Sustainable Management of Vineyards with Intercropping Systems of Cereals with Pea Under Mediterranean Conditions

Abstract

Viticulture is a notable economic activity in the Mediterranean basin, and the inter-row area is managed through tillage, which has several disadvantages and can lead to soil erosion. Also, there has been an increased trend in utilizing cover crops in vineyards, as they provide several ecosystem services. The objective of our experiment was to study the growth and yield of monocrops of triticale, barley and pea, and their intercrops when they were grown in a Mediterranean vineyard. The results show that pea–triticale and pea–barley intercropping systems exhibited higher or earlier peaks in leaf area index (up to 180%) than monocultures, indicating complementary canopy structures that improved light interception. Intercrops consistently produced higher biomass, with triticale–pea yielding up to 11.63 t ha⁻¹, though grain yield was more variable and sensitive to environmental stresses during reproductive stages. The indices that were determined showed the significant advantage of the intercrops compared to the monocrops. Also, intercrops showed higher environmental resource use efficiency, as measured with Radiation Use Efficiency (RUE) and Water Use Efficiency (WUE), compared to the monocrops. The present study demonstrates that cereal–legume intercropping in vineyards can increase biomass, grain production, and environmental resource use efficiency and can be used for sustainable intensification in Mediterranean cropping systems.

1. Introduction

Cover crops are used in vineyards as a sustainable viticultural practice that provides multiple agronomic and environmental benefits; however, their adoption remains limited, particularly in Mediterranean viticulture [1,2]. Common cover crops used in vineyards include legumes (e.g., faba bean, pea, clover) and cereals (e.g., ryegrass, oats), which are sown between vine rows or beneath the vine canopy and can improve soil properties and soil health, enhance nutrient cycling, reduce soil erosion, and regulate vine vigor [1,3]. Also, legumes can increase soil nitrogen content through N₂ fixation, while cereals can improve soil structure by increasing aeration and soil organic carbon [4,5,6].

Intercropping systems with cereals and legumes can be effectively used as cover crops in viticulture, as they provide important ecosystem services and make efficient use of natural nutrient cycling. Also, intercropping systems increase the biodiversity of agroecosystems, support beneficial soil microbial activity, and increase the population of beneficial organisms, increase water retention, reduce soil erosion, reduce excessive vine vigor, and can decrease the incidence of fungal diseases and improve grape quality without negatively impacting yield [3,7,8,9,10,11,12]. Therefore, these systems minimize the necessity for chemical inputs—especially fertilizers—reduce the soil disturbance caused by tillage, and also improve the sustainability and the resilience of vineyards [2,11].

In an intercropping system, there are several species that are used, such as cereals and legumes. Several species were used in this experiment, such as barley (Hordeum vulgare), triticale (×Triticosecale), and field pea (Pisum sativum), as they have significant agronomic and environmental advantages [1,13,14,15,16,17]. Barley is a resilient cool-season, fast-growing winter crop that suppresses weeds and has a deep root system that helps to stabilize soil structure, making it ideal for vineyards in Mediterranean climates [9,18,19,20]. Triticale is another winter cereal with high biomass production which cools the soil, maintains soil moisture, suppresses summer weeds, and provides a habitat for natural enemies [16,21,22,23,24]. Also, field pea is a fast-growing winter legume that can increase soil N₂ level [4,25].

Intercropping cereals with legumes has received increasing attention in recent years due to its numerous advantages, such as increased enhanced biodiversity, improved environmental resource use efficiency, and greater agroecosystem stability and resilience [16,17,26]. However, its adoption in agroforestry systems, and especially in vineyards, remains low because the productivity of this system depends on the management practices, the selection of plant species and cultivars, and also on the environmental conditions [15]. While cover crop growth can be influenced by competition with grapevines for nutrients, water, and light, this effect is limited for winter cover crops, as grapevines are dormant during the cover crop growth period [2,3]. Additionally, the inclusion of legumes such as peas enhances soil nitrogen content, which can further support the biomass production and growth of the cereal component [27].

The use of intercropping systems is quite complex because of the differing requirements of the component species, and this complexity is further increased when intercropping is applied in vineyards, as observed in agroforestry systems such as olive orchards [17,28,29]. The interactions among species in intercropping systems can be described by the “four Cs” principle, which includes competition, complementarity, cooperation, and compensation [28,29]. Among these, competition for environmental resources is the most prevalent interaction [28,29]. Reducing competition and optimizing complementarity in resource use is essential to increase yield in intercropping systems and, consequently, to enhance the productivity and sustainability of vineyard intercropping systems [17,26,28,29].

In vineyard agroforestry systems, the primary interaction among species is competition; however, empirical data on vine–cover crop interactions remain limited [30,31,32,33]. Various indices have been developed and applied in intercropping studies to quantify species interactions and system productivity [34,35,36,37,38,39,40,41,42,43,44]. Although these indices have been widely applied in annual crop systems, their use in vineyards remains limited, and they have not been employed to evaluate annual crop mixtures sown in vineyard alleys or inter-rows. Given the more complex environmental conditions and species interactions in vineyards, further research is needed to adapt and apply these indices in such systems [41,42,43,44].

