Comparison of Yield and Important Seed Quality Traits of Selected Legume Species

Abstract

Legumes are of great economic importance. Depending on the species, they are cultivated for food, fodder, green manure, and even as ornamentals. Legume seeds contain many valuable nutrients and also anti-nutritional substances. The aim of the study is to compare important seed quality traits in pea (Pisum sativum L.), faba bean (Vicia faba L.), white lupin (Lupinus albus L.), narrow-leafed lupin (Lupinus angustifolius L.), and yellow lupine (Lupinus luteus L.) to soybean (Glycine max (L.) Merr.). It was shown that the obtained parameters were significantly affected by the interaction of species with the years of study. Soybean was characterized by high seed and protein yield and favorable seed chemical composition (protein, fat, phosphorus, potassium, magnesium, and micronutrients, except manganese). Faba bean yields were high but varied over the years. Faba bean seeds were rich in phosphorus and copper. Pea yielded satisfactorily, and the seeds contained high iron and low fiber contents. Of the three lupin species, white lupin yielded the highest, while narrow-leafed and yellow lupin yields were low. However, yellow lupin seeds had a favorable chemical composition because they were rich in protein, calcium, phosphorus, magnesium, copper, and zinc. In conclusion, legumes are valued worldwide and could be a base for the development of many functional foods to promote human health.

1. Introduction

1.1. Importance of Legumes

Legumes play an important role in modern agriculture. This is due to their ability to establish symbiosis with papillary bacteria and a self-supply of nitrogen from atmospheric sources [1]. Depending on the species, they provide valuable food [2,3,4] and fodder seeds [5,6]. Mudryj et al. [7] reported that legumes have been consumed for at least 10,000 years and are among the most extensively used foods in the world. Multari et al. [8] pointed out that legumes had great potential to meet the world’s protein needs. As a result, it is possible to partially replace meat and dairy products in the human diet. Alghamdi [9] and Popović et al. [10] showed that the chemical composition of legume seeds is dependent on many factors, including weather, cultivar, and agriculture practices. In field experiments, the latter authors obtained significant interactions between the listed factors. Margier et al. [2] demonstrated that the macro- and micronutrient contents of legume seeds vary significantly. This is due to both genetic and habitat characteristics. Therefore, Jo et al. [11] argued that field experiments should be conducted for a minimum of two years to obtain reliable research results. However, they pointed out that even long-term crop experiments did not always produce consistent statistical results. Ji et al. [12] reported that the yield of plants could be estimated with modern measurement techniques. It is a good alternative to traditional methods that are time-consuming and labor-intensive. An interesting study on legumes was presented by Sterna et al. [4]. They showed that organic or conventional farming systems had no significant effect on seed protein content. Mitchell et al. [13] claimed that the consumption of legumes enriched the diet with valuable nutrients, including macro- and micronutrients. Martín-Cabrejas [14] and Carbonaro and Nucara [15] showed that legume plant seeds contain many health-promoting components that prevent lifestyle diseases. In addition, the demand for alternative sources of plant protein to replace animal protein is increasing in many countries [16,17]. Carbas et al. [18] and Elamine et al. [17] reported that legumes are an important food source in developing countries. However, they pointed out that seeds should be properly cooked, which should be communicated to consumers [19]. Prusiński [20] proved that white lupin seeds contained valuable nutrients but also allergens. Tirdilova et al. [21] indicated that legumes were able to accumulate some dangerous metals. Garbiec et al. [22] noted that the use of soybean as a functional food is not devoid of concerns related to the potential side effects of genistein, resulting from its estrogenic and goitrogenic effects. Didinger and Thompson [23] reported that some consumers were reluctant to eat legumes, reporting concerns about abdominal discomfort or a lack of knowledge about how best to prepare legumes. Teferra [24] argued that cooking seeds improved protein digestibility and inactivated certain harmful substances but could cause mineral leaching. Chaturvedi and Chakraborty [25] concluded that beverage production from legumes could be a good solution to these problems. They showed that such products had beneficial nutritional qualities and were sought after by consumers. Palmer et al. [26] reported that consumers needed detailed information on preparing legume dishes or had to be offered canned products. The study of Sterna et al. [4] showed the possibility of producing extruded products using legumes as a locally sourced raw material to produce high-value plant-based gluten-free protein foods. Marinangeli et al. [27] reported that 100 g or 125 mL (0.5 metric cup) of cooked legumes was a reasonable target for adapting strategies that promote the dietary and nutritional benefits of legumes.

