Impact of Foliar Application of Copper, Manganese, Molybdenum, and Zinc on the Chemical Composition and Malting Quality of Barley Cultivars

Abstract

The aim of this study was to evaluate the effect of foliar application of selected micro-nutrients on the chemical composition and malting quality of spring barley (Hordeum vulgare L.). The scientific literature lacks in-depth studies that assess the effect of foliar application of micronutrients on barley malting quality. Most studies (especially under field conditions) focus on nitrogen fertilization rather than individual micronutrients. Three brewing-type barley cultivars (Baryłka, KWS Irina, and RGT Planet) were evaluated under foliar micronutrient fertilization (Cu, Mn, Mo, Zn). Fertilizers were applied at doses of 2 L ha⁻¹ for Cu, Mn, and Zn and 1 L ha⁻¹ for Mo. The experiment examined the hectoliter mass, theoretical extractability, contents of selected micro- and macronutrients, and the protein, fat, fiber, and ash contents of the grain. Furthermore, the following characteristics of barley malt were determined, i.e., moisture, protein, extractivity, Kolbach index, and diastatic power. The results showed significant variability in grain and malt quality depending on the cultivar and year. The Baryłka cultivar was characterized by the highest grain density (66.3 kg hL⁻¹) and protein content (10.9% d.m.), while RGT Planet had the highest extractivity and the most favorable malting profile. Foliar supplementation had a slightly positive effect on the average content of trace elements in barley. Mn application increased grain Ca content by 5.6% compared with the control, while foliar Zn fertilization resulted in the highest zinc concentration (a 24.7% increase). No significant effect of fertilization on malt quality was observed, but a significant interaction of experimental factors in extractivity, Kolbach index, and diastatic power was noted. The obtained results indicate that a single foliar application of microelements affects the contents of minerals and protein in the grain, but it does not lead to a significant improvement in malting parameters. This suggests the need for further research on dosage, application date, and interactions between the cultivar and environmental conditions.

1. Introduction

Barley (Hordeum vulgare L.) is the fourth most important cereal grain in the world in terms of grain production after wheat, maize, and rice. In 2023, barley was cultivated on 46.2 million hectares worldwide, with a yield of over 145 million tons [1]. This species is considered one of the oldest crops, playing an important role in the development of human civilization and research in genetics, biochemistry, and developmental biology [2,3,4]. It is grown in a wide range of environments, both in high-input agricultural systems and in extensive agriculture. Approximately 65–70% of the grain produced is used for animal feed, while 33% is used by the brewing industry for malt production. Barley malt is the main source of fermentable sugars used by yeast in the traditional beer brewing process [5]. Only 2–3% is used directly for human consumption [6,7,8]. Barley in the human diet contributes to reducing the risk of civilization diseases due to the content of valuable bioactive compounds [9,10].

Nutrient deficiencies in plants limit agricultural production and also impact human nutrition, as crops (primarily cereal grain) constitute the main component of the diet. The level of macro- and micronutrients in the human body can be optimized by diversifying the diet and increasing their concentration or bioavailability in food products, e.g., by means of agrotechnical biofortification. One approach involves applying fertilizers enriched with beneficial elements, which offers a relatively simple and rapid means of supplementing crops with minerals [11,12,13]. Micronutrients such as zinc (Zn), copper (Cu), manganese (Mn), and molybdenum (Mo) play key biochemical roles in the human body, despite the relatively low requirements for these elements. The recommended daily intake for adults is approximately as follows: Cu—0.9 mg; Mn—2–5 mg; Zn—10–14 mg; and Mo—45 µg [14]. The concentration of microelements in barley grain is determined by genetic factors, soil conditions, and fertilization. Typical ranges of their concentration in barley are as follows: Zn 20–50 mg, Cu 3–8 mg, Mn 15–40 mg, and Mo 0.1–1.0 mg per 1 kg of grain. During the malting process, the microelement contents are generally maintained at similar levels [12,15].

There are two botanical types of barley: two-row and six-row. In Europe, Australia, and South America, two-row cultivars are used primarily for brewing purposes, while six-row malting barley was more widely cultivated in North America [16,17]. Typical two-row barley cultivars are plumper and have a larger proportion of starchy endosperm relative to six-row cultivars. Barley malt produced from two-row barley has a lower protein-to-starch ratio, resulting in higher fermentation extract yields [5]. There are many different barley traits that are important for malting, mainly related to the speed and consistency of germination, endosperm cell wall breakdown, and starch degradation to fermentable sugars [18,19].

The main component of barley grain is starch, which can constitute over 70% of the dry matter [20]. Protein content ranges from 10 to 14%, and fiber is 19–21% [21]. Protein affects the rate of starch degradation in barley through its interaction with starch granules, thus influencing the level of modification during malting. High protein content is not preferred in brewing because it can not only affect the rate of starch degradation but also affect the properties of the malt wort and the quality of the beer [22,23,24].

The quality criteria are stringent for the barley used in malting. The importance of the malting process has led to intensive research on grain structure, development, and germination in barley [2,25]. The quality of the malt depends on various grain parameters, such as grain shape, size, density, protein content, etc., which influence quality traits [26]. The grain used in the brewing industry should be from a pure variety, have a germination capacity of at least 95%, a protein content of 11% to 12.5% d.m., and a moisture content of at most 13.5%, and be free from diseases, pests, and thermal and mechanical damage [5,27,28].

The current goal of barley breeding is to optimize agrotechnical performance while improving processing efficiency. Identifying malting barley cultivars with desirable grain parameters is crucial for improving production efficiency and malt quality. Agronomic practice research is important to increase grain suitability for brewing purposes [19,26]. Previous research indicates that micronutrient deficiencies can lead to reduced yield, grain unevenness, changes in protein content, and a deterioration of traits important for malting. However, most of these studies refer to soil fertilization or the use of mixtures containing several micronutrients, making it difficult to assess the impact of individual elements. Furthermore, barley’s response to micronutrient supplementation depends on the dose, application timing, cultivar characteristics, and weather conditions, leading to ambiguous conclusions regarding their impact on malting quality. Few studies focus on the foliar application of single-nutrient fertilizers and their impact on both grain chemical composition and malt parameters. Despite the recognized physiological importance of micronutrients, previous research has provided inconsistent results regarding their agronomic and technological effects on barley. Most studies have focused on soil fertilization or the use of complex micronutrient mixtures rather than on single-element foliar application under field conditions [29,30]. The available evidence suggests that the dose, timing, and method of micronutrient application may influence grain yield, protein accumulation, and starch deposition; however, their effects on key malting parameters such as extractivity, Kolbach index, and diastatic power are still poorly understood. Liszewski and Błażewicz [31] examined the effect of foliar fertilization with Cu, Mn, and Fe on grain yield and the brewing value of spring barley, the Quench cultivar. The results of this study showed that the foliar application of fertilizers containing Cu and Fe contributed to improved malting suitability of malting grain. Previous studies on fertilization and grain quality of malting barley have focused primarily on the effect of nitrogen fertilization on the chemical composition of grain [32,33,34,35,36]. The level of nitrogen fertilization determines the protein content in the grain, and too high a percentage of this nutrient negatively affects the malting process by reducing extracts for the brewer. It also slows water absorption during steeping, potentially affecting the final malt quality. Low protein levels result in a deficiency of enzymes necessary for barley grain modification and starch degradation during brewing [19,24]. Therefore, there is a research gap regarding the extent to which individual micronutrients applied foliarly at specific developmental stages can modify malting barley grain quality and its malting suitability. Filling this gap is crucial to assessing whether targeted foliar treatments can be an effective agronomic tool to enhance malting quality. Agricultural techniques used have a significant impact on grain quality. In particular, they influence the grain’s size and chemical composition, which determine its suitability for beer production [37]. The foliar application of nutrients can modify the grain chemical composition and barley yield, which are primarily determined by the genotype [38,39,40]. Understanding the chemical variability of malting barley cultivars will allow for greater diversity of breeding programs to develop or improve product flavor [19].

