their own, under the influence of the weather conditions and the use of fertilization. The evaluation was made on a 9-point scale: the number 9 means the best grade (no pathogen infection), while the number 1 is the worst (complete pathogen infection). In each year, after the completion of the research, the lawn turf functional value (Wum) was calculated according to the following formula:

$$Wum=0.34·\mathrm{Ao}+0.33·\mathrm{D}+0.33·\mathrm{C}$$

(1)

where

Wum—turf functional value;

Ao—overall aspect of turf;

D—lawn compactness;

C—lawn color.

In individual years of the experiment, the effect of foliar fertilization on the content of chlorophyll was investigated. The leaf greenness index (SPAD) was measured with a Minolta SPAD 502DL chlorophyll meter (Minolta, Osaka, Japan) applied to the upper leaves. Measurements were made on each plot on thirty fully developed leaves. The content of minerals was determined using the Weende method [14].

2.5. Statistical Analysis

In order to show statistically significant differences between the fertilization variants, a one-way analysis of variance (ANOVA) was performed together with the Tukey HSD post hoc test. Statistical analysis was performed in the Statistica 13.0 (StatSoft—DELL Software, Round Rock, TX, USA) program at the significance level of p = 0.05.

3. Results

Table 1. Profitability value (p-value) for the parameters evaluated (results of two-way ANOVA).

Parameter	Year (n)	Dose (t)	Interaction (n∙t)
Overall Aspect (Spring)	0.0206	0.0000	0.9765
Overall Aspect (Summer)	0.0101	0.0000	0.9732
Overall Aspect (Autumn)	0.0356	0.0000	0.9545
Compactness (Spring)	0.0225	0.0000	0.9954
Compactness (Summer)	0.0094	0.0000	0.9868
Compactness (Autumn)	0.0161	0.0000	0.9763
Overwintering	0.0090	0.0000	0.9978
Leaf Color in Autumn	0.0002	0.0000	0.9846
Leaf Structure (Fineness)	0.0001	0.0000	0.9978
Susceptibility to diseases (Snow mold)	0.0007	0.0000	0.2251
Susceptibility to diseases (Brown leaf spot)	0.0022	0.0000	0.0194
Leaf Greenness Index (Spring)	0.0000	0.0043	0.9980
Leaf Greenness Index (Summer)	0.0000	0.0003	0.9862
Leaf Greenness Index (Autumn)	0.0000	0.0053	0.9849
P	0.8768	0.0228	0.8621
K	0.0000	0.1675	0.8150
Na	0.0017	0.5479	0.6096
Ca	0.1417	0.6049	0.8681
Mg	0.1806	0.2349	0.9825
Mn	0.1188	0.8092	0.9994
Fe	0.2583	0.7087	0.9367
Zn	0.0005	0.0205	0.7489
Cu	0.2438	0.4454	0.5822

shows the profitability value (p-value) results for two variables: the year (n), the dose of glycine-complexed iron fertilizer (t), and their interaction (n ∙ t). The obtained results allowed us to exclude the hypothesis regarding the significance of the interaction of both factors; only in the case of the susceptibility to diseases (Brown leaf spot) parameter did the interaction of the dose of iron fertilizer complexed with glycine and the year of the study show statistical significance (p-value = 0.0194). In other cases, the interaction of both factors was statistically insignificant; the p-value ranged from 0.2251 to 0.9994. In the case of the parameters responsible for the main and minor characteristics of lawns, it was observed that both the dose of glycine-complexed iron fertilizer and the growing season statistically affected their fundamental characteristics. Statistical analysis also showed that in the case of micronutrients and macroelements, the growing season statistically affected the content of Na, Zn, and K. The iron fertilizer dose statistically influenced the content of P and Zn.

Table 2. Scores for main lawn properties depending on fertilization variant.

