Impact of Spring Wheat Varieties and Legume Species Intercropping on Organic Wheat Production

Abstract

Intercropping, the cultivation of two or more crops in the same field, is known to have numerous environmental and economic benefits. The success of such systems depends on geographical location, climatic conditions, and the choice of crop varieties, especially in organic systems. This study aimed to assess the effect of the sowing method, wheat variety, legume species on wheat grain yield and quality, and macro-elements of soil and plants. A three-year field experiment in intercropping spring wheat and legume species was performed at an organic-certified field of Czech Agrifood Research Center, Prague. Three spring wheat varieties (Alicia, Hystrix, and Toccata), two legume species (pea and faba bean), and two sowing methods (mixed and row-by-row) were used. Although the intercropping of wheat variety and legume species did not improve wheat yield, wheat grain quality and soil and plant nutrition content were enhanced in wheat and legume mixtures compared to monoculture wheat. Notably, the mixed cropping method resulted in significantly higher yields than the row-by-row method. Furthermore, the baking quality of wheat grains from intercropping systems was superior to that of monoculture wheat. The results highlight the potential of tailored intercropping systems to optimize agricultural efficiency and sustainability, especially in the face of changes in climate change.

1. Introduction

Organic wheat farming offers numerous benefits but is marked by low input, especially the limited availability of soluble nitrogen (N) [1], resulting in lower grain yield and quality than conventional farming. Nitrogen is a key macronutrient significantly affecting wheat grain yield and quality [2]. In conventional farming, mineral N fertilizers are applied throughout the growing season to fulfil the crop’s N needs. This practice, however, is not permitted in organic cereal farming [3].

The diversity of cropping systems in agricultural practices is increasingly seen as a promising approach to enhance natural interactions and boost agroecosystem resilience. Implementing strategies to improve sustainable crop growth are achieving nitrogen self-sufficiency and enhancing nitrogen use efficiency, which is essential for long-term agricultural sustainability, especially in organic farming [4].

Intercropping, the simultaneous cultivation of two or more crops in the same field, is a cornerstone of sustainable agriculture [5]. Cropping systems incorporating crops offer several advantages over monocultures [6], particularly cereal–legume intercropping, which is recognized for enhancing agroecosystem efficiency by improving productivity and economic profitability, providing better pest and disease control, and offering greater ecological services [7]. Intercropping affects the yield, yield component formation, and cereal quality of crops through its interspecific competition [8], as well as through its impact on soil fertility [9].

Integrating crops such as wheat and legumes not only aims to increase yields but also plays a central role in the nutrient cycle, contributing to a more sustainable balance of organic matter and soil nutrients [10]. Cereal–legume intercropping is a productive and sustainable cropping practice [4] and becomes useful due to the benefits of legumes producing additional N resources due to symbiotic N fixation. Intercropping legumes with cereals has been suggested as the most promising approach to reduce N fertilizer application worldwide [11]. A significant amount of fixed N is provided into the system through atmospheric N₂ fixed by legumes, which can be transferred to neighbouring plants [12]. Intercropping optimizes the soil environment and promotes root growth and distribution by improving the physicochemical properties of the soil, promoting the formation of soil aggregates near crop roots, reducing bulk density, increasing soil porosity, and maintaining a higher oxygen content in the soil [13]. The diversity of legume species in the wheat–legume intercropping system is regarded as a significant advantage [14]. The selection of suitable cereal and legume species, as well as their genotype, influences the rhizosphere microbiome and plays a key role in intercropping compatibility in combinations for both species [15]. Pea and faba bean are the most commonly used legume species in intercropping experiments [16]. Paul et al. [17] concluded that the performance of selected spring wheat varieties in a mixture cannot be predicted from their performance in a monoculture. Therefore, combining species selection as a plant team is important for a successful intercropping design. In addition, the environment and crop play an important role in the performance of crop mixtures and their bidirectional interactions with varieties [17]. This interaction is particularly beneficial in organic farming, where the potential synergy between species can improve and stabilize cereal yields [17].

The success of intercropping systems depends on various factors, including environmental conditions, crop species, sowing techniques, and management practices [4,18]. Wheat yields in organic farming show great variability, mainly due to the limited availability of nitrogen and weed competition [19,20]. Intercropping faba bean with wheat resulted in higher yields compared to the cultivation of a sole crop [21]. However, the study of Hoang et al. [22,23] found contrasting results, where wheat grain yield did not increase and was even lower in wheat–legume mixtures than in monoculture wheat. Well-designed intercropping efficiently utilize natural resources, enhance biodiversity, control pests, and, in many cases, improve crop productivity, quality, and natural soil fertility while reducing input use [24]. Although intercropping offers numerous advantages, it also presents several challenges, such as concerns over increased pest vulnerability, the need for significant financial investment, complex agronomic practices, potential yield reductions, and more demanding management requirements [25]. In the case of simultaneous intercropping, additional management practices may be necessary to mitigate potential competition between legumes and cereal crops, as this could impact both grain yield and quality at harvest [26]. The competition for nutrients and light in simultaneous intercropping might limit or reduce the cereal yield in the case of vigorous growth or high legume crop density [27]. An alternative approach could involve sowing the cereal and legume in alternating separate rows [10]. The intercropping of winter wheat and legumes enhances diversity in the ecosystem, positively affecting weed control, enhancing soil fertility, and increasing the N use efficiency. This contributes to the concentration of crude protein and cereal quality compared to the monoculture systems [9]. The intercropping of wheat and legumes might improve wheat quality by increasing protein content and enhancing baking quality in organic farming systems [28,29].