1.2. Characteristics of the Selected Species

Soybean is known for its high protein content, and for this reason, it is widely used as one of the main food sources for humans and animals [28]. Cunha et al. [29] confirmed that soybeans contain a lot of protein as well as potassium, phosphorus, and magnesium. Hong et al. [30] reported well-documented negative correlations between protein and oil as well as oil and the amino acids Lys, Cys, Met, and Thr in soybeans. Gonyane and Sebetha [31] proved that soybean yield depends on many factors: weather, location, variety, and agrotechnics. In field experiments, they obtained from 1.7 to 6.1 t·ha⁻¹ seeds.

Plūduma-Pauniņa et al. [32] showed that the yield of faba bean depends on temperature and moisture conditions and the tested factors of the experiment. The highest yield was provided by the variety ‘Boxer’ in all years (6.10–7.74 t ha⁻¹). Paul et al. [33] reported that faba bean yields varied from 1.5 to 2.0 t·ha⁻¹ and the protein content in seeds varied from 31.5 to 34.2% DM. Ton et al. [34] proved that faba bean seeds contain many nutrients, depending on the variety. Genotypes Elazığ-34 and Muğla-47 had high protein content, while Bursa-79 and Antalya-51 were rich for Fe and Zn.

Greveniotis et al. [35] confirmed that pea yields are high, but the cultivars should be selected according to the local conditions of the habitat. Woźniak et al. [36] confirmed that the content of total protein in pea seeds was low but similar in all years of the study. Dahl et al. [37] proved that pea seeds had many valuable nutrients, but their content was usually lower compared to other legumes. Fordoński et al. [38] reported that narrow-leafed lupin yields were lower, but the protein content in seeds was satisfactory. In turn, Dymerska and Grabowska [39] reported that yellow lupin yields were lower and unreliable over the years. However, the seeds had a favorable chemical composition. Prusiński [20] drew attention to the high yield and chemical composition of white lupin seeds (especially manganese) and the potential for the wider dissemination of this species.

Farmers need the highest-yielding legume cultivars among pea, faba bean, white lupin, narrow-leafed lupin, yellow lupine, and soybean under the same agronomical conditions, whereas consumers request the best nutritional legume species. The objective of the experiment is to demonstrate differences in the seed yield and quality of selected legumes. The research hypothesis assumes that the observed differences between species will be modified by the pattern of weather conditions during the study years.

2. Materials and Methods

2.1. Field Data

A strict field experiment was carried out in the years 2019–2021 on the field of a private farm in Rzeszów (white lupin, narrow-leafed lupin, yellow lupin) and the fields of the Subcarpathian Agricultural Advisory Center in Boguchwała (soybean, faba bean, pea), Subcarpathian Voivodeship, Poland (Figure 1). The geographic coordinates of Rzeszów and Boguchwała are, respectively, 50°00′ N 22°00′ E, altitude 282,6 m a.s.l. and 49°59′ N 21°57′ E, altitude 222.5 m a.s.l.

The experiments were set up in four replicates in a randomized complete block design. The following legume species were the factors studied:

• Soybean (Glycine max (L.) Merr.), cultivar Mavka,
• Faba bean (Vicia faba var. minor), cultivar Albus,
• Pea (Pisum sativum L.), cultivar Batuta,
• White lupin (Lupinus albus L.), cultivar Butan,
• Narrow-leafed lupin (Lupinus angustifolius L.), cultivar Regent,
• Yellow lupin (Lupinus luteus L.), cultivar Mister.

The humidity and temperature were given according to the records of the Meteorological Station of the Subcarpathian Agricultural Advisory Center in Boguchwała. Weather conditions varied during the study years, which had a modifying effect on yield and seed quality parameters. Compared to multi-year data (2000–2020), 2019 was dry. Intense rainfall occurred in June 2020 and August 2021. During the analysis period, the highest precipitation was recorded in 2021. The average air temperature was highest in 2019 and lowest in 2021 (

Table 1. Weather conditions (Meteorological Station of the Subcarpathian Agricultural Advisory Center in Boguchwała).

