The Impact of Soil Protection Technologies on Selected Nutritional Parameters in Cereals

1. Introduction

In the production of primary food raw materials, agriculture represents the most important tool. However, conventional agricultural methods are traditionally characterized by the application of numerous chemical agents, such as pesticides and herbicides, as well as by intensive soil tillage [1], which in the long term may lead to disruption of soil structure, a reduction in soil organic matter content [2,3], and changes in soil microbial activity [4,5]. For this reason, it is currently necessary to approach agriculture and the production of primary raw materials in a more sustainable manner, to protect and restore the environment, and improve the quality of primary raw materials.

Many alternative agricultural approaches based on reducing mechanical soil disturbance and maintaining soil surface cover with plant residues can contribute to improvements in both the physical and chemical properties of soil, including increased soil carbon and nitrogen contents [6,7,8,9], as well as to improvements in the quality of the soil microbiome [10]. These factors may subsequently influence nutrient availability for plants as well as metabolic processes responsible for the synthesis of storage and structural components of crops.

Among the most important primary food raw materials whose quality can be directly affected by cultivation practices are cereals. Cereals represent a fundamental component of human nutrition in both developed and developing countries, as they contribute substantially to meeting human energetic and nutritional requirements. In terms of chemical composition, cereal grains predominantly contain carbohydrates, mainly starch, which accounts for approximately 50–80% of their content. Protein content ranges from 5–6%, while lipid content is typically between 1–10%. The consumption of cereals, especially whole-grain cereal products, is associated with the intake of nutrient-rich foods that provide, in addition to basic primary metabolites, a range of B-group vitamins, including thiamine (B1), riboflavin (B2), and niacin (B3), vitamin E, and minerals such as calcium, magnesium, potassium, phosphorus, iron, and sodium [11]. Currently, considerable attention is being devoted to the role of cereals in the diet, particularly whole grains, mainly due to their fibre and bioactive compound content.

The impact of agricultural technologies on dietary fibre components has been investigated in only a limited number of studies. In a study published in 2023, Korge et al. [12] reported a somewhat higher content of arabinoxylans in wheat grains grown under organic farming systems (3.3–5.4%) compared to conventional systems (2.2–4.3%), whereas in barley, the differences between cultivation systems were not statistically significant. Available studies indicate that the content of beta-glucans, an important fibre component in cereal grains, is significantly influenced by genotype and environmental factors [13]. When several genotypes of spring barley were cultivated using no-till technology, any reduction in the content of these polysaccharides (6.6–8.2%) was not observed compared to conventional agriculture [14]. Similarly, the application of organic farming principles, which are characterized by lower soil disturbance compared to conventional systems, may positively affect beta-glucan content in barley [15].

The positive effects of soil-conservation technologies on soil properties, particularly on soil organic carbon and nitrogen content, have been confirmed by several studies [16,17,18]. Total soil nitrogen content subsequently has a strong influence on protein content in cultivated crops [19]. In grains of bread wheat cultivated under no-till farming, the average protein content was 14.56%, which was 0.15% higher than in conventionally grown wheat [20]. In addition, it has been demonstrated that these systems can also affect the availability of soil micronutrients, such as calcium and magnesium cations [21], which are important factors influencing the nutritional composition of cultivated crops.

The influence of agricultural technology on starch content in cereal grains has also been described in studies comparing conventional and organic farming systems. In a study conducted in Hungary, a higher starch content was found in organically grown spring wheat (59.4%) compared to conventionally grown wheat (52.5%) [22]. In a study by Zörb et al. (2009) [23], content fractions of several metabolites, including lipids and fatty acids, were determined in wheat grains grown under conventional and organic systems. No statistically significant differences were observed between conventionally and organically grown wheat in the contents of free fatty acids, 1,2-diacylglycerols, triacylglycerols, or sterol lipids.

These results suggest that the impact of agricultural technologies on the nutritional composition of cereal grains is not clear and depends on multiple factors, including crop species, genotype, environmental conditions, and the duration of the experiment. To date, research has largely focused on evaluating the effects of different tillage systems on crop yields, soil physical and chemical properties, and biological activity, while the influence of agricultural technologies on the nutritional composition of cereal grains has been studied to a much lesser extent. Available studies often focus only on selected quality parameters, a single crop species, or short-term experiments that do not account for interannual variability in growing conditions. Comprehensive evaluations of multiple nutritionally relevant grain components in relation to different agricultural technologies, conducted within multi-year field experiments and including comparisons among several cereal species, therefore remain insufficiently explored.

This study aims to evaluate the effects of conventional and selected sustainable agricultural technologies, including no-till, minimum tillage, and mulch-till soil tillage systems, on the nutritional composition of grains of spring barley (Hordeum vulgare L.), winter wheat (Triticum aestivum L.), and corn (Zea mays L.). The contents of selected nutritionally important components, specifically beta-glucans, proteins, starch, lipids, and total dietary fibre, were analyzed. The experiment was performed as a two-year field trial, allowing for the consideration of variability in growing conditions between individual growing seasons. The results of this study may contribute to expanding knowledge on the relationships between soil management practices and the qualitative parameters of cereal grains under sustainable agriculture conditions.

