The Influence of the Farming System and Forecrop on the Yield and Chemical and Health-Promoting Composition of Spring Wheat Grain

Abstract

Spring wheat was grown on a loess-derived Luvisol under the conditions of two farming systems (conventional and organic) and five forecrops (sugar beet, spring barley, red clover, winter wheat, and oat) over the period 2021–2023. In the conventional system, mineral NPK fertilization and pesticides (herbicides, fungicide, insecticide, and retardant) were applied at the recommended rates for wheat. Mechanical weed control was also used (double harrowing). In the organic system, the organic fertilizer Humac Agro was applied and the fields under the wheat were harrowed twice. No plant protection products were used under organic farming conditions. The organic system was proven to have an effect on reducing spring wheat yield, on average by 23%, compared to the conventional system (the grain yield was, respectively, 4.59 t ha⁻¹ compared to 5.96 t ha⁻¹). In spite of the lower yield potential, the organic cultivation of spring wheat significantly improved the quality and health-promoting parameters of this cereal grain. Except for the total nitrogen and potassium content, the organic system contributed to a significant increase in the grain content of total dietary fiber (by 0.89 p.p.), o-dihydroxyphenols (by about 19%), and polyphenols (by about 12%), and increased the content of the following elements: Se, Mg, Ca, Cu, Mn, Fe, and Zn. Among the forecrops, red clover and sugar beet had the most beneficial effect on grain quality (including the amino acid composition and EAAI index), followed by oat (especially under organic farming conditions). The other wheat forecrops (spring barley and winter wheat) clearly deteriorated the yield and quality of spring wheat grain. To sum up the obtained research results, appropriate management of organic spring wheat cultivation (forecrop sugar beet or red clover, Humac Agro fertilizer) contributes to high grain nutritional quality relative to the conventional system and also reduces the yield gap relative to conventional farming.

1. Introduction

Alongside rice and maize, wheat is a cereal commonly grown at different latitudes in the world and it plays an important role in food economy of many countries [1]. Globally, about 70% of wheat grain production is used for food purposes, while in Europe, it is about 50% [2,3,4]. The US Department of Agriculture (USDA) forecasts that global wheat production in the 2024/2025 season will be a record 800 million tonnes. Taking into account the predicted need to further increase global food supplies by about 70% to 2050 [5] as well as climate and environmental change due to climate warming, wheat will be a species of essential importance for global food security [6].

Wheat, due to its high yield potential and chemical composition (grain rich in carbohydrates and having a higher protein content than other cereals), is the most commonly used cereal for food, industrial, and feed purposes. It is an important component of the human diet. Wheat grain is rich in carbohydrates and has a higher protein content than oat or barley. Wheat grain contains minerals (especially Zn and Fe), vitamins, and antioxidant components, among which free and esterified phenolic acids have the greatest beneficial potential for health. Wheat grain also provides other macro- and micronutrients as well as non-nutritional bioactive food components [7,8,9]. Protein quality and content in wheat grain are determined by many factors, including cultivar, climatic, and soil conditions, among others, and production technology (intensive, organic), and they affect the nutritional value of wheat products [10,11,12]. The most important factor (in the case of cereal grains) in determining the biological value of protein is its amino acid profile, including the proportions in the content of individual amino acids, especially exogenous ones (tryptophan, arginine, lysine, histidine, leucine, valine, phenylalanine, and methionine), which are not synthetized by the human body and must therefore be supplied with food [13,14]. The United Nations Food and Agriculture Organization (FAO) recommends paying attention not only to the amount of consumed protein, but also to its amino acid profile [15].

One of the challenges of modern agriculture is to seek methods of increasing the production of different cereal cultivars and species, at the same time guaranteeing their quality and also taking into account their economic and energy profitability [12,16,17]. In many countries in the world, spring wheat is a cereal that enables the production of grain with high quality parameters, but it has high environmental and agronomic requirements [18]. Unlike winter genotypes, spring crops require a higher temperature during the initial growth period. Hence, obtaining a high yield with satisfactory grain quality depends on the interaction of a genotype with the environment, in particular the amount and distribution of rainfall as well as temperature [19,20,21]. Wheat is also a plant that responds strongly to the forecrop and crop rotation. A well-planned crop rotation increases crop yields [22] and provides more sustainable production, especially in organic farming in which the possibilities of influencing the grain quality characteristics are limited [23].

Amirahmadi et al. [24] show that sugar beet grown on cattle manure (applied in autumn) is a site that ensures a high-quality yield and at the same time has the least negative impact on the soil environment. Kulig et al. [25] cite, using the example of faba bean, that legume crop residues leave soil rich in mineral nitrogen, thanks to which it is possible to obtain a high yield of spring wheat grain with relatively low nitrogen fertilization. Wanic et al. [26] also believe that legume or oil forecrops have a more beneficial effect on the yield and quality of wheat grain than cereal forecrops. The high yield-forming value of sugar beet and field bean forecrops is also cited by Jaroszewska et al. [27].

In conventional and sustainable agriculture, a wide spectrum of pesticides and artificial fertilizers is used to orient yield quality towards the industrial use of cereals (e.g., the production of bakery products, pastries, and pastas). In organic farming, on the other hand, grain quality is primarily determined by the selection of an appropriate cultivar, forecrops, and agronomic practices aimed at reducing pest risks [26,28,29].

The genotype (cultivar), soil and climatic conditions, agronomic practices used, and the interactions between the above-mentioned factors play a key role in wheat grain yield and quality. Currently, the European Union recommends sustainable application of mineral fertilizers and plant protection products in agricultural production (integrated production) or the use of exclusively natural production methods (organic farming) [30]. The popularity of organic farming stems from the production of highest quality food by using environmentally friendly agronomic practices [31,32]. Compared to products originating from conventional production systems, organic products are characterized by a higher nutritional value in the opinion of most consumers and therefore one can observe a growing demand in this sector of agriculture. A study on food carried out by Kwiatkowski et al. [33] confirms the high health-promoting qualities of agricultural produce obtained by organic methods.

Cereal cultivars that are suitable for organic systems should be characterized by a good nutrient uptake ability [34,35]. Organic farming positively affects the content of health-promoting compounds and, hence, products from this system should be taken into account in designing daily diet [33]. In conducting food preference tests, Mäder et al. [36] showed that rats significantly preferred organically over conventionally produced wheat. These results also demonstrate that high wheat quality in organic farming is achievable by lower inputs, which protects natural resources. Nevertheless, the results of many studies indicate differences in nutritional values between organically and conventionally grown cereals [37,38]. In a study by Żuchowski et al. [37], organic products, compared to conventional ones, usually had a lower content of macronutrients, particularly proteins, but also a higher concentration of secondary metabolites.

