Yield and Quality Parameters of Winter Wheat in a Wheat–Pea Mixed Cropping System

Abstract

Modern agriculture is based on plant specialization, where the decrease in biodiversity makes vulnerable of our cultivated crops against climate change and the fluctuated market demands. Mixed cropping is a planned diversity in space, which is a powerful tool to conserving soil fertility. Our experiment was carried out in three growing seasons (2020/2021, 2021/2022, 2022/2023) with the combination of three winter wheat varieties (GK Szilárd, Cellule, GK Csillag) and a winter pea variety (Aviron) in four repeats and three seeding rates to determine yield and quality parameters (protein, gluten, Zeleny index, W-value) of wheat. Yield varied every year: The highest value was provided by the 50:100 mixture of GK Csillag/Aviron in 2021 (pure stands + 24%), then it gradually decreased in the following years. In terms of protein, Zeleny index and W-value, the Cellule/Aviron 50:100 achieved outstanding values, while in 2022 was preferred GK Szilárd/Aviron 50:100 combination. We verified a statistical difference between the wheat varieties in the case of gluten (in each year) in favor of GK Csillag/Cellule/GK Csillag and for the W-value (in 2021) in favor of Cellule. Plant density and seeding rate determined the final crop proportion within the mixture and indirectly affected yield quantity and quality.

1. Introduction

Since the 1960s, the intensification of agriculture has led to the spread of such cropping systems, which are based on the cultivation of a couple of main crops in a simplified crop rotation, with the extensive use of agrochemical inputs [1]. Crop specialization resulted in large productivity increase, and this mainstream was aimed at maximizing short-term yields and profits in developed countries [2]. As a result, the cultivation of leguminous plants declined, and their role in facilitating soil fertility has become unused [3,4]. Due to the negative effects of climate change, maintaining the level of production requires greater investment and adaptability on the part of cultivated plants. The simplified sowing structure made the farmers vulnerable to the fluctuating market demands and increased the chance of developing an unfavorable pre-crop sequence [5]. While a traditional cultivation system is based on the rotation of plants of a single genotype, biodiversity is a powerful management tool [6]. Mixed cropping is a special kind of plant association, a spatially planned diversity, which is a simultaneous practical application of several ecological principles, such as diversity, competition, and facilitation. It usually means growing two or more plants at the same time at the same area [7]. One of the greatest advantages of combining cereal and legume is breaking the overwhelming dominance of cereals by increasing the number of cultivated plants as a multiple cropping system. Due to the nitrogen-fixing ability of legumes, a natural nitrogen source is used, which is adapted for the needs of the companion plant, and this positive effect already prevails in the year of sowing.

Many authors agree that the most important advantage of mixed cropping is the more efficient use of growth resources than in pure stands [8,9,10]. However, the effectiveness of each mixture may differ significantly and, in most cases, due to the complexity of the coordination, previous studies only provide rough guidelines [11]. Most research works pay little attention to plant density and seeding rates of the species within the mixture and focus only on the final yield. In addition to the changing growing conditions, the choice of the appropriate seeding rate is still a question. According to Hauggaard-Nielsen and Jensen [12], the composition of a plant association is primarily determined by the purpose of the cultivation and growing conditions. Due to the lower competitiveness of the leguminous companion plant, it may be necessary to use a higher seeding rate, which may even exceed the rate for pure stands [8,11]. In the case of mixture of two species, whether competition occurs depends on the plant density. Based on other findings of Hauggaard-Nielsen et al. [13], the increased plant density in barley and pea association had a positive effect only on pea and severely limited the growth of barley. This is confirmed by Willey [14], who believes that higher plant density increases the competition between the species and favors the dominant companion plant. In addition, Bedoussac et al. [15] described that the selection of seeding rate depends on the leguminous species: In durum wheat–pea mixture, the sowing density of pea can be the same as the recommended rate for pure stands, while horse bean seeding rate must be halved in order to achieve a 50% grain ratio in the harvested crop. The proportion of the companion plants within the mixture is also an important factor for mixed cropping, as it directly affects competitiveness. In the experiment of Guiducci et al. [16], in a temporary plant association of wheat and legumes, the competitive ability of pea, horse bean, and clover determined the level of nitrogen accumulation and nitrogen supply to wheat before their devitalization. Benincasa et al. [17] investigated initial interference in horse bean/wheat and rapeseed/clover mixtures in greenhouse experiments. The best performance of the mixture is realized with a 1:3 seeding rate of the dominant horse bean and rapeseed to the companion plant. Furthermore, in vetch–oat mixed cropping, the competition between the companion plants increased above the threshold limit (10%) of oat [18].

This paper is a part of a series of articles summarizing the results of the work of our research team. In our previous articles, we dealt with the parallel development process of the companion plants and the analysis of yield components [19], then we determined the interaction between wheat and pea based on competition indices and economic benefits [20]. The aim of this paper is to answer the following questions: (i) How much yield of winter wheat produces in pea mixed cropping compared to the monoculture? (ii) How the quality parameters of winter wheat change in plant association compared to pure stands? (iii) Does the choice of seeding rate and plant density affect the development of the final yield quantity and quality?

2. Materials and Methods

2.1. Experimental Design

The present experiment was conducted over a period of three growing seasons (2020–2023) at the Applied Agronomy Research Station of the Hungarian University of Agriculture and Life Sciences in Szeged-Öthalom. The Research Station is located in the Great Plain in Hungary at 46.291° N, 20.088° E, 70 m above the sea level. We used the mixed cropping type of intercropping, where the mixed plots were arranged in a randomized block design with four replicates. Each plot measured 10 square meters (1 × 10 m). The soil type of the sample area was identified as meadow chernozem soil, which is characterized by a slightly alkaline reaction (pH = 7.9), and the organic matter is 2.8–3.2% (0–20 cm depth), P: 0.24 g kg⁻¹, K: 0.2 g kg⁻¹, NO₃⁻ + NO₂: 0.24 g kg⁻¹. In each growing season, the previous crop was winter wheat. Although all the seeds were covered, the pea seeds were not inoculated. The sample area was not fertilized apart from multi-nutrient autumn fertilizer before sowing at a rate of 200 kg ha⁻¹ (N:P₂O₅:K₂O 8:15:15). Seedbed preparation was based on ploughing (20 cm), disk harrowing (15 cm), and cultivator (5–10 cm). The mixed cropping consisted of a combination of three winter wheat varieties (GK Szilárd, Cellule, GK Csillag) and one winter pea variety (Aviron), with three different seeding rates in accordance with the local standard cropping practice. The 100% sowing rate for wheat meant 5 million seed ha⁻¹, and 1 million seed ha⁻¹ for winter peas. We proceeded in the same way with the 50% and 75% seeding density. The species were cultivated at all seeding rates; thus, we had a total of 27 associated plots to which we added another 12 pure-sown plots. Thus, the total number of parcels were 156, each block separated by a cultivation path (3 m). The exact seeding rates are summarized in

Table 1. Seeding rates for each winter wheat and winter pea combination (adapted from Vályi-Nagy et al. [20].