Month	Sum of Precipitation [mm]				Temperature [°C]
	2019	2020	2021	Multi-Years	2019	2020	2021	Multi-Years
III	23	20	18	37	5.9	5.1	3.2	2.8
IV	21	10	49	46	9.9	9.2	6.5	8.7
V	74	83	64	77	13.1	11.3	12.8	13.7
VI	31	163	47	80	21.5	18.1	18.8	17.1
VII	50	19	55	95	19.1	18.8	21.6	19.0
VIII	61	7	107	65	20.3	19.9	17.5	18.4
IX	32	44	86	62	14.7	15.0	13.1	13.6
Sum/Mean	292	346	426	462	14.9	13.9	13.4	13.3

).

Soil chemical analysis was performed at the Regional Agricultural Chemical Station in Rzeszów. The soil at both locations was characterized by a slightly acidic pH (5.8–6.4 in KCl, respectively, in Rzeszów and Boguchwała) and an average humus content (1.27–1.82%, respectively, in Rzeszów and Boguchwała). The contents of available phosphorus (15.7–17.4 mg 100 g⁻¹ soil, respectively, in Rzeszów and Boguchwała) and potassium (20.4–22.6 mg 100 g⁻¹ soil, respectively, in Rzeszów and Boguchwała) were high, and the content of magnesium was average (5.8–6.5 mg 100 g⁻¹ soil, respectively, in Rzeszów and Boguchwała). Soil micronutrient content (Fe 2356.3–2536.8 Mn 219.3–256.5, Zn 14.3–16.2, Cu 3.7–4.1 mg 1000 g⁻¹ soil, respectively, in Rzeszów and Boguchwała) was average, and boron (B 1.3–1.6 mg 1000 g⁻¹ soil, respectively, in Rzeszów and Boguchwała) content was low. Chemical analyzes of the soil were performed in accordance with the Polish standards provided by Fotyma et al. [40].

2.2. Agrotechnics

Legume cultivation was carried out according to the agriculture practice requirements for a given species. The seeds were treated (Maxim 025 FS, active substance: fludioksonil), and a suitable inoculant was applied directly before sowing according to the manufacturer’s recommendations (BIOFOOD s.c. Wałcz). The area of a single plot was 15 m². The length of the plots, the number of rows on the plots, and the row-plant spaces were, respectively: 10 m, 5 pcs, and 5 cm. The forecrop was winter wheat, and in the case of yellow lupin, it was winter rye. The plants were chemically protected as required. The timing and dosages of the applied products (herbicides, fungicides, insecticides) were in accordance with the manufacturer’s recommendations. Ammonium nitrate 34% was used for nitrogen fertilization (25 kg ha⁻¹). Phosphorus and potassium fertilization was conducted under pre-winter plowing at the following dose: 60 kg ha⁻¹ P₂0₅ (simple superphosphate) and 90 kg ha⁻¹ K₂O (potassium salt). Harvest was carried out in one stage with a plot harvester at full maturity. Seed yield was calculated per hectare, taking into account the constant moisture of 14%. Seeds for chemical analyses were collected from each plot and subsequently dried and ground.

2.3. Chemical Analyses

The chemical composition of seeds (total protein, crude fat, fiber, ash) was determined by the near-infrared method using an FT-LSD MPA spectrometer (Bruker, Germany) in the laboratory of the Department of Plant Production, University of Rzeszów. FT-NIR technology offers many advantages compared to classical wet-chemical and chromatographic analyses. It simply measures the absorption of the near-infrared light of the sample at different wavelengths. The component yield per ha was calculated based on the seed yield and protein percentage. Magnesium and micronutrients were determined at the laboratory of the Faculty of Biology and Agriculture, the University of Rzeszów. To determine the elements, grain samples were mineralized in HNO₃:HClO₄:H₂SO₄ in a 20:5:1 ratio using an open system and a Tecator heating block. The content of macro- and micronutrients was determined in the samples by atomic absorption spectroscopy (FAAS) using a Hitachi Z-2000 apparatus (Konica minolta, Inc., Tokyo, Japan). In a typical FAAS instrument, the sample is atomized, thereby transiting from a ground state to higher energy levels. In the excited state, every element possesses a unique spectrum that distinguishes it from other elements. The spectra lines are very sharp, such that there is rarely overlap. A UV–VIS Shimadzu spectrophotometer (Konica minolta, Inc. Tokyo, Japan) was used for the determination of phosphorus (P) by the vanadate-molybdate method. The instrument features a keypad with a LED screen to enable user-friendly, intuitive measurements and instrument validation. Measurement modes include photometric, spectrum, quantitation, kinetics, time course, and bio-methods.