At the beginning of this study, a hypothesis was made that organic farming can bring satisfactory spring wheat yields if an appropriate forecrop is selected. It was also hypothesized that the organic system, in combination with the best crop stand (forecrop), would contribute to better quality of spring wheat grain, in particular its health-promoting qualities.

The aim of this study was to determine yield quantity and some grain quality characteristics of spring wheat grown in the conventional and organic systems, in relation to five forecrop species (sugar beet, spring barley, red clover, oat, and winter wheat). It was assumed that the determination of the optimal agronomic treatment (regarding the farming system–forecrop combination) would allow effective management of spring wheat growing.

2. Materials and Methods

2.1. Experiment Design and Field Management

A field experiment in growing spring wheat (Triticum aestivum L.—cv. “Harenda”) under organic and conventional farming systems was conducted over the period 2021–2023 at the Czesławice Experimental Farm (51°30′ N; 22°26′ E; Lubelskie Voivodeship, Poland). This was a continuation of a field experiment carried out during the period 2018–2020, whose results were published in a paper by Tomczyńska-Mleko et al. [29]. The experiment was set up as a split-plot design in 3 replicates in plots with an area of 80 m² (8 m ×10 m). The total area of the experiment (24 plots) was 1920 m². It was located on a loess-derived Luvisol, with the grain size distribution of silt loam (PWsp), classified as a good wheat soil complex (soil class II) [39]. Before the establishment of the experiment (autumn 2020, 2021, 2022), the soil was characterized by a medium content of available macronutrients (

Table 1. Soil characteristics prior to establishing the spring wheat experiment. “Table layout adopted from Tomczyńska-Mleko et al. [29]”.

Farming Treatment	Soil pH 1 M KCl	Nitrogen (N) (%)	Phosphorus (P) mg kg−1	Potassium (K) mg kg−1	Organic Carbon (C) (%)
			2020
Organic	6.4	0.10	129	210	1.17
Conventional	6.3	0.14	134	218	1.25
			2021
Organic	6.4	0.11	126	207	1.16
Conventional	6.3	0.15	131	216	1.23
			2022
Organic	6.4	0.11	127	212	1.18
Conventional	6.3	0.14	135	220	1.27

).

The experiment included:

I. Two farming systems of spring wheat: CS—conventional system—the recommended rates of mineral NPK (ammonium nitrate—34% N, enriched superphosphate—40% P₂O₅, potassium chloride—60% K₂O), seed dressing, fungicide and herbicide application, and mechanical weed control (harrowing before emergence and at the 3–4 leaf stage);

OS—organic system—mineral fertilization with the fertilizer Humac Agro and mechanical weed control (harrowing before emergence and at the 3–4 leaf stage).

II. Five forecrops for spring wheat: a. sugar beet (Beta vulgaris L. subsp. vulgaris)—cv. “Lumos”; b. spring barley (Hordeum vulgare L.)—cv. “Avatar”; c. red clover (Trifolium pratense L.)—cv. “Himalia”; d. winter wheat (Triticum aestivum L.)—cv. “Venecja”; e. oat (Avena sativa L.)—cv. “Refleks”.

The scheme of the experiment is shown in Figure 1, Figure 2 and Figure 3.

In each research season, plots with forecrops (in conventional and organic system) were randomly distributed in a different part of the field. Thus, in 2020–2022, forecrops were randomly distributed and sown, and in 2021–2023, spring wheat was sown in these locations.

In 2018 the field where the experiment was conducted had received an Organic Farming Certificate awarded by the company “Eco-guarantee”. The organically cultivated field was managed in accordance with the following organic farming principles: a buffer zone (200 m) from the conventionally cultivated fields and no application of pesticides and artificial fertilizers. The distance of the experimental plots from the nearest traffic road was 900 m. Spring wheat fertilization used in the conventional system in the years of research (2020–2022) it was as follows: N (kg ha⁻¹)—70 kg (30 kg before sowing, 40 kg in spring at stem elongation—BBCH 32–34), P (kg ha⁻¹)—50 (before sowing), K (kg ha⁻¹)—90 (before sowing).

The fertilizer Humac Agro was applied before sowing at the rate of 350 kg ha⁻¹. The chemical composition of the fertilizer Humac Agro is shown in

Table 2. Chemical composition of Humac Agro fertilizer.

Technical Parameters	Content
Humic acid content	62%
Carbon content of humic acid	up to 62%
Minerals in dry matter
Nitrogen (N)	10.3 g kg−1
Phosphorus (P)	1.05 g kg−1
Sodium (Na)	12.80 g kg−1
Potassium (K)	1.18 g kg−1
Calcium (Ca)	16.80 g kg−1
Ferrum (Fe)	14.50 g kg−1
Zinc (Zn)	64 mg kg−1
Brom (Br)	77 mg kg−1
Copper (Cu)	19 mg kg−1
Selenium (Se)	6 mg kg−1
Moisture content	20%

:

Agronomic treatments used in the cultivation of organically grown spring wheat involved only double harrowing of the field, whereas in the conventional system, apart from double harrowing, plant protection chemicals were applied (seed dressing, herbicide, fungicide, insecticide, and retardant). The following chemical protection of spring wheat crops was used in the conventional system: seed dressing − Omnix 025 FS (a.i. fludioxonil − 200 g L⁻¹) − 200 mL 100 kg⁻¹ of grain; herbicide − Axial One 50 EC (a.i. pinoxaden + florasulam) − 1.0 L ha⁻¹); fungicide − Azoksar super 250 SC (a.i. azoxystrobin 250 g L⁻¹) − 1.0 L ha⁻¹; insecticide − Decis Expert 100 EC 1 L⁻¹ (a.i. deltamethrin); retardant − Antywylegacz Płynny 725 SL 1.2 L⁻¹ (a.i. chlormequat chloride).

Tillage was typical for each plant species (spring wheat and forecrops for spring wheat).

During the research period, the dates of sowing and harvesting of spring wheat were identical in the conventional and organic systems (they were in the following range: April 18–23—sowing; August 21–23—harvest). The seeding rate of spring wheat was identical in the conventional and organic systems and amounted to 200 kg ha⁻¹.

The dates of sowing and harvesting of spring wheat forecrops in the years of research (2020–2022) were also the same in both farming systems and they were as follows:

-

sowing: sugar beet 19–23.04; spring barley 19–22.04; red clover 15–18.04; winter wheat 22–25.09; oat 12–15.04.

-

harvesting: sugar beet 17–20.10; spring barley 11–13.08; red clover 21–23.08; winter wheat 10–12.08; oat 19–21.08.

The fertilization of spring wheat forecrops was consistent with the farming system (conventional and organic). Detailed information on this subject is presented in

Table 3. Fertilization of spring wheat forecrops used in the conventional system (2021–2023).