The objectives of this study were to evaluate the growth, biomass production, and seed and yield components of barley, triticale, field pea, and their intercrops over three growing seasons in a vineyard. Additionally, this study aimed to assess environmental resource use efficiency and characterize the interactions among species in the intercrop treatments.

2. Materials and Methods

2.1. Setup of the Experiments

The experiments were conducted in Northern Greece at the Farm of the Aristotle University of Thessaloniki during three consecutive years (2020–2021, 2021–2022, and 2022–2023). The vines were 10 years old, the distance between the plants at the same row was 1 m, and the distance of each row was 2.5 m. The plant species that were used as cover crops were triticale (cv. Alkmini), barley (cv. Fatima), field pea (cv. Dodoni), and also barley–pea and triticale–pea intercrops (Figure 1). The seed sowing was carried out at the end of November for the three years using a commercial BEKAM-type sowing machine (working width 2.5 m), adapted for the length of the rows of the vines, with a seeding ratio of 200 kg ha⁻¹ and, for the intercrops, a ratio of 25:75 cereal:pea. The soil where the experiments was conducted was clay with 27 g kg⁻¹ organic matter, 7.7 pH (1:1 H₂O), 0.623 EC (dS m⁻¹), 23.5 kg ha⁻¹ N-NO₃, 23 kg ha⁻¹ P (Olsen), 740 kg ha⁻¹ exchangeable K, 259 kg ha⁻¹ Mg, and 4.68 kg ha⁻¹ Fe (DTPA). The main weather data are given in Figure 2, which include the average monthly temperature and the monthly precipitation for the three growing seasons.

During the growing period, the following characteristics were determined: leaf area index (LAI), chlorophyll content (SPAD), and plant height. These characteristics were measured at stem elongation (BBCH 30), at the beginning of flowering (BBCH 61), and at grain filling (BBCH 73), while the seed yield, yield components (the number of tillers/m², the number of spikes and pods/plant), and aboveground biomass were measured at harvest.

2.2. Leaf Area Index (LAI)

Leaf area index is an important characteristic that is affected by genotype and environmental conditions, and it was measured using an ACCUPAR LP80 device (Meter, München, Germany) between 11:00 AM and 1:00 PM. Measurements were taken at 3 points within each experimental plot, covering a representative area above plants and the average value was used for statistical analysis.

2.3. Plant Height

Plant height was determined during the growth season by selecting 10 random plants from the center rows of each plot per block at the three growth stages, as described before, using a measuring tape.

2.4. Leaf Greenness Index (SPAD)

The determination of the total chlorophyll content or leaf greenness index (SPAD) was determined using a SPAD 502DL (Minolta Camera Co. Ltd., Osaka, Japan). Ten plants were used from each plot and each replication to measure the chlorophyll content. Recordings were taken on the youngest fully expanded leaves during vegetative growth both for cereals and pea, while during the reproductive phase, the flag leaf of the cereals was used.

2.5. Aboveground Biomass, Seed Yield, and Yield Components

In order to determine the total aboveground biomass, seed yield, and yield components, an area of 1 m² was harvested from the center of each plot across all four blocks on mid-June for the three growing seasons. The samples were air-dried for 10 days in greenhouse conditions until a constant weight was achieved. The plant species were separated, and the grains were obtained using LD 350 laboratory thresher (Wintersteiger AG, Ried im Innkreis, Austria) for extracting the seeds. Also, once the different plant species were separated, they were used to determine the yield components such as the number of spikes and pods per plant and the number of seeds per spike and pod. The number of pods per plant for the field pea were determined after harvest at three plants per plot.

2.6. Environmental Resources Efficiency

In order to determine how the different cover crops contribute to environmental resource use efficiency, two parameters were determined for each experimental plot across all four replications. One was Water Use Efficiency (WUE), which was calculated by dividing the aboveground biomass and the grain yield by the total amount of rainfall (mm) [45,46]. The other parameter was Radiation Use Efficiency (RUE; g MJ⁻¹), which was determined by dividing the total aboveground biomass or the grain yield by the total cumulative radiation intercepted during the crop growth cycle according to Elhakeem et al. [47].

2.7. Intercrop and Competition Indices

We used several indices in order to determine the influence of using different cover crops in a vineyard and to study the interaction between the different species. More specifically, the indices were calculated for biomass and seed yield and are the Land Equivalent Ratio (LER), Actual Yield Loss (AYL), Relative Crowding Coefficient (K), Aggressivity (A), Land Equivalent Coefficient (LEC), System Productivity Index (SPI), and Percentage Yield Difference (PYD). Some of the indices were used for the first time to describe the different interactions of the cover crops in agroforestry systems, and more specifically when they are grown in a vineyard.