Fe Dose	Year	Overall Aspect			Compactness
		Spring	Summer	Autumn	Spring	Summer	Autumn
Control	2020	6.27 ± 0.06	5.27 ± 0.06	7.37 ± 0.06	7.03 ± 0.06	7.37 ± 0.06	7.37 ± 0.06
	2021	6.47 ± 0.25	5.43 ± 0.21	7.63 ± 0.31	7.27 ± 0.25	7.67 ± 0.35	7.67 ± 0.35
	2020–2021	6.37 b ± 0.20	5.35 a ± 0.16	7.50 a ± 0.24	7.15 b ± 0.21	7.52 a ± 0.28	7.52 a ± 0.28
Variant I: 60 g	2020	7.60 ± 0.10	5.40 ± 0.10	7.60 ± 0.10	7.50 ± 0.10	7.60 ± 0.10	7.80 ± 0.10
	2021	7.80 ± 0.30	5.63 ± 0.21	7.87 ± 0.32	7.73 ± 0.31	7.83 ± 0.31	8.03 ± 0.31
	2020–2021	7.70 c ± 0.23	5.52 a ± 0.19	7.73 a ± 0.26	7.62 c ± 0.24	7.72 ab ± 0.24	7.92 ab ± 0.24
Variant II: 100 g	2020	8.17 ± 0.06	6.60 ± 0.10	8.20 ± 0.10	7.93 ± 0.12	7.97 ± 0.15	8.17 ± 0.12
	2021	8.47 ± 0.35	6.83 ± 0.21	8.47 ± 0.35	8.13 ± 0.31	8.27 ± 0.25	8.47 ± 0.35
	2020–2021	8.32 a ± 0.28	6.72 b ± 0.19	8.33 b ± 0.27	8.03 a ± 0.23	8.11 bc ± 0.25	8.32 b ± 0.29
Variant III: 140 g	2020	8.50 ± 0.10	8.10 ± 0.10	8.70 ± 0.26	8.20 ± 0.10	8.37 ± 0.15	8.67 ± 0.15
	2021	8.73 ± 0.31	8.37 ± 0.35	8.83 ± 0.29	8.47 ± 0.35	8.70 ± 0.36	8.87 ± 0.23
	2020–2021	8.62 a ± 0.24	8.23 c ± 0.27	8.76 c ± 0.26	8.33 a ± 0.27	8.53 c ± 0.31	8.77 c ± 0.21
Standard Deviation		0.91	1.12	0.57	0.51	0.47	0.53
Variation Coefficient, %		11.8	18.5	6.97	6.51	5.91	6.52

The same markings (a–c) mean no statistically significant changes (p ≥ 0.05).

shows the scores for main lawn properties depending on the fertilization variant. In the case of the overall aspect, it can be noticed that increasing the dose of glycine-complexed iron increased the corresponding lawn’s overall aspect parameter; this trend was noticed in all seasons. Nevertheless, the overall aspect assessment varied between seasons. The lowest values were observed in summer; this season was characterized by the most significant variation in the parameter. The control sample (a lawn plot without an iron preparation) showed that, on average, over two years, the overall aspect’s mean value was 5.35 ± 0.16 and 5.52 ± 0.19 in variant I of fertilization (a change that is statistically insignificant). Only increasing the dose to 100 g and 140 g resulted in a significant increase in the overall aspects of lawns to 6.72 ± 0.19 and 8.23 ± 0.27, respectively. The same trend was observed for autumn, where the use of 60 g of glycine-complexed iron fertilizer increased the overall aspect from 7.50 ± 0.24 to 7.73 ± 0.26, without statistical significance, but the doses of 100 g and 140 g of the fertilizer resulted in a significant increase in the overall aspect (8.33 ± 0.27 and 8.76 ± 0.26, respectively). In the case of spring, the situation was slightly different. For the control sample, the average overall aspect score of 6.37 ± 0.20 was noted. The application of variant I of fertilization resulted in a significant increase in the parameter (7.70 ± 0.23). Further increasing the dose of glycine-complexed iron fertilizer also significantly increased the overall aspect (8.32 ± 0.28 and 8.62 ± 0.24 for variants II and III, respectively), but between these variants, the change was statistically insignificant.

