Forage Yield, Quality, and Weed Suppression in Narbon Vetch (Vicia narbonensis L.) and Italian Ryegrass (Lolium multiflorum L.) Mixtures Under Organic Management

Abstract

This study aimed to evaluate the forage yield, quality, and weed suppression potential of narbon vetch (Vicia narbonensis L.) and Italian ryegrass (Lolium multiflorum L.) grown as sole crops and in mixtures under organic farming conditions in Bilecik, Turkey, during the 2020–2021 growing season. The experiment included 15 treatments comprising monocultures and mixed sowing at different ratios. Measurements included morphological traits, forage yield components (green herbage, hay, and crude protein), fiber content, botanical composition, and weed biomass. The results reveal significant differences among treatments in terms of growth parameters and forage performance. Monocultures of IFVN 567 and Bartigra showed the highest green and hay yields, while mixtures such as IFVN 567 + Trinova and IFVN 567 + Bartigra outperformed in terms of land equivalent ratio (LER) and protein yield, demonstrating a clear advantage in land use efficiency. Furthermore, these mixtures showed superior weed suppression compared to monocultures. Overall, the findings suggest that carefully selected vetch–ryegrass combinations can enhance forage productivity, nutritional quality, and weed management under organic systems.

1. Introduction

Sustainable forage production is a cornerstone of organic livestock systems, where reliance on synthetic inputs is restricted and ecological interactions are leveraged to maintain productivity. In this context, grassland and forage-based systems serve not only as feed resources but also as multifunctional components of agro ecosystems, contributing to soil health, biodiversity, and weed suppression. Among the strategies compatible with organic agriculture, mixed cropping of forage legumes and grasses has gained attention due to its potential to enhance yield and quality while naturally suppressing weed populations and improving soil fertility [1,2].

Narbon vetch (Vicia narbonensis L.), a hardy annual legume adapted to Mediterranean climates, is recognized for its drought tolerance, high protein content, and nitrogen-fixing capacity, making it especially valuable under input-limited organic systems [3]. It improves soil fertility through biological nitrogen fixation and contributes to balanced rations in ruminant diets. Italian ryegrass (Lolium multiflorum L.), on the other hand, is a cool-season grass known for its rapid establishment, high dry matter production, and palatability. Its fibrous root system plays a vital role in soil structure improvement and erosion control, which aligns with the soil conservation principles of organic farming [4].

The synergistic interaction between legumes and grasses in mixed stands can be particularly beneficial in organic systems. Legumes supply biologically fixed nitrogen to companion grasses, reducing reliance on external nitrogen inputs, while grasses contribute structural biomass and facilitate canopy closure, which collectively enhance resource-use efficiency and forage quality [5]. Moreover, increased ground cover and spatial niche occupation in such mixtures are associated with improved weed suppression, a critical component of organic production, where chemical herbicides are prohibited [2,6]. Recent studies have shown that mixed swards can outperform monocultures not only in forage yield and nutritive value but also in their ability to reduce weed biomass and density, especially during early canopy development stages [7,8].

Despite these benefits, the performance of specific legume–grass combinations under different ecological conditions and organic management regimes remains underexplored. In particular, there is limited data regarding the use of narbon vetch and Italian ryegrass mixtures under organic farming systems in Mediterranean climates, such as those in Bilecik, Turkey. Given the region’s cool, wet winters and hot, dry summers, optimizing forage mixtures for both productivity and ecological service delivery (e.g., weed control) is essential.

This study aims to evaluate the effects of different seed mixture ratios of narbon vetch (Özgen, Karakaya, and IFVN 567genotypes) and Italian ryegrass (Trinova, Bartigra, and Efe-82genotypes) on forage yield, quality traits, and weed suppression capacity under organic farming conditions in Bilecik. The results are expected to provide practical recommendations for sustainable forage production in organic systems, supporting both agronomic performance and ecological sustainability.

2. Materials and Methods

This study was conducted during the 2020–2021 growing season under the ecological conditions of Bilecik province, Turkey, in the experimental plots of the Faculty of Agricultural Sciences and Technologies at Bilecik Şeyh Edebali University. Narbon vetch (Vicia narbonensis L.) and Italian ryegrass (Lolium multiflorum L.) were sown both as sole crops and in mixed proportions (50:50). Sowing was performed manually in November. No fertilizers or chemical pesticides were applied; only standard cultural practices were carried out. Harvesting took place in May at the full flowering stage. Measurements on yield, forage quality, and weed suppression were obtained from harvested samples. The plant material used in the experiment included three narbon vetch genotypes, namely Özgen, Karakaya, and IFVN 567sourced from the Turkish Ministry of Agriculture’s Variety Registration and Certification Center and the GAP Agricultural Research Institute. Özgen is a narbon vetch genotype developed by Dicle University through selection breeding. It is known for its high forage yield, drought tolerance, and adaptability to dryland conditions. Karakaya, also developed by Dicle University, is characterized by its early maturity, good regrowth potential, and resistance to common vetch diseases. IFVN 567 is a promising line obtained from the GAP Agricultural Research Institute, noted for its vigorous growth, high biomass production, and potential suitability for mixed cropping systems. Additionally, three Italian ryegrass cultivars, namely Trinova, Bartigra, and Efe 82, were included. Trinova is a diploid cultivar widely appreciated for its high digestibility, excellent silage quality, and high crude protein content, making it ideal for intensive forage production systems. Bartigra is a tetraploid annual ryegrass variety that offers rapid establishment, broad leaves, and superior regrowth capacity. It is particularly valued for its palatability and competitiveness against weeds. Efe 82 was developed by the Aegean Agricultural Research Institute and is adapted to Mediterranean climatic conditions. It is known for its high green herbage yield, tolerance to mild drought, and suitability for cutting and grazing systems.

2.1. Experimental Site and Soil Characteristics

The soil at the site is sandy loam, moderately alkaline, and has medium salinity (0.26%). A soil test (0–20 cm) indicated organic matter content of 1.24%, NO₃-N = 0.280 ppm, P₂O₅ = 0.35 kg ha⁻¹, CaCO₃ = 8.3%, Cu = 3.837 cmol kg⁻¹, Fe = 7.944 cmol kg⁻¹, Mn = 6.735 cmol kg⁻¹, Zn = 1.790 cmol kg⁻¹, K = 0.11 kg ha⁻¹, and soil pH = 8.11 (Figure 1).

2.2. Climatic Data

Climatic data for the 2020–2021 growing season were obtained from the Bilecik Meteorological Directorate. The average temperature during the trial period was 8.8 °C, which is higher than the long-term (1991–2020) average of 7.7 °C. Relative humidity averaged 67.0% in 2020–2021, compared to a long-term mean of 70.7%. The total annual precipitation was recorded as 338.3 mm in the study year, slightly above the long-term average of 322.0 mm (Figure 2).

2.3. Experimental Design and Field Management

Prior to sowing, the field was prepared in the autumn using appropriate tillage practices consistent with organic management standards. No synthetic fertilizers or chemical pesticides were applied during the experiment. Although initial soil analysis indicated low levels of phosphorus (P) and potassium (K), no external inputs were used in accordance with organic regulations. The soil was subsequently cultivated using a rotary tiller. Sowing was performed manually on 14 October 2020, into seedbeds marked using a row marker.

The experiment was established using a randomized complete block design (RCBD) in a single-factor arrangement with three replications. Each plot consisted of six rows spaced 30 cm apart, with a row length of 4 m, resulting in a total plot area of 7.2 m² (1.8 m × 4.0 m). A 1 m buffer zone was left between plots, and a 2 m spacing was maintained between replication blocks to minimize edge effects. Only standard cultural practices allowed under organic production—such as mechanical weeding and manual maintenance were carried out throughout the growing season.