This study was conducted to investigate the effect of foliar fertilization with microelements (copper, manganese, molybdenum, and zinc) on the malting suitability of grain of three malting barley cultivars. The research hypothesis assumes that foliar feeding with selected micronutrients positively affects grain nutrient content and malt quality parameters.

2. Materials and Methods

2.1. Field Experiment Scheme

Field studies were conducted in years 2019–2021 in southeastern Poland (49°47′ N, 22°34′ E). The experiment was designed using a two-factor split-block design with four replications. The experimental factors were as follows:

(1) two-row malting spring barley cultivar (Baryłka (Hodowla Roślin Strzelce Ltd., IHAR Group, Strzelce, Poland), KWS Irina (KWS Lochów Polska Ltd., Prusy, Poland), RGT Planet (R.A.G.T. Semences Polska Ltd., Toruń, Poland)), and (2) foliar micronutrient application. Foliar fertilization treatments included a control treatment (no fertilization) and application of single micronutrients: copper (Cu), manganese (Mn), molybdenum (Mo), or zinc (Zn). The sources of microelements were single-component fertilizers from the Mikrovit^® series (Intermag Ltd., Olkusz, Poland), applied foliarly in the form of aqueous solutions: MIKROVIT^® COPPER (75 g L⁻¹ copper sulfate CuSO₄ dose 2 L ha⁻¹); MIKROVIT^® MANGANESE (160 g L⁻¹ manganese sulfate MnSO₄ (65 g L⁻¹) and manganese nitrate Mn(NO₃)₂ (95 g L⁻¹) dose 2 L ha⁻¹); MIKROVIT^® MOLYBDENUM (33 g L⁻¹ ammonium molybdate (NH₄)₆Mo₇O₂ dose 1 L ha⁻¹); and MIKROVIT^® CYNK (112 g L⁻¹ zinc sulfate ZnSO₄, dose 2 L ha⁻¹). The applied doses of micronutrient fertilizers were selected in accordance with the manufacturer’s agronomic recommendations for cereal crops and are consistent with commonly used rates in field trials evaluating the effects of foliar micronutrient supplementation in barley and other cereals [29,30]. Spraying was carried out at the stem elongation stage (BBCH 30–32) [41] using a pressure sprayer in windless weather. Foliar fertilization is generally most effective during the stem elongation phase, as this is when the plant has a high nutrient demand and leaf assimilation activity. This allows for rapid and efficient nutrient absorption [30,42,43]. A detailed description of the agrotechnical treatments, soil conditions, and weather conditions during the field experiment is presented in Stadnik et al. [44] and Stadnik et al. [45]. Grain was harvested at full maturity (BBCH 89) [41] in the last ten days of July each year (22 July 2019, 30 July 2020, 25 July 2021). The yield from each plot was weighed, and the grain was cleaned and prepared for laboratory analysis.

2.2. Preparation of Material for Analysis

After harvest, the grain was cleaned, dried in the laboratory to a stable storage moisture, and conditioned to room temperature before being separated for analysis. Homogeneous analytical samples were prepared by grinding in a laboratory grinder, and the portion size and homogenization method were in accordance with the recommendations of the ISO standards appropriate for the assays described below. For quality control, a blank, reference material, or internal control was included in each analytical run, and at least 10% of the measurements were duplicated, using the repeatability criteria described in the individual standards [46,47,48,49].

2.3. Laboratory Analysis of Grain

2.3.1. Extractivity of Grain

Theoretical extractivity of barley grain (E) was calculated according to Bishop’s formula [50,51]. This formula, developed for two-row barley, has the following form:

$$E=84.5-0.75B+0.1\mathrm{T}\mathrm{G}\mathrm{W}$$

where B—protein content in grain (% d.m.); TGW—1000-grain weight (g). The value of 84.5 is a constant characteristic for two-row barley. TGW was presented in the study by Stadnik et al. [44].

2.3.2. Grain Density

The hectoliter mass of grain was determined with a Dramiński GMDM grain moisture and density meter, type WZW2 (Dramiński Inc., Sząbruk, Poland), using the routine method according to ISO 7971-3, and using a calibrated device for measuring mass per hectoliter. The sample was prepared in accordance with the requirements of the standard by performing triplicate measurements and calculating the result as an average [52].

2.3.3. Chemical Composition

Samples were prepared by uniform grinding in a knife mill Knifetec 1095 (Foss Tecator), designed for the rapid homogenization of cereal materials. Water content was determined using the reference method for cereals in accordance with PN-EN ISO 712:2012 [53] in the current version for the product. For barley, the Analytica EBC procedure for barley grain moisture, which refers to ISO 712 [54], was additionally considered, ensuring consistency with the methodology used in the assessment of brewing raw material. In both cases, the moisture result was used for conversion to dry matter in accordance with the reporting principles provided in the standard methods [54]. Total protein was determined from total nitrogen using the Kjeldahl method in accordance with PN-EN ISO 20483 [55], and for barley, procedural compliance was confirmed with the Analytica EBC 3.3.1 method for determining nitrogen in grain. Protein content was calculated using a conversion factor of 6.25 and related to dry matter [55,56]. Crude fat was determined by the extraction method in accordance with PN-EN ISO11085 [57], using the Randall/Soxtec procedure appropriate for cereal products. After the removal of solvent, the residue was dried to a constant weight, and the result was expressed as a percentage of dry matter [57]. Crude fiber was determined by the indirect filtration method in accordance with PN EN ISO6865, which involves digesting the sample with acid and alkali solutions under conditions specified in the standard for drying and ashing and calculating the fiber content from the difference in masses [58]. Total ash was determined gravimetrically by ashing the sample in a muffle furnace in accordance with PN-EN ISO2171 [59], and the result was expressed as a percentage by mass on a dry matter basis. All determinations were subject to ongoing quality control, including verification of repeatability based on three independent replicates and stability of results across analytical runs. Each determination was performed in triplicate, and the results were expressed as dry weight.

Mineralization was carried out in an open system on a Tecator heating block, using a mixture of HNO₃:HClO₄:H₂SO₄ in a volume ratio of 20:5:1, until clear solutions were obtained. The mixture and digestion regime were selected based on reference methodologies for the wet mineralization of plant material, while maintaining safety recommendations for HClO₄. Ca, Cu, Fe, K, Mg, Mn, and Zn were determined by flame atomic absorption spectrometry on a Hitachi Z 2000 spectrophotometer with air–acetylene atomization, and background correction using the Zeeman polarization effect. Analytical parameters and sample preparation for measurement were adapted to the requirements of the ISO6869 [60] reference method for AAS, including the use of the recommended analytical lines: 422.6 nm (Ca), 324.8 nm (Cu), 248.3 nm (Fe), 766.5 nm (K), 285.2 nm (Mg), 279.5 nm (Mn), and 213.8 nm (Zn). Calibration was performed using external standard solutions prepared in the same acidic environment as the samples; each sample was analyzed in triplicate, and a reagent blank was included in each series.