		Winter Pea (Number of Seeds × m−2)
		0	50	75	100
Winter wheat (number of seeds × m−2)	0	-	0:50	0:75	0:100
	250	50:0	50:50	50:75	50:100
	375	75:0	75:50	75:75	75:100
	500	100:0	100:50	100:75	100:100

.

GK Szilárd is a medium-ripening, awnless, and mill-quality winter wheat variety. This variety is notable for its high yield potential, its ability to thrive within a range of environmental conditions, and its robust stem structure. Cellule is also a mid-ripening wheat variety with strong tillering characteristics with awn. It exhibited high yield stability and nutrient utilization capacity even under unfavorable conditions. GK Csillag can be categorized as an early-maturing, awnless winter wheat variety. Thanks to its excellent adaptability to environmental conditions is a key factor contributing to its capacity to provide a high and balanced yield. It can be threshed easily. Aviron is a semi-leafless, medium-ripening winter pea variety with excellent winter hardiness and disease resistance.

The sowing was executed using a Wintersteiger Plotseeder Plotman machine (Wintersteiger GmbH, Ried, Austria) with a row width of 12.5 cm, at a depth of 4–6 cm. A one-stage harvest was conducted utilizing a Wintersteiger Nurserymaster plot combine (Wintersteiger GmbH, Ried, Austria), which was adapted to the full ripening stage of winter wheat (BBCH 89-92). After that, the crop was cleaned by a Pfeuffer SLN3 Sample Cleaner, and the quality parameters were measured with an Infratec^TM NIR Grain Analyser (Foss, Hilleroed, Denmark). In the case of winter wheat, the following parameters were determined: crude protein, gluten, Zeleny index, and W-value. In addition, the protein content of winter peas was ascertained. The sowing and harvesting dates of mixed cropping are given in

Table 2. Sowing and harvesting dates in the experimental years.

Growing Seasons	2020/2021	2021/2022	2022/2023
sowing time	2020.10.21	2021.10.19	2022.10.12
harvest time	2021.07.01	2022.06.22	2023.06.30

.

2.2. Weather Conditions

The annual precipitation and temperature data can be seen in Figure 1.

In the first growing season (2020/2021), it was rainy weather at the time of sowing, which had a favorable effect on the initial development of both companion plants. Later, the drier November and December and the lack of winter snow caused a decrease in soil water balance. April 2021 was not optimal in terms of the water needs of peas, but the rainfall in May proved to be enough for its development, which was facilitated the differentiation of the wheat ears. We measured very little precipitation in June, which mainly affected wheat sensitively. In contrast, the second growing season (2021/2022) was characterized by extreme, uneven rainfall distribution. The vegetation period started with much less rainfall than usual, which was critical for the development of both plants despite the heavy rains in December. Then, a strong lack of precipitation that occurred during the pea flowering period affected the plant in its most sensitive phase. This phenomenon had a negative effect on the formation of the number of ears, too. The wetter April and May were more favorable than this, which covered the maximum water demand for the development of the companion plants. The rainfall during the grain-filling period of wheat was less than the optimal level. The third growing season had the least amount of precipitation at the time of sowing. This initial disadvantage was significantly alleviated by the rainfall of the winter months. After that, another slightly drier period began in the spring of 2023, which did not benefit either species. Although the rainfall distribution was not as extreme as the previous year, the lack of rainfall occurred in the critical stages of the companion plants.

In terms of temperature, wheat was close to the optimal level during the entire development process in the first growing season (2020/2021). The flowering of peas started earlier than expected in mixed cropping. As a result, the temperature at the time of flowering was lower than the optimal level. None of the species surpassed the critical upper threshold value, which would have negatively affected the development of wheat and pea. In the second growing season (2021/2022), the winter was colder than the previous year, but the average temperature did not fall below the freezing point. February was slightly warmer than usual, but this did not cause a significant change in the development of the companion plants. On the other hand, high temperatures were experienced during the flowering and ripening of wheat and in many cases lasted for a long time. Wheat and pea also began to dry from below. The last growing season (2022/2023) was moderately warm and typical for the season. The warm days appeared again this year at the end of May, but this warming was gradual, which left enough time for the plants to acclimatize.

2.3. Statistical Analysis

The data of the wheat yield and quality values were analyzed statistically using the method of multivariate analysis of variance (MANOVA) in a three-way random block design with dependent variables yield, protein, gluten, Zeleny index, W-value as well as with the factors ‘variety’ (of winter wheat), Zpi (the seeding rate of winter peas in the mixture), and Zwi (the seeding rate of winter wheat in the mixture) and the three growing seasons as blocks. In each growing season, the experiment was based on a randomized block design, with 4 replications and 27 mixed cropping plots. The overall MANOVA was evaluated based on the unexplained variance rate expressed by Wilk’s lambda. Following a significant MANOVA result, subsequent three-way random block design univariate ANOVA tests were performed with Bonferroni’s correction to avoid Type I error probability inflation. To ensure the normality requirements of the linear model, W-value was subjected to an ln transformation. The normality of the model residuals was accepted based on the absolute values of their skewness and kurtosis, which were all below 1. The homogeneity of variances was tested using Levene’s test (p > 0.05). Finally, for the significant factors, post hoc tests were carried out using the Games–Howell method: The homogeneous groups of varieties were separated for all Zpi × Zwi combinations, while Zwi and Zpi levels were compared for all variety × Zpi and variety × Zwi combinations. The results are presented separately for the three years. All statistical analyses were performed using the statistical software IBM SPSS v.29 (IBM SPSS, Armonk, NY, USA, 2022) [21].

3. Results

3.1. Evaluation of Winter Wheat Yield

The significant values of the overall MANOVA are summarized in

Table 3. The significant values of the overall MANOVA.

Overall MANOVA	Significant Factors
	Variety	Zwi	Year	Variety × Year	Variety × Zwi	Variety × Year × Zpi
Wilk’s lambda value	0.82 ***	0.77 ***	0.34 ***	0.65 ***	0.74 ***	0.56 ***

significant at *** p < 0.001.

.

The subsequent three-way random block design univariate ANOVA tests showed a significant result for yield in the case of Zwi, Zpi and year, and year effects on all the wheat quality parameters. In the case of gluten, there was a variety and Zwi effect, too (

Table 4. The follow-up three-way univariate random block design ANOVA result highlighting the effects of factors wheat variety, wheat ratio (Zwi), and pea ratio (Zpi) and the year on the yield and the quality parameters of winter wheat (F-values with degrees of freedom 2 and 240).

		Yield	Protein	Gluten	Zeleny Index	W-Value
factors	Variety	2.85 ns	2.99 ns	7.14 ***	2.62 ns	1.96 ns
	Zwi	3.87 *	2.2 ns	10.69 ***	2.57 ns	0.44 ns
	Zpi	6.81 *	1.59 ns	1.34 ns	1.49 ns	0.52 ns
	Year	92.58 ***	56.92 ***	50.07 ***	64.83 ***	28.16 ***

significant at * p < 0.05, *** p < 0.001, ns: not significant.