Fertilization	Component	Crop Plants
		Sugar Beet	Spring Barley	Red Clover	Winter Wheat	Oat
Mineral fertilization (kg ha−1)	N (before sowing)	90	65	20	90	45
	P (before sowing)	90	45	30	70	35
	K (before sowing)	120	85	45	110	55
Manure fertilization (t ha−1)	(autumn; before sowing)	25	-	-	-	-

and

Table 4. Fertilization of spring wheat forecrops used in the organic system (2021–2023).

Mineral Fertilization	Crop Plants
	Sugar Beet	Spring Barley	Red Clover	Winter Wheat	Oat
Humac Agro; before sowing (kg ha−1)	450	320	55	380	280
Originating from organic livestock production; autumn; before sowing (t ha−1)	25	-	-	-	-

.

Doses of NPK mineral fertilizers used in the experiment for individual crops (spring wheat, forecrops) resulted from the agrotechnical recommendations for the given species and the input soil richness in nutrients.

2.2. Plant Sampling, Measurement, and Chemical Analyses of Spring Wheat Grain

Doses of Humac Agro for individual plants (spring wheat, forecrops) resulted from the recommendations for using this fertilizer for these plants. The doses also resulted from the input soil richness in nutrients.

In each year of the study after the harvest of spring wheat, the grain was dried to an about 14% moisture content. Grain samples were collected from each experimental treatment for laboratory analysis (in 3 replicates). It should be added that all laboratory analyses regarding the grain quality results presented in this manuscript were performed in the Certified Central Research Laboratory of the University of Life Sciences in Lublin.

-

Nitrogen determinations were made in grains extracted from collected ear samples by the Kjeldahl procedure, while crude protein content was calculated using the factor N × 5.3. The sample is digested in sulfuric acid, using CuSO₄/TiO₂ as catalysts, converting N to NH₃, which is distilled and titrated [40].

-

The amino acids were determined by HPLC using an automatic amino acid analyzer (AAA400; Ingos, Prague, Czech Republic) after previous acid hydrolysis with 6 M HCl for 24 h at 110 °C (method 994.12). Cysteine and methionine were determined after oxidative hydrolysis. Ion exchange chromatography was used to separation of amino acids using Tessek Ostion LG ANB (0.37 × 45 cm) column. Amino acid recognition was done by means of a photometric detector at a wavelength of 570 nm except for proline—440 nm [41,42].

-

For the determination of sulfur amino acids, the feed samples were oxidized (0 °C, 16 h) with formic acid and hydrogen peroxide (H₂O₂) (9:1/v:v) prior to HCl hydrolysis and then were separated using an Analysator AAA 400 Ingos (Prague, Czech Republic). For tryptophan content, the samples, after alkaline hydrolysis with lithium hydroxide (LiOH) (110 °C, 16 h) and 4-dimetylamino-benzaldehyde (DMAB), were examined colorimetrically at a wave length of 590 nm according to the Landry and Delhaye (1992) procedure [43].

-

Total dihydroxyphenol content was measured spectrophotometrically at a wavelength of λ = 725 nm (Shimadzu 1800 spectrophotometer, Shimadzu Corp. Kyoto, Japan) and expressed as caffeic acid equivalents. To make the measurement on the spectrophotometer, 50–500 µL of the extract (depending on the expected value of absorption of the tested sample) was transferred into a volumetric flask. A total of 2.0 mL methanol, 10 mL H₂O, 2 mL Folin reagent, and 1.0 mL of a 10% solution of Na₂CO₃ were added. After half an hour samples were made up with deionized water up to the mark and measured on a spectrophotometer at a wavelength of λ = 725 nm in relation to the control sample [44].

-

The determination of total dietary fiber content was done by the enzymatic gravimetric method using a FOSS Fibertec 2010 system. The sample was digested with 3 enzymes: thermostable alpha-amylase, pepsin, and pancreatin. The undigested residue was weighed and then the supernatant of soluble dietary fiber was precipitated and weighed [45]. The mineral analysis of the isolate to determine Ca, Mg, Mn, Cu, Zn, Fe, Se (absorption—Varian lamp), and K (emission—without lamp) was performed by atomic absorption spectrometry in acetylene-air flame (Varian Spectra A 280 FS).

-

Essential (exogenous) Amino Acid Index (EAAI) was calculated as the geometric mean of all participating exogenous amino acids compared to the concentration of these amino acids in the egg reference protein using the following formula [46]:

$$\mathrm{E}\mathrm{A}\mathrm{A}\mathrm{I}=\sqrt[n]{\left({\displaystyle \frac{a_1}{a_{1s }}}\right)\times 100\times \dots \times \left({\displaystyle \frac{a_n}{a_{ns}}}\right)\times 100}$$

where:

a_n—amino acid concentration in the protein tested, a_ns—amino acid concentration in the reference protein; n—the number of essential (exogenous) amino acids.

2.3. Statistical Analyses

The statistical analysis of the obtained research results was carried out using the Statistica PL 13.3 program (TIBCO Software Inc., Palo Alto, CA, USA). The Tukey test was used to verify the significance of differences—Honestly Significant Difference (HSD) at the level of p < 0.05. The tables provide average results from the years of the study, as no significant statistical differences were found between the individual seasons of the study (2021–2023). The standard deviation (SD ±) of the results is given for all the characteristics contained in the tables.

3. Results

Spring wheat grain yield was significantly dependent on the farming system, wheat forecrop, and the interaction of these experimental factors (

Table 5. Spring wheat grain yield (t ha⁻¹)—average from 2021–2023.

Wheat Forecrop (WF)	Farming System (FS)		Mean
	Organic	Conventional
Sugar beet	5.13 (±0.08) c	6.82 (±0.08) a	5.97 a
Spring barley	4.19 (±0.07) e	5.23 (±0.04) c	4.71 c
Red clover	4.77 (±0.09) d	6.31 (±0.07) b	5.54 b
Oat	4.81 (±0.05) d	6.27 (±0.09) b	5.54 b
Winter wheat	4.07 (±0.06) e	5.19 (±0.05) c	4.63 c
Mean	4.59 b	5.96 a	-

Different letters (a–e) denote a significant difference (HSD p ≥ 0.05) for FS, WF and interaction FS × WF, according to ANOVA and Tukey’s test.