Compactness, in contrast to the overall aspect, showed a lower parameter variability over the seasons. Lower values of the coefficient of variation were also obtained. It was observed that increasing the dose of glycine-complexed iron fertilizer had a positive effect on the compactness of the lawns, increasing their rating. In the case of spring, fertilization variant I caused a significant increase in the compactness result (an increase from 7.15 ± 0.21 to 7.62 ± 0.24). Further increasing the dose also significantly increased the compactness in the case of variant I and the control (8.03 ± 0.23 and 8.33 ± 0.27 for 100 g and 140 g). However, the difference between variants II and III was statistically insignificant. During summer and autumn, the applied fertilization variant I influenced the differences between the variants, but only variant II resulted in a significant increase (8.11 ± 0.25 and 8.32 ± 0.29 for summer and autumn, respectively) compared to the control (7.52 ± 0.28 and 7.52 ± 0.28 for summer and autumn, respectively). Increasing the fertilizer dose to 140 g also affected the compactness of the lawns, allowing for scores of 8.53 ± 0.31 and 8.77 ± 0.21 for summer and autumn, respectively.

Table 3. Scores for minor lawn properties depending on fertilization variant.

Fe Dose	Year	Overwintering	Leaf Color in Autumn	Leaf Structure (Fineness)	Susceptibility to Disease
					Snow Mold	Brown Leaf Spot
Control	2020	6.80 ± 0.10	6.07 ± 0.06	6.07 ± 0.06	7.60 ± 0.10	7.60 ± 0.10
	2021	7.07 ± 0.25	6.47 ± 0.25	6.47 ± 0.25	8.10 ± 0.36	8.10 ± 0.36
	2020–2021	6.93 a ± 0.23	6.27 c ± 0.27	6.27 a ± 0.27	7.85 a ± 0.36	7.85 b ± 0.36
Variant I: 60 g	2020	7.03 ± 0.06	7.30 ± 0.10	6.27 ± 0.06	8.30 ± 0.10	8.10 ± 0.10
	2021	7.27 ± 0.25	7.73 ± 0.31	6.67 ± 0.25	8.83 ± 0.29	8.63 ± 0.31
	2020–2021	7.15 ab ± 0.21	7.52 a ± 0.31	6.47 ab ± 0.27	8.57 b ± 0.35	8.37 c ± 0.36
Variant II: 100 g	2020	7.27 ± 0.06	7.50 ± 0.10	6.60 ± 0.10	8.70 ± 0.26	9.00 ± 0.00
	2021	7.53 ± 0.31	7.97 ± 0.35	7.03 ± 0.31	8.93 ± 0.12	9.00 ± 0.00
	2020–2021	7.40 b ± 0.25	7.73 ab ± 0.34	6.82 b ± 0.31	8.82 b ± 0.22	9.00 a ± 0.00
Variant III: 140 g	2020	7.80 ± 0.10	7.80 ± 0.10	7.10 ± 0.10	8.90 ± 0.10	9.00 ± 0.00
	2021	8.03 ± 0.31	8.30 ± 0.36	7.53 ± 0.31	9.00 ± 0.00	9.00 ± 0.00
	2020–2021	7.92 c ± 0.24	8.05 b ± 0.36	7.32 c ± 0.31	8.95 b ± 0.08	9.00 a ± 0.00
Standard Deviation		0.43	0.76	0.49	0.51	0.55
Variation Coefficient, %		5.87	10.2	7.3	5.92	6.38

The same markings (a–c) mean no statistically significant changes (p ≥ 0.05).

shows the scores for the minor lawn properties depending on the fertilization variant. Five properties were evaluated: overwintering, the leaf color in autumn, leaf structure (fineness), and susceptibility to diseases (snow mold and brown leaf spot). In the case of overwintering, it was observed that applying a higher dose of glycine-complexed iron fertilizer resulted in the better overwintering of the lawns. Variants II and III resulted in significantly better overwintering (7.40 ± 0.25 and 7.92 ± 0.24, respectively) compared to the control (6.93 ± 0.23). The leaf-color-in-autumn parameter showed a similar upward trend. The result from the control sample (6.27 ± 0.27) was significantly lower than for the fertilization variants used. For variants I, II, and III, the following values were obtained: 7.52 ± 0.31, 7.73 ± 0.34, and 8.05 ± 0.36. In terms of the leaf structure (fineness), the highest results were obtained for fertilization variant III (7.32 ± 0.31), which was significantly higher than the other variants. It is also worth emphasizing that only increasing the dose to 100 g (variant II) was statistically significant.