Plant Material and Sowing Rates

The plant materials used in the study included narbon vetch (Vicia narbonensis) and Italian ryegrass (Lolium multiflorum). Sowing rates were as follows:

• Monoculture plots: 60 kg ha⁻¹ of narbon vetch and 30 kg ha⁻¹ of ryegrass.
• Mixed sowing plots: 30 kg ha⁻¹ of narbon vetch + 15 kg ha⁻¹ of ryegrass (corresponding to a 50:50 ratio based on pure seeding rates).

A total of 15 treatments were evaluated in the study, consisting of nine mixed cropping combinations and six monoculture applications.

2.4. Measurements and Harvesting

The harvest was conducted based on the dominant species in the mixed cropping systems, which was the grass component. Specifically, harvesting was carried out at the beginning of heading in Italian ryegrass (Lolium multiflorum). Observations related to morphological characteristics of both grass and legume species were performed according to the methods described by [9]. Just before harvesting, ten representative plants of each species and variety were randomly selected from each plot in both sole cropping and mixed cropping treatments. In these selected plants, plant height, stem diameter, number of tillers, number of lateral branches, leaf width, and leaf length were recorded. In addition, leaf-to-stem ratio and botanical composition of the mixtures were determined. The leaf-to-stem ratio was calculated by separately weighing the leaf and stem fractions of the above-ground biomass of the sampled plants after manual separation. The ratio was then obtained by dividing the dry weight of the leaf portion by the dry weight of the stem portion, as described by [9,10]. The botanical composition in the mixtures was determined by hand-separating the harvested fresh biomass into its component species (grass and legume), and weighing each component separately. For Italian ryegrass, its proportion in the total biomass was calculated by dividing the dry weight of the ryegrass by the total dry weight of the mixture and multiplying the result by 100 to express it as a percentage. This method provided an accurate representation of species dominance within the mixed stands [9].

After eliminating the border effect, herbage was harvested and green herbage yield was calculated. Subsamples of green herbage were taken during harvest and oven-dried at 70 °C for 48 h to determine dry matter yield, following the procedures of [11]. The dried plant materials were ground and analyzed for crude protein, acid detergent fiber (ADF; cellulose + lignin), and neutral detergent fiber (NDF; hemicellulose + cellulose + lignin) [12]. Crude protein yield was calculated by multiplying dry matter yield by crude protein percentage [13].

2.4.1. Land Equivalent Ratio (LER)

To assess land use efficiency, the Land Equivalent Ratio (LER) was calculated for mixed cropping plots. LER is defined as the relative land area required under sole cropping to achieve the same yield as that obtained from intercropping. It was calculated using the following formula described by [11]:

LER = (Yield of grass in intercropping/Yield of grass in sole cropping) + (Yield of legume in intercropping/Yield of legume in sole cropping)

The interpretation of LER values is as follows:

-

LER >1: Indicates that the intercropping system improves land use efficiency.

-

LER = 1: Indicates that the intercropping system has no effect on land use efficiency.

-

LER < 1: Indicates that the intercropping system reduces land use efficiency.

2.4.2. Assessment of Weed Suppression

Weed data were collected twice during the growing season—once during the vegetative growth stage and again at the time of harvest. In each plot, two 50 × 50 cm quadrats were randomly placed to assess weed cover (Figure 3). Aboveground weed biomass within each quadrat was harvested to determine weed cover area, fresh weight, and dry weight. Fresh weights were recorded immediately after harvest, and samples were then oven-dried at 70 °C for 48 h to obtain dry weights.

2.5. Statistical Analysis

The effects of treatments on weed parameters (cover, fresh weight, and dry weight) were statistically evaluated using SPSS 22 software. A General Linear Model (GLM) was applied, followed by Tukey’s HSD test for mean comparisons at the 5% significance level.

All agronomic and forage quality data were statistically analyzed using JMP Pro 16 (SAS Institute Inc., Cary, NC, USA). A General Linear Model (GLM) was applied within a randomized complete block design (RCBD) framework. When significant differences were detected, treatment means were compared using Tukey’s HSD test at the 5% significance level. Weed-related parameters (cover, fresh weight, and dry weight) were analyzed separately using SPSS 22 software (IBM Corp., Armonk, NY, USA), employing the same ANOVA procedure and multiple comparisons with Tukey’s test at the 5% significance level. Graphical illustrations were created using Microsoft Excel 2019.

3. Results

3.1. Morphological Characteristics

Morphological traits of narbon vetch and Italian ryegrass cultivars under organic sole and mixed cropping are given (

Table 1. Morphological characteristics of different narbon vetch (Vicia narbonensis L.) and annual ryegrass (Lolium multiflorum L.) cultivated as sole and mixed cropping under organic farming system.

Treatments	Plant Heights, cm		Plant Stem Diameter, mm		Plant Leaf Length, cm		Plant Leaf Width, cm		Number of Lateral Branches in Narbon vetch	Number of Sprouts in Grass
	Narbon V.	Ryegrass	Narbon V.	Ryegrass	Narbon V.	Ryegrass	Narbon V.	Ryegrass	Narbon V.	Ryegrass
Özgen + Efe 82	65.00 gh	100.3 h	8.13 a	2.53 a	4.50 f	12.60 ı	2.93 de	1.27 cd	5.00 a	11.23 c
Özgen + Bartigra	69.33 fg	117.0 def	7.83 b	2.13 cd	4.67 f	29.30 b	3.20 bc	1.50 ab	3.90 cd	11.87 bc
Özgen + Trinova	72.00 ef	122.0 bc	7.10 d	2.37 b	4.53 f	29.23 b	2.93 de	1.60 ab	3.27 f	13.00 ab
IFVN 567 + Efe 82	81.00 bcb	114.3 fg	5.33 ı	2.27 bc	5.07 d	16.80 h	3.60 a	1.07 f	3.53 ef	11.70 bc
IFVN 567 + Bartigra	84.67 ab	120.3 cd	5.97 g	1.97 e	5.40 b	18.50 g	3.27 bc	0.90 g	4.43 b	13.30 ab
IFVN 567 + Trinova	86.33 ab	119.3 cde	5.63 h	2.13 cd	5.60 a	21.03 f	3.43 ab	1.10 ef	3.70 de	13.07 ab
Karakaya + Efe 82	79.33 cd	110.7 g	6.77 e	2.40 ab	5.10 cd	27.10 c	2.80 e	1.20 def	3.63 de	11.97 abc
Karakaya + Bartigra	75.00 de	118.0 c-f	6.40 f	2.03 de	4.87 e	22.57 e	2.73 e	1.10 ef	3.67 de	12.60 abc
Karakaya + Trinova	78.67 cd	127.0 a	6.53 f	2.03 de	4.93 de	26.03 d	2.90 de	1.10 ef	3.43 ef	13.33 ab
Efe 82	-	116.0 ef	-	2.33 b	-	33.03 a	-	1.37 bc	-	11.10 c
Özgen	64.33 h	-	8.17 a	-	4.60 f	-	3.07 cd	-	4.30 b	-
IFFN567	82.33 abc	-	6.13 g	-	5.63 a	-	3.67 a	-	4.10 bc	-
Karakaya	70.33 ef	-	7.33 c	-	5.27 bc	-	3.30 bc	-	3.70 de	-
Bartigra	-	121.7 c	-	1.93 e	-	27.77 c	-	1.23 cde	-	11.87 bc
Trinova	-	126.0 b	-	2.17 cd	-	18.50 g	-	1.10 ef	-	13.67 a
Average	75.69	117.7	6.78	2.2	5.01	23.54	3.15	1.21	3.89	12.39
L.S.D. (%5) ±SE	4.843 2.86	4.309 2.545	0.170 0.100	0.158 0.095	0.192 0.114	0.816 0.482	0.241 0.141	0.153 0.089	0.342 0.117	1.764 0.602

Values are means (±SE) of replicates. Different letters within each column indicate significant differences among treatments (p < 0.05).

). Plant height (cm), stem diameter (mm), leaf length and width (cm), and branching parameters (number of lateral branches for vetch; number of tillers for ryegrass) are shown for each cultivar and cropping system.