).

In order to improve transparency, the raw quantitative and qualitative data on wheat monoculture can be found in

Table A1. Mean and standard deviation of yield and quality parameters of Cellule winter wheat variety in monoculture.

2020/2021	Cellule 50	Cellule 75	Cellule 100
yield	5.76 ± 1.62	6.35 ± 0.99	6.59 ± 1.76
protein	12.23 ± 0.79	11.98 ± 0.77	12.08 ± 0.71
gluten	27.25 ± 2.22	26.83 ± 2.18	26.90 ± 2.31
Zeleny index	48.23 ± 6.26	47.28 ± 4.84	47.43 ± 5.20
W-value	197.00	196.00	200.00
2021/2022
yield	3.92 ± 0.36	4.36 ± 0.43	4.69 ± 0.60
protein	12.25 ± 0.25	11.95 ± 0.31	11.60 ± 0.48
gluten	28.25 ± 1.06	27.30 ± 0.80	26.10 ± 1.79
Zeleny index	52.38 ± 1.88	50.78 ± 1.77	48.90 ± 2.91
W-value	219.00	213.00	197.00
2022/2023
yield	10.30 ± 0.34	10.50 ± 0.62	9.76 ± 0.99
protein	11.35 ± 0.93	11.00 ± 1.00	11.03 ± 0.83
gluten	24.98 ± 2.79	23.80 ± 2.89	24.00 ± 2.45
Zeleny index	46.20 ± 6.30	43.10 ± 5.35	44.05 ± 4.39
W-value	110.00	104.00	97.00

,

Table A2. Mean and standard deviation of yield and quality parameters of GK Csillag winter wheat variety in monoculture.

2020/2021	GK Csillag 50	GK Csillag 75	GK Csillag 100
yield	5.25 ± 1.77	5.65 ± 2.05	5.47 ± 2.10
protein	12.30 ± 0.87	12.30 ± 0.81	12.18 ± 0.96
gluten	28.75 ± 2.23	28.73 ± 2.40	28.43 ± 2.54
Zeleny index	51.20 ± 7.72	50.78 ± 6.63	49.98 ± 7.91
W-value	219.00	223.00	219.00
2021/2022
yield	3.34 ± 0.52	3.63 ± 0.39	3.87 ± 0.35
protein	12.80 ± 0.56	12.30 ± 0.53	12.25 ± 0.53
gluten	28.43 ± 2.01	26.80 ± 1.75	27.10 ± 1.76
Zeleny index	59.33 ± 4.66	54.55 ± 5.41	54.20 ± 5.09
W-value	292.00	272.00	270.00
2022/2023
yield	9.24 ± 0.42	9.49 ± 0.25	9.36 ± 0.11
protein	12.93 ± 0.64	12.60 ± 1.07	12.50 ± 0.94
gluten	30.83 ± 1.76	29.88 ± 2.99	29.83 ± 2.56
Zeleny index	58.25 ± 4.92	56.20 ± 6.88	55.53 ± 6.24
W-value	209.00	198.00	203.00

and

Table A3. Mean and standard deviation of yield and quality parameters of GK Szilárd winter wheat variety in monoculture.

2020/2021	GK Szilárd 50	GK Szilárd 75	GK Szilárd 100
yield	4.73 ± 0.44	5.55 ± 0.59	5.51 ± 0.67
protein	12.13 ± 0.48	11.85 ± 1.03	11.75 ± 0.93
gluten	27.63 ± 1.38	26.63 ± 3.02	26.48 ± 2.77
Zeleny index	49.90 ± 3.62	47.88 ± 7.66	47.98 ± 7.63
W-value	197.00	185.00	185.00
2021/2022
yield	3.66 ± 0.39	4.28 ± 0.38	4.34 ± 0.67
protein	11.15 ± 0.76	10.88 ± 0.71	10.95 ± 0.77
gluten	24.48 ± 2.88	23.68 ± 2.69	23.73 ± 2.76
Zeleny index	47.03 ± 3.97	45.45 ± 4.42	45.60 ± 4.58
W-value	170.00	161.00	154.00
2022/2023
yield	8.41 ± 0.72	8.40 ± 0.46	7.91 ± 0.64
protein	12.38 ± 0.10	12.38 ± 0.53	12.48 ± 1.02
gluten	28.95 ± 0.19	29.00 ± 1.45	28.95 ± 2.46
Zeleny index	54.93 ± 1.13	55.18 ± 4.41	56.23 ± 8.98
W-value	176.00	176.00	168.00

in the Appendix A. Hereinafter, we used the percentage values of the mixtures relative to the monoculture as a basis for evaluating yield and quality parameters.

In the case of yield, each growing season showed different values. In the first two growing seasons, the associated wheat exceeded the value of pure stands in several cases. Wheat yield surplus for the 2020/2021 growing season was only observed in the association of GK Csillag (except of 50:100 seeding rate of GK Csillag/Aviron mixture). The highest yield was achieved at the 50:100 seeding rate of GK Csillag/Aviron (with the value of wheat in monoculture + 24%). In the next growing season, the mixture of other wheat varieties outperformed the control plots: GK Szilárd/Aviron at 50:50, 50:100, and 100:50 seeding rates, as well as Cellule/Aviron 75:100 and 100:50 combinations. The largest yield surplus was realized in the case of the already mentioned GK Szilárd/Aviron mixture at the 50:50 seeding rate (with the value of pure stand + 13%). Therefore, the wheat yield was not affected excessively by the severe drought, presumably because the dry and low-rainfall period did not occur during the critical phase of wheat. In contrast, the third growing season (2022/2023) showed a significant decline in wheat yield. The values were extremely low (between 64 and 85% compared to pure-sown wheat). This was probably a result of the lack of precipitation in the key phases of wheat. A significant difference could not be proved for any of the factors in the growing seasons.

Table 5. Mean and standard deviation of yield values compared to pure stands (100%) in 2020/2021 for mixed cropping of wheat varieties (GK Szilárd/Cellule/GK Csillag), and pea variety (Aviron) with different seeding ratios (Zwi/Zpi).

Wheat Yield in 2020/2021		Pea Ratio (Zpi)
		50	75	100
Wheat/Pea Variety	Wheat Ratio (Zwi)	Mean ± StDev	Mean ± StDev	Mean ± StDev
Cellule/Aviron	50	87.55 ± 10.18	87.82 ± 13.85	80.73 ± 13.14
	75	79.81 ± 6.17	83.85 ± 11.18	79.25 ± 12.21
	100	86.71 ± 12.68	89.28 ± 16.88	84.81 ± 13.56
GK Csillag/Aviron	50	107.26 ± 21.70	108.29 ± 38.09	98.59 ± 22.07
	75	111.98 ± 43.39	109.11 ± 41.08	107.99 ± 35.06
	100	124.24 ± 35.12	109.70 ± 27.95	110.24 ± 27.47
GK Szilárd/Aviron	50	94.74 ± 15.55	94.33 ± 14.13	88.17 ± 7.35
	75	82.35 ± 12.07	88.35 ± 18.88	79.31 ± 20.28
	100	90.50 ± 11.29	99.25 ± 16.32	88.57 ± 10.03

None of the effects of wheat variety, Zwi, or Zpi were found to be significant in 2020/2021 at p < 0.05.