2.4. Laboratory Analyses of Malt

2.4.1. Malt Production

The grain malting process was carried out on a laboratory scale according to the standard scheme for barley [61]. Malting was performed in three parallel replicates. Each sample consisted of a batch of grain weighing 425 g on a dry matter basis. Steeping (soaking) and germination took place in the micro-malting room at a constant air temperature of 14 ± 1 °C and at a relative humidity of above 95%. The grain was soaked in water at approximately 14 °C until the target hydration degree of 45% was achieved. The total steeping time was approximately 72 h, with the water changed every 24 h and the grain regularly aerated (with breaks to allow for air access). The steeping scheme was as follows: Day 1: 4 h under water, then ~20 h in air (during a break from steeping); Day 2: up to 2 h under water (soaking), and the rest of the time exposed to air; Day 3: the grain was sprayed with water to reach the target moisture content of 45%, after which it was left exposed to air until the next day (beginning of germination). After soaking, the grain was germinated for a total of 5 days under the same temperature and humidity conditions. The weight was monitored daily (weight increase indicating water uptake), and aeration was performed by gently moving and mixing the germinating grain in the germination tank to ensure even oxygen access and prevent clumping. After 5 days of germination, the obtained green malt (germinated grain) was subjected to convective drying in a single-screen dryer with warm air blowing. Drying was carried out for 23 h according to the following temperature program: 16 h at 50 °C (initial drying of the grain); 1 h at 60 °C; 1 h at 70 °C; and 5 h at 80 °C (final drying of the malt). After cooling, the dried malt was degermed. Root sprouts were removed by grating the malt on a sieve, which allowed for the separation of the brittle, dried roots. The resulting finished barley malt was stored in tightly sealed plastic containers until laboratory analysis.

2.4.2. Analysis of Malt Parameters

Malt quality analysis was performed on grist prepared just prior to testing by grinding the grain in a Knifetec1095 knife mill (Foss Tecator), ensuring a uniform grinding ratio appropriate to reference procedures consistent with EBC standards. Sampling and preparation of the material for testing were performed according to the principles of malt sampling and sample preparation described in the malt section of Analytica EBC to maintain representativeness and repeatability of results [62]. Moisture content in malt was determined by the mass loss method under reference conditions specified for malt in Analytica EBC, and the result was expressed as a percentage and related to dry matter [63]. Total protein content was calculated from total nitrogen determined by the Kjeldahl method according to the Analytica EBC malt procedure, using a conversion factor of 6.25 and converting the results to dry matter [64]. Malt extractivity was determined from laboratory wort obtained in a standard congress mash test conducted according to the temperature program and apparatus requirements specified by the European Brewing Convention; the result was reported as a percentage of extract per malt dry matter [65]. The Kolbach index was calculated as the ratio of soluble nitrogen in the congress wort to total nitrogen in the malt, expressed as a percentage. Soluble nitrogen was determined by the Kjeldahl method according to a dedicated malt procedure, in conjunction with the wort obtained in the congress test, while total nitrogen was determined according to method 4.3.1 [64,66]. Diastatic power was determined spectrophotometrically according to the reference document for malt, under the reaction conditions specified by Analytica EBC, and the result was reported in Windisch Kolbach units [67]. Each determination was performed in three independent replicates.

2.5. Statistical Analysis

Statistical analyses were performed using Statistica (TIBCO Statistica, version 13.3), employing ANOVA modules and mean comparison procedures. The experimental design was modeled as a two-factor analysis of variance with cultivar and foliar fertilization as factors, with year as a random effect and replications using a split-block design. For all traits, the assumptions of normality of residual distribution (Shapiro–Wilk test) and homogeneity of variance (Levene’s test) were verified. For significant main effects or interactions, Tukey’s HSD post hoc tests were performed at p ≤ 0.05. Results are presented as mean values with standard deviation (SD).

3. Results

3.1. Assessment of Barley Grain

3.1.1. Grain Density and Theoretical Extractability

In the experiment, the average grain bulk density was 64.3 kg hL⁻¹. The highest values for the Baryłka and RGT Planet cultivars were obtained after spraying plants with copper fertilizer (67.8 kg hL⁻¹ and 64.3 kg hL⁻¹, respectively), while the highest values for the KWS Irina cultivar were obtained after applying manganese fertilizer (64.2 kg hL⁻¹). Grain bulk density varied depending on the barley cultivar and harvest year. The Baryłka cultivar had a significantly higher average value (66.3 kg hL⁻¹) compared to the KWS Irina cultivars (63.1 kg hL⁻¹) and RGT Planet cultivars (63.5 kg hL⁻¹) (

Table 1. The hectoliter weight and theoretical extractivity of grain depending on the fertilization, cultivar, and year of the field experiment.

Cultivar (C)	Fertilization (F)	Hectoliter Weight of Barley	Extractivity of Grain
		kg hL−1	% d.m.
Baryłka	Control	64.4 ± 2.5 bc	81.5 ± 0.28 a–c
	Cu	67.8 ± 6.5 c	81.2 ± 0.36 a
	Mn	66.6 ± 1.8 bc	81.2 ± 0.46 ab
	Mo	65.5 ± 3.3 bc	81.2 ± 0.64 a
	Zn	67.4 ± 4.3 c	81.3 ± 0.46 ab
KWS Irina	Control	62.2 ± 1.9 a	81.8 ± 0.49 c–e
	Cu	63.3 ± 3.2 ab	81.8 ± 0.36 c–e
	Mn	64.2 ± 5.6 b	81.5 ± 0.37 a–d
	Mo	62.6 ± 3.4 a	81.6 ± 0.44 b–e
	Zn	63.3 ± 1.9 ab	81.5 ± 0.38 a–d
RGT Planet	Control	63.5 ± 1.9 b	81.8 ± 0.34 c–e
	Cu	64.3 ± 1.4 bc	81.8 ± 0.51 c–e
	Mn	63.5 ± 2.4 b	82.0 ± 0.39 e
	Mo	62.5 ± 5.3 a	81.9 ± 0.50 de
	Zn	63.7 ± 1.9 b	82.0 ± 0.41 e
HSD p ≤ 0.05 C × F		n.s. (0.7863)	* (0.0126)
Mean	Baryłka	66.3 ± 4.1 B	81.3 ± 0.45 A
	KWS Irina	63.1 ± 3.4 A	81.7 ± 0.41 B
	RGT Planet	63.5 ± 2.9 A	81.9 ± 0.43 C
HSD p ≤ 0.05 C		*** (0.0000)	*** (0.0000)
Mean	Control	63.4 ± 2.2 A	81.7 ± 0.40 A
	Cu	65.1 ± 4.6 A	81.6 ± 0.50 A
	Mn	64.7 ± 3.8 A	81.6 ± 0.52 A
	Mo	63.5 ± 4.2 A	81.6 ± 0.60 A
	Zn	64.8 ± 3.4 A	81.6 ± 0.51 A
HSD p ≤ 0.05 F		n.s. (0.0582)	n.s. (0.5881)
Year (Y)	2019	62.5 ± 2.0 A	81.3 ± 0.49 A
	2020	65.3 ± 2.0 B	81.7 ± 0.40 C
	2021	65.1 ± 5.4 B	81.9 ± 0.51 B
HSD p ≤ 0.05 Y		*** (0.0000)	*** (0.0000)
Average		64.3 ± 3.8	81.6 ± 0.50

*** and * indicate significant differences at p ≤ 0.001 and p ≤ 0.05; n.s.—non-significant, according to Tukey’s honestly significant difference test (HSD). Data are presented as mean ± standard deviation (SD). Different lowercase letters (a–e) indicate significant differences among treatments; uppercase letters (A–C) indicate significant differences among means for fertilization, cultivars, or years according to Tukey’s HSD at p ≤ 0.05.