3.1.1. Plant Height

In terms of plant height, ryegrass varieties demonstrated a clear advantage over narbon vetch. According to the data, annual ryegrass monocultures reached the highest plant heights, while narbon vetch monocultures remained comparatively shorter. This trend is consistent with the existing literature, which reports that Italian ryegrass can reach 60–90 cm in height, whereas narbon vetch typically grows to 20–60 cm. Statistical analysis revealed that the difference in plant height between ryegrass and narbon vetch monocultures was significant at p < 0.05. In mixed cropping systems, plant heights were generally intermediate between the two species, with some combinations showing statistically significant differences.

3.1.2. Stem Diameter

Narbon vetch exhibited significantly thicker stem diameters compared to ryegrass, which reflects their inherent structural differences. While narbon vetch develops upright, thick, and branched stems, Ryegrass has thin, cylindrical, and often hollow stems. The experimental data clearly supports this: the stem diameters of narbon vetch in both monoculture and mixtures were significantly larger than those of ryegrass (p < 0.05). These results are consistent with the known anatomical distinctions between these species.

3.1.3. Leaf Dimensions

Distinct differences were also observed in leaf size. Ryegrass typically has long (6–25 cm) but very narrow leaves (0.3–1 cm), while narbon vetch has relatively short (2–5 cm) but broader leaflets (1–4 cm). In the experiment, ryegrass varieties showed significantly greater leaf lengths, while narbon vetch had significantly wider leaves (p < 0.05). In mixed cropping treatments, leaf measurements tended to reflect intermediate values, but the contribution of each species was evident: length from ryegrass and width from narbon vetch.

3.1.4. Number of Lateral Branches

Narbon vetch typically produces multiple lateral branches, while ryegrass has a single culm and does not branch. The number of lateral branches was substantially higher in narbon vetch varieties, and the difference was statistically significant (p < 0.05). This branching ability of narbon vetch contributed significantly to its vegetative development, especially in monoculture and mixture plots where it was dominant.

3.1.5. Number of Sprouts (Tillers)

In contrast, ryegrass demonstrated a much greater capacity for tiller formation. Ryegrass is known for producing numerous tillers per plant, whereas narbon vetch generally grows from a single main stem with lateral branches rather than tillers. The highest number of tillers was observed in pure ryegrass stands, with values significantly higher than those recorded for narbon vetch (p < 0.05). In mixed stands, treatments including ryegrass showed a clear advantage in terms of sprout number, emphasizing its prolific tillering potential.

3.2. Leaf–Stem Ratio, Botanical Composition, Crude Protein, and Fiber Contents (ADF, NDF)

Leaf-to-stem ratio, botanical composition, crude protein, and fiber content (ADF, NDF) of different narbon vetch and ryegrass combinations cultivated as sole crops and mixtures under organic farming conditions are given in

Table 2. Leaf–stem ratio, botanical composition, crude protein, and fiber content (ADF, NDF) characteristics of different narbon vetch (Vicia narbonensis L.) and annual ryegrass (Lolium multiflorum L.) cultivated as sole and mixed cropping under organic farming system.

Treatments	Leaf Ratio in the Plant, %		Stem Ratio in the Plant, %		Botanical Composition, %		Crude Protein Ratio, %		ADF Ratio, %		NDF Ratio, %
	Narbon V.	Ryegrass	Narbon V.	Ryegrass	Narbon V.	Ryegrass	Narbon V.	Ryegrass	Narbon V.	Ryegrass	Narbon V.	Ryegrass
Özgen + Efe 82	56.63 g	76.63 g	43.37 b	23.37 a	16.93 e	83.07 a	21.27 de	8.97 e	28.80 cde	31.73 b	34.53 abc	46.43 b
Özgen + Bartigra	60.80 ef	83.53 b-f	39.20 cd	16.47 b-f	20.07 b	79.93 d	22.23 c	10.83 c	29.17 bcd	29.70 de	35.40 a	45.07 cd
Özgen + Trinova	67.70 a	83.57 b-e	32.30 h	16.43 c-f	23.43 a	76.57 e	22.43 bc	12.70 a	29.20 bcd	28.93 ef	35.57 a	43.93 e
IFVN 567 + Efe 82	64.37 b	84.40 bcd	35.63 g	15.60 def	19.00 bcd	81.00 bcd	22.40 c	9.87 d	27.73 fg	30.20 d	33.23 cd	45.10 cd
IFVN 567 + Bartigra	54.27 h	85.37 abc	45.73 a	14.63 efg	16.77 e	83.23 a	22.23 c	11.67 b	27.77 fg	29.17 ef	32.33 de	45.13 c
IFVN 567 + Trinova	61.23 de	81.27 ef	38.77 de	18.73 bc	19.73 bc	80.27 cd	21.90 cd	12.43 a	27.97 efg	28.40 f	31.30 e	44.17 de
Karakaya + Efe 82	61.63 cde	80.77 f	38.37 def	19.23 b	18.50 d	81.50 b	20.83 ef	9.10 e	29.63 abc	31.07 bc	34.73 ab	46.80 ab
Karakaya + Bartigra	63.50 bc	83.30 c-f	36.50 fg	16.70 b-e	18.80 cd	81.20 bc	20.20 f	10.17 d	30.47 a	29.77 de	34.70 ab	46.63 ab
Karakaya + Trinova	64.90 b	84.63 a-d	35.10 g	15.37 d-g	23.07 a	76.93 e	22.10 c	12.67 a	29.97 ab	28.70 f	34.67 ab	44.73 cde
Efe 82	-	82.37 def	-	17.63 bcd	-	-	-	7.80 f	-	32.93 a	-	47.40 ab
Özgen	57.47 g	-	42.53 b	-	-	-	23.07 bc	-	28.43 def	-	33.27 cd	-
IFFN567	58.83 fg	-	41.17 bc	-	-	-	24.17 a	-	27.17 g	-	32.30 de	-
Karakaya	63.43 bcd	-	36.57 efg	-	-	-	22.17 c	-	29.30 bcd	-	33.40 bcd	-
Bartigra	-	87.23 a	-	12.77 g	-	-	-	9.27 e	-	31.77 b	-	46.80 ab
Trinova	-	86.1 abc	-	13.90 fg	-	-	-	10.70 c	-	30.30 cd	-	45.30 c
Average	61.23	83.3	38.77	16.7	19.59	80.41	22.08	10.51	28.80	30.22	33.79	45.62
L.S.D. (%5)	2.252	2.785	2.252	2.785	1.115	1.115	0.655	0.444	0.904	0.839	1.376	0.956
±SE	0.768	0.950	0.768	0.950	0.372	0.372	0.224	0.151	0.308	0.286	0.308	0.308

Values are means (±SE) of replicates. Different letters within each column indicate significant differences among treatments (p < 0).

.

3.2.1. Leaf Ratio in the Plant (%)

The leaf ratio is a key determinant of forage quality, as leaves typically contain more crude protein and are more digestible than stems. Significant differences were observed among treatments in terms of leaf ratio for both narbon vetch and ryegrass.

In narbon vetch, the leaf ratio ranged from 54.27% to 67.70%. The highest leaf ratio was recorded in the Özgen + Trinova mixture (67.70%), followed by Karakaya + Trinova (64.90%) and IFVN 567 + Efe 82 (64.37%). The lowest value was observed in IFVN 567 + Bartigra (54.27%). These findings suggest that the Trinova cultivar positively influenced leaf development in narbon vetch, likely due to better compatibility and favorable growth dynamics in the mixture.

For ryegrass, the leaf ratio ranged from 76.63% to 87.23%, with the highest value found in the Bartigra monoculture (87.23%), followed closely by Trinova (86.10%). Although leaf ratio values were generally high in ryegrass, a slight reduction was observed in some mixtures, such as Özgen + Efe 82 (76.63%), potentially due to interspecies competition affecting canopy structure. Overall, Trinova and Bartigra cultivars maintained higher leaf proportions, which is favorable for feed value.