2. Materials and Methods

2.1. Field Experiment and Site Characteristics

Field experiments were conducted at the Borovce Experimental Station of the National Agricultural and Food Centre, Slovakia (GPS: 48°34'51.0" N 17°43'53.2" E). The plots were situated at an altitude of 167 m above sea level in a continental climate zone. In this study, the results of a two-year field experiment conducted during 2023–2024 were evaluated. Mean monthly air temperatures and precipitation totals recorded during the individual years of the experiment are presented in Table 1 and Table 2. The measured values are shown together with the long-term average (LTA) for the last 30 years (period of 1996-2026), according to data from the Meteorological Station in Borovce, the Slovak Republic. The annual precipitation in 2023 was 690.0 mm, while the average annual air temperature was 10.86 °C. The annual precipitation in 2024 was 657.0 mm, while the average annual air temperature was 12.45 °C.

2.2. Soil Characteristics

The soil was classified as Luvic Haplic Chernozem developed on loess, with a humus horizon depth of 0.4–0.5 m, medium phosphorus and potassium supply, neutral to slightly acidic pH, medium humus content in the topsoil, and low humus content in the subsoil layers.

The selected chemical properties of the soil were determined from samples collected from the 0–30 cm soil layer. The analysis included the determination of total nitrogen (N), carbon (C), humus content, available phosphorus (P), soil pH, ammonium nitrogen (NH₄⁺N), and nitrate nitrogen (NO₃^-N). The results are presented in Table 3. These parameters were used to characterize the initial soil conditions of the experimental site in the 2023 and 2024 growing seasons.

2.3. Plant Material and Crop Management

Four tillage systems were compared: conventional tillage, minimum tillage, mulch-till, and no-till. Tillage depth was 0.24 m in the conventional system and 0.15 m in both the reduced and mulch-till systems.

The crop rotation reflected the prevailing structure of crops in Slovakia (over 50% cereals) and included Triticum aestivum L. (winter wheat; cultivar PS Luana), Zea mays L. (corn; hybrid DKC-4391), and Hordeum vulgare L. (spring barley; cultivar IS Maltigo). Table 4 shows the sowing and harvest dates of individual crops during 2023 and 2024.

• (i) spring barley: 120 kg·ha⁻¹ N, 30 kg·ha⁻¹ P, 80 kg·ha⁻¹ K,.
• (ii) corn: 189 kg·ha⁻¹ N, 44 kg·ha⁻¹ P, 146 kg·ha⁻¹ K, and
• (iii) winter wheat: 163 kg·ha⁻¹ N, 34 kg·ha⁻¹ P, 105 kg·ha⁻¹ K.

Nitrogen fertilization was provided using Spring-LAV (27.5% N) and DAM-390; phosphorus was supplied as Hyperkorn (26% P₂O₅), and potassium as potassium salt (60% K₂O).

Fertilization was applied to reach the harvest levels of 6 t·ha⁻¹ for winter wheat, 7 t·ha⁻¹ for corn, and 5 t·ha⁻¹ for spring barley. Each experimental plot had an area of 9 m × 35 m, and grass strips were sown between plots. Each tillage treatment was arranged in three replications.

2.4. Sample Preparation and Grain Quality Analysis

Samples of all studied crops differed in cultivation approach. The soil tillage technologies applied in the cultivation of the analyzed crops included conventional tillage and conservation soil management practices (no-till, minimum tillage, and mulch-till).

For each crop, every quality parameter was determined in three samples (biological replicates), each measured in three parallel determinations (technical replicates). The evaluated grain quality parameters were the content of beta-glucans, proteins, starch, total dietary fibre, and lipids.

Before analysis, the samples were ground using an ultracentrifugal mill (ZM 100, Retsch, Haan, Germany) to a particle size of 0.5 mm and stored in sealed containers in the dark at 19 °C. Immediately before analysis, the dry matter content was determined at 110 °C using an automatic moisture analyser (MA 45, Sartorius AG, Göttingen, Germany) to recalculate the quality parameters on a dry matter basis. The procedure was validated by AOAC (Method 925.10) [24].

2.5. Determination of Beta-Glucan Content

The total beta-glucan (BG) content in the samples was determined using the β-Glucan (Mixed Linkage) assay kit (Megazyme by Neogen^®, Bray, Ireland). This streamlined procedure has been validated by the AACC (Method 32-23.01) [25], AOAC International (Method 995.16) [26], and the ICC (Standard Method No. 166) [27].

Mature grains of barley, wheat, and corn were suspended and hydrated in triplicate in sodium phosphate buffer (pH 6.5). The samples were then incubated with purified lichenase (EC 3.2.1.73) and subsequently filtered. An aliquot of the resulting filtrate was further hydrolysed using β-glucosidase (EC 3.2.1.21). The released glucose was quantified by a glucose oxidase/peroxidase assay, and the measured concentration was used to determine the BG content on a dry-weight basis in the sample.