Most cereal–legume intercrop studies in Europe focus on winter-sown intercrops [22,23,28], with some research on spring-sown intercrops [30,31,32]. However, limited information is available on spring-sown cereal–legume intercrops under our specific conditions. To assess the effectiveness of these intercrops, a three-year experiment was conducted at the Czech Agrifood Research Center (former Crop Research Institute) in Prague, using various spring wheat varieties and legume species to evaluate the spring wheat yield stability and the grain quality improvement. Our goal was to provide valuable insights into the potential of different wheat–legume mixtures as a sustainable strategy for organic farming and high-quality food production. This research could help farmers and policymakers make informed decisions, fostering greater spring wheat organic agriculture efficiency across diverse environmental conditions.

2. Materials and Methods

2.1. Experimental Site and Weather Conditions

Field experiments were conducted on a loamy clay, classified as Chernozem (IUUS/ISTRIC/FAO, 2006) [33], at the organic certified experiment farm of the Czech Agrifood Research Center in Prague, Czech Republic (50°05′11.4″ N, 14°18′11.3″ E), from 2020 to 2022. The site is located on the north-west side of Prague, at an elevation of 320 m, with annual precipitation of 472 mm, and mean annual air temperature of 8.4 °C. The average temperature and the total rainfall during the three growing seasons, as well as the long term, are shown in Figure 1.

The temperature in March and April 2020 was higher than the long-term average in 1991–2020, in contrast to May 2021, where the temperature was 1.8 °C lower than the long-term average. The number of tropical days with temperatures exceeding 30 °C was relatively low, with only two days in July and eight days in August 2020.

The weather in 2021 was atypical; from March to May, temperatures were lower than the long-term average, followed by high average temperatures in June (20.5 °C) and July (20.3 °C). June 2021 was characterized by summer temperatures, with five consecutive tropical days, followed by a cold August with temperatures approximately 2 °C lower than usual. The year 2022 was characterized by a colder April, but higher temperatures during the rest of the growing season, on many occasions reaching tropical temperatures.

The total rainfall in 2020 was higher compared to long-term average values, except for April, which recorded slightly less rainfall. Spring 2021 was characterized by a lack of precipitation in March and April, followed by nearly twice the amount of rainfall in May (104 mm) compared to May 2020 (52.3 mm), and almost seven times as much as in May 2022 (15.7 mm). These conditions affected the growth of spring wheats as well as the legumes. Irregular monthly and daily rainfall distribution was observed from 2020 to 2022, along abnormally high or low temperatures compared to the long-term period.

2.2. Wheat and Legume Varieties

Three spring wheat varieties (Triticum aestivum L.) with different baking quality characteristics were used in the study. Variety Alicia (group E) is medium to high-yielding with excellent baking quality and high bulk density; variety Hystrix (group A) has a high thousand-grain weight and medium bulk density, good baking quality; and variety Toccata (group B) is a high-yielding variety with low bulk density. Two legume species were used faba bean (Vicia faba L., cv. Merkur) and pea (Pisum sativum L., cv. Eco). The spring wheat varieties were sown at a density of 400 germinated seeds per m². The sowing density of legumes was 30% of the usual quantity 300 seeds per m² for pea and 150 seeds per m² for faba bean, regardless of the sowing method.

2.3. Experimental Design and Cultivation of Wheat Varieties and Legumes

The field trials were performed under organic farming conditions, artificial fertilizers, herbicides, and pesticides were strictly avoided in the organic agriculture trial plots. Emmer wheat as a pre-crop was used. The small plot experiment with a randomized complete block design (three replications) was used to assess the effects of sowing method (mixed and row-by-row), spring wheat varieties (Alicia, Hystrix, and Toccata), and legume species (pea and faba bean). The size of each plot was 12 m² (1.25 m × 9.6 m) with a row spacing of 12.5 cm. The trials were sown in two ways: (1) mixed sowing: spring wheat varieties and pea/faba bean seeds were mixed before sowing and sown together in one row; (2) row-by-row: wheat and legume were sown in separate rows, alternating one row of wheat with one row of legumes (so-called row-by-row) (Figure 2). Spring wheat varieties without legumes were sown as a control treatment.