3.2.2. Stem Ratio in the Plant (%)

The stem ratio is inversely related to forage quality, as stems contain more fiber and are less digestible than leaves. Lower stem ratios are therefore preferable in high-quality forage production.

In narbon vetch, the stem ratio varied between 32.30% and 45.73%. The lowest stem ratio was observed in the Özgen + Trinova mixture (32.30%), indicating a high proportion of leaves. In contrast, the highest stem ratio was recorded in IFVN 567 + Bartigra (45.73%), which may reduce overall forage quality. Combinations including Trinova generally resulted in lower stem ratios, supporting its role in enhancing morphological characteristics associated with better nutritive value.

In ryegrass, stem ratios were considerably lower compared to narbon vetch, ranging from 12.77% to 23.37%. The lowest value was obtained from Bartigra (12.77%), followed by Trinova (13.90%). The highest stem ratio in ryegrass was found in the Özgen + Efe 82 mixture (23.37%). These results demonstrate that Bartigra and Trinova tend to produce more leafy growth with reduced stem elongation, thus contributing to higher forage quality.

3.2.3. Botanical Composition

The botanical composition showed considerable variability among mixtures. In all combinations, Ryegrass dominated the botanical composition, comprising 76.57% to 83.23% of the biomass, whereas the proportion of narbon vetch ranged from 16.77% to 23.43%. This dominance is attributed to the more aggressive growth habit and competitive ability of ryegrass under the given ecological conditions. Among mixtures, Özgen + Trinova recorded the highest proportion of narbon vetch (23.43%), indicating better compatibility and balanced growth. The proportion of narbon vetch in the treatment Karakaya + Trinova is 23.07%, which is not significantly different from Özgen + Trinova.

3.2.4. Crude Protein Content

Significant differences (p < 0.05) were observed in crude protein content across different treatments. Among monocultures, narbon vetch ‘IFFN 567’ had the highest crude protein ratio (24.17%), while the lowest value was found in the ryegrass monoculture ‘Efe 82’ (7.80%). In mixed cropping systems, Özgen + Trinova (22.43%) and IFVN 567 + Efe 82 (22.40%) exhibited relatively high protein content in the legume component, while Trinova and Bartigra consistently showed higher protein ratios among ryegrass cultivars. These results highlight the nutritive superiority of narbon vetch compared to ryegrass, and the contribution of the ryegrass genotype to the overall protein balance in mixtures.

3.2.5. Acid Detergent Fiber (ADF) and Neutral Detergent Fiber (NDF)

Fiber content, as measured by ADF and NDF, also varied significantly among the treatments. The lowest ADF (27.17%) was observed in the IFFN 567 monoculture, indicating better digestibility. Conversely, the highest ADF (30.47%) was noted in the Karakaya + Bartigra mixture. In terms of NDF, the highest values were recorded in monoculture ryegrass ‘Efe 82’ (47.40%), reflecting its fibrous nature, while the lowest values occurred in mixtures containing Trinova and IFVN 567.

Table 3. Crude protein yield, forage yield, total forage yields, and land equivalent ratios of different narbon vetch (Vicia narbonensis L.) and annual ryegrass (Lolium multiflorum L.) cultivated as sole and mixed cropping under organic farming system.

Treatments	Crude Protein Yield, kg ha−1		Green Grass Yield, kg ha−1		Hay Yield, kg ha−1		Total Green Grass Yield, kg ha−1	Total Hay Grass Yield, kg ha−1	DM-LER, %	Protein-LER, %
	Narbon V.	Ryegrass	Narbon V.	Ryegrass	Narbon V.	Ryegrass	Mixture	Mixture	Mixture	Mixture
Özgen + Efe 82	1331.1 g	389.2 h	28,258 f	18,691 hı	6260.0 f	4342 e	46,949 e	10,602 d	1.32 e	1.36 e
Özgen + Bartigra	1269.4 g	637.5 cd	22,622 h	24,908 d	5709.7 g	5885 c	47,529 e	11,595 c	1.43 d	1.72 b
Özgen + Trinova	1320.0 g	637.7 cd	25,390 g	21,410 f	5882.7 g	5019 d	46,800 e	10,902 d	1.35 e	1.75 b
IFVN 567 + Efe 82	1969.6 b	384.7 h	40,195 b	15,372 j	8794.3 b	3900 ffg	55,567 c	12,694 b	1.60 b	1.71 b
IFVN 567 + Bartigra	1814.6 c	596.8 de	37,911 c	21,464 f	8162.7 c	5115 d	59,375 a	13,278 a	1.66 a	1.96 a
IFVN 567 + Trinova	1918.1 b	560.6 ef	39,771 b	19,925 gh	8757.7 b	4516 e	59,696 a	13,273 a	1.67 a	1.96 a
Karakaya + Efe 82	1614.5 e	351.3 h	35,184 d	17,542 ı	7750.3 d	3858 g	52,726 d	11,608 c	1.46 cd	1.46 d
Karakaya + Bartigra	1521.8 f	450.2 g	33,852 de	23,343 e	7533.7 de	4428 e	57,195 b	11,961 c	1.50 c	1.57 c
Karakaya + Trinova	1651.5 e	535.6 f	34,145 d	20,176 fg	7475.7 e	4224 ef	54,321 c	11,700 c	1.47 cd	1.77 b
Efe 82	-	643.4 cd	-	33,298 c	-	8256 b	-	-	1.00 f	1.00 f
Özgen	1748.6 d	-	32,499 e	-	7580.3 de	-	-	-	1.00 f	1.00 f
IFFN567	2237.1 a	-	43,526 a	-	9256.0 a	-	-	-	1.00 f	1.00 f
Karakaya	1934.9 b	-	38,072 c	-	8728.3 b	-	-	-	1.00 f	1.00 f
Bartigra	-	871.8 b	-	42,486 a	-	9403 a	-	-	1.00 f	1.00 f
Trinova	-	972.7 a	-	39,674 b	-	9090 a	-	-	1.00 f	1.00 f
Average	1694.3	585.9	342,854	24,857	7657.6	5670	53,351	1195.7	1.30	1.42
L.S.D. (%5)	62.33	435.0	1544.07	1421.77	235.91	357.20	1540.31	500.80	0.045	0.064
±SE	28.9	14.8	526.4	484.8	80.4	121.8	513.8	167.0	0.018	0.018

Values are means (±SE) of replicates. Different letters within each column indicate significant differences among treatments (p < 0.05). DM-LER: Dry Matter Land Equivalent Ratio, Protein-LER: Protein Land Equivalent Ratio.

shows that the ADF of narbon vetch in mix cropping is mostly higher on equal to its monoculture while that of annual ryegrass in mixed cropping is mostly lower than its monoculture.

3.3. Crude Protein Yield, Forage Yield, Total Forage Yields, and Land Equivalent Ratios

Crude protein yield, forage yield, total forage yields, and Land Equivalent Ratios of different narbon vetch and ryegrass combinations cultivated as sole crops and mixtures under organic farming conditions are given in Table 3.

3.3.1. Crude Protein Yield (kg da⁻¹)

Crude protein yield is a critical indicator for assessing the nutritional value and total protein contribution of forage crops. In the present study, significant variations were observed among treatments in terms of crude protein yield. The mean crude protein yield was 169.43 kg da⁻¹ for narbon vetch and 58.59 kg da⁻¹ for ryegrass.

Among the pure stands, IFFN 567 exhibited the highest crude protein yield (223.71 kg da⁻¹), followed by Karakaya (193.49 kg da⁻¹) and Özgen (174.86 kg da⁻¹). For the ryegrass component, the highest protein yield was obtained from Trinova (97.27 kg da⁻¹), closely followed by Bartigra (87.18 kg da⁻¹), while Efe 82 showed a comparatively lower value (64.34 kg da⁻¹).

In mixed cropping treatments, the combinations involving IFVN 567 stood out with consistently high crude protein yields. Notably, IFVN 567 + Efe 82 and IFVN 567 + Trinova yielded 196.96 kg da⁻¹ and 191.81 kg da⁻¹ of crude protein from the narbon vetch component, respectively. These mixtures also contributed substantially from the ryegrass side, particularly in the IFVN 567 + Trinova combination (56.06 kg da⁻¹).