2.4. Statistical Analyses

The obtained results were statistically analyzed using the Statistica 13.3.0 program (TIBCO Software Inc., Palo Alto, CA, USA). Two-way ANOVA was applied; Tukey’s HSD post-hoc test (p ≤ 0.05) was used to determine the differences between the mean values of the analyzed parameters. Ward’s method was used to estimate the distance between clusters. The result of the test is a dendrogram, i.e., a graphic interpretation of the obtained results. In order to estimate the sources of variation, Pearson’s correlation (r) and principal component analysis (PCA) were additionally performed.

3. Results and Discussion

3.1. Seed Yield

The yielding of legumes varied between species and the years of research. Soybeans had the highest yield, averaging 3.99 t ha⁻¹. Equally high seed yields were obtained for faba bean and white lupins in 2020 and pea in 2021. It should be noted that the faba bean yield was low in 2019 due to low rainfall. Narrow-leafed lupin and yellow lupin had the lowest seed yields in each year of the study (Figure 2).

Ton et al. [34] showed that faba bean yield varied from 2.3 to 3.1 t ha⁻¹, but the seeds contained high protein (393.8 g kg⁻¹). Jarecki et al. [41] obtained a higher faba bean yield (4.58 t ha⁻¹) but with a lower seed protein content (298 g kg⁻¹). Fordoński et al. [38] reported that faba bean and pea yielded highly but variably in individual years. Narrow-leafed lupin yields were lower, but the protein content in the seeds was satisfactory. Kozak et al. [42] obtained high soybean yields, but they were dependent on study years, cultivar, and agriculture practices. They demonstrated that the weather had the greatest modifying effect on yield. Dymerska and Grabowska [39] reported that yellow lupin yields were unreliable; thus, the economic importance of this species was low in many countries. Prusiński [20] argued that white lupin is still an undervalued species. Thus, he concluded that knowledge about legumes should be more widely disseminated.

3.2. Total Protein Yield

Protein yield depended on the interaction of the legume with the years of study. The highest protein yield was obtained from soybean cultivation in 2020 and 2021. Soybean protein yield in 2019 was similar to that of faba bean in 2020 and white lupin in 2020 and 2021. Narrow-leafed lupin and yellow lupin were characterized by low protein yields. However, satisfactory results were recorded in pea, especially in 2021. For faba bean, the protein yield varied across the study years, as shown in Figure 3.

Popović et al. [10] showed that soybean protein yield depended on the cultivar and years of study and averaged 1.9 t ha⁻¹. Jarecki [43] and Jarecki and Borecka-Jamro [44] reported that soybean protein yield varied from 1.25 to 1.46 t ha⁻¹, depending on the years of study. Fordoński et al. [38] demonstrated that the protein yield of faba bean was high, averaging 1.6 t ha⁻¹. Csajbók et al. [45,46] noted that the protein and oil contents of soybean varieties are mainly genetically regulated. The protein yield depends more on the seed yield than the protein content.

3.3. Chemical Composition of Seeds

Seed protein content varied from species to species. The highest protein concentration was determined in soybean (354.5–399.2 g kg⁻¹ DM) and yellow lupin (375.4–406.4 g kg⁻¹ DM) seeds. Soybean showed significant differences across the study years. White lupin was characterized by high protein content, but only in 2020. The least protein was obtained in pea seeds, regardless of the study year. Soybean seeds contained the highest fat content, which varied across study years. For the other species, differences between the years were not observed. White lupin was characterized by a high seed fat content, followed by narrow-leafed lupin and yellow lupin. Faba bean and pea seeds contained the lowest fat content. The highest amount of fiber was determined in seeds of narrow-leafed and yellow lupin. These were followed by white lupin, soybean, and faba bean. Significant differences between the listed species were dependent on the study year. Pea seeds contained the least amount of fiber, which was consistent across the years. Seed ash content was significantly different between the legumes and individual study years. The highest ash content was determined in yellow lupin seeds, followed by soybean. It was proved that narrow-leafed lupin contained more ash in the seeds than pea (

Table 2. Chemical composition of seeds in g kg⁻¹ DM.