). The cultivation of spring wheat in the conventional system, regardless of the forecrop, produced a grain yield of 5.96 t ha⁻¹ on average (higher by about 23% than that in the organic system). Regardless of the farming system, sugar beet was the forecrop that contributed to a significantly higher grain yield of spring wheat relative to the red clover and oat forecrops (by about 7.3%), but in particular compared to the spring barley and winter wheat forecrops (an increase in yield by 21% and 22.5%, respectively). It should also be noted that oat, as a forecrop, had a similar effect on spring wheat yield as red clover—this effect was significantly more beneficial than in the case of the spring barley and winter wheat forecrop. To sum up, it should be stated that the highest grain yield of spring wheat (on average 6.82 t ha⁻¹) was obtained when this cereal was conventionally grown after the sugar beet forecrop (Table 5).

Regardless of the forecrop, the organic system contributed to a significantly higher content of total dietary fiber (by 0.89 percentage points “p.p.”), o-dihydroxyphenols (by about 19%) and polyphenols (by about 12%) in spring wheat grain compared to the conventional system (

Table 6. Content of total dietary fiber, o-dihydroxyphenols and polyphenols in spring wheat grain—average from 2021–2023.

Specification	Total Dietary Fiber Content (%)	O-Dihydroxyphenol Content (g 100 g−1)	Polyphenol Content (mg Catechin g−1 DM)
Farming system (FS)
Organic	16.46 (±0.12) a	0.183 (±0.02) a	2.01 (±0.06) a
Conventional	15.57 (±0.10) b	0.149 (±0.02) b	1.77 (±0.05) b
Wheat forecrop (WF)
Sugar beet	16.59 (±0.09) a	0.182 (±0.03) a	2.05 (±0.05) a
Spring barley	15.22 (±0.08) c	0.157 (±0.01) c	1.76 (±0.03) c
Red clover	16.68 (±0.07) a	0.176 (±0.02) a	2.05 (±0.05) a
Oat	16.22 (±0.09) b	0.162 (±0.03) b	1.86 (±0.05) b
Winter wheat	15.37 (±0.06) c	0.152 (±0.02) c	1.74 (±0.04) c
Factor interaction
FS	**	**	**
WF	**	**	**
FS × WF	ns	ns	ns

Different letters (a–c) denote a significant difference (HSD p ≥ 0.05), according to ANOVA and Tukey’s test; **—significant difference; ns—not significant difference; ±SD—standard deviation.

). This study also proved significant differences in the spring wheat grain quality indicators specified in Table 5, as influenced by the forecrop. Irrespective of the farming system, the significantly highest grain content of protein, total dietary fiber, o-dihydroxyphenols and polyphenols was found in the grain of spring wheat grown after sugar beet and red clover, relative to all the three cereal forecrops. At the same time, oat, as a forecrop for spring wheat, contributed to statistically proven higher values of the grain quality parameters, shown in Table 6, in comparison to the other cereal forecrops (spring barley, winter wheat). In spite of the absence of a statistically significant interaction between the farming systems and forecrops, we should note a trend towards a higher content of the spring wheat grain components, shown in Table 6, when this cereal was organically grown after the sugar beet or red clover forecrop.

The conventional system resulted in a significantly higher total nitrogen and potassium content in wheat grain (1.6 and 1.3 times higher, respectively) in comparison with the organic system, when these parameters are considered independently of the forecrops (

Table 7. Content of total nitrogen, potassium, magnesium, and selenium in spring wheat grain—average from 2021–2023.

Specification	Total Nitrogen (%)	Potassium (g kg−1)	Magnesium (mg kg−1)	Selenium (µg kg−1)
Farming system (FS)
Organic	1.39 (±0.12) b	1.79 (±0.10) b	705 (±6) a	44.16 (±0.12) a
Conventional	2.23 (±0.09) a	2.37 (±0.13) a	611 (±5) b	22.54 (±0.12) b
Wheat forecrop (WF)
Sugar beet	1.97 (±0.11) a	2.26 (±0.12) a	716 (±7) a	38.25 (±0.12) b
Spring barley	1.72 (±0.08) c	1.92 (±0.11) c	610 (±4) d	26.25 (±0.13) d
Red clover	1.93 (±0.10) a	2.15 (±0.10) ab	698 (±5) b	41.35 (±0.11) a
Oat	1.62 (±0.07) d	1.94 (±0.08) c	642 (±6) c	26.40 (±0.14) d
Winter wheat	1.82 (±0.08) b	2.07 (±0.09) b	612 (±5) d	34.50 (±0.10) c
Factor interaction
FS	**	**	**	**
WF	**	**	**	**
FS × WF	**	**	**	**

Different letters (a–d) denote a significant difference (HSD p ≥ 0.05), according to ANOVA and Tukey’s test; **—significant difference; ±SD—standard deviation.

). The magnesium and selenium content in spring wheat grain, on the other hand, was significantly higher under organic farming conditions than for the conventional system—by about 14% (Mg) and by as much as about 97% (Se), respectively. The quality characteristics of spring wheat grain specified in Table 6 were subject to significant variation under the influence of the forecrop. Compared to the cereal forecrops, the sugar beet and red clover forecrops contributed to the significantly highest total nitrogen content in the grain. Among the cereal forecrops, significant differences in grain total nitrogen content were also observed—the cultivation of spring wheat after winter wheat had the most beneficial effect on the content of this component in the grain, followed by the spring barley forecrop, whereas the least beneficial effect was found for the stand after oat.

As in the case of N-total, the significantly highest K content was found after the sugar beet forecrop, followed by the red clover and winter wheat forecrops, whereas the significantly lowest K content in the grain was observed after the oat and spring barley forecrops. The sugar beet forecrop also resulted in the significantly highest Mg content in spring wheat grain in comparison with the other forecrops investigated in this study. For spring wheat grown after sugar beet, the grain content of this component was 716 mg kg⁻¹, being higher by about 15% relative to the Mg content determined in spring wheat grown after the least beneficial forecrops (spring barley and winter wheat).

Selenium content is very important in the context of the health-enhancing qualities of spring wheat grain. The significantly highest Se content was found in grain samples collected from the plots of spring wheat cultivated after red clover (41.35 µg kg⁻¹). The determined Se content was higher by about 8% than that found in the grain after the sugar beet forecrop, higher by about 17% than that found in the grain after the winter wheat forecrop, and by about 37% in the grain after the oat and spring barley forecrops (Table 7).

As far as N-total, K, Mg and Se content in spring wheat grain is concerned, the interaction of the experimental factors was found to be statistically significant (FS × WF)—Table 7 and

Table 8. Interaction for content of total nitrogen, potassium, magnesium and selenium between the farming system and wheat forecrop—average from 2021–2023.