Using glycine-complexed iron fertilizer resulted in a decrease in the susceptibility of the lawns to diseases. In the case of snow mold, changes in the ratings were observed with the increasing fertilizer dose. Although no statistically significant differences were observed between the variants (I: 8.57 ± 0.35, II: 8.82 ± 0.22, and III: 8.95 ± 0.07), all variants showed significant differences from the control (7.85 ± 0.36). Regarding brown leaf spots, the Fe fertilization in doses of 100 g and 140 g caused maximal resistance to this disease (9.00 ± 0.00). Variant I also showed decreased susceptibility (8.37 ± 0.36) compared to the control (7.85 ± 0.36) but its value was significantly lower than variants II and III.

Table 4. Effects of Fe fertilization on the leaf greenness index.

Fe Dose	Year	Leaf Greenness Index
		Spring	Summer	Autumn
Control	2020	23.4 ± 0.30	14.5 ± 0.15	25.6 ± 0.35
	2021	25.1 ± 0.97	15.5 ± 0.61	27.3 ± 1.07
	2020–2021	24.2 a ± 1.11	15.0 a ± 0.68	26.4 a ± 1.17
Variant I: 60 g	2020	23.6 ± 0.30	14.6 ± 0.15	26.0 ± 0.30
	2021	25.3 ± 0.97	15.7 ± 0.61	28.0 ± 1.07
	2020–2021	24.4 a ± 1.12	15.1 ab ± 0.72	27.0 a ± 1.29
Variant II: 100 g	2020	24.5 ± 0.31	15.4 ± 0.15	26.4 ± 0.35
	2021	26.2 ± 1.01	16.5 ± 0.67	28.4 ± 1.11
	2020–2021	25.4 a ± 1.13	16.0 ab ± 0.74	27.4 a ± 1.33
Variant III: 140 g	2020	25.0 ± 0.25	15.6 ± 0.15	27.4 ± 0.30
	2021	26.8 ± 1.07	16.8 ± 0.67	29.4 ± 1.17
	2020–2021	25.9 a ± 1.21	16.2 b ± 0.79	28.4 a ± 1.32
Standard Deviation		1.27	0.88	1.40
Variation Coefficient, %		5.07	5.65	5.13

The same markings (a,b) mean no statistically significant changes (p ≥ 0.05).

shows the effect of Fe fertilization on the leaf greenness index. The highest values of the parameter were observed in autumn and the lowest in spring. In all seasons, it was observed that an increase in the dose of iron fertilizer complexed with glycine caused different ratings in the leaf greenness index. In the case of spring, the value of the leaf greenness index ranged between 24.2 and 25.9, and in autumn and fall, it ranged from 26.4 to 28.4 (mean values). It is worth noting, however, that there were no statistically significant changes between these results. The summer SPAD values ranged from 15.0 to 16.2. Fertilization variant III showed a statistically significant difference compared to the control sample.

Table 5. Effect of Fe fertilization on the macroelement content in plants.