The Land Equivalent Ratio (LER) was determined according to the following equation:

LER = (Y_ci/Y_c) + (Y_pi/Y_p)

(1)

where Y_c is the cereal biomass or grain yield in monoculture, Y_ci is the cereal biomass or grain yield in intercrop, Y_p is the pea yield in monoculture, and Y_pi is the pea yield in intercrop. Also, partial LER for cereal (Y_ci/Y_c) and for pea (Y_pi/Y_p) were determined for each species. LER is an index that is widely used in intercropping systems, as when LER is above 1, intercrop outperforms the respective monoculture; in contrast, when LER is below 1, intercrop has a lower yield than monoculture. Also, partial LER can be used to examine the interaction of the species in a mixture [17,29,48].

In addition to LER, another commonly used index in intercropping systems is Actual Yield Loss (AYL). AYL quantifies the proportionate yield loss or gain of a species in an intercrop relative to its monocrop yield, while it also considers the sown density of each species [38]. AYL was calculated using the following formula [35,49]:

AYL_c = pLER_c × (100/Z_ci) − 1

(2)

AYL_p = pLER_p × (100/Z_pi) − 1

(3)

AYL = AYL_c + AYL_p

(4)

AYL_c represents the Actual Yield Loss of the cereal, while AYL_p represents the Actual Yield Loss of the pea. Z_ci and Z_pi denote the relative sowing proportions of cereal and pea in the mixtures, respectively. When AYL is greater than zero, the intercrop outperforms the monocrop, indicating a yield advantage. Conversely, if AYL is less than zero, the intercrop performs worse than the corresponding monocrop [49].

The Relative Crowding Coefficient (K) measures how much one species outcompetes another, and can be calculated with the equation [44]:

K_c = (Y_ci × Z_pi)/(Y_c − Y_ci) × Z_ci

(5)

K_p = (Y_pi × Z_ci)/(Y_p − Y_pi) × Z_pi

(6)

K = K_c × K_p

(7)

K_c represents the Relative Crowding Coefficient (RCC) for cereal, while K_p corresponds to pea. When K_c is greater than K_p, cereal is more competitive than pea; conversely, when K_p exceeds K_c, pea is the more competitive species [44]. Additionally, when K value is above 1, this indicates that there is a yield advantage and increased productivity in the intercrop, whereas a K value less than 1 implies the lower yield and reduced productivity of the intercropping system [38].

The Competitive Ratio (CR) quantifies the extent to which one species outcompetes another in an intercropping system. This index incorporates both the partial Land Equivalent Ratio (pLER) and the relative proportions of each species in the mixture. A CR value above 1 indicates that this species was more competitive than its component. For example, a value of 2 means that one crop is twice as competitive as the other crop. CR can be calculated using the following formula [39]:

CR_c = (pLER_c/pLER_p) × (Z_pi/Z_ci)

(8)

CR_p = (pLER_p/pLER_c) × (Z_ci/Z_pi)

(9)

CR_c and CR_p are the competitiveness of cereal and pea, respectively, while pLER_c and pLER_p are the partial Land Equivalent Ratios for cereal and pea, respectively, and, finally, Z_ci and Z_pi are seed ratios of cereal and pea in the mixture.

Aggressivity (A) is another index used to quantify the competitive interaction between two species cultivated together in an intercropping system [44]. This index indicates which crop is more dominant by comparing their relative performances in the mixture. A positive A value for a species means that it is the more aggressive and competitive component, whereas a negative value indicates that it is suppressed by its companion crop. Aggressivity can be calculated using the following formula [44]:

A_c = [Y_ci/(Y_c × Z_ci)] − [Y_pi/(Y_p × Z_pi)]

(10)

A_p = [Y_pi/(Y_p × Z_pi)] − [Y_ci/(Y_c × Z_ci)]

(11)

A_c and A_p stand for the Aggressivity values of cereal and pea, respectively, while Y_ci and Y_pi are the yields of cereal and pea when grown together in a mixture. Y_c and Y_p are the yield in monocropping. Also, Z_ci and Z_pi are the proportions of the cereal and pea seeds used in the intercropping mixture.

The Land Equivalent Coefficient (LEC) was used by Adetiloye et al. [41], and can be calculated with the following formula:

LEC = pLER_c × pLER_p

(12)

LEC provides more information on how the different crops compete or cooperate with each other in a mixture, and it is better than using the total Land Equivalent Ratio (LER) when measuring the yield balance and not just the yield advantage. If LEC drops below 0.25, it means that one crop is suppressed, and a value of 0.25 is important, as above that, the intercropping system has advantage in terms of yield balance after the interaction of one species to another.

The System Productivity Index (SPI) provides a clear means to measure the overall system productivity. It does this by turning the yield of the secondary crop (pea) into the same unit as the main crop: cereal. Basically, SPI compares how well an intercrop system performs by putting all the different yields on the same scale [42].