). Theoretical extractability of the grain averaged 81.2% d.m. The highest value of this parameter was observed in the RGT Planet cultivar from plots fertilized with manganese (82.0% d.m.), while the lowest value was observed in the Baryłka cultivar after application of Cu or M0 (80.8% d.m.).

Theoretical extractivity was determined by genotype. The highest result was obtained for the RGT Planet cultivar, while foliar fertilization had no significant effect on the mean values of the analyzed parameter (Table 1).

Both parameters varied significantly depending on the year of field testing. Higher values were recorded in 2020 and 2021 compared to 2019 (Table 1).

3.1.2. Elemental Profile of Grain

An analysis of the elemental composition of barley grain revealed significant differences in the response of individual barley cultivars to foliar fertilization. Significant interactions of experimental factors were demonstrated for the content of Ca, Fe, K, Mg, and Zn (

Table 2. The contents of selected macro- and microelements in barley grain depending on the fertilization, cultivar, and year of the field experiment.

Cultivar (C)	Fertilization (F)	Ca	Cu	Fe	K	Mg	Mn	Zn
		mg kg−1
Baryłka	Control	305 ± 35 cd	5.68 ± 0.78 cd	88.9 ± 46.0 d	4112 ± 302 ab	1128 ± 62 b	16.7 ± 4.94 b	30.8 ± 4.16 a
	Cu	265 ± 35 a	5.70 ± 0.97 cd	76.7 ± 25.8 b	3984 ± 475 a	1151 ± 80 b	12.9 ± 2.13 a	30.3 ± 5.34 a
	Mn	279 ± 47 bc	5.37 ± 1.18 b–d	88.5 ± 44.6 d	3899 ± 180 a	1165 ± 74 bc	14.0 ± 1.69 a	32.8 ± 10.9 a
	Mo	273 ± 45 b	5.45 ± 1.09 b–d	88.3 ± 54.7 d	3933 ± 288 a	1187 ± 46 d	13.1 ± 1.78 a	32.0 ± 10.1 a
	Zn	267 ± 52 a	6.00 ± 1.41 d	67.4 ± 18.5 a	3969 ± 357 a	1217 ± 71 e	13.5 ± 1.01 a	41.0 ± 13.6 b
KWS Irina	Control	267 ± 65 a	4.99 ± 0.61 a–c	84.5 ± 20.8 c	4649 ± 354 d	1165 ± 50 bc	13.7 ± 1.22 a	26.6 ± 8.76 a
	Cu	292 ± 65 bc	5.09 ± 1.30 a–c	60.1 ± 18.3 a	4652 ± 656 d	1176 ± 67 c	12.3 ± 0.82 a	28.1 ± 8.49 a
	Mn	283 ± 52 bc	4.81 ± 1.04 a–c	61.1 ± 18.6 a	4675 ± 422 d	1201 ± 106 d	12.5 ± 1.02 a	29.0 ± 7.22 a
	Mo	306 ± 20 d	4.62 ± 0.84 ab	70.0 ± 20.0 ab	4454 ± 499 cd	1190 ± 68 d	12.4 ± 1.23 a	27.5 ± 4.27 a
	Zn	272 ± 32 a	4.78 ± 0.89 a–c	65.9 ± 19.9 a	4366 ± 411 b	1191 ± 76 d	12.3 ± 0.91 a	30.1 ± 5.32 a
RGT Planet	Control	287 ± 49 bc	4.36 ± 0.39 a	76.9 ± 45.3 b	4438 ± 386 cd	1166 ± 33 bc	13.7 ± 2.76 a	26.4 ± 1.55 a
	Cu	304 ± 48 cd	4.73 ± 0.74 ab	66.7 ± 30.7 a	4244 ± 259 b	1087 ± 48 a	12.8 ± 1.20 a	27.7 ± 3.92 a
	Mn	343 ± 42 e	4.66 ± 0.82 ab	83.5 ± 48.2 c	4260 ± 426 b	1110 ± 77 ab	13.6 ± 1.72 a	30.2 ± 6.07 a
	Mo	298 ± 53 b–d	4.38 ± 0.53 a	95.2 ± 49.6 e	4291 ± 313 b	1098 ± 57 a	13.4 ± 1.86 a	27.4 ± 5.05 a
	Zn	307 ± 45 d	4.88 ± 1.02 a–c	70.3 ± 30.9 ab	4409 ± 372 b–d	1104 ± 85 ab	13.3 ± 1.46 a	33.3 ± 9.15 a
HSD p ≤ 0.05 C × F		*** (0.0000)	n.s. (0.5824)	*** (0.0001)	n.s. (0.4714)	*** (0.0006)	** (0.0019)	n.s. (0.2387)
Mean	Baryłka	278 ± 45 A	5.64 ± 1.09 B	81.9 ± 39.8 B	3979 ± 331 A	1170 ± 72 B	14.1 ± 2.94 C	33.4 ± 10.0 B
	KWS Irina	284 ± 50 A	4.86 ± 0.94 A	68.4 ± 20.09 A	4559 ± 480 C	1185 ± 74 B	12.6 ± 1.15 A	28.3 ± 6.90 A
	RGT Planet	308 ± 50 B	4.60 ± 0.74 A	78.5 ± 41.6 B	4328 ± 353 B	1113 ± 67 A	13.4 ± 1.84 B	29.0 ± 6.07 A
HSD p ≤ 0.05 C		*** (0.0000)	*** (0.0000)	*** (0.0000)	*** (0.0000)	*** (0.0000)	*** (0.0000)	*** (0.0000)
Mean	Control	286 ± 52 A	5.01 ± 0.81 A	83.4 ± 38.4 B	4400 ± 406 A	1153 ± 51 A	14.7 ± 3.56 B	27.9 ± 5.87 A
	Cu	287 ± 52 A	5.17 ± 1.08 A	67.8 ± 25.7 A	4293 ± 552 A	1138 ± 75 A	12.7 ± 1.47 A	28.7 ± 6.15 A
	Mn	302 ± 55 B	4.95 ± 1.04 A	77.7 ± 40.1 B	4278 ± 476 A	1159 ± 93 A	13.4 ± 1.60 A	30.6 ± 8.23 A
	Mo	292 ± 43 AB	4.82 ± 0.95 A	84.5 ± 44.2 B	4226 ± 429 A	1158 ± 71 A	13.0 ± 1.66 A	29.0 ± 7.13 A
	Zn	282 ± 46 A	5.22 ± 1.23 A	67.9 ± 23.1 A	4248 ± 421 A	1171 ± 90 A	13.0 ± 1.24 A	34.8 ± 10.7 B
HSD p ≤ 0.05 F		** (0.0044)	n.s. (0.0820)	*** (0.0000)	n.s. (0.2896)	n.s. (0.1701)	*** (0.0000)	*** (0.0000)
Year (Y)	2019	309 ± 31 B	5.61 ± 1.23 C	68.0 ± 17.3 B	4090 ± 450 A	1170 ± 76 B	13.1 ± 2.95 A	36.3 ± 9.39 C
	2020	244 ± 45 A	5.11 ± 0.80 B	48.2 ± 11.6 A	4279 ± 473 B	1178 ± 86 B	12.9 ± 1.55 A	28.8 ± 6.66 B
	2021	317 ± 34 B	4.39 ± 0.56 A	112.6 ± 34.7 C	4497 ± 357 C	1119 ± 52 A	14.1 ± 1.58 B	25.6 ± 2.30 A
HSD p ≤ 0.05 Y		*** (0.0000)	*** (0.0000)	*** (0.0000)	*** (0.0000)	*** (0.0000)	*** (0.0000)	*** (0.0000)
Average		290 ± 50	5.03 ± 1.03	76.3 ± 35.7	4289 ± 459	1156 ± 77	13.3 ± 2.18	30.2 ± 8.12