Ploughing was performed annually in November before spring tillage using a Kvernland ES 95 reversible plough (Kverneland Group, Klepp Stasjon, Norway) to a depth of 20 cm. Before sowing, the soil was prepared with the Lemken Korund seedbed combination system (Lemken GmbH & Co., KG, Alpen, Germany) to a depth of 4 cm. Sowing was carried out with an Oyord Wintersteiger seed drill (Wintersteiger Seedmech, Ried, Austria). Harrowing with a spring tine harrow (Hatzenbichler, Sankt Andrae, Austria) was conducted. Harvesting took place with a Wintersteiger NM-Elite harvester (Wintersteiger Seedmech, Ried, Austria). All agronomic management practices for each growing season are presented in

Table 1. Agronomic practices management in three growing seasons.

Season	Ploughing	Seedbed	Sowing	Harrowing	Harvested	Days of Mature (Days)
2020	11/2019	3/4/2020 *	6/4/2020	27/4/2020	19/8/2020	134
2021	11/2020	29/3/2021	31/3/2021	19/4/2021	14/8/2021	136
2022	11/2021	28/3/2022	30/3/2022	4/4/2022	28/7/2022	120

*: dd/mm/yyyy.

, and the details of the experimental variants are shown in Table S1.

2.4. Nitrogen and Selected Nutrient Content in Soils and Plants

Soil samples for the determination of N were taken before sowing and after the wheat harvest. All samples were taken from a depth of 0–30 cm in four replicates based on the intercropping system: without legumes, pea, or faba bean. The N in soils was determined as follows: 50 g of moist soil was stirred with 250 mL of 1% K₂SO₄ at 200 rpm for one hour. After filtration on Whatman Grade 40 filters, the clear solutions were measured with the colorimeter SANplus SKALAR (Skalar Analytical B.V., Breda, The Netherlands). The initial N content in soil samples before the experiment were as follows: 2020—22.9 kg N ha⁻¹; 2021—11.91 kg N ha⁻¹; and 77.5 kg N ha⁻¹. The nutrient contents in the soil samples were measured by the Mehlich 3 method, which evaluates the availability of key nutrients (K, P, Ca, Mg) in chemical forms accessible to plants [34]. Briefly, 100 mL of the Mehlich 3 extractant (0.2 mol L⁻¹ CH₃COOH, 0.015 mol L⁻¹ NH₄F, 0.013 mol L⁻¹ HNO₃, 0.25 mol L⁻¹ NH₄NO₃, 0.001 mol L⁻¹ EDTA) was mixed with 10 g of air-dried soil and shaken at 200 rpm in a 250 mL plastic flask.

Plant samples were collected as whole plants in each plot at the harvest stage, with three replicates for laboratory analyses. The harvested samples were stored in a dry place, and the dry matter content of both plants and seeds was determined. The concentrations of nutrients (N, P, K, Ca, and Mg) in plant samples were determined from 0.5 g of powdered plant material after digestion in 6 mL of concentrated HNO₃ and 1 mL of 30% H₂O₂ using Milestone 1200 microwave (Shelton, CT, USA) under the following conditions: 2 min—250 W, 2 min—0 W, 5 min 250 W, 5 min—400 W, 5 min 250 W, 5 min—ventilation.

All soil and plant sample solutions were filtered on Whatman Grade 40 filters and subsequently analyzed for nutrient content using a Thermo Fisher Scientific 7400 iCAP ICP-OES analyzer (Carlsbad, CA, USA).

2.5. Crop Yields and Qualitative Characteristics

A 1 m² area was randomly selected and marked for spike number assessment in each replicate plot with three replicates. The yield of spring wheat varieties was determined after harvesting individual plots with a plot combine harvester and converted into hectares. The grains of spring wheat and legume were separated using sieves after harvesting. All grain samples were dried, and the remaining impurities were removed. To evaluate the dry matter (dm) content of the grain, 5 g of ground seed samples were dried in an electric hot-air drier at 135 °C for 4 h, according to the standard method (AACC International Method 44-11.01.). For thousand kernel weight (TKW), a representative grain sample was taken, and the TKW was determined by weighing 1000 kernels using a precision balance at a moisture level of 14%. The grains of spring wheat and legume were separated using sieves. The samples were stored in a cold (4 °C) and dark place in plastic bags for future laboratory analyses. All samples were prepared in three replicates, and the results are expressed as the mean. The wheat samples milled in a laboratory grinder PSY MP 20 (Mezos, Hradec Králové, Czech Republic) and with a laboratory mill Quadrumat Junior (Brabender, Duisburg, Germany). The baking quality analysis of the wheat samples was conducted using the following methods: protein content (PC) was determined using the Kjeldahl method (ICC-standard No. 105/2) with Kjeltec KT 200 (FOSS, Hilleröd, Sweden) [35], based on N x 5.7 (in grain dry matter); falling number (FN) was evaluated using Falling number 1400 (Hagberg-Perten, Hägesten, Sweden), according to ICC-standard No. 107/1 [36]; Zeleny sedimentation value test (ZST) according to ICC-standard No. 116/1 [37]; wet gluten content (WG) (in grain dry matter) was determined using Glutomatic 2200 and Centrifuge 2015 (Perten Instruments, Hägersten, Sweden), according to ICC-standard No. 137/1 [38], AACC International method 56–81B; and hectolitre weight (HW) was measured according to ISO 7971-3:2019 [39].