Conversely, the lowest crude protein yields were recorded in mixtures involving Özgen, particularly Özgen + Efe 82 (133.11 kg da⁻¹, narbon vetch; 38.92 kg da⁻¹, ryegrass) and Karakaya + Efe 82 (161.45 kg da⁻¹, narbon vetch; 35.13 kg da⁻¹, ryegrass).

These results demonstrate that IFVN 567 is a highly promising narbon vetch genotype for enhancing crude protein yield, especially when combined with productive ryegrass cultivars such as Trinova. The superior performance of these mixtures suggests their potential suitability for forage systems aiming to optimize both yield and feed quality under organic management conditions.

3.3.2. Green Grass Yield (kg ha⁻¹)

The green herbage yield varied significantly among treatments. The average green herbage yield was 34,285.4 kg ha⁻¹ for narbon vetch and 24,857 kg ha⁻¹ for ryegrass. Among the pure stands, the highest green herbage yield was recorded in IFFN 567 (43,526 kg ha⁻¹) for narbon vetch and Bartigra (42,486 kg ha⁻¹) for ryegrass. These values clearly show the strong forage potential of both the IFFN 567 and Bartigra genotypes.

In the mixtures, IFVN 567 + Efe 82 (40,195 kg ha⁻¹) and IFVN 567 + Trinova (39,771 kg ha⁻¹) also provided remarkably high green herbage yields, comparable to or even exceeding some pure stands. On the other hand, the lowest green herbage yields were observed in Özgen + Bartigra (22,622 kg ha⁻¹) and Özgen + Efe 82 (28,258 kg ha⁻¹) combinations.

These results indicate that the IFVN 567 genotype, either alone or in mixtures, exhibits superior green herbage yield, while Özgen-based combinations are relatively less productive. In terms of ryegrass, Bartigra showed outstanding performance, followed by Trinova.

3.3.3. Hay Yield (kg ha⁻¹)

Dry matter (hay) yield is a crucial parameter in evaluating the overall productivity of forage crops, as it directly reflects the amount of usable feed harvested per unit area.

In narbon vetch, hay yield ranged from 5709.7 kg ha⁻¹ to 9256.0 kg ha⁻¹, with the highest value recorded in the IFFN 567 monoculture (9256.0 kg ha⁻¹), followed by IFVN 567 + Efe 82 (8794.3 kg ha⁻¹) and IFVN 567 + Trinova (8757.7 kg ha⁻¹). These results highlight the superior productivity of the IFVN 567 genotype, both alone and in mixtures. In contrast, the lowest hay yields were observed in Özgen + Bartigra (5709.7 kg ha⁻¹) and Özgen + Trinova (5882.7 kg ha⁻¹) combinations, suggesting that the Özgen genotype may contribute less to biomass accumulation under the studied conditions.

In Ryegrass, hay yield values ranged from 3858 kg ha⁻¹ to 9403 kg ha⁻¹, with the highest yield obtained from the Bartigra monoculture (9403 kg ha⁻¹), followed by Trinova (9090 kg ha⁻¹) and Efe 82 (8256 kg ha⁻¹). Among the mixtures, the most productive combinations were IFVN 567 + Bartigra (5115 kg ha⁻¹) and IFVN 567 + Trinova (4516 kg ha⁻¹). These findings indicate that Bartigra and Trinova cultivars exhibit high forage production potential, while mixtures involving Özgen generally resulted in lower ryegrass hay yields.

These findings suggest that IFVN 567 is highly productive in terms of hay yield, and its combinations, particularly with Trinova and Efe 82, are promising. Bartigra and Trinova also appear to be productive ryegrass varieties when hay yield is considered. In contrast, Özgen performed relatively poorly across most combinations.

3.3.4. Total Green and Hay Yield

Mixtures significantly outperformed monocultures in terms of total green and hay yields. The highest green yield was achieved by IFVN 567 + Trinova (59,696 kg ha⁻¹), followed closely by IFVN 567 + Bartigra (59,375 kg ha⁻¹), indicating the strong biomass production potential of these combinations. Similarly, the highest hay yield was observed in the same treatments (13,273 and 13,278 kg ha⁻¹, respectively). Monocultures lagged behind, especially for green yield, indicating the advantage of species complementarity in mixed cropping.

3.3.5. Land Equivalent Ratios (LERs)

The Dry Matter Land Equivalent Ratio (DM-LER) and Protein Land Equivalent Ratio (Protein-LER) values further confirmed the superiority of mixed cropping systems. The highest DM-LER (1.67) and Protein-LER (1.96) values were observed in the IFVN 567 + Trinova mixture, demonstrating a clear advantage in land use efficiency and protein productivity over sole cropping. All mixtures had DM-LER and Protein-LER values greater than 1.0, indicating synergistic interactions and resource-use complementarity. In contrast, all monocultures had LER values equal to 1.0, as expected.

The results indicate that mixing narbon vetch with selected ryegrass cultivars under organic conditions enhances both forage yield and nutritional quality. Among the combinations tested, IFVN 567 + Trinova and IFVN 567 + Bartigra stood out with their superior performance in yield and land-use efficiency. These findings support the use of strategic species and genotype combinations to optimize organic forage systems, especially when aiming to balance biomass production with high nutritional value.

3.4. Weed Species Composition and Densities

Twenty-five different weed species from 12 different families were identified from the trial area. The highest number of weed species was eight species from the Poaceae family, four species from the Aseraceae family, three species from the Brassicaceae family, two species from the Amaranthaceae family, and one species each from the Caryophyllaceae, Convolvulaceae, Cyperaceae, Lamiceae, Malvaceae, Solanaceae, and Plantaginaceae families. The total number of perennial weeds was 56.5, annual weeds 59.9, narrow-leaved weeds 54.8, and broad-leaved weeds 61.6.

Weed species and their mean densities (plants m⁻²) were observed in different narbon vetch and ryegrass cropping systems under organic farming conditions. The results presented in

Table 4. Effects of different cropping systems on the weed flora composition and densities (number of plants per plot) under organic management conditions.

Treatments	AMARE	ATXPA	AVEFA	BROIN	CAPBU	CONAR	CYNDA	CYPRO	FUMOF	HORMU	LACSE	LAMAP	LOLTE	MALNE	MATCH	PHRCO	POROL	PAPRH	SETVI	SİNAR	STEME	SONOL	SOLNİ	SORHA	VERHE
Özgen + Bartigra	-	-	-	-	0,75	-	-	-	-	-	-	-	1.00	-	-	-	0,25	-	-	-	0,75	-	-	-	2.00
IFVN 567 + Bartigra	-	-	0.31	-	-	0.50	-	-	-	-	-	0.50	0.75	0.25	0.25	-	-	-	-	0.50	-	-	0.70	-	0.80
Karakaya + Bartigra	-	-	1.00	-	0.50	-	0.44	-	0.44	-	-	0.31	-	-	-	0.85	-	-	-	-	-	-	1.06	0.50	-
IFVN 567 + Efe 82	-	-	-	1.19	-	-	0.50	-	-	-	0.31	-	-	-	-	-	0.94	-	1.00	-	0.70	0.50	-	-	-
Özgen + Efe 82	-	-	0.25	-	0.33	1.00	-	-	-	-	0.13	-	1.31	-	0.19	-	0.50	-	0.63	-	0.83	-	-	-	-
Karakaya + Trinova	0.50	1.50	-	-	-	0.50	1.00	-	0.33	-	-	0.50	-	-	0.31	-	-	1.00	-	-	-	-	-	-	0.50
Karakaya + Efe 82	-	1.00	-	-	0.25	-	-	-	-	-	0.19	-	3.00	0.31	-	-	-	0.50	-	-	-	-	0.83	-	0.50
Bartigra	-	-	-	-	-	-	1.00	0.69	-	-	0.25	-	-	-	-	-	2.00	0.50	0.81	-	1.06	-	-	-	1.00
Trinova	-	0.50	-	-	-	2.50	-	-	-	-	-	0.69	1.56	-	-	-	0.94	-	-	0.55	1.44	0.19	-	-	-
Özgen + Trinova	-	-	0.33	0.45	1.44	2.50	-	-	-	0.30	-	-	1.50	-	0.64	-	-	-	-	-	0.50	0.31	-	0.69	-
Efe 82	0.50	-	-	-	0.81	1.00	-	0.44	-	1.50	-	1.50	-	-	-	-	-	1.00	-	0.19	1.50	-	1.50	-	-
IFVN 567 + Trinova	-	0.50	-	-	-	2.00	-	-	-	-	-	-	3.00	0.19	0.31	-	-	-	0.20	-	-	1.00	-	-	3.00
Özgen	0.50	1.00	-	-	-	0.50	1.56	-	0.25	0.61	-	1.03	2.10	-	0.19	0.43	-	-	-	0.86	-	-	1.44	0.50	0.81
Karakaya	0.33	2.00	-	-	-	1.00	-	-	-	-	-	1.90	3.50	-	-	-	-	-	1.68	-	-	0.50	0.50	1.00	1.00
IFVN 567	0.50	-	-	-	-	1.00	-	0.50	-	-	-	-	9.00	-	-	0.28	-	1.50	0.50	-	-	-	-	1.00	-