SPI can be calculated according to the following equation:

SPI = Y_ci + Y_c/Y_p × Y_pi

(13)

The Percentage Yield Difference (PYD) expresses the percentage difference in yield between mixtures and monoculture [45]. When PYD has a negative value, this indicates a greater intercropping advantage because PYD is inversely proportional to the yield advantage. PYD can be estimated according to the following equation [44]:

PYD = 100 − [((Y_c − Y_ci)/Y_c) + ((Y_p − Y_pi)/Y_p)] × 100

(14)

2.8. Statistical Analysis

All statistical assessments were conducted separately for each growing season and growth stage. The measurements for plant height, Leaf Greenness Index (SPAD), spike number per plant, and seed number per spike were examined separately for each species using analysis of variance (ANOVA) within a General Linear Model framework. The model specification integrated the fixed effects of “block” (four blocks) and “treatment” (each cereal grown as a monocrop and its corresponding intercrop), following a randomized complete block (RCBD) design [50,51]. Regarding the leaf area index (LAI), dry biomass, grain yield, Water Use Efficiency, and Radiation Use Efficiency, ANOVA models likewise incorporated the fixed effects of block and treatment, where treatments comprised the monocrops of the three species and the two intercrop combinations. The intercropping performance metrics that were used include the Land Equivalent Ratio (LER), Actual Yield Loss, Relative Crowding Coefficient, Competitive Ratio, Aggressivity, Land Equivalent Coefficient, System Productivity Index, and Percentage Yield Difference, which were also analyzed using ANOVA with an RCB design. The differences between the treatment means were assessed using the protected Least Significant Difference (LSD) test. Statistical significance was set at α = 0.05 (p ≤ 0.05). All analyses were performed using IBM SPSS Statistics v26.0. Assumptions of homoscedasticity, normality of residuals, and model additivity were confirmed for each dataset, and there were not any substantial violations.

3. Results

All datasets were prescreened, and they showed significant differences among the three growing seasons, and also the “growth stage” factor showed a very large effect size.

3.1. Leaf Area Index

According to the results for leaf area index (LAI) (

Table 1. Leaf area index measured during three consecutive growing seasons for five cropping systems evaluated at three growth stages in the vineyard.

Growing Season	Cropping System	Growth Stage
		Jointing	Full Bloom	Grain Filling
2021	Barley	0.54 c Ϯ	1.29 c	3.22 c
	Triticale	0.88 bc	2.21 b	3.89 b
	Pea	1.34 a	2.39 b	4.48 a
	Barley–Pea	1.24 ab	2.63 ab	4.11 ab
	Triticale–Pea	1.54 a	3.03 a	4.67 a
	SE	0.04	0.05	0.06
2022	Barley	1.07 a	3.00 bc	2.38 c
	Triticale	0.77 a	1.91 d	2.72 bc
	Pea	1.23 a	4.56 a	3.39 ab
	Barley–Pea	1.03 a	3.94 ab	3.82 a
	Triticale–Pea	0.92 a	2.89 c	3.33 abc
	SE	0.06	0.09	0.10
2023	Barley	1.22 ab	1.31 bc	1.42 a
	Triticale	0.65 b	1.12 c	0.98 a
	Pea	1.37 ab	3.29 a	1.75 a
	Barley–Pea	1.84 a	3.18 a	1.52 a
	Triticale–Pea	1.05 ab	2.95 ab	1.37 a
	SE	0.10	0.18	0.09

^Ϯ Within each year, means followed by different letters are significantly different according to the protected LSD test (α = 0.05). SE = standard error of the mean of cropping systems within each year and growth stage.

), during the 2021 growing season, the highest LAI values were observed in the triticale–pea intercrop across all growth stages, ranging from 1.54 at jointing to 4.67 at grain filling, with significant differences compared to the barley and triticale monocultures, which consistently exhibited the lowest values. In addition, the pea monoculture had a high LAI value (4.48) at the grain-filling stage. The barley–pea intercrop showed intermediate values, suggesting the beneficial effect of intercropping on canopy development. During the second growing season (2022), pea and triticale–pea showed the highest LAI values, especially at full bloom (2.39 for pea and 3.03 for triticale–pea) and grain filling (3.39 for pea and 3.33 for triticale–pea). Also, barley had the lowest LAI and the intercrops of barley, with pea obtaining a higher LAI compared to the monocrops of barley. A different trend was followed during the 2023 growing season, as LAI values were lower than previous years, and barley had the lowest and pea had the highest values. Moreover, in 2023, a reduction in LAI was observed. Across all treatments, LAI generally increased from the jointing to the full-bloom stage—by up to 180%—before declining at grain filling, except in 2021, when the values remained relatively high.

3.2. Plant Height

According to

Table 2. Plant height measured during three consecutive growing seasons for five cropping schemes evaluated at three growth stages in the vineyard.