2.6. Statistical Analysis

All statistical analyses were performed using STATISTICA (version 13.2, StatSoft, Inc., Palo Alto, CA, USA) and JMP v.14 (SAS, Cary, NC, USA). Tukey’s HSD (Honest Significant Difference) test was performed at a significance level of p < 0.05. Statistical analysis was carried out to assess the effect of growing season, sowing method, spring wheat varieties, legume species, and their interactions. Principle component analysis (PCA) was applied for each wheat variety to determine parameter correlations between grain yield and grain quality, as well as the different responses between spring wheat varieties and legume species cultivation.

3. Results and Discussion

3.1. Mineral Nitrogen (N) and Selected Nutrients Content in Soil Samples

Nitrogen (N), phosphorus (P), and potassium (K) are the vital nutrients required for optimum growth, development, and productivity of plants [40]. Maintaining macro-elements in the soil is an effective approach for sustainable crop production due to its positive impact on soil ecological functions and health [7]. The simultaneous cultivation of legumes or legume residue left on the soil surface contributes to increasing not only available soil total N but also P and K, which is helpful for plants grown simultaneously with legumes or for the following crop [40]. The results of the mineral nitrogen content (N) in the soil samples taken before sowing and after harvest are presented in Figure 3. The macro-elements—N, P, and K (mg kg⁻¹)—in the soil from the experiment after harvesting are shown in Figure 4. The results showed that the macro-elements improved in wheat and legume species intercropped than that in monoculture spring wheat.

After harvesting, the nitrogen content (N) value was lower than before sowing (Figure 3), indicating that plant nutrient uptake reduces soil nitrogen levels in this research. This process supports plant growth and development, optimizing yield and seed quality. Intercropping wheat with legumes (pea and faba bean) improved nitrogen content compared to monoculture wheat (Figure 3 and Figure 4) during the three-year growing season. This is consistent with a review on nitrogen fixation through legume intercropping by [40]. For instance, maize + faba bean, barley + pea, and wheat + soybean intercropping systems showed improved N acquisition compared to sole cropping.

Legume intercropping not only enhances N and P availability but also improves the cycling and availability of other essential macro- and micronutrients. These benefits are achieved through mechanisms like root exudation, microbial activity, and the enhancement of soil organic matter [40,41]. These nutrients are vital for plant growth, productivity, and soil health, making legume intercropping an effective tool for addressing nutrient deficiencies [40]. Intercropping legumes with cereals enhances nutrient availability through the root exudation of organic acids, releasing them from non-exchangeable reserves [40]. For example, Wang et al. [42] reported maize + legume intercropping has shown a 15–20% increase in soil-exchangeable K compared to monocropping. This practice can reduce dependence on potassium fertilizers, particularly in soils deficient in potassium. This finding is similar to our study, in addition to nitrogen (N), the levels of phosphorus (P) and potassium (K) in the soil were also greater in the wheat–legume intercrop than in monoculture wheat (Figure 4), such as K in case wheat + faba bean in 2020 and P in case wheat + faba bean in 2021. A noticeable trend in phosphorus (P) and potassium (K) levels was observed, with values nearly doubling in 2020 and 2022 compared to 2021, while the control variant consistently showed lower values than the intercropping systems with peas or beans (Figure 4). These findings confirm that intercropping spring wheat with legumes improves soil fertility, highlighting the benefits of this practice for sustainable agriculture. Accordingly, legume cultivation enhances the nutrient pool and maintains soil fertility, potentially reducing the input of synthetic fertilizer and addressing environmental concerns.

Higher soil nutrient levels were observed in the wheat and legume mixture compared to sole wheat cultivation. In this study, the soil nutrient supplementation from wheat–legume mixtures did not increase wheat yield, which may be due to competition between wheat and legumes, similar to the findings in other studies [27]. However, the higher soil nutrient content in the case of wheat + pea/faba bean compared to monoculture wheat (Figure 3 and Figure 4) improved wheat quality (

Table 2. Grain yield and quality affected by growing season, sowing method, wheat variety, and legume species in the spring wheat and legumes intercropping field experimental over three years in 2020–2022.