2.6. Determination of Starch Content

Starch content was analyzed in triplicate using the Ewers polarimetric method in accordance with ISO 10520:1997 / EN ISO 10520:2002 (Native starch — Determination of starch content) [28] and ICC Standard No. 123/1 [29] by using an optical polarimeter (AP-300, Atago^®, Saitama, Japan).

This procedure is based on the partial hydrolysis of starch with hydrochloric acid. Subsequently, the optical rotation of the resulting solution is measured in a 200 mm polarimetric cell at 21 °C, and the recorded values are converted to the starch content.

2.7. Determination of Total Dietary Fibre

Total dietary fibre (TDF) was determined using the enzymatic-gravimetric method with the Megazyme K-TDFR kit (Megazyme by Neogen^®, Bray, Ireland). One gram of ground sample was sequentially treated with thermostable α-amylase (EC 3.2.1.1), protease (EC 3.1.3.48), and amyloglucosidase (EC 3.2.1.3) under controlled pH and temperature conditions to remove starch and protein components.

After digestion, TDF was precipitated with ethanol, filtered through pre-weighed crucibles, dried to constant weight, and gravimetrically quantified. The residue was corrected for protein (nitrogen determined by the Dumas method, AACC Method 46-30 [30]) and ash (incineration at 525 °C, AACC Method 08-01.01 [31]), including blank corrections. Results were expressed as a percentage of dry matter.

2.8. Determination of Protein Content

The nitrogen content was determined by the Dumas combustion method. Approximately 200 mg of each sample was weighed in duplicate into a ceramic boat and introduced into the automatic sampler of an automatic analyser (TruMac CNS Macro Analyzer, LECO Corp., St. Joseph, Michigan, USA). Upon completion of the analysis, the instrument software automatically calculated the concentration of total nitrogenous compounds.

The total protein content was subsequently calculated using a conversion factor of 5.70 for wheat, 5.83 for barley, and 6.25 for corn, in accordance with ICC Standard No. 105/2 [32].

2.9. Determination of Lipid Content

Samples were extracted with n-hexane (30, 20, 15, and 12 mL) in centrifuge tubes. Extraction was performed using microwave-assisted heating (6 × 30 s), with shaking and repositioning of the tubes between cycles to ensure uniform heating. The extracts were centrifuged (Universal 320R, Hettich GmbH, Tuttlingen, Germany) at 4200 RPM for 5 min, and the supernatants were collected.

Combined extracts were filtered through anhydrous sodium sulphate, and the residue was rinsed with n-hexane (3 × 3 mL). The solvent was evaporated using a rotary vacuum evaporator (Laborota 4001, Heidolph Instruments GmbH & Co. KG, Schwabach, Germany) at 60 °C. After 24 h at laboratory temperature in a desiccator, the flasks were weighed (m₂), and oil content was determined gravimetrically from the mass difference (m₂ – m₁), expressed as a percentage of dry matter.

2.10. Statistical Evaluation

Statistical analysis was performed using a three-factor analysis of variance (ANOVA), followed by Tukey’s HSD (Honestly Significant Difference) post-hoc test to evaluate significant differences among samples collected. The considered factors were F1—Type of Cereal (‘TC’; namely barley, corn, wheat), F2—Harvest Year (‘HY’; namely 2023, 2024), and F3—Soil Tillage Technology (‘STT’, covering conventional tillage, minimum tillage, mulch-till, and no-till attitude). The effects of the listed factors were compared using a stacked column plot of variance components, focusing on the five principal nutritional components of cereal grain. The significance level was set at p < 0.05. All three factors were used as supplementary (explaining variables) to build a model of the Principal Components Analysis (PCA), based on correlations; the goal of PCA is to confirm well-known relationships between cereal grain compounds as well as to contrast F1 vs F2 vs F3. Owing to the interaction of three factors, the samples' score plot was visualized from the viewpoint of three combinations of the factors’ pairs. All statistical analyses were conducted using Statistica 64 (v. 13.0; Dell, Tulsa, OK, USA).

3. Results

3.1. Nutritional Composition of Cereal Grains Tested

Analysis of the selected nutritional parameters revealed that starch is the predominant primary metabolite in cereal grains. The highest starch content was observed in corn grain (mean: 77.20%), followed by winter wheat (66.05%) and spring barley (59.92%). In the cereal grain, starch serves as the storage substance and energy source for the developing sprout. In human nutrition, starchy raw materials are an important and irreplaceable source of energy and glucose.

TDF is a complex of various non-starch polysaccharides that are either not hydrolysed or only partially hydrolysed by microorganisms in the human intestinal microbiome. In plant organisms, they primarily have a structural role in cell walls. For the human organism, the consumption of dietary fibre components is an energy source and brings various physiological benefits for the body and its functions. In our experiment, barley grain had the highest average TDF content (13.36%). Lower content was observed in the wheat grain (10.35%), and the lowest content was found in corn grain (8.65%).