,

Table 6. Mean and standard deviation of yield values compared to pure stands (100%) in 2021/2022 for mixed cropping of wheat varieties (GK Szilárd/Cellule/GK Csillag), and pea variety (Aviron) with different seeding ratios (Zwi/Zpi).

Wheat Yield in 2021/2022		Pea Ratio (Zpi)
		50	75	100
Wheat/Pea Variety	Wheat Ratio (Zwi)	Mean ± StDev	Mean ± StDev	Mean ± StDev
Cellule/Aviron	50	97.00 ± 12.88	94.59 ± 8.05	89.49 ± 10.65
	75	102.24 ± 7.93	100.34 ± 8.53	89.45 ± 7.48
	100	102.26 ± 10.83	93.48 ± 6.59	92.99 ± 6.76
GK Csillag/Aviron	50	99.99 ± 3.74	90.22 ± 12.50	83.96 ± 9.03
	75	93.84 ± 10.65	91.17 ± 5.20	86.71 ± 13.25
	100	92.18 ± 6.43	95.16 ± 12.78	90.31 ± 8.88
GK Szilárd/Aviron	50	113.34 ± 6.36	95.80 ± 13.55	104.07 ± 11.42
	75	97.39 ± 9.78	97.08 ± 7.79	96.17 ± 9.00
	100	103.60 ± 14.98	92.37 ± 20.18	99.30 ± 13.58

None of the effects of wheat variety, Zwi, or Zpi were found to be significant in 2021/2022 at p < 0.05.

and

Table 7. Mean and standard deviation of yield values compared to pure stands (100%) in 2022/2023 for mixed cropping of wheat varieties (GK Szilárd/Cellule/GK Csillag), and pea variety (Aviron) with different seeding ratios (Zwi/Zpi).

Wheat Yield in 2022/2023		Pea Ratio (Zpi)
		50	75	100
Wheat/Pea Variety	Wheat Ratio (Zwi)	Mean ± StDev	Mean ± StDev	Mean ± StDev
Cellule/Aviron	50	75.40 ± 3.40	70.46 ± 4.06	64.09 ± 8.36
	75	77.58 ± 7.99	76.69 ± 10.05	74.93 ± 7.15
	100	85.74 ± 15.65	76.25 ± 10.36	76.95 ± 8.93
GK Csillag/Aviron	50	73.82 ± 6.73	74.56 ± 3.79	66.96 ± 4.95
	75	75.90 ± 9.42	71.06 ± 12.19	68.29 ± 8.24
	100	77.69 ± 7.62	77.00 ± 4.50	78.13 ± 6.36
GK Szilárd/Aviron	50	77.31 ± 7.55	77.05 ± 11.84	69.04 ± 6.93
	75	78.64 ± 16.93	69.08 ± 6.83	78.40 ± 17.09
	100	81.52 ± 6.02	78.38 ± 3.00	73.72 ± 1.81

None of the effects of wheat variety, Zwi, or Zpi were found to be significant in 2022/2023 at p < 0.05.

show the percentage value of the yield compared to the monoculture.

3.2. Examination of Wheat Quality Parameters

3.2.1. Protein Content

The protein content of winter wheat in the first growing season (2020/2021) was close to the values of pure-sown plots, but only the mixtures of Cellule/Aviron with 50:100 and 75:50 seeding rates exceeded it by 1%. In the second growing season (2021/2022), we measured higher protein content in several cases: GK Szilárd/Aviron with 50:50, 50:75, 50:100, 75:75, and 75:100 seeding rates, and in the case of GK Csillag/Aviron, the 50:50, 50:75, 75:100 mixtures. Even in a drought year, the highest protein value exceeded the level of monoculture wheat by 5% (in the plant association of GK Szilárd/Aviron 50:75, 50:100). In the third growing season (2022/2023), all combinations of the experiment had a protein surplus compared to pure stands, with highest value reaching +11% at the 50:100 seeding density of Cellule/Aviron. A significant difference could not be proved for any of the factors in the growing season.

Table 8. Mean and standard deviation of protein values compared to pure stands (100%) in 2020/2021 for mixed cropping of wheat varieties (GK Szilárd/Cellule/GK Csillag), and pea variety (Aviron) with different seeding ratios (Zwi/Zpi).

Wheat Protein in 2020/2021		Pea Ratio (Zpi)
		50	75	100
Wheat/Pea Variety	Wheat Ratio (Zwi)	Mean ± StDev	Mean ± StDev	Mean ± StDev
Cellule/Aviron	50	95.12 ± 6.09	97.21 ± 9.24	101.11 ± 5.27
	75	100.93 ± 5.53	97.85 ± 2.69	99.30 ± 2.35
	100	96.87 ± 2.07	94.86 ± 3.80	94.10 ± 4.78
GK Csillag/Aviron	50	98.30 ± 7.32	98.95 ± 4.62	95.18 ± 7.11
	75	94.50 ± 6.05	94.09 ± 4.09	97.33 ± 2.66
	100	97.69 ± 6.74	97.14 ± 7.96	96.84 ± 9.45
GK Szilárd/Aviron	50	91.60 ± 8.52	89.42 ± 3.69	91.53 ± 4.93
	75	90.94 ± 9.02	96.31 ± 14.29	92.83 ± 8.04
	100	88.71 ± 6.77	93.31 ± 7.13	93.57 ± 8.85

None of the effects of wheat variety, Zwi, or Zpi were found to be significant in 2020/2021 at p < 0.05.

,

Table 9. Mean and standard deviation of protein values compared to pure stands (100%) in 2021/2022 for mixed cropping of wheat varieties (GK Szilárd/Cellule/GK Csillag), and pea variety (Aviron) with different seeding ratios (Zwi/Zpi).

Wheat Protein in 2021/2022		Pea Ratio (Zpi)
		50	75	100
Wheat/Pea Variety	Wheat Ratio (Zwi)	Mean ± StDev	Mean ± StDev	Mean ± StDev
Cellule/Aviron	50	98.71 ± 6.20	99.32 ± 10.18	98.40 ± 9.55
	75	95.66 ± 10.19	96.71 ± 9.23	100.06 ± 7.51
	100	97.25 ± 10.47	96.96 ± 7.94	97.43 ± 6.91
GK Csillag/Aviron	50	100.66 ± 7.55	100.88 ± 4.28	99.75 ± 2.80
	75	98.84 ± 6.01	99.86 ± 4.78	101.04 ± 7.69
	100	95.73 ± 7.85	98.14 ± 8.34	100.43 ± 6.46
GK Szilárd/Aviron	50	101.13 ± 9.02	104.60 ± 11.06	105.25 ± 11.03
	75	99.36 ± 5.50	100.97 ± 7.00	101.65 ± 6.27
	100	94.61 ± 6.46	95.38 ± 8.45	96.81 ± 4.18

None of the effects of wheat variety, Zwi, or Zpi were found to be significant in 2021/2022 at p < 0.05.

and

Table 10. Mean and standard deviation of protein values compared to pure stands (100%) in 2022/2023 for mixed cropping of wheat varieties (GK Szilárd/Cellule/GK Csillag), and pea variety (Aviron) with different seeding ratios (Zwi/Zpi).