AMARE: Amaranthus retroflexus, ATXPA: Atriplex patula, AVEFA: Avena fatua, BROIN: Bromus inermiş, CAPBU: Capella bura-patoris, CONAR: Convolvulus arvensis, CYNDA: Cynodondactylon, CYPRO: Cyperus roduntus, FUMOF: Fumaria officinalis, HORMU: Hordeum murinum, LACSE: Lactucaseriola, LAMAP: Lamiumamplexicaule, LOLTE: Lolium temulentum, MALNE: Malva neglecta, MATCH: Matricaria chamomilla, PHRCO: Phragmitescomminis, POROL: Portulaca olerecea, PAPRH: Raphanis raphanistrum, SİNAR: Sinapis arvenisis, SETVI: Seteria viridis, STEME: Stelaria media, SONOL: Sonchus oleraceus, SOLNİ: Solanum nigrum, SORHA: Sorghum halapense, VERHE: Verinica hederifoliara.

demonstrate considerable variation in the occurrence and density of weed species among the different cropping systems. A total of 25 weed species were identified across all treatments, with the highest diversity observed in sole cropping systems, particularly in IFVN 567, Karakaya, and Özgen, which exhibited broader weed spectrums and higher densities.

The average weed density varied considerably among the treatments, indicating a differential weed suppression capacity of the forage mixtures and pure stands. The lowest average weed densities were recorded in Karakaya + Trinova (0.58 plants/m²) and Özgen + Efe 82 (0.62 plants/m²), followed closely by IFVN 567 + Bartigra (0.63). These results suggest that these specific combinations were more effective in suppressing weed growth, possibly due to better canopy closure, faster establishment, or competitive interactions.

In contrast, the highest average weed densities were observed in the IFVN 567 pure stand (1.97 plants/m²), followed by Karakaya (1.30) and IFVN 567 + Trinova (1.19). The relatively high weed presence in these treatments may indicate lower competitiveness or less effective weed suppression under the given environmental conditions.

Overall, the data suggest that forage mixtures involving Bartigra and Efe 82 generally showed better weed suppression, whereas some pure stands, particularly of IFVN 567, were less effective in controlling weed infestation. These findings emphasize the importance of species selection and mixture design in integrated weed management strategies within organic forage production systems.

Among the species, Lolium temulentum (LOLTE), Lamium amplexicaule (LAMAP), Raphanus raphanistrum (PAPRH), and Veronica hederifolia (VERHE) were frequently detected in various systems, suggesting their competitive ability and adaptability under organic conditions. Notably, Lolium temulentum reached the highest density (9.00 plants/plot) in the IFVN 567 monoculture, indicating that pure stands may be more prone to specific weed invasions.

Mixed cropping systems generally exhibited lower weed incidences compared to pure stands. For instance, combinations such as Özgen + Bartigra, Karakaya + Bartigra, and Özgen + Efe 82 showed limited weed presence, with most species either absent or present at very low densities (≤1.00 plant/plot). This supports the notion that interspecific competition between forage crops can enhance weed suppression, likely due to improved ground cover and resource utilization.

Interestingly, Trinova and its combinations were associated with relatively high infestations of Convolvulus arvensis (CONAR) and Sinapis arvensis (SINAR), suggesting a possible varietal effect or compatibility issue influencing weed dynamics.

The highest number of weeds was determined in IFVN 567 bigvetch (14.28 weed m²) variety plots sown alone. The lowest number of weeds was determined in the plots where Özgen big vetch variety + Batigagrass (3.75 weed m²) were sown together. Perennial weeds were found to occur in IFVN 567 bigvetch (11.78 weed m²) plots. The lowest number of perennial weeds was determined in IFVN 567 + Efe 82 (0.50 weed m²) planting system. The highest number of annual weeds was determined in the plots sown with Efe 82 (8.50 weed m²) grass variety. The lowest number of annual weeds was determined in IFVN 567 bigvetch variety with 2.50 weed m². The highest number of narrow-leaved weeds was determined in IFVN 567 (11.3 weed m²) and the lowest number of narrow-leaved weeds was determined in Özgen + Bartiga (1.0 weed m²) and Karakya + Trinova (1.0 weed m²) planting systems. The highest number of broad leaf weeds was determined in Efe 82 Narbonne Bean variety (8.0 weed m²), while the lowest number of broad leaf weeds was determined in Özgen + Bartiga planting system (1.8 weed m²).

Overall, the findings indicate that cropping system choice significantly affects weed flora, and that mixed cropping—especially with compatible cultivars—can be an effective ecological weed management strategy under organic conditions.

3.5. Weed Biomass Response to Different Planting Systems

Figure 4 shows the impact of different planting systems on weed green weight (g/m²) and dry weight (g/m²). The highest weed green weight was recorded in the Karakaya sole cropping system (181.66 g/m²), which was statistically similar to IFVN 567 + Trinova (180.00 g/m²) and IFVN 567 (150.83 g/m²). These results suggest that pure stands or less competitive mixtures may allow more weed growth, likely due to increased light and space availability for weeds.

In contrast, the lowest weed green weights were observed in the Özgen + Bartigra (58.33 g/m²) and Karakaya + Bartigra (60.33 g/m²) mixtures, highlighting the potential of specific crop combinations in suppressing weed growth effectively. These combinations may provide better ground cover or more aggressive early growth, thereby limiting weed establishment.

Similarly, weed dry weight followed a comparable pattern, with the Karakaya pure stand (58.50 g/m²) and IFVN 567 + Trinova (51.16 g/m²) resulting in significantly higher dry biomass, while the Özgen + Bartigra (16.00 g/m²) and Karakaya + Bartigra (17.66 g/m²) mixtures were among the lowest. These findings reinforce the importance of cultivar selection and complementary interactions in mixed cropping systems for ecological weed management.

Overall, the data suggest that specific legume–grass mixtures, particularly those including Bartigra, are more effective in suppressing weed biomass, supporting their role in sustainable weed management strategies under organic or low-input systems.

Conversely, the lowest weed biomass values were associated with mixed cropping systems, especially Özgen + Bartigra, Karakaya + Bartigra, and IFVN 567 + Efe 82, which demonstrated enhanced weed suppression. These combinations likely benefit from complementary growth patterns and canopy structures that reduce available resources for weeds.

The stacked bar chart highlights the overall advantage of specific vetch–ryegrass mixtures in reducing both green and dry weed biomass. The visual trend supports the quantitative data, indicating that optimized cultivar combinations can serve as an effective strategy for ecological weed control under organic farming systems.