Factor	No. Spike	TKW (g)	Yield (t ha−1)	HW (kg hL−1)	Protein (%)	Gluten (%)	Zeleny (mL)	FN (s)
Harvest year
Y2020	208.35 ± 8.88 b	42.97 ± 0.44 a	4.21 ± 0.11 b	74.98 ± 0.23 c	11.87 ± 0.07 c	25.03 ± 0.26 c	38.49 ± 0.47 c	363.79 ± 2.93 a
Y2021	140.80 ± 7.06 c	39.89 ± 0.57 b	2.76 ± 0.11 c	75.67 ± 0.19 b	14.40 ± 0.08 a	30.66 ± 0.40 a	61.33 ± 0.88 b	304.90 ± 6.72 b
Y2022	372.00 ± 9.61 a	41.87 ± 0.46 a	6.41 ± 0.10 a	77.08 ± 0.11 a	13.60 ± 0.04 b	29.02 ± 0.13 b	68.28 ± 0.74 a	281.08 ± 2.45 c
Sowing method
Mixed	273.15 ± 12.35 a	42.02 ± 0.38 a	4.94 ± 0.19 a	76.17 ± 0.17 a	13.10 ± 0.14 a	27.73 ± 0.35 a	55.07 ± 1.70 a	314.96 ± 5.38 b
Row-by-row	239.25 ± 13.03 b	41.68 ± 0.45 a	4.53 ± 0.20 b	75.70 ± 0.21 b	13.11 ± 0.13 a	27.94 ± 0.35 a	55.22 ± 1.80 a	322.63 ± 5.41 a
Variety
Alicia	261.05 ± 19.84 a	39.51 ± 0.43 b	4.80 ± 0.23 a	77.02 ± 0.16 a	13.24 ± 0.19 a	29.25 ± 0.39 a	58.09 ± 2.31 a	333.78 ± 6.15 a
Toccata	245.50 ± 12.62 a	43.09 ± 0.44 a	4.59 ± 0.24 b	74.54 ± 0.21 c	12.79 ± 0.16 b	26.74 ± 0.40 c	51.29 ± 1.73 c	314.80 ± 6.90 c
Hystrix	264.85 ± 17.08 a	42.96 ± 0.47 a	4.84 ± 0.25 a	76.28 ± 0.16 b	13.28 ± 0.14 a	27.50 ± 0.40 b	56.02 ± 2.22 b	307.37 ± 6.29 b
Legume
Wheat	265.70 ± 17.49 a	42.27 ± 0.49 a	5.30 ± 0.23 a	76.13 ± 0.20 a	12.92 ± 0.19 b	27.50 ± 0.46 c	53.92 ± 2.28 c	317.75 ± 4.73 b
Wheat x Pea	256.15 ± 14.00 a	41.55 ± 0.51 a	4.42 ± 0.25 b	75.59 ± 0.25 a	13.22 ± 0.15 a	27.77 ± 0.42 b	55.36 ± 1.90 b	322.49 ± 6.41 a
Wheat x Bean	248.80 ± 15.54 a	41.72 ± 0.54 a	4.47 ± 0.23 b	76.13 ± 0.24 a	13.18 ± 0.15 a	28.27 ± 0.39 a	56.28 ± 2.20 a	315.37 ± 8.65 c
ANOVA
Year (1)	**	**	**	**	**	**	**	**
Sowing (2)	**	ns	**	**	ns	ns	ns	**
Variety (3)	ns	**	*	**	*	**	**	**
Legume (4)	ns	ns	**	ns	*	*	**	**
2 × 3	ns	ns	ns	**	*	**	ns	ns
2 × 4	*	ns	**	ns	*	**	**	**
3 × 4	ns	ns	ns	ns	*	**	*	**
2 × 3 × 4	ns	ns	ns	ns	*	**	*	**

TKW: thousand kernel weight; HW: hectoliter weight; FN: Falling number. Mean ± SE. ns: non significantly different; * p < 0.05; ** p < 0.01. Different letters in the column for each factor show a statistical difference between treatments at p < 0.05.

) in our study. This suggests that nutritional factors, especially nitrogen, are essential for the growth and development of crops, as well as grain yield and quality. Therefore, intercropping cereals with legumes can enhance crop production efficiency in organic farming, reducing the need for inorganic fertilizers in conventional agriculture and contributing to sustainable agriculture in the context of current climate change.