Farming System (FS)	Wheat Forecrop (WF)	Total Nitrogen (%)	Potassium (g kg−1)	Magnesium (mg kg−1)	Selenium (µg kg−1)
Organic	Sugar beet	1.53 (±0.09) c	1.97 (±0.05) d	766 (±7) a	48.2 (±0.11) b
	Spring barley	1.42 (±0.07) c	1.72 (±0.04) e	673 (±4) c	37.3 (±0.09) c
	Red clover	1.50 (±0.08) c	1.84 (±0.07) d	732 (±6) b	51.0 (±0.10) a
	Oat	1.19 (±0.04) d	1.65 (±0.07) e	696 (±5) c	47.2 (±0.13) b
	Winter wheat	1.43 (±0.06) c	1.79 (±0.06) e	659 (±3) c	38.1 (±0.10) c
Conventional	Sugar beet	2.41 (±0.05) a	2.66 (±0.10) a	688 (±6) c	28.3 (±0.08) d
	Spring barley	2.12 (±0.06) b	2.12 (±0.08) c	548 (±3) e	15.2 (±0.07) f
	Red clover	2.37 (±0.04) a	2.46 (±0.11) b	665 (±4) c	31.7 (±0.10) d
	Oat	2.06 (±0.05) b	2.24 (±0.09) c	589 (±7) d	22.8 (±0.08) e
	Winter wheat	2.22 (±0.06) b	2.35 (±0.08) b	566 (±6) e	14.7 (±0.09) f

Different letters (a–f) denote a significant difference (HSD p ≥ 0.05) for interaction FS × WF, according to ANOVA and Tukey’s test; ±SD—standard deviation.

. The significantly lowest total nitrogen content in spring wheat grain was observed when this cereal was organically grown in the field after oat. The grain potassium content was the significantly highest in conventionally grown spring wheat after the sugar beet forecrop. The sugar beet forecrop resulted in the significantly highest grain magnesium content when spring wheat was organically grown, whereas the highest selenium content in the grain was also found for organically grown spring wheat, but in the field after red clover (Table 8).

As regards the influence of the farming system on the Ca, Cu, Mn, Fe and Zn content in spring wheat grain, regardless of the forecrop, we note that in all the cases the organic system caused a significant increase in the percentage of these elements, respectively by 16.5%, 16.3%, 10.1%, 8.2%, and 8.5%, compared to the conventional system (

Table 9. Content of calcium, copper, manganese, iron, and zinc in spring wheat grain—average from 2021–2023.

Specification	Calcium (mg kg−1)	Copper (mg kg−1)	Manganese (mg kg−1)	Iron (mg kg−1)	Zinc (mg kg−1)
Farming system (FS)
Organic	347 (±4) a	4.35 (±0.6) a	40.5 (±0.9) a	39.3 (±0.4) a	30.6 (±0.3) a
Conventional	290 (±3) b	3.64 (±0.7) b	36.4 (±1.0) b	36.1 (±0.3) b	28.0 (±0.2) b
Wheat forecrop (WF)
Sugar beet	338 (±2) a	4.25 (±0.8) a	40.3 (±1.1) a	39.7 (±0.5) a	31.6 (±0.3) a
Spring barley	308 (±4) c	3.75 (±0.7) c	37.4 (±0.8) c	36.2 (±0.6) bc	27.5 (±0.2) b
Red clover	335 (±5) a	4.15 (±0.6) a	39.6 (±1.2) ab	39.9 (±0.2) a	32.0 (±0.3) a
Oat	313 (±4) b	4.02 (±0.4) b	38.2 (±0.9) b	37.4 (±0.4) b	28.3 (±0.4) b
Winter wheat	296 (±3) c	3.83 (±0.5) c	36.7 (±1.3) c	35.5 (±0.3) c	27.3 (±0.1) b
Factor interaction
FS	**	**	**	**	**
WF	**	**	**	**	**
FS × WF	ns	ns	ns	ns	ns

Different letters (a–c) denote a significant difference (HSD p ≥ 0.05), according to ANOVA and Tukey’s test; **—significant difference; ns—not significant difference; ±SD—standard deviation.

).

In the case of the elements specified in Table 9, it was confirmed that the non-cereal forecrops for spring wheat (sugar beet, red clover) had a significantly more beneficial effect on their grain content in comparison to the oat, spring barley and winter wheat forecrops, irrespective of the farming system. At the same time, among the cereal forecrops, oat had a significantly more beneficial effect on the Ca, Cu, Mn, and Fe content in spring wheat grain compared to spring barley and winter wheat. Only the Zn content in spring wheat grain, as influenced by the oat, spring barley and winter wheat forecrops, was similar. As far as the characteristics contained in Table 9 are concerned, no statistically significant interaction was found between the farming system and forecrops.

The farming system and forecrops for spring wheat included in this study significantly modified the amino acid composition in the grain of this cereal (

Table 10. Amino acid content (g kg⁻¹) in spring wheat grain depending on the farming system and forecrop—average from 2021–2023.

Amin.	Sugar Beet		FI	Spring Barley		FI	Red Clover		FI	Oat		FI	Winter Wheat		FI
	Conv.	Org.		Conv.	Org.		Conv.	Org.		Conv.	Org.		Conv.	Org.
Asp *	6.31 a	5.94 b	**	5.97 a	5.33 b	**	6.15 a	5.88 b	**	5.82 a	5.21 b	**	5.79 a	5.13 b	**
Thr	3.66 a	3.51 a	ns	3.44 a	3.31 a	ns	3.72 a	3.64 a	ns	3.52 a	3.54 a	ns	3.24 a	3.34 a	ns
Ser	6.24 a	5.52 b	**	5.95 a	5.15 b	**	6.32 a	5.47 b	**	5.99 a	5.23 b	**	5.84 a	5.09 b	**
Glu	35.8 b	40.0 a	**	35.7 a	33.1 b	**	36.2 b	38.9 a	**	34.5 a	35.7 a	ns	34.1 a	33.8 a	ns
Pro	12.2 b	13.1 a	**	12.7 a	11.2 b	**	11.8 b	12.9 a	**	11.3 b	12.5 a	**	11.6 a	10.9 a	ns
Gly	4.86 b	5.22 a	**	5.06 a	4.78 b	**	4.91 b	5.12 a	**	5.00 a	4.65 b	**	4.88 a	4.72 a	ns
Ala	4.65 a	4.11 b	**	4.23 a	4.18 a	ns	4.75 a	4.70 a	ns	4.38 a	4.43 a	ns	4.19 a	4.02 a	ns
Cys-A	3.05 a	2.08 b	**	2.94 a	2.00 b	**	3.22 a	2.43 b	**	2.99 a	2.80 a	ns	2.85 a	1.93 b	**
Val	4.19 b	5.22 a	**	3.95 b	4.77 a	**	4.02 b	5.19 a	**	4.01 b	5.16 a	**	3.88 b	4.67 a	**
Met	1.16 b	2.12 a	**	1.07 b	2.02 a	**	1.75 b	3.77 a	**	1.55 b	2.97 a	**	1.21 b	2.19 a	**
Ile	3.95 a	3.67 b	**	3.62 a	3.41 a	ns	3.98 a	3.79 a	ns	3.58 a	3.50 a	ns	3.38 a	3.29 a	ns
Leu	8.36 a	7.91 b	**	7.94 a	7.21 b	**	8.41 a	8.22 a	ns	8.16 a	8.08 a	ns	7.77 a	7.56 a	ns
Tyr	2.85 a	2.36 b	**	2.73 a	2.21 b	**	2.90 a	2.77 b	**	2.81 a	2.70 a	ns	2.69 a	2.59 a	ns
Phe	5.52 a	4.86 b	**	5.02 a	4.46 b	**	5.60 a	5.39 a	ns	5.13 a	5.02 a	ns	4.78 a	4.68 a	ns
His	2.71 a	2.58 a	ns	2.64 a	2.39 b	**	2.82 a	2.70 a	ns	2.63 a	2.51 a	ns	2.47 a	2.43 a	ns
Lys	2.44 b	3.43 a	**	2.23 b	3.11 a	**	2.49 b	3.61 a	**	2.17 b	3.25 a	**	2.19 b	3.09 a	**
Arg	4.72 b	5.35 a	**	5.01 a	4.63 b	**	4.25 b	4.98 a	**	4.19 b	4.87 a	**	4.97 a	4.15 b	**
Trp	0.29 b	0.87 a	**	0.15 b	0.45 a	**	0.33 b	0.82 a	**	0.41 b	0.65 a	**	0.21 b	0.38 a	**
Total Amino Acids	112.96 a	117.85 a	ns	110.35 a	103.71 b	**	113.62 a	120.28 a	ns	108.14 a	112.77 a	ns	106.04 a	103.96 a	ns
EAAI **	73.9 b	81.2 a	**	66.7 a	69.3 a	ns	75.8 b	85.4 a	**	71.8 b	79.2 a	**	64.1 a	66.3 a	ns