*** and ** indicate significant differences at p ≤ 0.001, and p ≤ 0.01; n.s.—non-significant, according to Tukey’s honestly significant difference test (HSD). Data are presented as mean ± standard deviation (SD). Different lowercase letters (a–e) indicate significant differences among treatments; uppercase letters (A–C) indicate significant differences among means for fertilization, cultivars, or years according to Tukey’s HSD at p ≤ 0.05.

).

The highest Ca content was observed in the Baryłka cultivar from the control treatment (305 mg kg⁻¹), in the KWS Irina cultivar after Mo application (306 mg kg⁻¹), and in the RGT Planet cultivar from plots with Mn application (343 mg kg⁻¹).

The Baryłka cultivar demonstrated relatively stable Fe content regardless of the fertilization type (approximately 76–89 mg kg⁻¹), while KWS Irina responded strongly to foliar fertilization. The highest iron content was found in the RGT Planet cultivar from plots fertilized with Mo (95.2 mg kg⁻¹). In the experiment, the highest Mg content was found in the grain of the KWS Irina cultivar after the foliar application of Mn (1201 mg kg⁻¹), while the lowest content of this element was found in the RGT Planet cultivar after the application of Mo (1098 mg kg⁻¹).

The foliar application of the tested micronutrients had a significant effect on the average Ca, Fe, Mn, and Zn contents in grain. The highest Ca content was obtained after Mn fertilization (302 mg kg⁻¹), while the lowest Ca content was obtained in the Mo fertilization variant (292 mg kg⁻¹). The Fe content was the highest in the control treatments and after Mo fertilization (84.5 mg kg⁻¹). The application of each of the tested micronutrient fertilizers resulted in a significant increase in Mn content in grain compared to the control. The application of zinc fertilizer significantly increased Zn content in grain (34.8 mg kg⁻¹) compared to the other fertilization treatments.

The statistical analysis of the experimental results demonstrated a strong effect of cultivar on the average content of the analyzed elements in grain. The Baryłka cultivar had the highest concentration of Cu, Fe, Mn, and Zn in grain, while the highest K and Mg values were found in the KWS Irina cultivar. The RGT Planet cultivar had a significantly higher Ca content (30 mg kg⁻¹ compared to Baryłka and 24 mg kg⁻¹ compared to KWS Irina, respectively) (Table 2).

The year of study had a significant, strong effect (p ≤ 0.001) on the content of all analyzed minerals. In 2019, the highest average Cu and Zn contents were recorded, while in 2020, the lowest Fe and Ca values were obtained. In turn, in 2021, the highest Fe and K levels were observed (Table 2).

3.1.3. Organic Chemical and Ash Content

In the experiment, the average protein content was 10.4% d.m. Spraying the plants with each of the tested micronutrient fertilizers resulted in a significant increase in the average protein content compared to the control, with the highest content recorded after the application of Mo (by 0.2% d.m.). The grain of the Baryłka cultivar contained the highest protein content (by 0.6% and 0.9% d.m., respectively, compared to the KWS Irina and RGT Planet cultivars).

The fat content of the tested grain averaged 2.39% d.m. In the Baryłka and KWS Irina cultivars, the highest fat content was recorded in grain from the control plots, while in the RGT Planet cultivar, the highest percentage of this nutrient was observed after the foliar application of zinc. Statistical analysis showed a significant decrease in the fat content in the grain of plants fertilized with micronutrients compared to the control. The lowest value (2.33% d.m.) was recorded on the plots fertilized with Cu (

Table 3. The chemical composition of grain depending on the fertilization, cultivar, and year of the field experiment.

Cultivar (C)	Fertilization (F)	Protein	Fat	Fiber	Ash
		[% d.m.]
Baryłka	Control	10.6 ± 0.44 bc	2.49 ± 0.22 c	3.97 ± 0.42 a	2.75 ± 0.16 ab
	Cu	11.0 ± 0.42 c	2.20 ± 0.24 ab	4.40 ± 0.77 c	2.86 ± 0.15 c
	Mn	11.0 ± 0.55 c	2.28 ± 0.18 a–c	4.26 ± 0.74 bc	2.86 ± 0.18 c
	Mo	11.0 ± 0.65 c	2.19 ± 0.16 a	4.30 ± 0.74 bc	2.87 ± 0.19 c
	Zn	10.9 ± 0.51 c	2.21 ± 0.20 ab	4.33 ± 0.66 c	2.83 ± 0.17 bc
KWS Irina	Control	10.1 ± 0.50 a	2.50 ± 0.22 cd	3.97 ± 0.86 a	2.71 ± 0.17 a
	Cu	10.2 ± 0.61 ab	2.40 ± 0.26 b-d	4.01 ± 0.69 bc	2.71 ± 0.13 a
	Mn	10.4 ± 0.63 ab	2.38 ± 0.21 b	3.99 ± 0.76 b	2.73 ± 0.17 ab
	Mo	10.4 ± 0.69 ab	2.44 ± 0.18 cd	3.90 ± 0.92 b	2.71 ± 0.15 ab
	Zn	10.4 ± 0.61 ab	2.37 ± 0.25 b	4.13 ± 0.77 bc	2.73 ± 0.16 ab
RGT Planet	Control	10.0 ± 0.33 ab	2.49 ± 0.36 c	3.95 ± 1.34 b	2.67 ± 0.15 a
	Cu	10.0 ± 0.56 a	2.38 ± 0.25 b–d	3.87 ± 0.68 b	2.69 ± 0.20 a
	Mn	10.0 ± 0.53 a	2.46 ± 0.17 c	3.77 ± 0.71 ab	2.65 ± 0.19 a
	Mo	10.1 ± 0.61 a	2.47 ± 0.24 cd	3.87 ± 0.80 b	2.67 ± 0.20 a
	Zn	10.0 ± 0.65 a	2.57 ± 0.15 d	3.70 ± 0.64 a	2.65 ± 0.22 a
HSD p ≤ 0.05 C × F		n.s. (0.1281)	* (0.0282)	n.s. (0.1322)	n.s. (0.0765)
Mean	Baryłka	10.9 ± 0.53 C	2.27 ± 0.22 A	4.25 ± 0.67 C	2.83 ± 0.17 C
	KWS Irina	10.3 ± 0.60 B	2.42 ± 0.22 B	4.00 ± 0.78 B	2.72 ± 0.15 B
	RGT Planet	10.0 ± 0.53 A	2.48 ± 0.24 B	3.83 ± 0.85 A	2.67 ± 0.19 A
HSD p ≤ 0.05 C		*** (0.0000)	*** (0.0000)	*** (0.0000)	*** (0.0000)
Mean	Control	10.3 ± 0.48 A	2.49 ± 0.26 B	3.96 ± 0.92 A	2.71 ± 0.16 A
	Cu	10.4 ± 0.67 AB	2.33 ± 0.26 A	4.09 ± 0.73 A	2.75 ± 0.18 A
	Mn	10.4 ± 0.68 AB	2.37 ± 0.20 A	4.01 ± 0.74 A	2.75 ± 0.19 A
	Mo	10.5 ± 0.76 B	2.37 ± 0.23 A	4.03 ± 0.83 A	2.75 ± 0.20 A
	Zn	10.4 ± 0.67 AB	2.38 ± 0.25 AB	4.05 ± 0.73 A	2.74 ± 0.19 A
HSD p ≤ 0.05 F		* (0.0451)	** (0.0018)	n.s. (0.6789)	n.s. (0.0711)
Year (Y)	2019	10.8 ± 0.50 C	2.26 ± 0.22 A	4.90 ± 0.49 C	2.92 ± 0.10 C
	2020	9.94 ± 0.57 A	2.50 ± 0.23 C	3.45 ± 0.48 A	2.57 ± 0.11 A
	2021	10.5 ± 0.60 B	2.40 ± 0.23 B	3.73 ± 0.44 B	2.73 ± 0.12 B
HSD p ≤ 0.05 Y		*** (0.0000)	*** (0.0000)	*** (0.0000)	*** (0.0000)
Average		10.4 ± 0.66	2.39 ± 0.25	4.03 ± 0.79	2.74 ± 0.18