The group of soluble dietary fibre includes BG. They have been studied not only because of the number of physiological functions in the plant cell, but also for the consumer, for their health-beneficial properties, and technological importance in the food industry. Barley grains are known as good sources of this polysaccharide. In our experiment, an average content of 3.75% was detected. Significantly lower contents were found in wheat and corn grains, 0.71% and 0.12% on average, respectively.

Proteins are an essential component of every living organism, and in cereal grains, they are an important indicator of nutritional quality and subsequent use. The average content of this primary metabolite was detected as follows: the highest content was in wheat (12.02%), followed by barley (11.19%) and corn (7.94%).

Lipids belong to the primary metabolites with nutritional significance for the consumer. Cereal grains are not their ideal natural source, but their location and composition, with a higher proportion of unsaturated and essential fatty acids, make them justified. We observed the highest content of lipids in corn grain (3.66%). The content of lipids in wheat and barley grains was almost similar and was in the average values of 2.37% and 2.22%, respectively (Table 5).

To compare the growing seasons, it can be confirmed that in barley grains, an increase in starch content was detected in 2024 compared to 2023 (59.56% in 2023 and 60.29% in 2024, representing a 1.23% increase), as well as TDF (12.68% compared to 14.04%, corresponding to a 10.73% increase), proteins (9.87% compared to 11.23%; so 11.23% is 13.78% higher than 9.87%), and lipids (the value increased from 2.18% to 2.27%, corresponding to a 4.13% increase). On the other hand, a decrease was detected in the content of BG. The value decreased from 3.88% in 2023 to 3.62% in 2024, representing a 6.70% decrease (Figure 1).

In corn grains, the content of TDF and proteins increased between the two harvest years. Specifically, TDF increased from 7.15% in 2023 to 10.15% in 2024, representing a 41.96% increase, while protein content increased from 7.55% to 8.32%, corresponding to a 10.20% increase. In contrast, decreases were observed in the contents of starch, lipids, and BG. Starch content decreased from 78.31% in 2023 to 76.09% in 2024 (2.83% decrease), lipid content from 3.82% to 3.49% (8.64% decrease), and BG content from 0.16% to 0.09% (43.75% decrease).

Wheat grain exhibited an overall increasing trend in TDF, protein, and BG contents between the two harvest years. A slight increase was observed in TDF and BG. In the case of TDF, it was from 10.19% in 2023 to 10.50% in 2024 (3.05% increase), and in the case of BG, the increase was 4.29%, from 0.70% to 0.73%. Protein content increased more significantly, from 10.94% to 13.09% (19.65% increase). Conversely, starch and lipid contents decreased over the same period, from 67.59% to 64.50% (4.58% decrease) and from 2.78% to 1.95% (29.86% decrease), respectively.

By evaluating nutritional parameters, it can be confirmed that in 2024, compared to 2023, the starch content increased only in barley; in corn and wheat, the trend was decreasing. The content of TDF and proteins was higher in 2024 compared to 2023 in all cereals analyzed. In the case of lipids, in 2024 compared to 2023, the content was increasing only in barley and decreasing in corn and wheat. BG showed an increasing trend between the two harvest years only in wheat grains. In grains of barley and corn, the content of BG in the grain decreased from 2023 to 2024.

3.2. Comparison of the Soil Tillage Technologies Applied

By analysing the influence of soil tillage technologies on the selected nutritional properties of the cereal grain, it can be shown that the effect was different in relation to the cereal type, harvest year, and soil tillage technology. Compared to conventional technology, it can be detected that in barley grain, the no-till technology increased the content of lipids, starch, and BG similarly in both analyzed years. An increasing trend was also observed in the mulch-till technology in starch content and TDF in barley grain. Minimum technology also showed an increase in the content of BG in both analyzed years uniformly.

In corn grains, it can be detected that no-till technology increased the content of lipids, proteins, and TDF compared to conventional technology, and in both analyzed harvest years. An increase was also observed by applying mulch-till, specifically in the content of lipids, starch, and BG. Minimum tillage led to an increase in starch and BG content in corn grain in both years compared to conventional soil technology.

Minimum tillage was also successful in increasing the content of proteins in wheat grain, and very slightly and not significantly the content of BG in 2023 and lipids in 2024. No-till technology increased the content of TDF in wheat grain in both analyzed years and very slightly increased the content of BG in 2023. Compared to barley and corn, the influence of soil tillage technologies on wheat was very ambiguous. Except for the few cases mentioned above, a decreasing trend was detected in the content of starch, most of the lipids, and BG. By generalizing the evaluated data, the most successful technology increasing the content of analyzed nutritional parameters in cereals seems to be the no-till technology (Figure 1).