Growing Season	Cropping System	Growth Stage
		Jointing		Full Bloom		Grain Filling
		Cereal	Legume	Cereal	Legume	Cereal	Legume
2021	Barley	46.0 a Ϯ	-	63.7 a	-	77.2 a	-
	Barley–Pea	42.0 a	53.0 b	60.7 a	71.7 b	73.2 a	84.2 b
	Triticale	63.7 a	-	76.2 a	-	87.7 a
	Triticale–Pea	69.0 a	84.0 a	79.2 a	100.00 a	94.2 a	111.2 a
	Pea	-	93.0 a	-	111.25 a	-	125.2 a
	SE	2.76	3.43	3.50	4.29	4.15	4.89
2022	Barley	35.8 a	-	83.1 a	-	78.7 b	-
	Barley–Pea	35.4 a	32.3 a	84.8 a	109.35 a	83.5 a	120.3 a
	Triticale	45.9 a	-	90.0 a	-	97.9 a	-
	Triticale–Pea	48.2 a	32.95 a	95.4 a	104.2 ab	97.4 a	122.8 a
	Pea	-	35.9 a	-	94.7 b	-	121.3 a
	SE	2.07	1.63	4.42	5.34	4.47	6.08
2023	Barley	29.5 a	-	69.3 a	-	85.9 a	-
	Barley–Pea	33.3 a	49.0 a	71.8 a	125.7 a	84.0 a	180.8 a
	Triticale	48.0 a	-	100.1 a	-	101.7 a	-
	Triticale–Pea	44.7 a	47.3 a	101.6 a	114.9 a	112.4 a	173.0 a
	Pea	-	51 a	-	115.95 a	-	169.95 a
	SE	1.94	2.41	4.29	6.02	4.80	8.85

^Ϯ Within each year, means followed by different letters are significantly different according to the protected LSD test (α = 0.05). SE = standard error of the mean of cropping systems within each year and growth stage.

, during the 2021 growing season, triticale–pea and pea monoculture exhibited the highest values for plant height at the jointing stage, with the pea monocrop reaching 93.0 cm. In the full bloom stage, pea in the monocrop (111.2 cm) and intercrop with triticale (100.0 cm) showed significantly higher values than its intercrop with barley (71.7 cm) in the vineyard. A similar tendency was observed in the grain filling stage, where pea maintained superior height in these treatments, particularly in the pea monoculture, with an average of 125.2 cm. In 2022, no significant differences between cereals in barley, barley–pea, triticale, and triticale–pea during jointing and full bloom were observed, whereas barley had taller plants in the monocrop treatments compared to its intercrop with pea during grain filling. Also, in the full bloom stage, pea had taller plants in intercropping systems than the monoculture. On the other hand, in the 2023 season, there were no significant differences between treatments across all growth stages. However, similar to previous years, pea plants recorded higher values of plant height compared to cereal plants. Also, barley in monoculture consistently exhibited the lowest height values across all stages. Overall, plant height increased progressively from jointing to full bloom and grain filling, with pea recording a greater height than cereals. Across the three years, a slight variation in plant height was observed, with 2023 showing increased values, particularly at the full bloom and grain filling stages.

3.3. Leaf Greenness Index (SPAD)

Regarding the results of chlorophyll content (SPAD values), according to

Table 3. Chlorophyll content measured during three consecutive growing seasons for five cropping systems evaluated at three growth stages in the vineyard.

Growing Season	Cropping System	Growth Stage
		Full Bloom		Grain Filling
		Cereal	Legume	Cereal	Legume
2021	Barley	44.9 a Ϯ	-	49.8 a	-
	Barley–Pea	48.4 a	51.0 ab	47.9 a	53.8 a
	Triticale	47.0 a	-	48.1 a	-
	Triticale–Pea	54.6 a	46.4 b	52.7 a	51.5 a
	Pea	-	54.7 a	-	51.4 a
	SE	2.44	2.54	2.48	2.61
2022	Barley	58.2 a	-	39.0 a	-
	Barley–Pea	51.6 a	39.6 a	43.4 a	43.6 a
	Triticale	57.6 a	-	51.8 a	-
	Triticale–Pea	49.4 a	35.4 a	55.1 a	44.7 a
	Pea	-	37.9 a	-	47.5 a
	SE	2.71	1.88	2.37	2.26
2023	Barley	37.6 b	-	36.4 b	-
	Barley–Pea	41.8 a	38.5 a	41.5 a	39.9 a
	Triticale	42.5 a	-	40.3 a	-
	Triticale–Pea	49.6 a	39.1 a	48.1 a	42.4 a
	Pea	-	37.8 a	-	41.0 a
	SE	2.14	1.92	2.08	2.06

^Ϯ Within each year, means followed by different letters are significantly different according to the protected LSD test (α = 0.05). SE = standard error of the mean of cropping systems within each year and growth stage.