Wheat Protein in 2022/2023		Pea Ratio (Zpi)
		50	75	100
Wheat/Pea Variety	Wheat Ratio (Zwi)	Mean ± StDev	Mean ± StDev	Mean ± StDev
Cellule/Aviron	50	105.64 ± 10.14	107.23 ± 10.18	111.29 ± 6.54
	75	108.48 ± 7.48	109.75 ± 7.88	109.06 ± 8.25
	100	108.99 ± 9.00	107.76 ± 5.38	110.19 ± 10.07
GK Csillag/Aviron	50	104.32 ± 3.66	106.97 ± 3.33	109.72 ± 3.16
	75	106.75 ± 8.95	105.97 ± 7.55	106.18 ± 7.40
	100	100.58 ± 7.82	104.17 ± 3.30	104.70 ± 4.23
GK Szilárd/Aviron	50	102.83 ± 6.96	104.27 ± 10.57	107.32 ± 16.57
	75	106.19 ± 10.68	107.34 ± 6.53	102.60 ± 3.53
	100	99.93 ± 6.57	104.88 ± 5.63	105.90 ± 9.20

None of the effects of wheat variety, Zwi, or Zpi were found to be significant in 2022/2023 at p < 0.05.

show the percentage value of protein compared to the monoculture.

3.2.2. Gluten Content

In the first growing season (2020/2021), the gluten content exceeded the values of pure-sown wheat in four cases; these mixtures were Cellule/Aviron at the seeding rates 50:100 and 75:50, and in terms of GK Csillag/Aviron, the 50:50 and 50:75 combinations. The latter mixture also achieved the highest gluten level this year (pure-sown wheat + 3%). There was a significant difference between the two GK varieties in favor of GK Csillag. In the second growing season (2021/2022), five combinations showed a higher gluten content compared to the control wheat plot at the seeding density of GK Szilárd/Aviron 50:100, Cellule/Aviron 50:50 and 50:75, and GK Csillag 50:50 and 50:75. In addition, the two Cellule combinations achieved the highest gluten content (pure stands + 15% and + 13%, respectively). We could prove a significant difference in wheat varieties this year as well, but in this case the Cellule surpassed the GK Szilárd variety. Similar to the protein content, the third growing season (2022/2023) was also the best year in terms of gluten (except of six associations). The GK Csillag/Aviron mixture was detected with the highest value at the seeding rate of 50:75 (pure stands + 39%). Based on this extremely high value, a statistically significant difference was verified between GK Csillag and the other two varieties in favor of GK Csillag. These results can be seen in

Table 11. Mean and standard deviation of gluten values compared to pure stands (100%) in 2020/2021 for mixed cropping of wheat varieties (GK Szilárd/Cellule/GK Csillag), and pea variety (Aviron) with different seeding ratios (Zwi/Zpi).

Wheat Gluten in 2020/2021		Pea Ratio (Zpi)
		50	75	100
Wheat/Pea Variety	Wheat Ratio (Zwi)	Mean ± StDev	Mean ± StDev	Mean ± StDev
Cellule/Aviron	50	94.91 ± 4.50	97.96 ± 8.57 ab	101.09 ± 5.56
	75	100.62 ± 7.59	96.90 ± 3.34	98.06 ± 2.90
	100	94.68 ± 3.17	91.66 ± 7.95	93.13 ± 5.75
GK Csillag/Aviron	50	101.85 ± 14.48	103.50 ± 10.41 b	94.94 ± 8.12
	75	94.81 ± 4.43	94.17 ± 2.88	98.05 ± 3.01
	100	95.93 ± 4.73	95.12 ± 7.03	97.35 ± 12.50
GK Szilárd/Aviron	50	88.87 ± 10.05	86.17 ± 4.34 a	89.18 ± 5.61
	75	88.97 ± 10.85	95.69 ± 18.70	91.98 ± 9.47
	100	86.01 ± 8.93	90.87 ± 7.26	92.61 ± 10.68

Significantly different groups are marked with a lowercase letter with a shade of gray background in the cells inside the columns when testing the effect of wheat variety under fixed wheat ratio (Zwi) and pea ratio (Zpi) (Games–Howell’s p < 0.05). The effects of Zwi and Zpi were not proved to be significant in 2021 (p > 0.05).

,

Table 12. Mean and standard deviation of gluten values compared to pure stands (100%) in 2021/2022 for mixed cropping of wheat varieties (GK Szilárd/Cellule/GK Csillag), and pea variety (Aviron) with different seeding ratios (Zwi/Zpi).

Wheat Gluten in 2021/2022		Pea Ratio (Zpi)
		50	75	100
Wheat/Pea Variety	Wheat Ratio (Zwi)	Mean ± StDev	Mean ± StDev	Mean ± StDev
Cellule/Aviron	50	115.24 ± 6.73 b	113.02 ± 13.54	94.97 ± 13.87
	75	87.57 ± 14.96	89.72 ± 13.62	95.20 ± 9.80
	100	87.44 ± 16.22	87.30 ± 14.92	92.81 ± 12.43
GK Csillag/Aviron	50	107.45 ± 12.31 ab	106.72 ± 8.46	97.43 ± 2.32
	75	90.11 ± 8.06	91.30 ± 7.48	97.92 ± 11.44
	100	91.56 ± 11.52	94.95 ± 12.76	95.49 ± 7.37
GK Szilárd/Aviron	50	88.88 ± 10.72 a	95.93 ± 9.60	106.36 ± 18.32
	75	92.81 ± 12.17	93.81 ± 9.66	99.46 ± 9.19
	100	87.40 ± 6.94	88.19 ± 11.36	90.20 ± 7.97

Significantly different groups are marked with a lowercase letter with a shade of gray background in the cells inside the columns when testing the effect of wheat variety under fixed wheat ratio (Zwi) and pea ratio (Zpi) (Games–Howell’s p < 0.05). The effects of Zwi and Zpi were not proved to be significant in 2022 (p > 0.05).

and

Table 13. Mean and standard deviation of gluten values compared to pure stands (100%) in 2022/2023 for mixed cropping of wheat varieties (GK Szilárd/Cellule/GK Csillag), and pea variety (Aviron) with different seeding ratios (Zwi/Zpi).