Legumes	Year	Total Protein	Crude Fat	Fiber	Ash
Soybean	2019	354.5 ± 9.5 bcde	211.4 ± 3.0 ab	114.9 ± 2.4 cdf	55.6 ± 0.8 bc
	2020	382.0 ± 10.4 abc	219.5 ± 2.3 a	108.3 ± 7.4 defg	52.9 ± 0.9 cd
	2021	399.2 ± 8.8 a	208.3 ± 3.0 b	108.0 ± 7.7 efg	50.2 ± 1.3 d
Faba bean	2019	291.6 ± 3.9 h	8.4 ± 0.7 e	96.9 ± 2.4 fg	36.9 ± 1.1 fgh
	2020	309.3 ± 2.9 fgh	9.5 ± 0.5 e	74.3 ± 3.6 hi	36.4 ± 0.6 fgh
	2021	292.1 ± 4.2 gh	8.5 ± 0.6 e	90.6 ± 8.0 gh	41.8 ± 2.5 e
Pea	2019	234.8 ± 4.8 i	14.0 ± 0.2 e	63.3 ± 0.9 i	34.0 ± 1.0 h
	2020	247.9 ± 3.2 i	14.1 ± 1.0 e	60.4 ± 1.4 i	33.7 ± 2.2 h
	2021	235.9 ± 4.5 i	14.1 ± 0.3 e	54.4 ± 14.8 i	33.2 ± 0.8 h
White lupine	2019	347.9 ± 18.1 cde	109.1 ± 8.3 c	120.4 ± 9.8 cde	36.5 ± 1.3 fgh
	2020	389.3 ± 11.7 ab	104.8 ± 8.7 c	112.6 ± 9.7 cdef	34.8 ± 1.8 gh
	2021	349.5 ± 19.2 cde	109.5 ± 6.2 c	120.6 ± 8.6 cde	36.2 ± 1.9 fgh
Narrow-leaved lupine	2019	339.8 ± 8.7 def	46.3 ± 4.3 d	165.8 ± 11.8 a	39.4 ± 0.6 ef
	2020	334.6 ± 11.6 ef	46.6 ± 4.7 d	159.3 ± 10.8 a	38.4 ± 0.8 efg
	2021	328.9 ± 9.0 efg	44.1 ± 4.0 d	149.0 ± 11.1 ab	38.2 ± 1.5 efg
Yellow lupine	2019	406.4 ± 14.2 a	50.7 ± 1.6 d	129.2 ± 5.0 bcd	60.8 ± 1.5 a
	2020	389.3 ± 15.9 ab	49.4 ± 4.4 d	131.4 ± 6.1 bc	58.4 ± 1.8 ab
	2021	375.4 ± 42.1 abcd	53.4 ± 3.8 d	128.3 ± 5.7 bcde	59.6 ± 1.6 a
Legumes × Year		***	*	*	***

Results are expressed as mean value ± standard deviations. Different letters in the same column indicate significant differences according to the analysis of variance (ANOVA). ***, * indicate significant differences at p < 0.001 and p < 0.05, according to Tukey’s honestly significant difference (HSD) test.

).

Sterna et al. [4] reported that the protein content of legume seeds was dependent on species, variety, and habitat factors. Their overall results (of a five-year analysis) showed that the protein content of pea, faba bean, and soybean ranged from 20.0 to 26.1%, 26.6 to 30.5%, and 35.9 to 40.9%, respectively. The corresponding values of total crude fat ranged from 0.8 to 1.2%, 0.7 to 1.3%, and 16.6 to 19.3%, respectively. In turn, Woźniak et al. [36] showed that the protein content of pea seeds was approximately 200 g kg⁻¹ DM and was stable over the years. Agapie et al. [47] reported that soybean seeds were rich in protein and fat and other nutrients. These authors demonstrated that seed protein content increased with increasing nitrogen fertilization while fat content decreased. Szpunar-Krok and Wondołowska-Grabowska [48] reported that fat quality indices for soybean seeds were strongly determined by weather conditions. Didinger and Thompson [49] indicated that legumes were a source of two important dietary components: dietary fiber and potassium.

3.4. The Content of Macronutrients

High phosphorus content was determined in yellow lupin seeds. With respect to soybean and faba bean, the results were similar or lower, depending on the study year. Low content of the discussed component was obtained for pea in 2019 and 2021. The least phosphorus was determined in white lupin seeds. Soybean seeds were characterized by high potassium content and pea seeds by the lowest. Regarding other species, potassium content was significantly dependent on the study year. The highest magnesium concentration was determined in soybean and yellow lupin seeds. The results were reproducible across study years. A lower concentration of magnesium was found in narrow-leafed lupin and the lowest in the remaining studied species. The highest amount of calcium was determined in the seeds of narrow-leafed and yellow lupin. In the case of other species, the results depended on the years of research. The least amount of calcium was determined in the seeds of faba bean and pea (

Table 3. Macronutrient contents in seeds (g kg⁻¹ DM).