* Asp—aspartic acid, Thr—threonine, Ser—serine, Glu—glutamic acid, Pro—proline, Gly—glycine, Ala—alanine, Cys-A—cysteine, Val—valine, Met—methionine, Ile—isoleucine, Leu—leucine, Tyr—tyrosine, Phe—phenylalanine, His—histidine, Lys—lysine, Arg—arginine, Trp—tryptophan. Different letters (a–b) denote a significant difference (HSD p ≥ 0.05), according to ANOVA and Tukey’s test; FI—factor interaction; **—significant difference; ns—not significant difference; ** EAAI—essential amino acid index; means in rows with different letters (a,b) are significantly different (p ≥ 0.05) for forecrops and farming system.

). The organic system, in combination with the sugar beet and red clover forecrops, contributed to a significantly higher content of eight amino acids (Glu, Pro, Gly, Val, Met, Lys, Arg, Trp) in spring wheat grain, including three exogenous ones, relative to the conventional system. As regards its interaction with the oat forecrop, the organic system caused a significantly higher content of six amino acids (Pro, Val, Met, Lys, Arg, Trp) in spring wheat grain, whereas in the interaction with the spring barley and winter wheat forecrops, it contributed to a significantly higher content of 4 amino acids (Val, Met, Lys, Trp) compared to the conventional system. It should be noted that in the case of all the forecrops, organic farming of spring wheat resulted in a significantly higher content of exogenous amino acids (lysine, methionine, and tryptophan), which is of great positive importance for the health-promoting qualities of the grain harvested from these plots.

In comparison to the organic system, the conventional system contributed to a significantly higher content of the following amino acids in wheat grain: the grain from the field after sugar beet (Asp, Ser, Ala, Cys-A, Ile, Leu, Tyr, Phe), the field after red clover (Asp, Ser, Cys-A, Tyr), the field after oat (Asp, Ser, Gly), and the field after spring barley (Asp, Ser, Cys-A, Leu, Tyr, Phe, His, Arg). The conventional cultivation of spring wheat in the field after winter wheat resulted in a significantly higher grain content of Asp, Ser, Cys-A and Arg amino acids. Interestingly, in the case of the red clover and winter wheat forecrops, the amino acid content showed a statistically insignificant difference between the conventional system and organic system (9 and 10 amino acids, respectively).

The calculated values of total nitrogen acid in wheat grain in the interaction of farming system × forecrop show that a statistically significant relationship in favor of the conventional system was found in the conditions of spring barley forecrop. In the conditions of the forecrops sugar beet, red clover, and oat, only a tendency (statistically insignificant) of greater total nitrogen acid in the organic system was noted, and in the conditions of the forecrop winter wheat—greater total nitrogen acid in the conventional system (Table 10)

The integrated essential amino acid index (EAAI) calculated based on the laboratory results displays a significant dependence of this grain quality parameter on the farming system and forecrop (Table 10). The EAAI determined in the tests for protein indicates that spring wheat grain protein is characterized by a significantly higher biological value in the case of the organic cultivation of this cereal after the sugar beet, red clover, and oat forecrops, in comparison with the conventional system. Growing spring wheat in the fields after spring barley and winter wheat did not cause differences in the EAAI value between the organic system and the conventional system. The EAAI (85.4) determined in the grain of organically grown spring wheat in the field after red clover showed the significantly highest biological value (Table 10).

4. Discussion

4.1. The Influence of the Farming System and Forecrop on the Yield of Spring Wheat

In the present study, the experimental factors significantly modified spring wheat grain yield. The conventional farming system caused an about 23% increase in grain yield compared to the organic system. Likewise, in the studies by Mäder et al. [36] and Cox et al. [47], the organic wheat yield was lower by 13–14% than that of conventionally grown wheat. In the opinion of these authors, this was due to the fact that in the organic system there was an about 70% lower addition of plant-available nitrogen and no other means of production (pesticides) were used in the organic field plots.

Feledyn-Szewczyk et al. [48], in turn, proved that spring wheat yield in the conventional system was higher by as much as 67% than in the organic system. This was attributable to the fact that no mineral NPK fertilizers were used in the organic system. An increased occurrence of agricultural pests (weeds, fungal pathogens) in the organic fields as well as a lower ear density per unit area and a lower 1000 grain weight were also observed as a result of organic farming.

Based on a 5-year study, Verdi et al. [49] find that lower wheat yields, on average by 45.9%, are obtained in organic farming than in conventional farming. van Stappen et al. [50] report similar differences in the yield of wheat grown under the soil and climatic conditions of Wallonia (Belgium) in conventional farming (on average 8.5 t ha⁻¹) compared to this cereal’s yields in the organic system (on average 4.5 t ha⁻¹).