The influence of harvest year was a statistically significant source of variability in the content of lipids, proteins, and TDF in cereals. In the case of proteins and TDF, there was a moderate positive correlation. Weak negative correlations were observed in the content of lipids. Generally evaluated, we can conclude based on the results that the positive correlation coefficient indicates that the metabolite contents measured in the two years varied in the same direction, suggesting temporal consistency in their accumulation among samples. This means that samples with higher protein and fibre content in the year 2023 also tended to have higher content of these metabolites in the year 2024, and conversely, samples with lower values in 2023 tended to stay lower in 2024. A weak negative correlation observed between lipid contents measured in the two years, indicates a slight inverse relationship, although the association is limited (Table 6).

Pearson correlation analysis indicated no significant relationship between soil tillage technology and cereal nutritional parameters, suggesting that tillage practices had a limited influence on grain composition under the studied conditions. On the other hand, the type of cereal was a significant source of variability in all analyzed nutritional parameters (proteins, starch, TDF, and BG) except for the content of lipids. In proteins and starch was the correlation moderate positive. The content of TDF and BG was strongly and very strongly negative, respectively, showing a significant influence of cereal grain type on the accumulation of BG in cell walls.

Comparing the analyzed metabolites with nutritional value in cereals, it can be seen that a very strong negative correlation (r = –0.797) was observed between protein and lipid contents, indicating that samples with higher protein concentrations tended to contain lower lipid levels. A negative correlation with the same negative strength was also detected in the case of starch and TDF content (r = –0.823) and starch and BG content (r = –0.827). Strong negative correlation was observed between the content of lipids and TDF (r = –0.665), lipids and BG (r = –0.606), and proteins and starch content (r = –0.699).

A positive Pearson’s correlation coefficient indicates that two variables move in the same direction: as one variable increases, the other increases too, and as one decreases, the other also decreases. A very strong positive correlation was observed in our experiment between the content of lipids and starch (r =0.874) and between the content of TDF and BG (r = 0.804). Moderate positive correlation was detected between proteins and TDF content (r = 0.492) and a weak positive correlation between proteins and BG (r = 0.260; Table 6).

Comparing the three types of cereals, it can be concluded that the barley grain is characterized by the highest content of BG and TDF and the lowest content of lipids and starch. Starch and lipids represented the predominant metabolites in corn grain. Conversely, corn kernels are the poorest in terms of protein and TDF content. Wheat grain accumulates the highest concentrations of proteins among the analyzed cereals. All differences between crops were statistically significant in the nutritional parameters analyzed (Figure 2a).

When evaluated collectively across all cereals and soil tillage technologies, the assessed parameters showed statistically significant differences between years. By comparing the years 2023 and 2024, an increase was observed in the content of proteins and TDF. On the contrary, a decline was detected in the content of starch, lipids, and BG (Figure 2b).

By joint evaluation of soil tillage technologies, it is shown that the content of proteins was not influenced by the technology, and the average content was stable and not significantly different among all technologies. Variability was monitored depending on the technology for other parameters, while the most significant differences were in the content of TDF and starch. The highest content was observed using no-till technology, and the lowest by minimum technology. The highest content of starch was in the minimum technology, and the lowest was obtained by applying mulch-till. Significant variability was also detected in the case of lipids and BG. The highest lipid content was shown by no-till technology, and the lowest by minimum soil tillage technology. BG content was the highest in no-till technology and the lowest in mulch-till technology. Protein content was not significantly affected by soil tillage technology. In contrast, significant differences among technologies were observed for TDF, starch, lipids, and BG. No-till technology generally resulted in the highest contents of TDF, lipids, and BG, whereas minimum technology showed the lowest values in TDF and lipids but the highest starch content. Mulch-till technology resulted in the lowest BG and starch contents. Conventional technology showed intermediate values and was not identified as either the highest or the lowest for any assessed parameter (Figure 2c).

The variability of nutritional parameters in cereals was primarily determined by Type of Cereal (F1), which accounted for the largest proportion of the explained variance for all analyzed traits. This variability factor was particularly dominant in the BG content and, to a slightly lesser but still marked extent, in the starch content of the cereal samples. Harvest Year (F2) contributed moderately to the variability in protein accumulation and TDF. Soil Tillage Technology (F3) had a comparatively minor effect. Interaction effects among factors were generally low (Figure 3).

Since the factor F1–Type of Cereal appeared to be the most significant source of variability in the content of the analyzed metabolites, by individually evaluating the influence of the year, soil tillage technology, and their combination, it can be stated that, in the case of barley, the Harvest Year (F1) appeared to be a more significant factor of variability compared to Soil Tillage Technology (F2). The year most significantly affected the protein content (80%), followed by TDF (49%), and BG (39%). The weak influence of the year was in the case of the content of starch (10%) and lipids (7%). Soil tillage technology mainly affected the TDF content (35%), and to a lesser extent, the lipids (19%), BG (18%), and starch content (17%). Protein content was not affected by the applied technology on the soil. A combination of factors (F1 x F2) was responsible for the variability in content lipids (20%), proteins (17%), and BG (15%). Very slightly and almost negligibly contributed F1 x F2 to the variability in content starch and TDF (8% and 2%, respectively) (Figure 4a).