Legumes	Year	Phosphorus	Potassium	Magnesium	Calcium
Soybean	2019	5.36 ± 0.24 de	18.3 ± 0.37 a	2.25 ± 0.06 a	1.15 ± 0.12 de
	2020	5.84 ± 0.08 cd	16.7 ± 0.41 ab	2.12 ± 0.11 a	0.85 ± 0.11 ef
	2021	6.53 ± 0.26 ab	16.1 ± 0.97 b	2.14 ± 0.09 a	0.63 ± 0.06 fg
Faba bean	2019	6.00 ± 0.17 bc	11.1 ± 0.96 cdef	1.15 ± 0.16 ef	0.50 ± 0.12 fg
	2020	5.70 ± 0.27 cde	10.2 ± 0.18 cdefg	0.99 ± 0.08 f	0.49 ± 0.09 fg
	2021	6.54 ± 0.53 ab	11.6 ± 0.38 c	1.16 ± 0.13 def	0.65 ± 0.09 fg
Pea	2019	4.19 ± 0.29 f	9.2 ± 0.88 ghi	1.20 ± 0.04 def	0.31 ± 0.07 g
	2020	5.22 ± 0.11 e	7.5 ± 0.53 i	1.30 ± 0.04 cde	0.35 ± 0.11 g
	2021	3.43 ± 0.38 g	7.4 ± 0.34 i	1.18 ± 0.03 def	0.28 ± 0.03 g
White lupine	2019	3.50 ± 0.13 g	9.5 ± 0.68 fgh	1.17 ± 0.10 def	0.81 ± 0.12 ef
	2020	3.88 ± 0.10 fg	10.2 ± 0.76 cdefg	1.34 ± 0.08 cde	1.16 ± 0.36 de
	2021	3.81 ± 0.13 fg	7.9 ± 0.75 hi	1.32 ± 0.06 cde	0.91 ± 0.14 ef
Narrow-leaved lupine	2019	5.47 ± 0.05 cde	9.7 ± 1.08 defgh	1.64 ± 0.16 b	2.08 ± 0.09 a
	2020	5.36 ± 0.07 de	9.6 ± 0.51 efgh	1.54 ± 0.22 bc	1.59 ± 0.06 bc
	2021	5.24 ± 0.10 de	9.8 ± 0.21 cdefg	1.45 ± 0.20 bcd	1.69 ± 0.02 abc
Yellow lupine	2019	7.10 ± 0.04 a	11.2 ± 0.57 cdef	2.22 ± 0.07 a	1.97 ± 0.06 ab
	2020	7.07 ± 0.06 a	11.5 ± 0.71 cd	2.20 ± 0.04 a	1.79 ± 0.14 abc
	2021	6.90 ± 0.40 a	11.4 ± 1.30 cde	2.15 ± 0.12 a	1.50 ± 0.45 cd
Legumes × Year		***	***	*	***

Results are expressed as mean value ± standard deviations. Different letters in the same column indicate significant differences according to the analysis of variance (ANOVA). ***, * indicate significant differences at p < 0.001 and p < 0.05, according to Tukey’s honestly significant difference (HSD) test.

).

Ton et al. [34] reported slightly different macronutrient contents (P, K, and Mg) in faba bean seeds. Fordoński et al. [38] showed that faba bean seeds were rich in potassium and phosphorus and narrow-leafed lupin seeds were high in calcium and magnesium. Kozak et al. [42] proved that the macronutrient content of soybean seeds was dependent on weather conditions and, to a lesser extent, cultivar and agriculture practices. In turn, Jarecki et al. [43] reported that the content of some macronutrients and micronutrients in soybean seeds was dependent on inoculation and/or nitrogen fertilization. Dahl et al. [37] proved that pea seeds had many valuable nutrients, but their content was usually lower compared to other legumes. Prusiński [20] drew attention to the chemical composition of white lupin seeds and the potential for the wider dissemination of this species.