Wheat Gluten in 2022/2023		Pea Ratio (Zpi)
		50	75	100
Wheat/Pea Variety	Wheat Ratio (Zwi)	Mean ± StDev	Mean ± StDev	Mean ± StDev
Cellule/Aviron	50	94.47 ± 10.10 a	98.45 ± 10.84 a	114.04 ± 14.65
	75	107.60 ± 12.79	107.85 ± 15.80	113.84 ± 12.87
	100	115.17 ± 19.79	111.95 ± 12.06	115.88 ± 16.31
GK Csillag/Aviron	50	134.96 ± 14.67 b	139.43 ± 12.82 b	108.05 ± 4.81
	75	95.07 ± 18.57	103.62 ± 3.48	104.26 ± 9.30
	100	97.22 ± 13.25	104.48 ± 6.37	105.56 ± 4.19
GK Szilárd/Aviron	50	102.66 ± 5.49 a	104.17 ± 11.75 a	107.90 ± 17.10
	75	105.16 ± 17.14	109.16 ± 13.63	102.97 ± 4.42
	100	98.39 ± 8.19	105.32 ± 11.72	108.03 ± 11.25

Significantly different groups are marked with a lowercase letter with a shade of gray background in the cells inside the columns when testing the effect of wheat variety under fixed wheat ratio (Zwi) and pea ratio (Zpi) (Games–Howell’s p < 0.05). The effects of Zwi and Zpi were not proved to be significant in 2023 (p > 0.05).

, which show the percentage value of gluten compared to the monoculture.

3.2.3. Zeleny Index

Regarding the Zeleny index, in the first growing season (2020/2021) only two associations reached the level of pure-sown wheat: one was Cellule/Aviron with a seeding rate of 50:100 (pure stands + 2%), and the other was the same species combination at a ratio of 75:50 (equal to monoculture wheat). In comparison, in the second growing season (2021/2022), the value of Zeleny index surpassed the level of pure stands in the case of the lowest seeding rate of the GK Szilárd and Cellule varieties, as well as the 75:75 and 75:100 mixtures of GK Szilárd/Aviron. In the GK Csillag variety, the Zeleny index exceeded the control value at the 50:75, 75:75, 75:100, and 100:100 seeding rates, but it was equal to this value in the case of the 50:50, 50:100, and 75:50 mixtures. We could also see a similar Zeleny index to the control at the 75:100 Cellule/Aviron seeding ratio. The maximum value was achieved with the 50:100 mixture of the GK Szilárd/Aviron combination (pure-sown + 10%). In the third growing season (2022/2023), except for only one association, all the mixtures represented a higher value than the control; the highest Zeleny index was provided by the 50:100 seeding ratio of Cellule/Aviron with + 19%. No significant difference could be detected in the case of the wheat variety, Zwi, or Zpi in the experimental years.

Table 14. Mean and standard deviation of Zeleny index compared to pure stands (100%) in 2020/2021 for mixed cropping of wheat varieties (GK Szilárd/Cellule/GK Csillag), and pea variety (Aviron) with different seeding ratios (Zwi/Zpi).

Wheat Zeleny Index in 2020/2021		Pea Ratio (Zpi)
		50	75	100
Wheat/Pea Variety	Wheat Ratio (Zwi)	Mean ± StDev	Mean ± StDev	Mean ± StDev
Cellule/Aviron	50	91.61 ± 8.76	94.72 ± 15.09	101.78 ± 8.01
	75	99.77 ± 8.50	94.35 ± 4.84	96.41 ± 5.24
	100	94.35 ± 4.03	89.94 ± 7.10	89.50 ± 9.10
GK Csillag/Aviron	50	95.61 ± 11.91	97.06 ± 8.16	90.77 ± 11.11
	75	90.58 ± 9.95	89.08 ± 5.94	94.79 ± 5.00
	100	95.42 ± 12.16	95.25 ± 13.89	93.57 ± 16.67
GK Szilárd/Aviron	50	85.48 ± 15.22	81.51 ± 6.21	84.00 ± 8.03
	75	83.88 ± 14.37	93.14 ± 26.15	87.50 ± 13.73
	100	79.28 ± 11.08	86.65 ± 12.84	87.62 ± 15.46

None of the effects of wheat variety, Zwi, or Zpi were found to be significant in 2020/2021 at p < 0.05.

,

Table 15. Mean and standard deviation of Zeleny index compared to pure stands (100%) in 2021/2022 for mixed cropping of wheat varieties (GK Szilárd/Cellule/GK Csillag), and pea variety (Aviron) with different seeding ratios (Zwi/Zpi).

Wheat Zeleny Index in 2021/2022		Pea Ratio (Zpi)
		50	75	100
Wheat/Pea Variety	Wheat Ratio (Zwi)	Mean ± StDev	Mean ± StDev	Mean ± StDev
Cellule/Aviron	50	101.50 ± 9.83	102.30 ± 16.95	100.78 ± 16.47
	75	93.20 ± 12.56	96.58 ± 12.39	100.36 ± 9.50
	100	95.50 ± 15.37	94.69 ± 10.63	96.78 ± 9.57
GK Csillag/Aviron	50	99.67 ± 12.85	101.60 ± 8.12	99.95 ± 6.26
	75	99.66 ± 13.46	101.99 ± 10.41	103.30 ± 16.00
	100	93.70 ± 12.67	98.96 ± 13.90	101.60 ± 12.04
GK Szilárd/Aviron	50	102.52 ± 14.14	107.90 ± 15.98	109.96 ± 15.20
	75	99.36 ± 7.26	103.17 ± 10.16	104.96 ± 9.92
	100	94.81 ± 10.70	94.42 ± 12.45	96.68 ± 7.94

None of the effects of wheat variety, Zwi, or Zpi were found to be significant in 2021/2022 at p < 0.05.

and

Table 16. Mean and standard deviation of Zeleny index compared to pure stands (100%) in 2022/2023 for mixed cropping of wheat varieties (GK Szilárd/Cellule/GK Csillag), and pea variety (Aviron) with different seeding ratios (Zwi/Zpi).

Wheat Zeleny Index in 2022/2023		Pea Ratio (Zpi)
		50	75	100
Wheat/Pea Variety	Wheat Ratio (Zwi)	Mean ± StDev	Mean ± StDev	Mean ± StDev
Cellule/Aviron	50	110.10 ± 17.13	109.59 ± 15.46	119.36 ± 17.36
	75	117.22 ± 9.76	118.49 ± 10.97	116.71 ± 11.00
	100	114.74 ± 13.48	112.31 ± 6.62	115.86 ± 14.52
GK Csillag/Aviron	50	106.78 ± 4.22	111.20 ± 3.91	113.66 ± 6.83
	75	107.82 ± 14.60	106.70 ± 12.21	107.32 ± 11.68
	100	99.46 ± 5.90	102.72 ± 4.27	104.74 ± 7.45
GK Szilárd/Aviron	50	107.55 ± 15.86	109.12 ± 19.41	111.31 ± 21.37
	75	109.53 ± 13.13	114.66 ± 11.04	106.07 ± 7.61
	100	102.38 ± 12.17	109.44 ± 12.76	113.43 ± 19.67

None of the effects of wheat variety, Zwi, or Zpi were found to be significant in 2022/2023 at p < 0.05.

show the percentage value of Zeleny index compared to the monoculture.