In corn, our results show that the most dominant factors of variability were the Harvest Year (F1) and the combination F1 x F2. Harvest year influenced the content of TDF by 87%. In BG, it was 57%, 51% for starch content, and 17% and 9% in the case of proteins and lipids. Soil Tillage Technology (F2) was a weak factor of variability in the variability of nutritional parameters in corn grains. It influences only the BG content (16%), TDF, and starch (9% each). A combination of factors is responsible for the strong variability in the protein content (79%) and lipid content (77%). A milder impact it had on the content of starch (27%), BG (11%), and minimally on the TDF content (1%) (Figure 4b).

The content of nutritionally important metabolites in wheat grain was, in our experiment, influenced mostly by the harvest year (F1). A strong impact was detected in the content of proteins (88%) and lipids (85%), then by 61% in starch content, and a weak effect was observed in the content of BG (7%) and TDF (3%). Soil tillage technology was a source of variability only in the content of BG (47%), TDF (23%), and starch (19%). The content of lipids and proteins in wheat grain was not influenced by the soil tillage technology applied in our experiment. The combination of factors (F1 x F2) contributed to the variability in TDF content by 17%, 13% each in the case of the content of starch and BG, and slightly in proteins (9%) and lipids (2%) content (Figure 4c).

3.3. Data Exploration by Principal Component Analysis

Figure 5 presents the multivariate statistics of the chemical composition of cereal grains cultivated under different soil tillage technologies and harvested in two consecutive years. The first two principal components (PC) explained 72% of the total variability, with PC1 accounting for 50% and PC2 for 22% (Figure 5).

The loading plot (Figure 5a) shows that starch and lipids were positively associated with PC1, whereas TDF, BG, and proteins were negatively associated with this component. In the case of PC2, it was mainly influenced by protein content and the type of cereal. These reciprocally negative relations correspond to the fact that all these compounds share the same space in a cereal grain. In the first score plot of their trio (Figure 5b), wheat samples were positioned in the upper region of the plot, associated with higher protein concentrations, while barley samples were in the lower-left quadrant, closely related to TDF and BG contents. Corn samples clustered on the +PC1 semi-axis and were strongly associated with starch and lipid contents.

The score plots (Figure 5b) demonstrate a clear separation of samples according to cereal species and harvest year. In the figure, barley, wheat, and corn formed distinct clusters, indicating marked compositional differences among cereal types. Wheat samples were characterized by higher PC2 values, barley by negative PC1 and PC2 scores, and corn by positive PC1 values. However, wheat sub-clusters demonstrated the longest inter-centre distance, i.e., this type of cereal was more susceptible to effect of the climate of the harvest years 2022/23 and 2023/24. Considering the furthest items of the wheat, corn and barley bi-clusters in the PC1 × PC2 areas, the longest distances were estimated to 2.65, 1.90 and 1.92 PC-units, respectively. Figure 5c reveals a consistent separation between harvest years 2023 and 2024 within each cereal species, suggesting a significant harvest year effect on grain composition, likely related to environmental and climatic conditions during crop development.

In contrast, the distribution of samples according to soil tillage technologies (Figure 5d) showed substantial overlap among conventional, minimum tillage, no-till, and mulch-till systems. This indicates that the cultivation technology had a weaker influence on the evaluated compositional parameters compared with the type of cereal and the harvest year. Within simple clusters in the PC1 × PC2 plane, no significant trend between four soil tillage technologies could be identified in general. Maybe for wheat of both harvest years 2003 and 2004, ‘green’ samples bred under the conventional system fell to the bottom margin of the relative sub-clusters. In a reversal manner for barley, ‘violet’ mulch-till samples are located on the upper border of the imminent sub-groups within the III. quadrant of Figure 5b.

Overall, multivariable PCA was able to confirm that cereal type was the dominant factor determining grain composition, followed by harvest year (Figure 5), whereas soil conservation technology exerted a comparatively smaller effect (as quantified supra in plots of variance components on Figure 5d).

4. Discussion

The results obtained from the evaluation of nutritional parameters in the cultivated crops confirm that individual cereal species show significant differences in their composition. These differences are related not only to their importance in human nutrition but also to their technological and functional use in the food industry. The observed compositional patterns further indicate that genotype is the primary determinant of cereal nutritional profiles, demonstrating strong genetic control over metabolite accumulation. Based on these species-specific differences, cereals therefore cannot be evaluated only according to agronomic parameters or their energy value, but also according to their contribution to a balanced diet and their suitability for specific technological applications.