3.2. Nitrogen and Selected Nutrient Content in Plants

The macro-element content of plants is presented in Figure 5. The observed year-to-year variability suggests that factors such as climate conditions, soil microbial activity, and specific crop combinations significantly influence nutrient availability. In any growing system, adequate N content in the soil plays a crucial role in achieving optimal wheat yields and maintaining grain quality. In general, the required amount of nitrogen as a fertilizer to produce 1 tonne of wheat grain is about 25 kg [43]. However, sustainable nitrogen management is essential to reduce dependency on synthetic fertilizers and mitigate environmental impacts such as nitrate leaching and greenhouse emissions [44]. Intercropping with legumes can increase nitrogen content through biological N-fixation and improves overall soil fertility [4,11]. The finding of this study supports previous research showing that intercropping wheat with legumes significantly increases nitrogen content compared to monoculture wheat systems. This statement corresponded with the findings that intercropping legumes and cereal can maximize resource use and increase yields, as legume root nodules enhance nitrogen fixation [11]. Figure 5 shows that N content was the same trend in the first and second season; N content was higher in wheat and legume intercrop (wheat + pea) than in monoculture wheat. The observed nitrogen content in intercropped wheat–legume systems aligns with the previous findings. Kumar and Goh [45] found that more than 80% of the N was derived from biological nitrogen fixation (BNF). However, the difference of wheat varieties and legume species in intercropping suggests that nutrient competition between wheat and legumes or variations in nitrogen uptake efficiency may influence final nitrogen levels [46,47]. In contrast to the first two years, the N value was lower in the third year under wheat + pea/faba bean intercropping compared to monoculture wheat (Figure 5). Phosphorus (P) differed across different years. While monoculture wheat and wheat + legume did not significantly differ in phosphorus content in the first and third year, wheat–legume intercropping demonstrated improved phosphorus uptake in the second years (wheat + pea). This result suggests that the long-term benefits of intercropping may gradually enhance phosphorus mobilization, possibly due to increased microbial activity and root exudation, which facilitate phosphorus solubilization and uptake [48]. Additionally, it has been reported that legume intercropping due to niche complementarity and interspecific facilitation contributes to increased P acquisition in [49]. The absence of a significant difference in phosphorus content between intercropped and monoculture wheat may indicate that phosphorus availability is influenced by seasonal variations, soil conditions, and crop rotation history [50]. Mg and Ca content values in wheat plants did not significantly differ over the three-year experiment between wheat + legume crops and monoculture wheat (Figure 5). This could be due to competition for cation uptake sites, differences in root architecture, or varying Mg requirements among species [51]. Previous studies have indicated that legume intercropping can improve Mg and Ca availability in some conditions, particularly in low-input or organic farming systems where nutrient cycling is largely dependent on plant–soil interactions [52].

3.3. Yield and Quality of the Spring Wheat

The changing weather has affected the annual variation in spring wheat yields [53]. In fact, during the 2020–2022 study period, weather variability was observed not only between the study years but also between months, weeks, and even days. Specifically, the Czech Republic experienced higher temperatures and lower rainfall, leading to reduced agricultural productivity and lower yields, as reported by Trnka et al. [53]. In particular, the cold spring of 2021 and the slow warming of the soil delayed wheat emergence and suppressed the germination and subsequent growth of legumes. As a result, the number of spikes per m² in 2021 was lower compared to 2020 and 2022. Additionally, the high summer temperatures (>25 °C) and tropical temperatures (>30 °C) [54] in June 2021, following the cool spring, further impaired crop growth. In April 2022, slightly higher rainfall was recorded compared to 2020 and 2021. However, drought conditions in May and the first three weeks of June 2022 may have affected wheat growth. In contrast, heavier rainfall in the last week of June 2022 (108 mm) helped mitigate the risk of leaf tip drying and stalk reduction. Combined with a higher N content, this contributed to the highest spring wheat yields compared to previous years.

The above evidence suggests that weather changes are one of the key factors that have significantly impacted wheat yield and quality changes over the years. Spring wheat yields and quality were affected by the weather conditions (Table 2). The grain yield, spike number, and TKW were lower in the 2021 growing season compared to the 2020 and 2022 growing seasons. The temperature was colder in 2021 than in 2020 and 2022. In particular, the high rainfall in May 2021 and lower temperatures led to slower plant growth and delayed the harvest. Spike number and grain yield were highest in 2022 at 372.00 spike number m⁻² and 6.41 t ha⁻¹, followed by the 2020 growing season at 208.35 spike number per m² and 4.21 t ha⁻¹. In contrast, the 2021 growing season had the lowest values, with only 140.80 number per m² and 2.67 t ha⁻¹, which was less than half of the yield in 2022 (Table 2). Our findings are consistent with those of Hoang et al. [22,23], who also reported that the weather conditions significantly affected spike number and wheat grain yield. However, Mitura et al. [55] showed that the growing season did not significantly affect grain yield, but different cultivars affected grain yield. Previous studies reported that the cultivar mentioned plays a key role in wheat grain yield and yield components [55]. In our research, spike number was not significantly affected by wheat varieties (Table 2). A higher grain yield was observed in Alicia and Hystrix compared to Toccata. The spike number per m², TKW and yields of the tested wheat varieties varied between the two sowing methods and legume intercropping. A slightly lower spike number per m², TKW and yields were recorded in the row-by-row sowing method compared to the mixed sowing method. Intercropping between spring wheat varieties and legume species did not significantly affect the spike number per m² and TKW. However, wheat grain yield was lower in wheat–legume (pea and faba bean) intercropping compared to individual wheat varieties (Table 2 and Figure 6). The yield reduction was due to cultivation in combination with both legume species in both sowing treatments compared to the control varieties.