3.2.4. The W-Value

In the first growing season, only the W-value of the Cellule/Aviron mixture at the 50:100 seeding density exceeded the level of pure stands with +3%. In the case of the same mixture, a significant difference was noted for wheat variety between Cellule and GK Szilárd, in favor of Cellule. In contrast, in the second growing season (2021/2022), a W-value of 100% or more was achieved only with GK Szilárd; it exceeded the control value for the 50:50, 50:75, 50:100, 75:100 seeding rates, and in the case of the 75:50 and 75:75 mixtures, it was the similar to the control level. The maximum W-value was provided by the 50:100 combination of GK Szilárd/Aviron (pure stands + 25%). In the third growing season (2022/2023), except for two mixed crops, all of them produced higher W-values than the monoculture. In the last two years, there were no significant differences in any of the examined factors. A detailed statistical analysis is contained in

Table 17. Mean and standard deviation of W-values compared to pure stands (100%) in 2020/2021 for mixed cropping of wheat varieties (GK Szilárd/Cellule/GK Csillag), and pea variety (Aviron) with different seeding ratios (Zwi/Zpi).

Wheat W-Value in 2020/2021		Pea Ratio (Zpi)
		50	75	100
Wheat/Pea Variety	Wheat Ratio (Zwi)	Mean ± StDev	Mean ± StDev	Mean ± StDev
Cellule /Aviron	50	88.29 ± 15.04	94.62 ± 22.56	102.89 ± 12.09 b
	75	98.53 ± 11.91	94.14 ± 4.85	83.98 ± 20.94
	100	91.65 ± 7.68	85.86 ± 12.48	85.41 ± 6.04
GK Csillag/Aviron	50	96.62 ± 19.56	95.46 ± 14.27	92.89 ± 16.81 ab
	75	87.89 ± 12.83	85.20 ± 11.18	95.22 ± 5.84
	100	92.29 ± 19.27	91.85 ± 21.92	92.66 ± 27.96
GK Szilárd/Aviron	50	76.86 ± 24.37	69.46 ± 13.08	75.95 ± 12.20 a
	75	74.64 ± 15.19	90.93 ± 33.31	82.17 ± 19.52
	100	69.87 ± 15.65	82.18 ± 23.28	80.24 ± 24.26

Significantly different groups are marked with a lowercase letter with a shade of gray background in the cells inside the columns when testing the effect of wheat variety under fixed wheat ratio (Zwi) and pea ratio (Zpi) (Games–Howell’s p < 0.05). The effects of Zwi and Zpi were not proved to be significant in 2021 (p > 0.05).

,

Table 18. Mean and standard deviation of W-values compared to pure stands (100%) in 2021/2022 for mixed cropping of wheat varieties (GK Szilárd/Cellule/GK Csillag), and pea variety (Aviron) with different seeding ratios (Zwi/Zpi).

Wheat W-Value in 2021/2022		Pea Ratio (Zpi)
		50	75	100
Wheat/Pea Variety	Wheat Ratio (Zwi)	Mean ± StDev	Mean ± StDev	Mean ± StDev
Cellule /Aviron	50	94.13 ± 10.67	86.76 ± 24.74	96.06 ± 22.15
	75	87.83 ± 27.44	91.41 ± 26.20	80.29 ± 17.51
	100	84.00 ± 21.60	83.55 ± 34.54	86.20 ± 23.69
GK Csillag/Aviron	50	94.86 ± 15.19	86.79 ± 12.53	92.64 ± 6.40
	75	91.84 ± 20.34	91.78 ± 19.91	87.22 ± 22.87
	100	87.71 ± 18.08	90.19 ± 16.57	95.31 ± 11.89
GK Szilárd/Aviron	50	100.75 ± 63.82	117.13 ± 32.83	125.44 ± 39.23
	75	99.63 ± 9.69	99.75 ± 22.42	110.01 ± 12.87
	100	97.39 ± 16.35	89.59 ± 11.89	94.47 ± 29.71

None of the effects of wheat variety, Zwi, or Zpi were found to be significant in 2021/2022 at p < 0.05

and

Table 19. Mean and standard deviation of W-values compared to pure stands (100%) in 2022/2023 for mixed cropping of wheat varieties (GK Szilárd/Cellule/GK Csillag), and pea variety (Aviron) with different seeding ratios (Zwi/Zpi).

Wheat W-Value in 2022/2023		Pea Ratio (Zpi)
		50	75	100
Wheat/Pea Variety	Wheat Ratio (Zwi)	Mean ± StDev	Mean ± StDev	Mean ± StDev
Cellule /Aviron	50	142.26 ± 42.06	149.04 ± 38.83	146.08 ± 74.81
	75	135.74 ± 40.43	133.82 ± 79.63	144.65 ± 52.66
	100	181.99 ± 118.10	161.19 ± 93.24	157.34 ± 72.97
GK Csillag/Aviron	50	108.57 ± 37.28	124.01 ± 27.61	117.52 ± 32.44
	75	119.81 ± 46.48	125.06 ± 31.19	99.55 ± 38.84
	100	84.74 ± 49.86	112.66 ± 20.36	120.47 ± 20.94
GK Szilárd/Aviron	50	106.39 ± 24.75	110.59 ± 31.69	118.07 ± 27.42
	75	106.70 ± 46.04	120.52 ± 11.71	102.46 ± 24.82
	100	105.93 ± 23.63	107.82 ± 16.96	129.02 ± 25.57

None of the effects of wheat variety, Zwi, or Zpi were found to be significant in 2022/2023 at p < 0.05

, which present the percentage of W-value compared to the monoculture.

4. Discussion

Although mixed cropping is a widely used cultivation method in the world, in practice it still receives more emphasis in developing countries [22]. Despite the many advantages of its application, the direction of agronomic research is largely limited to a single crop or a single cultivar [1,2], since a plant association raises more complex problems compared to a monoculture [11].