Döring and Neuhoff [51] observe that the main factor limiting wheat yield is nitrogen fertilization. The use of mineral nitrogen (N) fertilizers in conventional farming is unsustainable because of its high fossil energy requirements and a considerable enrichment of the biosphere with reactive N. In organic farming, biological nitrogen fixation (BNF) from leguminous crops is the most important renewable source of primary N. But it is not known to what degree BNF can sustainably replace mineral N, eliminate the difference in yields between organic and conventional crops, and also contribute to food security.

A study by Paunescu et al. [52] also indicates the leading role of mineral nitrogen supplied with fertilizers in determining the wheat yield potential. Likewise, Mitura et al. [30] are of opinion that lower wheat yields in the organic system are caused by soil nitrogen deficiency, compared to the conventional system. Nonetheless, these authors add that it largely depends on the selection of a spring wheat cultivar because some cultivars better tolerate extensive organic farming conditions. Zhang et al. [53] report that successively increasing the nitrogen rate (180, 240, and 300 kg N ha⁻¹) in the conventional system increased the wheat grain yield by about 58, 61, and 65%, respectively, in their field experiment. Haliniarz et al. [54] found similar relationships in their research. In a study by Jańczak-Pieniążek et al. [55], the conventional cultivation of wheat also produced a higher grain yield than in the organic system as a result of an improvement of some physiological parameters such as LAI, chlorophyll content, and better gas exchange parameters. This observation is reflected in the articles by Kubar et al. [56] and Katamadze et al. [57].

In this study, irrespective of the farming system, the sugar beet forecrop had the most beneficial influence on spring wheat yield, followed by red clover and oat. The other cereal forecrops (wheat and barley), however, caused a significant reduction in spring wheat yield. Similarly, Kulig et al. [25], Thomsen et al. [58], and Wanic et al. [26] prove that good forecrops (red clover, pea, faba bean, oilseed rape, white mustard) have the most beneficial effect on wheat yield compared to cereal forecrops, particularly in wheat monoculture. In a study by Vinogradow and Vysotskaya [59], vetch was the most effective forecrop for wheat, especially when it was grown in a mixture with oat. The present study also confirms the suitability of oat as a forecrop for wheat—it was a much better forecrop for spring wheat than barley or winter wheat. Szymańska et al. [60] demonstrate the special suitability of Fabaceae plants (legumes) as forecrops for wheat. They substantially replenish N deficits in the soil and hence are a useful link in the organic system, in which, as a rule, mineral nitrogen fertilization is not used. This thesis was confirmed in the present study on the example of the red clover forecrop.

Knapp and van der Heijden [61] find that organic agriculture has, per yield unit, much lower temporal stability (−15%) in comparison with conventional agriculture. Thus, although organic farming promotes biodiversity and is generally a more environmentally friendly method of farming, future efforts should focus on reducing yield variability in this system. The authors also point out that, for example, the use of crop rotation with legumes, green fertilizers or natural/organic mineral fertilizers in organic farming can reduce the yield stability gap between organic and conventional agriculture. In this study, the organic mineral fertilizer Humac Agro was applied, which probably contributed to a lower yield variation between the farming systems studied, in particular when the good forecrops (sugar beet, red clover) were used.

4.2. The Influence of the Farming System and Forecrop on the Quality of Spring Wheat Grain

A review of the literature of the subject reveals that the influence of the farming system on the quality and health-promoting parameters of wheat grain is different. In this experiment, the organic system contributed to a significantly higher content of protein, total dietary fiber, o-dihydroxyphenols and polyphenols in spring wheat grain in comparison with the conventional system. The content of magnesium, selenium, calcium, manganese, copper, iron, and zinc in the grain was also more favorable. The conventional system only promoted a higher nitrogen and potassium content in wheat grain. Krejčířová et al. [28] proved that conventionally grown wheat varieties generally achieved higher crude protein contents in grain dry matter compared to organic growing. Likewise, based on their research, Mitura et al. [30] claim that the protein content in wheat grain is the significantly highest in the case of the conventional system, while it is the lowest for the organic system. Wilkinson et al. [62] and Rempelos et al. [63] also state that, both variety choice and fertilization regimes used in organic farming contribute to the lower yields and higher nutritional quality of organic compared with conventional spring wheat grain.

In a study by Zhang et al. [53], the protein content and total essential amino acid content in wheat grain increased with increasing nitrogen rate.

The obtained results of qualitative studies show that the nitrogen (N) content in oat grain was significantly higher in the conditions of the conventional system than in the organic one. In turn, in the case of amino acid total content in grain, the relationships were similar in both farming systems. In turn, in the case of protein content in grain, the relationships were reversed—significantly higher content of this component in the organic system compared to the conventional one. This should be explained by the fact that in the conventional system mineral fertilization N (ammonium nitrate) was used, and such fertilization does not build all the nitrogen content into the protein. Part of the nitrogen is deposited in the grain in the non-protein form of nitrogen (in the form of nitrates) [64,65]. On the other hand, in wheat grain harvested from the organic system, non-protein parts of nitrogen were not deposited. In the Humac Agro organic fertilizer, nitrogen occurs in a different form than in ammonium nitrate. In addition, Humac Agro contains humic acid, which also contributes to better protein accumulation in grain. It should be added that the Humac Agro fertilizer was also used for each forecrop plant for spring wheat, hence the “effect of this fertilizer” occurs indirectly at this stage of the cultivation cycle. Humic acids play an important role in binding, possibly releasing various ions and changing pH. Soil nutrients, macro and microelements are bound in chelate complexes, from which plants can more easily absorb them [66,67]. Humic acids optimize the use of nutrients by plants and reduce the need for mineral fertilizers. The result is an expansion of the volume of the root system of cultivated plants, which better tolerate stress factors. This, in turn, increases both the quantity and quality of agricultural production [68]. Bera et al. [69] report that humic acid additions accelerate plant metabolism, promote root development, and increase nutrient uptake, leading to increased growth and development. In addition, humic acids play a significant role in improving soil structure, moisture retention, and nutrient availability, thereby creating a favorable environment for plant growth. Studies have shown that humic acid application can lead to increased yields in a wide range of crops.

In the present study, the amino acid composition of spring wheat grain was significantly dependent on both experimental factors and their interaction. Both farming systems, in combination with the individual forecrops, resulted in a higher content of different amino acid groups. In combination with the sugar beet and red clover forecrops, organic farming positively modified the content of Glu, Pro, Gly, Val, Met, Lys, Arg, and Trp. The conventional system in combination with the sugar beet forecrop, in turn, contributed to a higher content of Asp, Ser, Ala, Cys-A, Ile, Leu, Tyr, and Phe, while in the field after red clover: Asp, Ser, Cys-A, and Tyr. In a study by Shoup et al. [70], the concentrations of histidine, arginine, threonine, glycine, and methionine in protein were negatively correlated, whereas the concentrations of glutamic acid and proline were positively correlated with the total protein content in wheat. The content of almost all amino acids increased with increasing protein content in wheat samples.