Fe Dose	Year	P	K	Ca	Mg	Na
		g∙kg−1 d.m.
Control	2020	1.20 ± 0.05	33.4 ± 1.81	2.70 ± 0.15	1.43 ± 0.17	0.089 ± 0.022
	2021	1.24 ± 0.05	27.4 ± 2.59	3.24 ± 1.24	1.34 ± 0.23	0.052 ± 0.011
	2020–2021	1.22 a ± 0.05	30.4 a ± 3.87	2.97 a ± 0.84	1.39 a ± 0.19	0.071 a ± 0.026
Variant I: 60 g	2020	1.23 ± 0.05	33.8 ± 1.77	2.82 ± 0.19	1.49 ± 0.15	0.106 ± 0.029
	2021	1.25 ± 0.05	27.4 ± 2.55	3.24 ± 1.36	1.32 ± 0.18	0.056 ± 0.010
	2020–2021	1.24 ab ± 0.05	30.6 a ± 4.03	3.03 a ± 0.90	1.41 a ± 0.18	0.810 a ± 0.033
Variant II: 100 g	2020	1.35 ± 0.09	34.3 ± 0.45	3.08 ± 0.20	1.62 ± 0.15	0.148 ± 0.085
	2021	1.33 ± 0.10	29.7 ± 1.57	4.77 ± 2.99	1.53 ± 0.25	0.057 ± 0.008
	2020–2021	1.34 b ± 0.09	32.0 a ± 2.73	3.93 a ± 2.11	1.58 a ± 0.19	0.102 a ± 0.073
Variant III: 140 g	2020	1.36 ± 0.10	35.0 ± 0.65	3.17 ± 0.25	1.62 ± 0.13	0.147 ± 0.082
	2021	1.33 ± 0.10	29.8 ± 1.71	4.75 ± 3.16	1.52 ± 0.27	0.054 ± 0.006
	2020–2021	1.35 b ± 0.09	32.4 a ± 3.07	3.96 a ± 2.18	1.57 a ± 0.20	0.101 a ± 0.073
Standard Deviation		0.088	3.36	1.60	0.198	0.054
Variation Coefficient, %		6.835	10.7	46.1	13.3	60.8

The same markings (a,b) mean no statistically significant changes (p ≥ 0.05).

shows the effect of Fe fertilization on the macroelement content in plants. The results are given on a dry matter basis. In the case of most elements, a difference in the content of macroelements in plants was observed along with an increase in the dose of fertilizer (except for Mg and Ca, where, for variant III, the values were slightly lower than for variant II). Only in the case of P, the content of which was in the range of 1.22 g∙kg⁻¹ (d.m.)–1.35 g∙kg⁻¹ (d.m.), were statistically significant changes between the variants observed. In the case of the remaining elements, no statistically significant changes occurred despite a difference in the ratings. The K content in the plants was in the range of 30.4 g∙kg⁻¹ (d.m.)–32.4 g∙kg⁻¹ (d.m.); the Ca content was in the range of 2.97 g∙kg⁻¹ (d.m.)–3.96 g∙kg⁻¹ (d.m.); the Mg content was in the range of 1.39 g∙kg⁻¹ (d.m.)–1.58 g∙kg⁻¹ (d.m.); and the Na content was in the range of 0.071 g∙kg⁻¹ (d.m.)–0.102 g∙kg⁻¹ (d.m.) (mean values from 2 years).

Table 6. Effect of Fe fertilization on the microelement content in plants.

Fe Dose	Year	Cu	Mn	Zn	Fe
		mg∙kg−1 d.m.
Control	2020	7.13 ± 1.08	164 ± 25.6	42.2 ± 1.69	223 ± 59.3
	2021	7.53 ± 1.74	119 ± 87.3	38.0 ± 2.45	252 ± 59.0
	2020–2021	7.33 a ± 1.31	142 a ± 62.7	40.1 a ± 2.97	238 a ± 55.2
Variant I: 60 g	2020	8.17 ± 0.57	169 ± 22.3	44.0 ± 1.81	234 ± 57.4
	2021	7.21 ± 1.15	117± 84.0	37.6 ± 4.07	264 ± 92.9
	2020–2021	7.69 a ± 0.97	143 a ± 62.0	40.8 a ± 4.46	249 a ± 71.1
Variant II: 100 g	2020	8.07 ± 0.36	194 ± 3.95	47.5 ± 3.02	253 ± 21.8
	2021	7.69 ± 1.02	150 ± 105	42.8 ± 5.23	354 ± 212
	2020–2021	7.88 a ± 0.71	172 a ± 70.7	45.2 a ± 4.63	303 a ± 148
Variant III: 140 g	2020	8.79 ± 0.77	188 ± 19.8	49.4 ± 1.57	260 ± 38.6
	2021	7.76 ± 0.55	146 ± 101	41.4 ± 4.40	312 ± 172
	2020–2021	8.28 a ± 0.82	167 a ± 69.2	45.4 a ± 5.30	286 a ± 115
Standard Deviation		0.978	63.4	4.8	101
Variation Coefficient, %		12.5	40.6	11.2	37.5