3.5. The Content of Micronutrients

The iron content in soybean ranged from 61 to 99.2 mg kg⁻¹ and significantly depended on the study year. Lower contents of the discussed component were found in yellow lupin seeds, but they were stable over the years. The iron content in pea seeds was also high. The lowest amount of iron was determined in the seeds of faba bean, white lupin, and narrow-leafed lupin. Low diversity of micronutrients was shown in the seeds of narrow-leafed lupin. White lupin seeds were characterized by very high manganese content. In 2020, it was 474.8 mg kg⁻¹, and it was 636.9 mg kg⁻¹ in 2019. In the case of the remaining species, the content of the discussed component was statistically equal and stable over the years. High zinc content was determined in soybean and yellow lupin seeds. For soybean, this parameter was significantly dependent on study years. The seeds of narrow-leafed lupin and pea in 2019 were characterized by the low content of the element in question. Copper content depended on the interaction of the legume with the year of study. High copper content was determined in 2019 in faba bean and yellow lupin, in 2020 in soybean, and in 2021 in soybean and faba bean. The lowest content of the analyzed element was found in seeds of narrow-leafed lupin, which was reproducible over the years (

Table 4. Micronutrient contents in seeds (mg kg⁻¹ DM).

Legumes	Year	Iron	Manganese	Zinc	Copper
Soybean	2019	61.0 ± 8.4 c	14.6 ± 0.5 c	35.7 ± 1.3 de	11.1 ± 1.1 cdef
	2020	75.8 ± 8.5 b	18.2 ± 1.5 c	47.6 ± 1.7 ab	12.8 ± 0.6 abcd
	2021	99.2 ± 3.6 a	23.5 ± 0.4 c	50.2 ± 2.3 a	14.3 ± 0.3 ab
Faba bean	2019	35.4 ± 3.5 efg	13.7 ± 1.6 c	35.0 ± 1.4 de	13.1 ± 0.9 abc
	2020	33.4 ± 2.9 fg	12.7 ± 1.1 c	33.5 ± 0.8 de	11.7 ± 0.7 bcde
	2021	46.8 ± 5.6 de	14.7 ± 1.4 c	38.4 ± 8.0 cd	14.5 ± 2.0 a
Pea	2019	44.7 ± 2.8 def	6.1 ± 0.5 c	21.2 ± 3.1 g	4.8 ± 0.7 hi
	2020	53.3 ± 3.1 cd	9.2 ± 0.3 c	39.8 ± 2.5 bcd	9.9 ± 0.7 efg
	2021	51.1 ± 1.6 cd	8.3 ± 0.4 c	35.4 ± 4.7 de	10.3 ± 1.1 def
White lupine	2019	32.1 ± 1.2 g	636.9 ± 8.8 a	37.8 ± 1.9 de	7.2 ± 1.2 gh
	2020	30.9 ± 2.3 g	474.8 ± 96.2 b	30.0 ± 2.0 ef	5.8 ± 0.7 hi
	2021	36.7 ± 4.9 efg	608.5 ± 20.4 a	34.1 ± 1.2 de	4.5 ± 1.0 hi
Narrow-leaved lupine	2019	31.1 ± 1.3 g	45.0 ± 7.5 c	23.3 ± 2.9 fg	3.8 ± 0.5 i
	2020	30.1 ± 2.5 g	43.5 ± 9.3 c	22.0 ± 2.9 fg	3.6 ± 0.7 i
	2021	30.7 ± 1.5 g	42.9 ± 7.5 c	20.8 ± 2.8 g	3.5 ± 1.3 i
Yellow lupine	2019	55.9 ± 5.4 cd	54.6 ± 8.8 c	46.2 ± 2.3 abc	12.0 ± 0.6 abcde
	2020	52.5 ± 6.2 cd	41.1 ± 5.4 c	48.1 ± 2.2 a	8.7 ± 0.7 fg
	2021	54.1 ± 6.9 cd	51.7 ± 8.4 c	47.2 ± 3.2 ab	10.6 ± 2.2 cdef
Legumes × Year		***	***	***	***

Results are expressed as mean value ± standard deviations. Different letters in the same column indicate significant differences according to the analysis of variance (ANOVA). *** indicate significant differences at p < 0.001, according to Tukey’s honestly significant difference (HSD) test.

).

Mudryj et al. [7] reported that legumes provided protein and fiber and were a significant source of vitamins and minerals, such as iron, zinc, folate, and magnesium. Cabrera et al. [50] reported that the elemental content of legume seeds depended on the species. The average fluctuations were: 1.5–5.0 μg Cu/g, 0.05–0.60 μg Cr/g, 18.8–82.4 μg Fe/g, 32.6–70.2 μg Zn/g, 2.7–45.8 μg Al./g, 0.02–0.35 μg Ni/g, 0.32–0.70 μg Pb/g, and not detectable—0.018 μg Cd/g. Ton et al. [34] determined high micronutrient contents in faba bean seeds. In addition, they obtained significant varietal differences in seed chemical composition. Fordoński et al. [38] proved that faba bean seeds were rich in copper and zinc and narrow-leafed lupin seeds were high in manganese. Woźniak et al. [36] reported that pea seeds were rich in iron. Jankauskienė et al. [51] showed that the iron and zinc contents of soybean seeds were similar in the cultivars tested. Prusiński [20] confirmed that white lupin seeds were exceptionally rich in manganese.