The highest starch content in corn confirms its importance as an energy-rich cereal. From a nutritional point of view, corn grain represents an important source of energy; however, its lower content of TDF and BG indicates a smaller contribution in terms of functional dietary components. Nevertheless, corn is widely used in many technological and industrial applications, such as the production of starch, sweeteners, and bioethanol [33,34]. Due to its high starch and lipid contents, corn also has an important position in feed production, where it belongs to the most important energy feeds for cattle, pigs, and poultry, being used not only in the form of grain but also as a whole plant for silage production [35].

Barley has a markedly different nutritional profile due to its lower starch content but substantially higher content of TDF and BG, together with lower lipid accumulation. Compounds of TDF and BG possess many health-promoting properties, mainly associated with lowering LDL cholesterol levels in the blood [36], reducing the glycaemic index [37], preventing cardiovascular diseases [38], and supporting gut health [39]. This nutritional composition highlights the importance of barley as an essential component for the preparation of functional foods [40,41,42].

The importance of wheat as a staple food crop is also based on its composition in terms of protein content. Wheat proteins, particularly gliadins and glutenins involved in the formation of the gluten network, are essential for the proper rheological and structural properties of dough and for the sensory quality of bakery products [43,44]. The higher protein concentration observed in wheat further confirms its technological importance and suitability for bakery processing.

Our results further confirm that cereal species is the dominant source of variation in grain composition, with BG and starch showing particularly strong genotype dependence. These traits reflect inherent differences in carbon partitioning and cell wall biosynthesis, with barley specialized for structural polysaccharide accumulation and corn for starch deposition. Such stability across environments underscores their value as key breeding targets.

Overall, it can be concluded that each of the studied crops has its own specific characteristics in terms of nutritional and technological importance. However, the observed differences in nutritional composition are not related only to species differences but are also determined by the effects of several cultivation-related [14,16] and environmental factors [45]. The content of the analyzed primary metabolites is largely determined by genotypic characteristics; however, their final amount in the grain may depend on the harvest year, meteorological conditions, nutrient availability in the soil, and, finally, the selected soil tillage technology [12,17,18]. For this reason, when evaluating the nutritional properties of cereals, it is important to consider not only the cereal species itself, but also the conditions under which the grain was grown.

The nutritional composition of cereal grain is the result of complex interactions between genetic factors, environmental conditions, and agronomic practices [46]. The observed differences in the content of individual metabolites suggest that species-specific characteristics are among the main determinants of the overall nutritional profile, which was also confirmed by the correlation analysis. The nutritional composition of cereals varied considerably between 2023 and 2024, indicating a strong influence of climatic and environmental conditions. Numerous studies have shown that factors such as temperature, precipitation, heat stress, and soil moisture can substantially affect the accumulation of primary metabolites in cereal grains [47].

Harvest year induced consistent but secondary shifts in grain composition, with increased protein and TDF contents and reduced starch, lipids, and BG in 2024. These trends indicate environmentally driven reallocation of assimilates during grain filling and suggest metabolic trade-offs between storage and structural compounds under variable growing conditions. Harvest year effects were mainly associated with proteins and fibre and were likely mediated by climatic modulation of nitrogen metabolism, carbohydrate allocation, and grain-filling dynamics.

When comparing both harvest years, several opposite trends were observed in the accumulation of individual metabolites in the grains, particularly starch and proteins. Environmental stress, such as drought or elevated temperature, may reduce carbohydrate deposition while simultaneously increasing the relative concentration of proteins [48]. In contrast, soil tillage exerted a comparatively weaker effect, with protein content remaining relatively stable across systems, indicating greater genetic buffering of nitrogen-related metabolism compared with carbon-based fractions.

Another interesting finding was the negative correlation between starch content and fibre fractions in some cereals, suggesting metabolic differences in carbon allocation between storage carbohydrates and structural cell wall carbohydrates during grain maturation. This phenomenon was also reported by Panahabadi et al. (2021) in a genome-wide mapping study of carbohydrate composition in rice (Oryza sativa L.) [49]. From a nutritional perspective, this relationship is important, as starch mainly serves as an energy component of the grain, whereas TDF and BG are associated with beneficial physiological effects and the use of cereals in the development of functional foods [50].

The results, particularly those shown in Figure 1, suggest that soil conservation systems may have a favourable effect on selected nutritional indicators, with no-till technology generally appearing to be one of the most promising variants. This effect may be associated with improved soil structure, higher organic matter content [6], increased activity of the soil microbiome [51], and reduced soil erosion [52]. The observed management effects were metabolite-specific, indicating that soil tillage may subtly modulate the balance between energy-storage compounds and functional quality traits. In general, no-till technology tended to increase TDF, lipids, and BG, whereas minimum tillage favoured starch accumulation, while mulch-till was associated with lower starch and BG contents.

However, it is important to emphasize that the positive effects were not universal and depended on the cereal species, harvest year, and specific metabolite. According to Pearson’s correlation analysis, the factor of soil tillage technology alone did not show a significant correlation with the content of nutritional indicators. These findings suggest that soil tillage remained a comparatively minor source of variability, reinforcing the assumption that agronomic practices primarily fine-tune rather than fundamentally restructure cereal grain composition.