There are conflicting reports on the impact of legumes in wheat and legume intercropping and sowing methods on wheat grain yield. In the case of mixed intercropping, the competition between legumes and cereal may need to be considered [26]; intercropping crops can reduce the yield of mixtures compared to sole cereal crops [56] because simultaneous intercropping might limit or reduce the cereal yield in a case of high growth and high density of the legume, resulting competition for nutrient resources and light [27,28]. The alternative cropping may be considered where the cereal and legume are sown in separate rows alternately [1] to reduce competition between the main crop and intercrop. However, the row-by-row sowing method with legumes may be more suitable for winter wheat, as winter-sown legume plants exhibit poorer growth and, consequently, lower competitive ability compared to spring-sown legumes. The row-by-row sowing method resulted in a lower grain yield than the mixed sowing method (Table 2). Consistent with our findings, Dvořák et al. [28] indicated that mixed sowing with legumes led to a higher wheat grain yield compared to sowing legumes in separate, alternating rows, in both organic and conventional farming systems. Hoang et al. [22] reported no significant difference between the row and mixed methods in the case of wheat and legume intercropping. In different sowing methods, there was no significant difference between monoculture wheat and wheat and pea/bean intercropping on protein content. However, in the row-by-row method, wheat grain yield was lower in wheat–legume intercropping compared to monoculture wheat (Figure 6).

The hectolitre weight (HW) is considered an essential predictor of the milling yield and is used as an indicator of the general grain quality. Various factors can influence the HW value of wheat, including genetics, the moisture content of the grain, agriculture systems, nutrients, or changes in weather conditions [57]. In this study, the HW values were within the threshold required for top-quality milling wheat (Table 2, 74.54–77.02 kg hL⁻¹), with 76 kg hL⁻¹ being standard for top-quality milling wheat [57,58]. The HW was significantly affected by the growing season, wheat varieties, and sowing methods, while there was no significant difference in intercropped wheat and legume (Table 2). HW was higher in the 2022 growing season, followed by 2021 and 2020. This is consistent with the study by Hoang et al. [22], which found that the growing season significant affected HW. The sowing method influenced HW, with the mixed method (76.17 kg hL⁻¹) resulting in a higher HW than the row-by-row (75.70 kg hL⁻¹) sowing method. Among the varieties, Alicia (77.02 kg hL⁻¹) had higher HW than Hystrix (76.28 kg hL⁻¹) and Toccata (74.54 kg hL⁻¹). Additionally, the different agricultural systems and nutrient availability also affect HW. According to the previous studies, Przystalski et al. [59] found that HW was always lower in organic conditions compared to conventional condition because of lower N input. Similarly, Murphy et al. [60] identified differences in HW among winter wheat cultivars in the USA depending on growing season and location. However, the research shows no significant difference; for example, Annicchiarico et al. [61] reported that HW ranged between 81.2 kg hL⁻¹ and 82.3 kg hL⁻¹ in organic and conventional farming.

The PC in wheat grain was significantly influenced by the growing season, wheat variety, and wheat–legume intercropping (Table 2 and Figure 6 and Figure 7). The highest PC was obtained in 2021 (14.40%), followed by 2022 (13.60%) and 2020 (11.81%). The significant influence of weather conditions in shaping the number of protein substances in wheat grain has also been indicated by the results of the study conducted by Sułek et al. [62]. The significantly highest PC was observed in the grain of the Alicia (13.24%) and Hystrix (13.28%), while Toccata had a lower PC (12.79%). The variability in PC among wheat cultivars has been shown in previous studies [63,64,65]. Wheat–legume intercropping is an effective tool for the long-term strategy for regulating nitrogen nutrition [66]. The provision of N-fixation into the soil from wheat and legume intercropped improved grain quality, as confirmed by studies conducted by Hoang et al. [22] and Dvořák et al. [28]. The consistency indicated in our research showed higher protein content in wheat and pea/faba bean intercropping than in monoculture wheat. However, the grain yield remained unchanged under both mixed and row-by-row sowing methods.

The influence of weather conditions on the accumulation of gluten proteins in wheat grain was reported in many previous studies [55,62]. Our findings confirm this, as WG was significantly influenced by the growing season, wheat variety, and wheat–legume species intercropping (Table 2 and Figure 7). However, WG was not affected by sowing methods. Wheat grain from the 2021 harvest had significantly higher WG values (30.66%) compared to grain harvested in 2022 (29.02%) and 2020 (25.03%) (Table 2 and Figure 7). A significant effect of weather conditions on WG values has also been reported [67]. The significantly higher WG was observed in the wheat grain of Alicia (29.25%), followed by Hystrix (27.50%) and Toccata (26.74%). The wheat variety differences in WG have been indicated in works’ Mitura et al., and Sulek and Cacak-Pietrzak [55,65]. WG was significantly different in the grain of the wheat–legume species mixtures (Table 2 and Figure 7), with WG being higher in the intercropped wheat and legumes compared to monoculture wheat. Gluten protein quantity and quality are important parameters for assessing the suitability of wheat grain as a raw material for baking flour. According to Mitura et al. [55], the WG content in wheat grain should not be lower than 27%. The results of our study show that WG met the gluten quality requirement.