Żuchowski et al. [37] proved that organically produced spring wheat had a much higher total phenolic acid content than conventional wheat, though the differences in the levels of phenolic compounds were not large. The results of a study by Kwiatkowski et al. [71] reveal that the difference in the antioxidant parameters of cereal grains between the organic system and the conventional system is not great. There is only a tendency towards more beneficial antioxidant properties of organically grown grain.

The results of a study by Ciołek et al. [31] prove that organically grown wheat grain contained more Mn and significantly more Fe, Zn, Ca, and Mg in comparison with conventionally grown grain. On the other hand, higher potassium availability in the soil, resulting from the application of potassium salt fertilization, manifests itself in a higher content of this macronutrient in conventionally grown wheat grain, which is confirmed in the present study. Škrbić and Onija [72], in turn, are of opinion that the micronutrient content in wheat grain depends on the type of soil and its nutrient availability and is a derivative of the scope of application and rates of agrochemicals (mineral fertilizers and pesticides). Zhao et al. [73] studied 150 lines of bread wheat and found that grain Fe, Zn and Se content exhibits the greatest variation. The Zn concentration in the grain was negatively correlated with the wheat grain yield. The concentration of both Zn and Fe in the grain was positively and significantly correlated with the grain protein content and P concentration. Suchowilska et al. [74], on the other hand, found a strong correlation for the Zn, Fe, and Mn content in wheat grain, which may have significant implications for wheat quality breeding.

Wiśniowska-Kielan and Klima [75] conducted an assessment of the micronutrient content in wheat grain originating from neighboring 50 organic farms and 50 conventional farms. They demonstrated relatively small differences in the Fe, Mn, Zn, and Cu content in the grain from both farming systems. The micronutrient content decreased as follows: Fe > Zn > Mn > Cu. On the other hand, the average contents of all micronutrients were slightly higher in wheat grain from the conventional farms.

In this research, the contents of most minerals determined in the grain of conventionally grown spring wheat were similar to the determinations made by Ekholm et al. [76]. Gebruers et al. [77] report that the difference in the dietary fiber content in wheat grain is more correlated to the types and varieties of this cereal than to the farming system.

Mie et al. [78] and Kwiatkowski et al. [33] report that bioactive substances valuable for health are found in organic agricultural produce in increased amounts due to the fact that organic crops take up much less nitrogen compounds than conventionally grown crops. The so-called carbon and nitrogen theory says that owing to the absence of excess nitrogen taken up, plants in organic farming generate processes leading to the production of compounds containing carbon atoms in their structure. Useful, in terms of quality assessment, substances are thus formed, in particular those that are antioxidant in nature (for instance, organic raw materials and products are characterized by a higher percentage of polyphenols than those originating from conventional farming) [79]. In turn, Mäder et al. [36] found that the nutritional value of wheat grain (protein content, amino acid composition, and mineral and trace element content) was not affected by the farming systems.

The quality and chemical composition of cereal grain depend on the appropriate selection of crops that have a beneficial effect on the habitat of succeeding crops. This study proves that the forecrop for spring wheat had an important influence on all the grain quality parameters studied, including the health-promoting ones. The most favorable nutritional composition of wheat grain was found after the sugar beet and red clover forecrops. The cereal forecrops (wheat and barley), except for oat, significantly deteriorated the grain quality. Wanic et al. [26] found that growing wheat after pea had a positive influence on the grain protein content. In the grain of wheat grown after itself, the values of this parameter were lower than in the grain of wheat grown after pea and oilseed rape. This is also confirmed in the studies by Woźniak [80] and Woźniak and Makarski [81]. In crop rotations with excessive saturation of cereals, these authors found a decrease in protein and starch content, but an increase in fiber and phytate content. Moreover, the grain from a cereal monoculture had a lower content of phosphorus, calcium, iron, and zinc than the grain from a crop rotation. In the study by Wanic et al. [26], the forecrops did not affect the grain content of phosphorus, potassium, magnesium, calcium, and copper. The grain contained more iron when wheat was grown after oilseed rape and more zinc when it was grown after pea, compared to other (cereal) forecrops. Amirahmadi et al. [24], Jaroszewska et al. [27] and Szuba-Trznadel et al. [82] emphasize the need to seek opportunities to increase the protein content in wheat grain in the era of deficit in the structure of legume crops. They also indicate the beneficial role of the preceding crop enriching the soil with nutrients (sugar beet, legumes) in determining the quality of spring wheat grain.

To sum up, the quality and health-promoting parameters of wheat grain obtained in this experiment (regardless of the farming system) were within the standard range for the individual components, whereas their contents (including the amino acid composition) were similar to the determinations reported by other authors [75,77,83,84,85].

5. Conclusions

The cultivation of spring wheat in the organic system, regardless of the forecrop, resulted in a statistically significant reduction in the grain yield of this cereal, on average by 23% (1.37 t ha⁻¹), compared to the conventional system. The forecrops significantly modified the wheat grain yield in both farming systems. The divergence in spring wheat yields in the organic system was as follows: 4.07 t ha⁻¹ (winter wheat forecrop)–5.13 t ha⁻¹ (sugar beet forecrop), whereas in the conventional system, the grain yield was within the following range: 5.19 t ha⁻¹ (winter wheat forecrop)–6.82 t ha⁻¹ (sugar beet forecrop). As a result, a favorable forecrop for spring wheat in the organic system provided the same quantity of grain yield as the yield obtained in the conventional system after the worse forecrops (winter wheat, spring barley).

Higher grain contents of protein, total dietary fiber, o-dihydroxyphenols, polyphenols, selenium, magnesium, calcium, copper, manganese, iron, and zinc, respectively, were found under organic farming conditions. The quality of spring wheat grain was also positively correlated with the most favorable forecrops for spring wheat (red clover, sugar beet, and, to a less extent, oat).

The influence of the farming system on the amino acid composition in spring wheat grain varied. It should however be noted that the organic system resulted in, among others, a higher content of exogenous amino acids (lysine, methionine, tryptophan), which is of significance in the food consumer market. The essential amino acid index (EAAI) determined for organically grown wheat after the sugar beet, red clover, and oat forecrops had the significantly highest values. This demonstrates that protein in the grain of organically grown spring wheat is characterized by a higher biological value compared to the conventional system.

This study confirmed that appropriate management of the organic cultivation of spring wheat (sugar beet forecrop, fertilizer Humac Agro) contributes to high grain nutritional quality relative to the conventional system and also reduces the yield gap relative to conventional farming.