3.6. Statistical Dependencies

The statistical calculations presented in the diagram show that faba bean and pea or narrow-leafed lupin and yellow lupin cultivation resulted in a similar effect. The greatest differences were found between soybean and white lupin, as shown in Figure 4. In terms of the similarity of chemical composition between the analyzed species, two internal clusters were identified: Cluster I (faba bean and pea, distance 66.41) and Cluster II (narrow-leaved lupine and yellow lupine, distance 75.31). In the next merger, there was a significant increase in distance (to 198.73), combining the internal groups into one cluster (faba bean, pea, narrow-leaved lupine, and yellow lupine). The remaining species, soybean (distance 265.79) and white lupine (distance 830.44), were included in subsequent steps.

Fordoński et al. [38] obtained similar dendrogram results. The chemical composition of faba bean and pea was similar but different from that of narrow-leafed lupin.

Positive and negative correlations between the individual components were also evident for the traits analyzed (Figure 5). It was shown that seed yield (r = 0.82) was very strongly positively correlated with protein yield. Seed protein content was highly negatively correlated with fat but positively highly correlated with K content and highly correlated with the content of Mg. Ash was highly correlated with Mg and K contents, while fiber showed a very strong correlation with the content of Ca. Csajbók et al. [46] showed that protein yield was determined by seed yield rather than protein content. Hong et al. [30] showed a negative correlation between protein and oil contents in soybean.

In order to estimate the sources of variability, the relationship between the quality parameters of the legume species in question was assessed using the principal component analysis (PCA) method (Figure 6). In this analysis, seed yield, protein yield, seed chemical composition, and macro- and micronutrient contents were taken into account (Figure 2 and Figure 3, Table 2, Table 3 and Table 4). Of the fourteen parameters studied, three extracted principal components were selected for analysis as these components contribute a greater load of variation than the individual variables. The eigenvalues of the selected components are greater than 1. The first component was 5.54, and the percentage of explained variance was 39.58%. The eigenvalue of the second component was 3.94, with a percentage of explained variance of 28.11%. The third component explained 16.56% of the variance, and its eigenvalue was 2.32. The first three components carry 84.25% of the variation in the raw data. The eigenvalue criterion greater than 1 (Kaiser criterion) was used to determine the number of principal components, so the approximation of the original data set was only possible in two dimensions. The first two principal components carried 67.70% of the variability in the original data. Its importance is confirmed by the scatter plot, which allows the three-dimensional space to be reduced to two principal components. For the first principal component, the content of ash and protein, the macronutrients K and Mg and the micronutrients Fe and Zn were most responsible for its formation. The second principal component was mainly determined by grain yield, protein yield, fiber content, and Ca and Cu.

4. Conclusions

The size and quality of legume seed yields significantly depended on the interaction of species and study year. Weather conditions modified most of the obtained results. On average, during the three-year study period, soybean (3.85–4.1 t ha⁻¹), faba bean (3.07–4.03 t ha⁻¹), and pea (3.45–4.02 t ha⁻¹) yielded high, with soybean (1.37–1.64 t ha⁻¹) having the highest protein yield. Satisfactory protein yield was also obtained in white lupin. Narrow-leafed lupin and yellow lupin had the lowest protein yield in each year of the study. The protein yield depended more on the seed yield than the protein content. Soybean and yellow lupin seeds were characterized by favorable chemical composition. The protein content of soybean and yellow lupin seeds was 354.5–399.2 and 375.4–406.4 g kg⁻¹ DM, respectively. Phosphorus and copper contents were high in faba bean seeds, while pea seeds were high in iron and low in fiber. Narrow-leafed (1.87–2.22 t ha⁻¹) and yellow lupins (1.82–1.87 t ha⁻¹) had low yields, and their seeds were rich in calcium and fiber. The results of the experiment allowed us to broaden our knowledge about legumes. In a further experiment, seed chemical analyses will be expanded to include other nutrients.