Highly significant differences were observed in Zeleny sedimentation (ZS) based on the harvested years, wheat variety, and wheat–legume intercropping (Table 2 and Figure 7). ZS was higher than double in 2022 (68.28 mL) and 2021 (61.33 mL) compared to 2020 (38.49 mL). Higher ZS was observed in Alicia (58.09 mL), followed by Hystrix (56.02 mL) and Toccata (51.29 mL). ZS is an important test for assessing both gluten quality and quantity in wheat genotypes. Evidence suggests that ZS provides the best prediction of bread-baking potential and strength for hard wheat. ZS was not significantly affected by the mixed and row-by-row method; the values ranged between 55.07 and 55.22 mL (Table 2). Under the effect of wheat and legume intercropping, and in line with the conclusions of Dvořák et al. [28], our results showed that wheat intercropped with legumes reached higher ZS. A significant statistical difference was observed between monoculture wheat and wheat–legume intercropping from our site. The highest ZS was found in wheat + faba bean, followed by wheat + pea, with the lowest ZS observed in monoculture wheat (Table 2 and Figure 7).

The falling number (FN), an indicator of α-amylase activity, was influenced by the harvested year, wheat variety, sowing methods, and combinations of wheat and legume species (Table 2 and Figure 7). Significantly, the lowest amylolytic enzyme activity was observed in the grain harvested in 2022 (363.79 s) due to the lower rainfall during the maturation and harvesting of wheat compared to the first and second seasons (Figure 1). This is consistent with the studies of Mitura et al. and Sulek and Cacak-Pietrzak [55,65], which reported that weather conditions significantly affected FN. Similar trends were observed when comparing wheat varieties; significantly higher FN values were obtained for the grain of Alicia (333.78 s) compared to Toccata (314.80 s) and Hystrix (307.37 s) (Table 2 and Figure 7). Amylolytic enzyme activity is an important parameter in selecting grain for milling into baking flour. A low FN (<150 s) indicates grain sprouting, which disqualifies its use for food processing. Grain intended for milling into flour should be characterized by an FN of at least 200–250 s [55]. This requirement was met by the grain harvested from our experiment. FN was also affected by wheat–legume mixtures and sowing methods (Table 2 and Figure 7). Row-by-row cropping method had a positive effect on FN compared to mixed cropping. Intercropping with pea resulted in a higher FN, whereas intercropping with bean led to a lower FN than monoculture wheat. In all cases, the FN values obtained were significantly higher than the requirement for baking quality.

3.4. Principal Component Analysis (PCA) and Correlation Analysis

Correlation coefficients among the grain yield, yield components, and baking quality were calculated and are given in

Table 3. Correlations are significant at p < 0.05 between yield, yield component, and quality of grain spring wheat under effect of wheat–legume intercropping.

	No. Spike	TKW	Yield	HW	Protein	Gluten	Zeleny	FN
No. spike	-	0.05	0.83 *	0.53 *	0.04	0.04	0.45 *	−0.44 *
TKW		-	0.13	−0.24 *	−0.33 *	−0.49 *	−0.29 *	−0.02
Yield			-	0.54 *	−0.07	−0.04	0.38 *	−0.41 *
HW				-	0.41 *	0.50 *	0.60 *	−0.41 *
Protein					-	0.88 *	0.84 *	−0.62 *
Gluten						-	0.78 *	−0.50 *
Zeleny							-	−0.71 *
FN								-

TKW: thousand kernel weight; HW: hectolitre weight; FN: falling number. * p < 0.05.

. PCA’s result is presented in Figure 8.

There were significant positive correlations between grain yield and yield component, particularly the number per m² (no. spike per m²) (Table 3). Higher yield components (no. spike per m² and TKW) contribute to an increase in the grain yield of spring wheat. Grain yield was positively correlated with HW and Zeleny test, but negative correlated with yield and grain quality as protein content, gluten, and falling number (Table 3). Similarly to the PCA results, grain yield showed a positive correlation with yield components, including no. spike per m² and TKW, as well as HW. However, a negative correlation was observed between grain yield and grain quality (Figure 8). Overall, the results indicated that the correlation between yield and yield components, as well as the relationship between grain yield and grain quality, could be valuable for breeders. Grain yield could be increased through field management, such as increasing/decreasing the number of plants/spikes per m² or TKW. However, selecting and developing a new variety with high grain yield and grain quality simultaneously remain a challenge. Our results were not as expected when incorporating legumes to improve grain yield and quality in organic spring wheat production. Grain quality was improved, but grain yield did not increase. In the different spring wheat varieties, the response of the effect legume species was similar. Mixed intercropping proved to be more effective than row intercropping. The Toccata variety had slightly higher protein content and wet gluten but lower grain yield in wheat legume mixtures compared to the Alicia and Hystrix varieties.

4. Conclusions

Intercropping spring wheat with legumes such as faba beans or peas proves to be beneficial, enhancing grain quality and soil health and fostering a sustainable farming approach. In this study, three spring wheat varieties were cultivated single or in mixtures with two legumes under organic cultivation systems. The study shows that the soil’s mineral nitrogen content and macro-elements were higher in wheat–pea/faba bean compared to monoculture wheat cultivation. While the intercropping method did not increase wheat grain yield, it contributed positively to improved grain quality. The mixed sowing method also outperformed row-by-row planting in terms of wheat yield. These findings provide valuable insights for future research, emphasizing the potential of optimizing intercropping systems through genetic and agronomic innovations.