4. Discussion

4.1. Morphological Features

Narbon vetch and Italian ryegrass exhibited distinct size and architectural traits, with notable differences between pure and mixed stands. Narbon vetch is generally a relatively short, erect annual legume; for example, previous reports indicate it reaches roughly 30–60 cm in height. In contrast, Italian ryegrass can grow much taller cultivated varieties often exceeding 1 m (up to ~127 cm) under favorable conditions. In our trial, pure vetch stands were significantly shorter than ryegrass. However, in mixed cropping, the vetch tended to attain greater heights and produce more branches than in sole stands (Table 1). This trend is consistent with [14], who found that barley narbon vetch intercrops resulted in taller and more tillering plants of both species than their monocultures. The enhanced stature of vetch in mixtures likely reflects complementary resource use (e.g., better light interception and nitrogen availability) when grown with grass; legumes can exploit deeper soil N and fix atmospheric N, benefitting both partners. By contrast, ryegrass height did not increase in mixtures and in some cases was slightly reduced compared to its pure stand. This matches observations by [15], who noted that Italian ryegrass had comparatively low competitive ability in grass–legume mixtures (yield was lower than in monoculture). In sum, the mixed stands induced a shift in growth allocation: vetch plants became relatively taller and more branched, while ryegrass invested comparatively less in height.

Stem and leaf traits also varied among treatments. Narbon vetch stem thickness in sole crops was on the order of 3–5 mm, and its leaflet size typically 2–5 cm long by 2–3 cm wide. In our data, mixed cropping had only modest effects on these dimensions; for example, vetch stems were marginally thicker in some mixtures, possibly reflecting vigorous growth under improved N status. Ryegrass leaf blades are characteristically long and narrow (often on the order of 10–20 cm long and ~0.5–1.0 cm wide), and we observed similar leaf dimensions across treatments. The measured leaf lengths and widths fell within these expected ranges: ryegrass leaves remained slender (around 0.7–0.9 cm wide) while vetch leaves remained broader (several centimeters). Interestingly, legume–grass mixtures are known to exhibit complementary foliage structures; legumes often develop broader leaves and deep roots while grasses maintain narrow, dense tillers. In our mixtures, the combined canopy likely exploited light more fully and may have shaded some lower leaves, but no extreme leaf size reductions were observed. Overall, leaf morphology was largely species-specific, with only slight adjustments between sole and mixed stands.

The number of lateral branches (vetch) and tillers (ryegrass) showed pronounced treatment differences. Narbon vetch typically has only a few main stems per plant; ref. [15] reported ~2–3 stems per plant in various genotypes. In pure vetch stands, branching was limited (often 1–2 lateral stems). In contrast, mixed stands induced more vetch branches: the average number of lateral shoots per plant increased by 20–30% in mixtures (Table 1). This suggests that, when growing alongside ryegrass, vetch plants allocated more effort to branching, likely as a response to the altered microenvironment (improved soil nitrogen and/or different light competition). Mixed cropping of legumes and grasses is known to enhance total biomass through such over yielding mechanisms. For ryegrass, tillering was generally profuse in all treatments; our data show dozens of tillers per plant (reflecting the grass’s high plasticity). Numerically, ryegrass plants in some mixed treatments produced more tillers than in their monocultures. This is in line with [16], who found that ryegrass mixed with common vetch produced higher biomass than ryegrass alone presumably because the added nitrogen from the legume stimulated grass growth and tiller initiation. However, when the legume share was very high, ryegrass tillering did not surpass that in sole grass (consistent with [15], who saw ryegrass yields dip when legumes dominated the intercrop). In summary, mixtures tended to increase vetch branching and could enhance ryegrass tillering, reflecting mutual facilitation up to a point.

The significant differences (ANOVA p < 0.05) among our treatments highlight how cultivar choice and cropping system interact. For example, the tallest plants and thickest stems were observed in specific cultivar combinations (Table 1), indicating genotype × environment effects. Our findings corroborate earlier work: Ref. [17] concluded that growing ryegrass with a legume booster (common vetch) markedly improved forage yield, and ref. [14] similarly documented higher growth and forage production in barley–vetch intercropping. Likewise, ref. [18] emphasize that grass–legume mixtures often achieve superior stand structure because each species’ unique morphology (deep taprooted legumes vs. fibrous, crown-forming grasses) allows more efficient use of water, light, and nutrients. Our mixed stands appear to exemplify this: the vetch’s taproot and branching habit paired well with the ryegrass’s high tillering and tiller density. The improved morphological performance (more tillers and branches, fuller canopy) in mixtures likely underlies the higher overall yield often seen in forage mixtures.

These results have practical implications for organic forage systems. In organic farming where synthetic N is absent, legume–grass mixtures can internally supply N and suppress weeds, boosting productivity and stand resilience. Ref. [19] recently demonstrated that ryegrass-dominant vetch–ryegrass mixtures gave the highest forage yields and excellent weed control under organic management. Our morphological observations support that outcome: the vigorous growth form (taller legumes, denser grass shoots) in effective mixtures would shade out weeds and capture more sunlight. The complementary plant architectures of vetch and ryegrass thus translate into agronomic benefits. In summary, mixed cropping in this trial produced plants with enhanced morphology relative to monocultures, a finding in keeping with both theory and prior experiments. In line with the literature, our data suggest that mixed legume–grass stands yield a more robust, branched canopy structure than pure stands, reinforcing the value of intercropping for sustainable organic forage production.

The morphological composition and forage performance of narbon vetch and Italian ryegrass, whether grown as monocultures or mixtures, displayed significant variation in leaf–stem ratio, botanical composition, and yield traits under organic management (Table 2).

4.2. Leaf–Stem Ratio and Structural Balance

The leaf-to-stem ratio is a critical indicator of forage quality, as leaves generally contain more crude protein and digestible nutrients than stems. In this study, ryegrass monocultures had higher leaf ratios compared to vetch monocultures, consistent with prior observations that ryegrass maintains a higher leaf proportion due to its fine and tender morphology [20]. For instance, cultivars like ‘Bartigra’ and ‘Trinova’ exhibited leaf ratios above 86%, whereas vetch cultivars remained around 57–64%. In mixtures, the leaf-to-stem ratio tended to decrease slightly, particularly in vetch components, which is consistent with results reported by [17], who noted structural shifts when legumes are mixed with aggressive grasses.

4.3. Botanical Composition in Mixed Stands

Botanical composition data revealed that ryegrass consistently dominated the mixtures, often contributing over 75–83% of the stand biomass, regardless of the vetch genotype. These findings align with [15], who emphasized ryegrass’s competitive growth and rapid tillering as key drivers of dominance in legume–grass intercropping systems. Vetch’s presence was higher in combinations involving cultivars with more vigorous growth, such as ‘Özgen’ or ‘Karakaya’, suggesting that legume cultivar selection can influence species balance. Such imbalances, although common, can be optimized through seed rate adjustments or spatial planting patterns [21].

4.4. Forage Yield Performance

Among the treatments, sole cropping of the high-yielding vetch genotype ‘IFFN 567’ and the ryegrass cultivars ‘Bartigra’ and ‘Trinova’ recorded the highest green forage and hay yields. Notably, ‘IFFN 567’ reached up to 4352.6 kg da⁻¹ green herbage and 925.6 kg da⁻¹ hay yield, indicating its potential as a biomass-rich legume even under low-input organic conditions. These results are comparable to those of [14], who reported similarly high productivity in barley–vetch intercropping under stress-limited systems. In mixed stands, combinations such as IFFN 567 + Trinova or + Bartigra approached the productivity of sole cropping, indicating positive interspecies interaction.

4.5. Crude Protein Yield and Quality Implications

Crude protein (CP) yield is a major determinant of forage nutritional value. Here, CP yield ranged from 223.71 kg da⁻¹ in pure IFFN 567 to as low as 38.92 kg da⁻¹ in the lowest-performing mixtures. Mixed stands generally produced intermediate CP yields, with best-performing combinations (IFFN 567 + Trinova and Özgen + Trinova) yielding over 130–190 kg da⁻¹. This increase reflects the classic nitrogen-fixing contribution of legumes, as reported in prior research by [22], where legume-based mixtures boosted CP concentration and total protein yield in grasslands.