, significantly different values were observed among treatments, particularly in the first year. In 2021, the highest chlorophyll content for cereals was recorded during full bloom in the triticale–pea intercrop, whereas it was recorded for pea in its monoculture. The barley monoculture exhibited lower SPAD values, while barley–pea presented an intermediate value (48.4), indicating the potential benefit of intercropping. During grain filling, SPAD values remained consistently stable among the treatments, showing no noteworthy differences either for cereals or for pea. However, pea in intercropping systems, especially in barley–pea, showed a higher SPAD value of 53.8. During the second and third growing seasons, SPAD values were similar across treatments, with no significant differences across them. However, in 2022, barley recorded the highest chlorophyll content at full bloom among cereals, while a decrease in SPAD values was noted at grain filling, particularly in barley monoculture, suggesting earlier chlorophyll degradation. In addition, in the triticale–pea intercrop, the highest SPAD value among cereals at grain filling (55.1) was observed, indicating prolonged chlorophyll retention. In 2023, a general decline in SPAD values compared to the previous growing season was recorded across treatments, with barley showing the lowest values at both growth stages. Additionally, the mixtures of barley–pea and triticale–pea demonstrated high SPAD values, especially for cereals, suggesting a positive effect on chlorophyll content. Comparing growth stages, chlorophyll content was generally higher at full bloom and declined towards grain filling, reflecting the plants’ senescence. Over the years, a decrease in SPAD values was observed, particularly in barley in 2023, suggesting possible environmental effects that may have influenced chlorophyll content.

3.4. Yield Components

The yield components for pea and cereals showed significant differences across the years and treatments used (

Table 4. Yield components (spikes per plant and seeds per spike for cereals; pods per plant and seeds per pod for pea) measured over three consecutive growing seasons for the five cropping systems.

Growing Season	Cropping System	Spikes per Plant	Seeds per Spike	Pods per Plant	Seeds per Pod
2021	Barley	4.00 a Ϯ	28.00 a	-	-
	Barley–Pea	3.75 a	20.25 a	6.25 a	4.00 c
	Triticale	2.75 a	37.75 a	-	-
	Triticale–Pea	3.00 a	28.75 b	7.25 a	4.75 b
	Pea	-	-	7.75 a	5.75 a
	SE	0.16	1.43	0.35	0.26
2022	Barley	10.16 a	27.50 a	-	-
	Barley–Pea	8.66 a	28.58 a	18.92 b	4.92 a
	Triticale	8.67 a	41.25 a	-	-
	Triticale–Pea	7.75 b	44.50 a	25.41 a	5.42 a
	Pea	-	-	19.75 ab	5.16 a
	SE	0.44	1.77	1.07	0.26
2023	Barley	9.00 a	19.42 a	-	-
	Barley–Pea	16.08 a	22.08 a	11.50 a	5.00 a
	Triticale	4.25 a	42.58 a	-	-
	Triticale–Pea	5.75 a	48.25 a	9.50 a	5.33 a
	Pea	-	-	9.58 a	5.42 a
	SE	0.44	1.65	0.51	0.26

^Ϯ Within each year, means followed by different letters are significantly different according to the protected LSD test (α = 0.05). SE = standard error of the mean of cropping systems within each year.

). More specifically, regarding barley, the number of spikes per plant and seeds per spike did not differ significantly between the monoculture and intercropping treatments across the three growing seasons. However, variations were observed with the number of spikes per plant, as in 2022, in which they were higher compared to 2021 (10.16 vs. 4.00), and even more-so in 2023 (up to 16.08) in the intercrop treatment. Yield components for triticale differed significantly over the years. In 2021, the number of seeds per spike was significantly lower in the triticale–pea intercrop (28.75) compared to the monoculture (37.75), although there were no differences detected across treatments regarding spikes per plant. On the other hand, in 2022, intercropping resulted in a significant reduction in the number of spikes per plant (7.75) compared to the sole crop (8.67), while the seeds per spike remained unaffected. No significant differences were observed between triticale treatments in 2023 either for spikes per plant or seeds per spike. Lastly, regarding the field pea yield, significant component effects were observed in the first two growing seasons. In 2021, seeds per pod were 5.75 in monoculture, significantly higher compared to both intercrops, especially in the mixture with barley, which recorded the lowest value (4.00). In 2022, pea, in its mixture with triticale, produced the highest number of pods per plant, 25.41, which was significantly greater than the barley–pea intercrop with 18.92. No significant differences were found for pea yield components in 2023, while monoculture treatments showed intermediate values across all seasons.

3.5. Dry Biomass and Grain Yield

The dry biomass and grain yield of the different cropping systems exhibited significant variations across years and treatments according to

Table 5. Dry biomass and grain yield over three consecutive growing seasons under five cropping systems in a vineyard.