The two-year duration of the experiment is relatively short for a thorough verification of the effect of soil conservation technologies on the nutritional quality of cereal grain. Therefore, it will be necessary to continue the analysis and evaluation of individual cereals in the following years of the ongoing experiment. Processes such as changes in organic matter content, microbial activity, and soil structure are cumulative in nature and may not become evident immediately; consequently, the effect on changes in the content of individual nutritional indicators in cereal grains may not yet be very pronounced. These assumptions are also supported by several long-term field experiments in which the positive effects of conservation agricultural technologies became evident only over a longer time horizon [53,54,55,56].

Some cereals, particularly wheat, showed a less pronounced response to different types of agricultural technology compared with corn and barley. This may be because genetic characteristics or year-specific conditions play a greater role in wheat in the accumulation of individual metabolites in the grain than soil management itself [57]. However, Martínez-Peña et al. (2023), analysing different durum wheat genotypes typical of Spanish regions, found a stronger influence of climatic and agronomic conditions compared with genotype, which further confirms the complexity of interactions among individual factors [58].

Overall, it can be concluded that harvest year, cereal species, and soil tillage technology jointly shape the nutritional composition of cereal grain, while their effects are specific to both the primary metabolite and the cereal species itself. Low interaction effects indicate stable genotypic ranking across environments, supporting robust genetic control of nutritional traits and confirming that species-specific characteristics remain the primary determinant of grain composition. Across cereals, harvest year consistently exerted stronger effects than soil tillage, highlighting the predominance of climatic regulation over management practices.

However, response patterns differed markedly among species. Barley showed pronounced year effects on proteins, TDF, and BG, with relatively stable starch and lipid contents. Corn exhibited high environmental sensitivity with strong interaction effects across multiple metabolites, indicating pronounced genotype–environment–management interplay. Wheat showed strong year-driven variation in proteins, lipids, and starch, while TDF and BG were comparatively stable, with a specific responsiveness of BG to soil tillage. Overall, proteins and TDF were the most environmentally responsive fractions; starch and lipids exhibited greater stability, and BG showed strong species- and management-dependent variability.

Soil conservation tillage technologies appear promising in terms of sustainable production and the potential improvement of selected nutritional parameters; however, their effect cannot be considered universal. These results emphasize that agronomic effects are strongly context-dependent and mediated by genotype–environment interactions. For breeding, agronomic practice, and the food industry, it is therefore essential to adopt a targeted approach to cereal selection and cropping systems according to the desired nutritional profile and stability of quality traits.

5. Conclusions

The results of this study clearly show that the nutritional composition of cereal grains is influenced predominantly by the genotype, with cereal species serving as the principal source of variation across all measured metabolites. Distinct metabolic profiles were evident: spring barley exhibited elevated levels of TDF and BG but comparatively low starch and lipid contents; winter wheat was characterized by consistently higher protein concentrations, and corn displayed pronounced accumulation of starch and lipids. These patterns underscore strong species-specific metabolic specialization and reaffirm the central role of genotype in determining grain quality traits.

Environmental conditions associated with the harvest year exerted a measurable, though secondary, influence on grain composition. In 2024, cereals generally accumulated more protein and TDF, while starch, lipids, and BG tended to decrease. Such shifts point to environmentally mediated adjustments in carbon and nitrogen partitioning during grain filling, as well as intrinsic metabolic trade-offs among storage and structural components.

In contrast, soil tillage practices produced relatively modest and context-dependent effects. No-till systems occasionally enhanced specific quality attributes—particularly TDF, BG, and lipids—yet protein content remained largely stable, suggesting strong genetic buffering against management-level perturbations. Overall, tillage influenced grain composition far less than genotype or environment, indicating that agronomic practices primarily fine-tune rather than fundamentally reshape cereal nutritional profiles.

Multivariate analyses reinforced these conclusions. Species and harvest years formed well-defined clusters, whereas tillage treatments overlapped extensively. Principal component patterns highlighted core metabolic relationships, including the inverse association between energy-dense compounds (starch, lipids) and structural or functional constituents (protein, TDF, BG), as well as the strong genotype dependence of starch and BG accumulation.

Taken together, these findings demonstrate that cereal grain quality emerges from a hierarchical interplay of factors, with genotype as the dominant determinant, followed by environmental conditions, and only minor contributions from soil management. This hierarchy emphasizes the need for breeding programs that prioritize genetic enhancement of nutritional traits, supported by adaptive agronomic strategies capable of optimizing specific components under variable environmental conditions. Conservation-oriented tillage may offer targeted benefits for selected nutritional fractions, but its influence remains species- and environment-specific.

Overall, the study provides compelling evidence that sustainable improvement of cereal nutritional quality will require an integrated approach combining genotype selection with environment-responsive agronomy to ensure both stable productivity and enhanced functional value of cereal-based foods.