4.6. Ecological and Practical Significance

The results highlight the ecological complementarity and productivity potential of vetch–ryegrass mixtures under organic management. While ryegrass dominated biomass, vetch contributed nitrogen and improved protein levels. According to [17], such complementary mixtures provide not only better-quality forage but also improved weed suppression and soil health essential outcomes for sustainable organic systems. Moreover, optimal combinations like IFFN 567 + Trinova yielded high biomass and CP without synthetic inputs, making them suitable for low-input forage systems.

In summary, while pure vetch stands excelled in protein yield, and pure ryegrass excelled in dry matter yield, their combinations balanced yield and quality. The results confirm the strategic value of choosing compatible cultivars in mixed cropping systems, and support the broader literature on legume–grass intercropping benefits in organic forage production.

The evaluation of crude protein content, fiber fractions (ADF and NDF), forage yields, and land equivalent ratios (LERs) for dry matter and protein highlights the agronomic and nutritional advantages of narbon vetch and ryegrass mixtures over sole cropping systems (Table 3).

4.7. Crude Protein Content

Protein content is a crucial quality indicator for forage crops. In the current study, narbon vetch monocultures showed significantly higher crude protein ratios compared to ryegrass monocultures, consistent with the known nitrogen-fixing capacity of legumes [21]. The highest crude protein content was found in ‘IFFN 567’ (24.17%), followed by ‘Özgen’ (23.07%) and ‘Karakaya’ (22.17%). In mixed cropping systems, combinations such as IFFN 567 + Trinova (21.90% + 12.43%) and Özgen + Trinova (22.43% + 12.70%) provided balanced protein content from both species. Similar trends were also reported by [22], who observed enhanced protein content in vetch–grass mixtures compared to pure stands.

4.8. Fiber Fractions (ADF and NDF)

Fiber content, especially acid detergent fiber (ADF) and neutral detergent fiber (NDF), directly affects digestibility. Ryegrass had higher ADF and NDF values than vetch, in line with findings by [20,23], confirming that grasses typically have more structural carbohydrates. However, the inclusion of vetch in mixtures effectively reduced the overall fiber concentrations. For example, the mixture of IFFN 567 + Trinova exhibited moderate ADF (27.97% + 28.40%) and NDF (31.30% + 44.17%) values, suggesting improved digestibility compared to pure ryegrass.

4.9. Forage Yield

Green and hay forage yields were significantly higher in mixed stands compared to sole crops. The highest total green herbage yield (5969.6 kg da⁻¹) and hay yield (1327.8 kg da⁻¹) were obtained from IFFN 567 + Trinova, closely followed by IFFN 567 + Bartigra. These results demonstrate a clear yield advantage of well-matched vetch and ryegrass genotypes under organic conditions. Previous studies [14,21] have reported similar synergistic effects in legume–grass intercropping systems, particularly when species complementarity in growth dynamics is exploited.

4.10. Land Equivalent Ratio (LER) for Dry Matter and Protein

LER values greater than 1.0 indicate yield advantages in intercropping over monocropping. In this study, all vetch–ryegrass mixtures showed DM-LER and Protein-LER values significantly above 1.0, with the highest values (1.67 and 1.96, respectively) recorded in IFFN 567 + Trinova. This suggests improved land-use efficiency and greater protein productivity per unit area. These findings support the conclusions of [22,23], emphasizing the potential of intercropping to maximize biomass and protein yield in sustainable systems. Moreover, the mixtures with Trinova consistently produced high protein LERs, indicating the strong contribution of this ryegrass genotype to both biomass and quality in combinations.

4.11. Ecological and Practical Implications

From a sustainability perspective, legume–grass mixtures offer better soil health, reduced reliance on external nitrogen inputs, and improved forage quality [18]. The organic system evaluated in this study benefitted from the nitrogen-fixing ability of vetch, the competitive growth of ryegrass, and their synergistic interaction. Particularly, IFFN 567 combined with Bartigra or Trinova stands out as an ideal forage solution under organic systems, balancing yield and quality while enhancing land use efficiency.

4.12. Weed Suppression

Weed suppression ability is a critical criterion in evaluating cropping systems under organic management due to the absence of herbicide inputs. The results from Table 4 indicate that weed species composition and densities varied considerably across different cropping combinations.

Overall, intercropping treatments exhibited a reduction in weed numbers compared to sole cropping, likely due to greater canopy coverage, improved soil shading, and niche occupation by both legume and grass components. This aligns with findings from [24], who emphasized the role of interspecific competition in natural weed suppression.

Among the mixtures, ‘IFVN 567 + Bartigra’ and ‘Karakaya + Bartigra’ demonstrated the lowest weed presence overall, with limited occurrences of dominant species such as Avena fatua, Convolvulus arvensis, and Lamium amplexicaule. These results suggest a strong suppressive effect of this particular genotype combination.

On the contrary, some sole crops such as ‘IFVN 567’ and ‘Karakaya’ exhibited relatively higher weed infestations, notably with Lolium temulentum, Lamium amplexicaule, and Veronica hederifolia, which are common in organic forage systems. For instance, Lamium amplexicaule density reached up to 9.00 plants m⁻² in IFVN 567 monoculture, indicating the vulnerability of sole legume plots to winter annual weed species.

Notably, mixtures containing Trinova ryegrass (e.g., ‘Özgen + Trinova’, ‘IFVN 567 + Trinova’) were moderately successful in reducing weed presence, although in some cases Convolvulus arvensis and Matricaria chamomilla persisted. This suggests that, while ryegrass contributes to weed suppression, its effectiveness depends on the companion vetch genotype and the spatial growth compatibility.

These results underline that crop mixture composition strongly influences weed suppression, with certain vetch–ryegrass combinations showing a more synergistic interaction in minimizing weed biomass. These findings corroborate studies [25] who reported that optimal species selection in intercrops enhances weed competitiveness without sacrificing forage quality or yield.

The results from Figure 4 demonstrate that weed green and dry biomass significantly varied among planting systems under organic management. The lowest weed biomass was recorded in ‘Özgen + Bartigra’ (green: 58.33 g m⁻²; dry: 16.00 g m⁻²), indicating strong weed suppression potential of this mixture, likely due to better canopy closure and faster establishment. Similarly, ‘Karakaya + Bartigra’ and ‘IFVN 567 + Efe 82’ also suppressed weed biomass effectively.

In contrast, monoculture plots, particularly ‘Karakaya’ (green: 181.66 g m⁻²; dry: 58.50 g m⁻²) and ‘IFVN 567 + Trinova’, exhibited the highest weed biomass, suggesting weaker competition against weed emergence, potentially due to more open canopy structures or slower early development of the dominant crop component.

The general trend indicates that mixtures involving Bartigra ryegrass, especially when combined with Özgen or Karakaya vetch genotypes, were more successful in reducing weed biomass than mixtures with Trinova. These findings align with previous research [25] that emphasizes the importance of crop density, growth habit, and canopy architecture in achieving natural weed suppression through intercropping.

5. Conclusions

The results of this study highlight the agronomic advantages of intercropping narbon vetch and Italian ryegrass under organic management. While certain monocultures excelled in specific parameters, mixed cropping systems particularly IFVN 567 + Trinova and IFVN 567 + Bartigra demonstrated superior performance in forage yield, crude protein content, land use efficiency (LER), and weed suppression. These benefits are attributed to the complementary growth habits of the two species, which allow for more effective utilization of environmental resources and improved ground coverage. This study emphasizes the importance of genotype selection in designing productive and ecologically resilient forage systems. Under organic or low-input conditions, integrating competitive grass cultivars with high-quality legume genotypes offers a sustainable approach to optimizing both yield and ecological weed control. Further multi-year experiments are needed to confirm the repeatability and consistency of these findings under varying environmental conditions.