***, **, and * indicate significant differences at p ≤ 0.001, p ≤ 0.01, and p ≤ 0.05; n.s.—non-significant, according to Tukey’s honestly significant difference test (HSD). Data are presented as mean ± standard deviation (SD). Different lowercase letters (a–d) indicate significant differences among treatments; uppercase letters (A–C) indicate significant differences among means for fertilization, cultivars, or years according to Tukey’s HSD at p ≤ 0.05.

).

The experiment demonstrated an interaction between experimental factors in grain fiber content. In the Baryłka and KWS Irina cultivars, the fiber content in grain was the highest after the application of copper or zinc, while in the RGT Planet cultivar, the highest values were recorded in the grain of control plants. Genotype significantly determined fiber content. Grain of the Baryłka cultivar was characterized by a significantly higher content of this nutrient compared those of the KWS Irina and RGT Planet cultivars (an increase of 0.25 and 0.42%, respectively). The foliar application of each of the micronutrient fertilizers increased the average fiber content compared to the control, and the highest value was recorded after the application of copper (4.09% d.m.); however, these differences were not statistically confirmed (Table 3).

Barley grain averaged 2.74% d.m. of ash. The highest ash content in the Baryłka cultivar was recorded in grain fertilized with molybdenum (2.87% d.m.), while the lowest ash content (2.65% d.m.) was recorded in the RGT Planet cultivar after manganese and zinc application. The ash content in grain was significantly determined by the cultivar. Baryłka cultivars recorded 0.11% d.m. and 0.16% d.m. higher values than KWS Irina and RGT Planet, respectively (Table 3).

The chemical composition of grain depended on the year of the field experiment. Over the three-year field study, the grain of the tested cultivars contained significantly more protein, fiber, and ash in 2019, while the content of these components was the lowest in 2020. The fat content was higher in 2020 and 2021 compared to 2019 (Table 3).

3.2. Malt Quality Parameters

The experiment found that both the barley cultivar and the growing year had a significant impact on the analyzed quality characteristics of the malted grain, while the application of foliar micronutrients did not cause significant changes in the studied quality parameters compared to the control (without fertilization). Higher average extractivity and diastatic power were noted after the application of Mo and Zn, but these were not statistically significant. The statistical analysis of the results confirmed differences between the cultivars in terms of moisture, protein content, extractivity, Kolbach index, and diastatic power of the malt.

The analysis of malt showed a significant interaction between fertilization and cultivar in the values of extractivity, Kolbach index, and diastatic power. In the Baryłka cultivar, the highest extractivity was recorded after the application of Zn; in the KWS Irina cultivar, this parameter was the highest after the application of Mo, while in the RGT Planet cultivar, the best results were obtained in the Mn and Zn variants. The highest Kolbach index was observed in malt obtained from the KWS Irina grain after Mn application (43.5%). This cultivar also had the highest diastatic power (294 W.K.) after Mo fertilization.

Malt obtained from the Baryłka cultivar was characterized by the highest total protein content (11.4% d.m.) and moisture (4.01%). The KWS Irina cultivar achieved the highest Kolbach index values (average 42.9%) and diastatic power (288 W.K. units). Malt from the RGT Planet cultivar exhibited the highest extractivity (82.8% d.m.) with the lowest protein content (10.5% d.m.) and moisture content (3.92%) (

Table 4. The characteristics of barley malt depending on experimental factors and the year of grain harvest.