The same markings (a) mean no statistically significant changes (p ≥ 0.05).

shows the effect of Fe fertilization on the microelement content in plants. As in the case of the macroelements, fertilization with iron fertilizer with complexed glycine caused visible differences in the content of microelements in plants (however, no statistically significant differences were observed at the significance level of p = 0.05). In the case of Mn and Fe, the lowest values were observed for the controls (142 mg∙kg⁻¹ (d.m.) ± 62.7 mg∙kg⁻¹ (d.m.) and 238 mg∙kg⁻¹ (d.m.) ± 55.2 mg∙kg⁻¹ (d.m.), respectively), and the highest for fertilization variant II (172 mg∙kg⁻¹ (d.m.) ± 70.7 mg∙kg⁻¹ (d.m.) and 303 mg∙kg⁻¹ (d.m.) ± 148 mg∙kg⁻¹ (d.m.), respectively). On the other hand, for Cu and Zn, the lowest values were obtained for the controls (7.33 mg∙kg⁻¹ (d.m.) ± 1.31 mg∙kg⁻¹ (d.m.) and 40.1 mg∙kg⁻¹ (d.m.) ± 2.97 mg∙kg⁻¹ (d.m.), respectively), and the highest for fertilization variant III (8.28 mg∙kg⁻¹ (d.m.) ± 0.82 mg∙kg⁻¹ (d.m.) and 45.4 mg∙kg⁻¹ (d.m.) ± 5.30 mg∙kg⁻¹ (d.m.), respectively).

Figure 2 shows the Wum depending on the season and fertilizer variant. The highest values of the functional assessment were obtained in the autumn and the lowest in the summer. It can be seen that the use of iron fertilizer with complexed glycine has a positive effect on the utility value of the lawns. In each case, a dose of 60 g of iron fertilizer (variant I) delivered a significantly higher functional value than the control. The highest values of the lawns’ functional assessment were obtained for variant III (140 g Fe), which were, on average, 8.34, 8.27, and 8.53 for spring, summer, and autumn, respectively. In the case of summer, variant III showed statistically significant differences from the other variants. In the case of spring and autumn, variant III showed no statistically significant differences to variant II (but between variant I and the control, it did).

4. Discussion

In the experiment, it was observed that the foliar application of an iron fertilizer complexed with glycine (and its subsequent increase in dose) positively influenced the overall aspect of the lawns and their compactness. This consistency was obtained for all seasons, which is an interesting supplement to the research conducted by Bierman et al. [18], who noticed that the foliar application of iron fertilizer improved the quality of the turf in the first two days after the treatment. Previous studies have shown that using a biostimulator with a high content of biologically active amino acids (L-alpha) with the addition of micronutrients shows a similar relationship in shaping the visual features of lawns [19]. The research carried out in this experiment confirms that the complexation of micronutrients with amino acids (in this case, glycine) can significantly increase the quality of a lawn. The selection of the microelement also plays a unique role; iron, as an activator of the formation of chlorophyll and an essential component for specific proteins [20], significantly impacts the bonitation value of lawns. This was confirmed mainly in Daneshvar et al.’s [21] experiment, which noted an increase in turfs’ visual quality after using a biostimulator with an increased iron content in plant tissues. The stark differences noted between the highest dose of biostimulator used and the control sample with respect to the visual features of turfs may indicate that chlorophyll biosynthesis occurred as a result of the application of the biostimulator and that the concentration of this compound in plants rapidly increased. As a result of this action, a better coloration of the lawn was noted because the high concentration of chlorophyll strongly correlates with a darker color of the turf [22,23,24]. This phenomenon has been described earlier in the studies of various authors who found that the concentration of chlorophyll can be used to quantify the color of turfgrasses [22,25,26]. As a result of such action, as expected, an increase in the values of the parameters (summer mainly) of the remaining visual values was noted, because high correlations between the individual components of the visual characteristics of the turfs were observed [19].