Growing Season	Cropping System	Dry Biomass (t ha−1)			Grain Yield (t ha−1)
		Cereal	Legume	Total	Cereal	Legume	Total
2021	Barley	7.93 a Ϯ	-	7.93 b	3.32 a	-	3.32 b
	Barley–Pea	2.94 b	4.42 a	7.37 bc	1.24 b	1.85 a	3.09 b
	Triticale	7.53 a	-	7.53 bc	4.74 a	-	4.74 a
	Triticale–Pea	5.25 b	6.38 a	11.63 a	1.61 b	1.78 a	3.39 b
	Pea	-	4.58 a	4.58 c	-	1.73 a	1.73 c
	SE	0.35	0.57	0.30	0.11	0.17	0.09
2022	Barley	11.39 a	-	11.39 a	2.85 a	-	2.85 a
	Barley–Pea	4.86 a	3.54 a	8.40 a	0.85 b	1.31 a	2.16 a
	Triticale	8.63 a	-	8.63 a	2.33 ab	-	2.33 a
	Triticale–Pea	5.70 a	3.68 a	9.38 a	1.08 b	1.34 a	2.42 a
	Pea	-	5.96 a	5.96 a	-	2.00 a	2.00 a
	SE	1.13	0.33	0.92	0.22	0.13	0.18
2023	Barley	8.65 a	-	8.65 a	4.08 a	-	4.08 a
	Barley–Pea	2.83 b	7.18 a	10.00 a	0.57 b	0.65 a	1.22 b
	Triticale	9.98 a	-	9.98 a	3.54 a	-	3.54 a
	Triticale–Pea	3.63 b	6.85 a	10.48 a	0.75 b	0.61 a	1.36 b
	Pea	-	9.15 a	9.15 a	-	0.74 a	0.74 b
	SE	0.05	0.67	0.36	0.22	0.10	0.16

^Ϯ Within each year, means followed by different letters are significantly different according to the protected LSD test (α = 0.05). SE = standard error of the mean of cropping systems within each year.

. Specifically, in 2021, sole barley produced 7.93 t ha⁻¹ of dry biomass and 3.32 t ha⁻¹ of grain yield, while the barley–pea intercrop had significantly lower cereal biomass (2.94 t ha⁻¹), but an additional biomass of 4.42 t ha⁻¹ from pea resulted a total of 7.37 t ha⁻¹. Triticale in intercrop with pea had the highest total biomass (11.63 t ha⁻¹), although only 5.25 t ha⁻¹ was attributed to triticale production, which was significantly lower than in its sole crop. A similar tendency was observed in grain yield, with sole triticale achieving the highest yield (4.74 t ha⁻¹), whereas intercropping reduced cereal yield (either for barley or triticale) but compensated with a stable legume production across treatments. In 2022, total biomass was generally higher across treatments compared to the previous year, especially for barley. While there were not any significant differences between monocrops and intercrops, sole barley produced 11.39 t ha⁻¹ of biomass and sole triticale reached 8.63 t ha⁻¹, while the barley–pea triticale–pea intercrop recorded 8.40 t ha⁻¹ and 9.38 t ha⁻¹ total biomass, respectively. For the grain yield, the uppermost value was noted in sole barley, with 2.85 t ha⁻¹, significantly higher compared to its intercrop with pea (0.85 t ha⁻¹). A similar trend followed the grain yield of triticale, with the monoculture recording 2.33 t ha⁻¹ and intercropping 1.08 t ha⁻¹, with pea production significantly affecting the total grain yield of the mixtures, while pea as a sole crop produced 5.96 t ha⁻¹ of biomass and 2.00 t ha⁻¹ of grain yield, without significant differences with its intercrops. In 2023, biomass values were comparable to those in 2021. Barley monocrop produced 8.65 t ha⁻¹ of biomass and 4.08 t ha⁻¹ of grain yield, significantly higher than its intercrop with pea (2.83 t ha⁻¹ dry biomass and 0.57 t ha⁻¹ grain yield). Similarly, triticale reached its highest biomass and grain yield in monoculture treatments (9.98 t ha⁻¹ and 3.54 t ha⁻¹, respectively), while in intercropping triticale, yields were suppressed, resulting in a total biomass of 10.48 t ha⁻¹. Again, in this growing season, the contribution of pea species to the total biomass was significant, resulting in sufficient yield. However, pea as a sole crop exhibited high biomass production (9.15 t ha⁻¹) but relatively low grain yield (0.74 t ha⁻¹), negatively affecting the total grain yield of intercropping systems, also.

3.6. Water Use Efficiency (WUE)

Table 6. Water Use Efficiency over three consecutive growing seasons under five cropping systems in a vineyard.