Cultivar	Fertilization (F)	Moisture	Protein	Extractivity	Kolbach Index	Diastatic Power
		[%]	[% d. m.]	[% d. m.]	[%]	[W.K. Units]
Baryłka	Control	3.87 ± 0.35 a	11.1 ± 0.15 bc	82.2 ± 0.18 a–c	40.9 ± 0.27 c	273 ± 3.45 a
	Cu	3.95 ± 0.25 c	11.5 ± 0.53 c	81.3 ± 0.42 a	40.6 ± 0.31 bc	278 ± 5.12 ab
	Mn	3.96 ± 0.12 bc	11.5 ± 0.24 c	82.1 ± 0.36 ab	40.3 ± 0.33 b	284 ± 5.82 b
	Mo	4.03 ± 0.24 bc	11.5 ± 0.35 c	82.4 ± 0.12 a	40.9 ± 0.12 c	283 ± 3.14 b
	Zn	4.23 ± 0.06 c	11.4 ± 0.51 c	82.9 ± 0.38 ab	40.8 ± 0.29 c	277 ± 6.07 ab
KWS Irina	Control	3.87 ± 0.86 a	10.6 ± 0.33 a	82.6 ± 0.41 c–e	42.4 ± 0.17 d	291 ± 3.69 c
	Cu	4.01 ± 0.69 bc	10.7 ± 0.41 ab	82.7 ± 0.22 c–e	43.1 ± 0.15 e	277 ± 5.97 ab
	Mn	3.95 ± 0.76 b	10.9 ± 0.13 ab	82.5 ± 0.19 a–d	43.5 ± 0.34 e	285 ± 4.83 bc
	Mo	3.94 ± 0.92 b	10.9 ± 0.63 ab	82.8 ± 0.23 b–e	43.3 ± 0.51 e	294 ± 3.54 d
	Zn	4.01 ± 0.77 bc	10.9 ± 0.29 ab	82.5 ± 0.11 a–d	42.0 ± 0.36 d	292 ± 6.50 cd
RGT Planet	Control	3.99 ± 1.34 b	10.6 ± 0.47 ab	82.7 ± 0.46 c–e	39.6 ± 0.29 a	288 ± 3.12 bc
	Cu	3.95 ± 0.68 b	10.5 ± 0.26 a	82.9 ± 0.37 c–e	39.8 ± 0.11 a	279 ± 4.76 ab
	Mn	3.91 ± 0.71 ab	10.5 ± 0.49 a	82.9 ± 0.49 e	38.9 ± 0.34 a	274 ± 4.88 a
	Mo	3.96 ± 0.80 b	10.5 ± 0.41 a	82.8 ± 0.53 de	39.6 ± 0.12 a	285 ± 3.87 bc
	Zn	3.81 ± 0.64 a	10.5 ± 0.27 a	82.9 ± 0.11 e	39.7 ± 0.56 a	291 ± 4.02 c
HSD p ≤ 0.05 C × F		n.s. (0.2971)	n.s. (0.3039)	* (0.0201)	* (0.0152)	* (0.0195)
Mean	Baryłka	4.01 ± 0.14 C	11.4 ± 0.53 C	82.2 ± 0.58 A	40.7 ± 0.27 B	279 ± 4.53 A
	KWS Irina	3.96 ± 0.06 B	10.8 ± 0.60 B	82.6 ± 0.13 B	42.9 ± 0.65 C	288 ± 6.91 C
	RGT Planet	3.92 ± 0.07 A	10.5 ± 0.53 A	82.8 ± 0.09 C	39.5 ± 0.34 A	283 ± 6.88 B
HSD p ≤ 0.05 C		*** (0.0000)	*** (0.0000)	*** (0.0000)	*** (0.0000)	*** (0.0000)
Mean	Control	3.91 ± 0.07 A	10.8 ± 0.48 A	82.5 ± 0.26 A	40.9 ± 1.39 A	284 ± 9.64 A
	Cu	3.97 ± 0.03 A	10.9 ± 0.67 A	82.3 ± 0.87 A	41.1 ± 1.75 A	278 ± 1.00 A
	Mn	3.94 ± 0.03 A	10.9 ± 0.68 A	82.5± 0.40 A	40.9 ± 2.36 A	281 ± 6.08 A
	Mo	3.98 ± 0.05 A	11.0 ± 0.76 A	82.7 ± 0.23 A	41.3 ± 1.91 A	287 ± 5.86 A
	Zn	4.02 ± 0.21 A	10.9 ± 0.67 A	82.8 ± 0.23 A	40.8 ± 1.15 A	287 ± 8.39 A
HSD p ≤ 0.05 F		n.s. (0.6789)	n.s. (0.2901)	n.s. (0.5932)	n.s. (0.6021)	n.s. (0.4854)
Year (Y)	2019	3.99 ± 0.27 C	11.3 ± 0.50 C	82.2 ± 0.58 A	40.6 ± 0.65 B	271 ± 5.41 A
	2020	3.80 ± 0.29 A	10.4 ± 0.57 A	82.6 ± 0.13 C	42.8 ± 0.43 C	283 ± 3.95 B
	2021	3.91 ± 0.24 B	11.0 ± 0.60 B	82.8 ± 0.09 B	39.7 ± 0.47 A	288 ± 6.07 C
HSD p ≤ 0.05 Y		*** (0.0000)	*** (0.0000)	*** (0.0000)	*** (0.0000)	*** (0.0000)
Average		3.96 ± 0.09	10.9 ± 0.66	82.5 ± 0.43	41.0 ± 1.50	283 ± 6.84

*** and * indicate significant differences at p ≤ 0.001 and p ≤ 0.05; n.s.—non-significant, according to Tukey’s honestly significant difference test (HSD). Data are presented as mean ± standard deviation (SD). Different lowercase letters (a–e) indicate significant differences among treatments; uppercase letters (A–C) indicate significant differences among means for fertilization, cultivars, or years according to Tukey’s HSD at p ≤ 0.05.

).

Significant differences were found in the assessed parameters depending on the year of the field experiment. Malt obtained from grain produced in 2019 was characterized by the highest protein content (11.3%) and moisture (3.99%) and the lowest diastatic power (271 W.K.). In 2020, the lowest moisture (3.80%) and protein content (10.4%) and the highest Kolbach index (42.8%) were recorded, while in 2021, extractivity and diastatic power were the highest (Table 4).

4. Discussion

Malting is a process in which cereal grain is germinated and biochemically modified, and its starch becomes available for conversion into simple sugars, which constitute the substrate for fermentation [19]. Because barley is soaked prior to malting, determining the physical properties of the grain is important, which helps improve malt production technology [68,69]. One of the longest-used quality measures of malting barley is the specific gravity of grain. It is a measure of bulk density, i.e., the weight of the grain per unit volume [70,71]. This characteristic plays an important role in determining appropriate storage, transport, and processing conditions, and provides indirect information about the starch and protein content of the grain [69,72].

The typical weight of a hectoliter of malting barley grain is 68–75 kg hL⁻¹ [61,73]. Kumar et al. [72] indicate that values above 65 kg hL⁻¹ are considered optimal for malting barley. In our study, grain obtained from a field experiment in 2019 was characterized by lower density (Table 1). Of the cultivars tested, only the Baryłka cultivar had an average bulk density above 65 kg hL⁻¹. These differences may result from the genetic characteristics of individual cultivars, which influence grain structure and composition, and consequently affect its density. This was also confirmed in the study by Sharma and Verma [74]. However, Hoyle et al. [71] did not demonstrate a significant effect of cultivar on this parameter. The foliar application of Cu had the most beneficial effect on the hectoliter weight of grain. This effect was not demonstrated in the study by Karamanos et al. [75] in which the foliar application of CuSO₄ 5H₂O was used in the cultivation of another cereal, wheat.

Theoretical extractivity is a useful indicator of the malting suitability of barley grain, particularly in multi-year studies, as it enables the accurate prediction of extract yields for Pilsen-type malts [51]. The effect of fertilization on grain density and theoretical extractivity was statistically insignificant, suggesting that under the study conditions, the doses and types of fertilizers used were not crucial for these parameters. Minor differences between fertilization groups could be masked by natural variability in varietal characteristics and environmental conditions. However, a significant interaction between cultivar and fertilization was observed in terms of theoretical extractivity, indicating that different cultivars may respond differently to fertilization.

An analysis of the effect of experimental factors on the elemental composition of grain showed that the application of Cu effectively increased the content of this trace element in grain, especially in the Baryłka and RGT Planet cultivars. This effect was also observed in the experiment for manganese and zinc. This confirms the effectiveness of exogenous application of trace elements in increasing their concentration in grain. The high Fe content in the control treatments and after Mo fertilization suggests that foliar application of molybdenum may indirectly support Fe accumulation by influencing nitrogen metabolism and protein synthesis associated with iron transport [76,77]. Overall, foliar fertilization with trace elements had a positive effect on the mineral composition of barley grain. It can be concluded that the foliar application of trace elements is an effective way to biofortify barley grain with valuable minerals, which may improve its malting and nutritional value.