Additionally, iron significantly influences the proper development of plants and their growth [27], which is of great importance, especially in shaping the turf’s compactness. It is also worth emphasizing that, according to [28], amino acids such as glycine and glutamic acid are essential metabolites in creating healthy leaf tissue and synthesizing chlorophyll. The complexation of iron with glycine could, therefore, significantly intensify the increase in chlorophyll concentration in plants, thanks to which photosynthesis could proceed more efficiently. The results of the visual value indicate that the use of this type of biostimulant can be helpful in the regeneration of lawns with a low functional value, for example, due to their intensive use or presence in environments and conditions where iron availability is low (high pH and no oxygen in the root zone).

Using glycine-complexed iron fertilizer decreased susceptibility to snow mold and brown leaf spots. Indeed, statistically significant differences were not observed everywhere, but in both cases, there was a clear upward trend in resistance when increasing the dose of the biostimulator. Similar results were obtained in the experiment in [29], where a biostimulator reduced the susceptibility to fungal diseases of mixtures of perennial ryegrass and Kentucky Bluegrass. A reduction in the incidence of fungal diseases in grass mixtures was also noted in studies where the effect of using a biostimulator produced from brown algae (Phaeophyceae, containing various essential chemical compounds including amino acids, vitamins, alginic acid, and microelements) [30] and an amino acid biostimulator [19] was investigated. The results of this experiment and other studies indicate the synergistic effect of biostimulating preparations, which allow for the acquirement of high-quality turf with an increased resistance to fungal diseases. This is likely because the iron levels in a plant’s nutritional profile can control the outcome of infection by affecting pathogen virulence and host defense [31]. However, on the basis of the obtained results, it is recommended that further research in this area should focus on: (1) determining the maximum dose of the biostimulant, beyond which the visual and functional value of the lawn is reduced; (2) the effect of combining the use of the biostimulator with other agrochemicals on the functional and visual value of lawn turfs.

A positive effect of the foliar application of glycine-complexed iron fertilizer on the content of microelements and macroelements in plants was also noted. Although statistically significant differences were rarely observed, in almost all cases, an upward trend in the presence of these compounds was observed with the increasing fertilizer dose. First, between the variants, the iron level increased rapidly, confirming the validity of using this element as a fertilizer complex. Compared to conventional chelates, the glycine complex is lighter, which allows the grass mixture plants to absorb iron better. However, there is very little information in the literature related to the content of elements in grass plants due to their treatment with biostimulants, which significantly hinders their scientific interpretation. In a previous experiment, as a result of fertilization with a micronutrient fertilizer complexed with amino acids [19], a statistically significant increase in such elements as N, P, K, and Mg was obtained. In this experiment, statistically significant differences were observed only for phosphorus, which is consistent with the research of Nikbakht and Pessarakli [32], according to whom phosphorus is more available for plants subjected to the application of a biostimulator since it forms complexes with iron.

5. Conclusions

The use of glycine-complexed iron fertilizer and a further increase in its dose positively affected the lawn’s visual features, significantly improving its overall aspect, color, and turf compactness. A synergistic effect was obtained, improving the visual value of the lawns while increasing their resistance to fungal diseases such as snow mold and brown leaf spots. Additionally, the same effect was obtained for the utility features of the lawns. Thanks to foliar fertilization with a biostimulator, significantly better overwintering and slender leaf blades were obtained. It is also worth noting that in the plants, as a result of the application of the biostimulator, the content of micronutrients and macronutrients, especially P, increased, which can be explained by the fact that this element forms complexes with iron. Based on the obtained results, it can be stated that applying a higher dose of foliar iron fertilizer complexed with glycine allows one to obtain a high-quality lawn in terms of visual and functional features.

However, the fundamental relationship between glycine-complexed iron fertilizer and functional/visual lawn turf value is still not clearly elucidated, so more research is needed to explain these phenomena in detail. After the determination of this step, further research on the effects of using amino acid-based biostimulants for fertilizing lawns, in particular for optimizing the dose to maximize the functional value of lawns and the possibility of combining these agents with other agrochemicals, is needed.