One of these issues is the yield advantage of mixed cropping, which many studies consider a key feature, especially under low nitrogen fertilizer supply [13,23]. In contrast, according to Willey [14], the yield of intercrops may exceed the total yield of the individual species grown separately. In the research work of Pelzer et al. [24], the yield of the low-input wheat and pea mixed cropping only approached the level of the conventionally fertilized pure stands of cereal crops. The results of these studies are consistent to a certain degree with our experiment, where only a limited number of combinations surpassed the values of pure stands. In the first growing season (2020/2021), the highest yield was achieved with the GK Csillag variety (control + 24%). Meanwhile, in the second growing season (2021/2022), there was a yield surplus for GK Szilárd and Cellule wheat varieties, but the maximum value was represented by GK Szilárd (control + 13%). On the other hand, there was no significant difference between the yield values of the wheat varieties, which was also confirmed by the statistical analysis. In our experiment, we did not use nitrogen fertilizer, so the analysis purely shows the performance of mixed cropping. In those plant associations where nitrogen fertilization takes place, the yield-increasing effect is predominantly observed in wheat, while there is a substantial decline in pea yield [25]. In terms of the final crop, the total yield represents at least the same value as pure stands, but the ratio of the companion plants within the mixture shifts in the direction of wheat. A similar result is obtained if the mineral nitrogen supply in the soil is already at a high level, or if the competitive balance between the companion plants is upset due to overcrowding. In the second case, the high plant density increases the competition between the companion plants, a phenomenon that primarily favors the dominant species [14]. A decline in the proportion of legumes within the mixture has been demonstrated to result in a decrease in nitrogen fixation [26]. The presence of competitive hierarchy not only reduces the benefits of legumes but also impairs the efficiency of the association. In the case of wheat, the backwardness is not necessarily visible, yet it has the capacity to contribute to the formation of yield quantity and quality, and it is evident that the plant allocates a significant proportion of its energy expenditure to competition. This phenomenon was realized in our experiment, which becomes visible with the change in the proportion of wheat within the harvested crop from the original seeding rate (Figure 2).

The proportion of wheat in the final crop in each growing season increased by an equivalent amount to the decrease in pea yield. There was only one mixture in 2020/2021, when the proportion of wheat became less than the original seeding rate. According to Bedoussac et al. [15], this compensation enables peas to produce yield despite the strong dominance of wheat.

Another key issue of mixed cropping is increased yield stability [15,27], where several plants growing simultaneously is a guarantee against yield loss even under unfavorable growing conditions and provides greater financial stability compared to the monoculture [11]. Due to the distinct growing seasons of the companion plants, at least one of them can be grown successfully, which is not possible in pure stands [28]. According to Pelzer et al. [24], yield stability between the growing seasons depends on several factors, such as soil climatic conditions, seeding rate, sowing time, the proportion of the companion plants within the mixture or nitrogen distribution. In the present experiment, no significant deviation in yield was observed between the first two years, although the second year was characterized by severe drought, and the symptoms of heat stress were observed in the entire standing crop. This phenomenon suggests that the number and duration of hot days did not occur during the critical stage of wheat; consequently, the decline in yield was not of significant proportion. Moreover, in the second growing season (2021/2022), a yield surplus appeared for the two medium-ripening wheat varieties (GK Csillag was just below the control level), which indicates that the specific microclimate of mixed cropping provided a kind of protection against unfavorable environmental conditions. In the third year, the recurrent absence of precipitation resulted in a significant decline in yield, regardless of the wheat variety. It can be assumed that the factors affecting yield fluctuations could have caused a lower yield together, rather than separately.

In recent years, the paradigm of crop cultivation has evolved. The emphasis gradually shifted from the pursuit of quantity to quality. In the contemporary context, a cultivation method that meets the criteria of sustainability is considered effective in the long term. One of the basic pillars of this is high-quality plant production [5]. In winter wheat and winter pea mixed sowing, there was a mixture every year whose quality parameters exceeded the value of pure stands. However, this surplus did not occur with the same wheat variety. In the case of protein, the Cellule/Aviron 50:100 mixture just exceeded the value of pure stands in the first year, while in the third year it achieved the best value of all (pure stands + 11%). In the second year, outstanding results were attained by the GK Szilárd/Aviron combination with the 50:75 and 50:100 seeding rates. The same wheat variety selection process was carried out for the Zeleny index and W-value, with the difference that in the first year, the W-value showed a significant difference between the Cellule and GK Szilárd varieties, in favor of Cellule. In the second year, the baking values were much higher than in the monoculture (Zeleny index: + 10%, W-value +25%). High values in the third year occurred in almost all mixtures, which was also true for gluten, but this quality parameter differed from the others in terms of wheat variety selection. In the first and the third years, the aforementioned Cellule/Aviron combination in the same seeding rate (50:100 and 75:50) also appeared among the mixtures exceeding pure stands, but the GK Csillag/Aviron 50:75 combination achieved even higher values (pure stands + 3% and 39%). In these years, we were able to prove a statistical difference between wheat varieties in favor of GK Csillag. We observed a similar significance in the second year, but already with the Cellule variety. In this drought year, the Cellule/Aviron 50:50 mixture proved to be better than the others.

In summary, the composition of our experiment with a high wheat seeding rate was beneficial for baking qualities; the experimental results showed consistently high values for certain mixtures even under unfavorable conditions. However, it should be noted that the performance of mixed cropping fell short of the level that could have been achieved by reducing the seeding rate of the dominant wheat species in favor of peas, as Benincasa et al. [17] also experienced with a mixture of horse bean and wheat. This contradicts the statement of Bedoussiac et al. [15] that the sowing density of peas in a mixture can be equal to the value of pure stands. With regard to the further direction of research work, the question is to what extent the quality parameters of the companion plants would change within the mixture by increasing the proportion of peas.

5. Conclusions

The largest challenge of the current crop production is the choice of a cultivation method that is environmentally friendly, resistant to the negative effects of climate change, and adapts to changing market demands. In most cases, implementing crop rotation reduces the area dedicated the cereal crops, but mixed cropping fulfills all the requirements at once. The efficiency of the plant association depends to a large extent on plant density and the proportion of the species within the mixture, as we could have seen in the case of yield quantity and quality:

• In our experiment, the mixed cropping without nitrogen fertilizer did not provide a yield surplus for all mixtures. The maximum yield is represented by GK Csillag/Aviron 100:50 (control + 24%) in the first year, while in the second year the highest yield was achieved with the GK Szilárd/Aviron 50:50 (control + 13%). The values remained under the control in the third year.
• The proportion of the companion plants in the final crop shifted in favor of wheat due to the imbalance between them. The high plant density clearly increased the competition between the species, determining the order of the hierarchy. The increase in wheat yield was proportional to the decrease in pea yield; consequently, the efficiency of mixed cropping was also reached at a lower level.
• The occurrence of drought did not cause a significant yield loss. Moreover, GK Szilárd/Aviron 50:50, 100:50, and 50:100 and Cellule/Aviron 75:50 and 100:50 mixtures achieved a yield surplus in this second year, and the different levels of drought tolerance induced a variety change between the experimental years. The specific microclimate of mixed cropping no longer provided an advantage against unfavorable weather conditions in the third year.
• The mixture of Cellules/Aviron at a seeding rate of 50:100 reached maximum values for protein, Zeleny index, and W-value in the first and the third years. The drought also caused a variety change in the case of these quality indicators; the best values were achieved for the 50:75 and 50:100 mixtures of GK Szilárd. A statistical difference could be verified in the case of the W-value between wheat varieties in favor of Cellule in the first year.
• The third year, with only a few exceptions, showed high quality values, including for gluten. The best value was provided by the GK Csillag/Aviron mixture at a 50:75 seeding rate in both the first and the third years. We only experienced a deviation from this in the drought year, when the Cellule/Aviron 50:50 mixture proved to be better. A significant difference between wheat varieties was observed in every experimental year in favor of GK Csillag (in the first and third years) and Cellule (in the second year).