Barley grain characteristics such as protein content and moisture determine the malting process and result. Protein content in barley grain influences the metabolomic composition and enzyme levels in malt. High protein content limits starch degradation, affects beer flavor, influences foam stability, and reduces malt extractability [19,24]. Conversely, low protein content limits enzymatic activity [19]. Genotypic differences in barley and the harvest year or location influence malting and brewing processes. Barley cultivars exhibit very different malting properties and flavor characteristics, which can influence other quality parameters, such as enzyme levels, protein levels, and flavor [19,78].

An analysis of the chemical composition of barley grain revealed higher total protein and crude ash content in plants foliarly fertilized with micronutrients. Genotypic differences were also noted. Similar results were demonstrated in the study by Tobiasz-Salach et al. [40]. In the conducted experiment, the foliar application of Mo resulted in the greatest increase in grain protein content among the elements tested. Molybdenum, although required by plants in very small amounts, plays a key role in nitrogen metabolism, primarily as an active component of enzymes such as nitrite reductase (NR) and nitrogenoreductase (NiR), as well as nitrogenase in legumes [79,80]. The foliar application of molybdenum allows for bypassing the limitations associated with the uptake of this element from the soil, particularly in acidic conditions, where its mobility and bioavailability are limited [81]. Increased Mo availability supports efficient mineral nitrogen metabolism in the plant, i.e., the conversion of nitrates (NO₃⁻) to ammonium forms (NH₄⁺), which are directly used for amino acid and protein synthesis. As a result, a higher protein concentration was observed in the grain. Furthermore, molybdenum can increase the activity of enzymes involved in the biosynthesis of nucleic acids and other nitrogen compounds, promoting more intensive general plant metabolism and more efficient utilization of nitrogen taken up from basal fertilization [82]. Similar effects were demonstrated in studies conducted by Khot et al. [83] on wheat, where the foliar application of molybdenum on low-pH soil led to an increase in protein content in the grain.

The activity of all starch-degrading factors in barley malt is called diastatic power, which is an important parameter used in the malting industry. Alpha- and beta-amylase together constitute over 99% of the total diastatic activity of malt [84]. Despite some differences observed at the mean value level, micronutrient spraying did not demonstrate a statistically significant effect on the analyzed malt quality parameters. These observations are consistent with previous studies, which indicate that the effect of micronutrients on grain quality is often dependent on the site conditions, plant development stage, and interactions with other nutrients [85]. The results obtained in this study do not confirm the findings of Liszewski and Błażewicz [31], who reported an improvement in malting suitability following the foliar application of Cu and Fe. This discrepancy may be explained by differences in soil micronutrient availability, cultivar sensitivity, and the impact of environmental conditions. Under conditions of sufficient Cu supply, additional foliar application may increase the element concentration in the grain without translating into changes in enzymatic activity or extractability. It is possible that the application of micronutrients for the application date or rate was insufficient to achieve a qualitative effect, or that the response potential was dependent on the cultivar.

The stem-shooting phase is a period of high metabolic activity, but key processes responsible for the synthesis of storage proteins and amylolytic enzymes occur primarily during grain pouring [86]. Applying trace elements too early may not have directly affected these processes, as the metabolic shift toward the formation of malting enzymes occurs later. This may explain the lack of differences in diastatic power and Kolbach index between the treatments. Although foliar supplementation increased the concentration of micronutrients in the grain, this effect did not translate into significant changes in the analyzed malting parameters. A likely explanation lies in the physiological thresholds required for micronutrients to influence key biochemical processes during grain filling. If the plant is not experiencing functional micronutrient deficiency, additional foliar supply may increase the elemental concentration in tissues without triggering measurable changes in metabolic pathways responsible for protein modification or enzyme synthesis [29,87]. Furthermore, the efficiency of foliar uptake and subsequent translocation to developing kernels varies among micronutrients. Elements such as Mn and Zn are moderately mobile in the phloem, while Cu and Fe show restricted mobility, which may limit their delivery to the grain even when leaves are adequately supplied [42]. This suggests that the applied doses may have been sufficient to correct or maintain tissue micronutrient status but not high enough to surpass the metabolic threshold necessary to affect diastatic activity, protein solubility, or extractability. Consequently, the lack of significant changes in malt quality parameters can be interpreted not as a general ineffectiveness of foliar fertilization, but as evidence that the effects of micronutrients are strongly influenced by the initial nutritional status, the needs of a given cultivar, and environmental factors during grain development. The results of the conducted research confirm the significant influence of both cultivars and the year of cultivation on the quality of malt raw material. Consistent with previous reports [88,89], cultivar differences determine basic biochemical parameters of barley grain, directly affecting its suitability for malting and beer production. The higher total protein content found in the Baryłka cultivar may indicate its greater enzymatic potential, but from a practical perspective, excessive protein can limit extractability and compromise malt wort clarity. RGT Planet, on the other hand, with its lower protein content but its highest extractability, demonstrates superior characteristics from the perspective of the brewing industry, where high extraction efficiency is crucial. KWS Irina demonstrated a balanced profile, particularly favorable in terms of Kolbach index and diastatic power, which may indicate good protein solubility and high enzymatic activity, important in mashing processes [90]. Malt extractivity is the main qualitative characteristic of malting barley grain. It determines the total amount of extractable substances that can be obtained from malt during the process of obtaining beer wort [91].

Significant qualitative differences between the study years confirm the high sensitivity of malting barley to climatic variability. It should be noted that wide variability in environmental conditions may mask the effects of foliar treatments, which may be a limitation of this study. Dry and hot climates tend to produce more protein [24]. The highest extractive yield and enzymatic activity values recorded in 2021 suggest beneficial conditions for the synthesis of amylolytic and proteolytic enzymes, which is confirmed by previous studies on the effect of atmospheric conditions on malt quality [72,92].

5. Conclusions

Under the conditions of this study, the foliar application of the examined micronutrients modified the chemical composition of the grain, and differences in the grain’s elemental composition were observed depending on the treatment. Protein content (an important quality parameter) increased as a result of fertilization, particularly after molybdenum application. The higher protein levels observed following molybdenum treatment indicate that its use in malting barley should be approached with caution to avoid exceeding acceptable limits. The research hypothesis that the exogenous application of micronutrients has a significant impact on the parameters characterizing malt quality was not confirmed. The genotype and year of barley harvest had the greatest impact on the studied parameters. The RGT Planet cultivar demonstrated the highest extractive properties, while KWS Irina showed the most favorable enzymatic profile. Significant differences in grain chemical composition and malting properties were observed between years, highlighting the strong impact of environmental conditions on the tested material. The obtained results confirm the key role of cultivar selection in obtaining high-quality grain, while the effect of fertilization (particularly micronutrients) appears to be more complex and requires further detailed investigation. Considering the interactions between cultivar, fertilization, and climatic conditions allows for a better adjustment of agronomic practices to optimize grain yield and quality. A single foliar application of Cu, Mn, Mo, and Zn at the stem-shooting stage altered the mineral composition of the grain and slightly increased protein content, without a significant main effect on extractivity, Kolbach index, and diastatic power. Future research should test different doses, forms, and application timings, including later developmental stages, under multisite conditions, which remains a limitation of the present study.