Growing Season	Cropping System	Water Use Efficiency Based on Biomass (kg ha−1 mm−1)			Water Use Efficiency Based on Grain (kg ha−1 mm−1)
		Cereal	Legume	Total	Cereal	Legume	Total
2020–2021	Barley	29.84 a Ϯ	-	29.84 b	12.48 b	-	12.48 b
	Barley–Pea	11.08 b	16.64 a	27.72 bc	4.65 c	6.96 a	11.62 b
	Triticale	28.34 a	-	28.34 bc	17.84 a	-	17.84 a
	Triticale–Pea	19.77 ab	24.00 a	43.76 a	6.04 c	6.71 a	12.72 b
	Pea	-	17.24 a	17.24 c	-	6.50 a	6.50 c
	SE	1.32	2.15	1.15	0.42	0.64	0.34
2021–2022	Barley	41.96 a	-	41.96 a	10.48 a	-	10.48 a
	Barley–Pea	17.92 a	13.03 a	30.95 a	3.13 b	4.82 a	7.95 a
	Triticale	31.81 a	-	31.81 a	8.59 ab	-	8.59 a
	Triticale–Pea	21.01 a	13.54 a	34.55 a	3.99 ab	4.94 a	8.93 a
	Pea	-	21.94 a	21.94 a	-	7.35 a	7.35 a
	SE	4.18	1.21	3.37	0.81	0.46	0.67
2022–2023	Barley	24.22 a	-	24.22 a	11.42 a	-	11.42 a
	Barley–Pea	7.91 b	20.09 a	28.00 a	1.60 b	1.82 a	3.42 b
	Triticale	27.93 a	-	27.93 a	9.91 a	-	9.91 a
	Triticale–Pea	10.15 b	19.18 a	29.33 a	2.11 b	1.71 a	3.81 b
	Pea	-	25.62 a	25.62 a	-	2.07 a	2.07 b
	SE	1.42	1.87	1.01	0.62	0.29	0.46

^Ϯ Within each year, means followed by different letters are significantly different according to the protected LSD test (α = 0.05). SE = standard error of the mean of cropping systems within each year.

presents the Water Use Efficiency (WUE) of the different cropping systems that were used within the vineyard, evaluating both biomass and grain production over three seasons. In 2020–2021, the WUE based on the total biomass for barley monoculture (29.84 kg ha⁻¹ mm⁻¹) showed increased WUE compared to barley in the intercropping system (27.72 kg ha⁻¹ mm⁻¹). Also, triticale in its intercrop with pea obtained the highest value of WUE (28.34 kg ha⁻¹ mm⁻¹), accompanied by triticale monoculture (28.34 kg ha⁻¹ mm⁻¹), while pea gave a WUE of 17.24 kg ha⁻¹ mm⁻¹ when cultivated as a monocrop. Analyzing the WUE regarding grain yield, a similar pattern was observed between barley and pea monocrops and their intercrop; however, triticale achieved higher values of WUE in monocrop (17.84 kg ha⁻¹ mm⁻¹) compared to triticale–pea intercrop (12.75 kg ha⁻¹ mm⁻¹). On the other hand, in the 2021–2022 cultivation season, significant differences were not recorded for WUE between the treatments, either when WUE was calculated based on the total biomass or the total seed yield. The only statistical difference noted was for the WUE of cereals based on grain yield, where barley monocrop recorded the highest value (10.48 kg ha⁻¹ mm⁻¹) accompanied by triticale monocrop (8.59 kg ha⁻¹ mm⁻¹), while the two intercropping systems decreased their WUE values significantly. Finally, in the season of 2022–2023, all treatments showed a similar behavior to those of the first season, with WUE values based on total biomass being higher when intercropped (28.00 kg ha⁻¹ mm⁻¹ for barley–pea and 29.33 kg ha⁻¹ mm⁻¹ for triticale–pea) compared to monoculture treatments (24.22 kg ha⁻¹ mm⁻¹ for barley and 27.93 kg ha⁻¹ mm⁻¹ for triticale). For the WUE based on grain yield, both cereal species showed a similar pattern this season, with higher values recorded in their monocultures (11.42 kg ha⁻¹ mm⁻¹ and 9.91 kg ha⁻¹ mm⁻¹ for barley and triticale, respectively), which can mainly be attributed to cereals’ grain yield, whereas pea monocrop obtained the lowest mean value (2.07 kg ha⁻¹ mm⁻¹).

Across the three seasons, the Radiation Use Efficiency (RUE) calculated for biomass (

Table 7. Radiation Use Efficiency (RUE) for the three consecutive growing seasons of the five cropping systems used in the vineyard.

Growing Season	Cropping System	Radiation Use Efficiency Based on Biomass (g MJ−1)			Radiation Use Efficiency Based on Grain (g MJ−1)
		Cereal	Pea	Total	Cereal	Pea	Total
2020–2021	Barley	0.58 a Ϯ	-	0.58 b	0.24 b	-	0.24 b
	Barley–Pea	0.21 b	0.32 a	0.53 bc	0.09 c	0.13 a	0.22 b
	Triticale	0.55 a	-	0.55 bc	0.34 a	-	0.34 a
	Triticale–Pea	0.38 ab	0.47 a	0.85 a	0.12 c	0.13 a	0.24 b
	Pea	-	0.33 a	0.33 c	-	0.12 a	0.12 c
	SE	0.02	0.02	0.03	0.01	0.01	0.01
2021–2022	Barley	0.91 a	-	0.91 a	0.22 a	-	0.22 a
	Barley–Pea	0.39 a	0.28 a	0.67 a	0.06 b	0.10 a	0.17 a
	Triticale	0.69 a	-	0.69 a	0.18 ab	-	0.18 a
	Triticale–Pea	0.46 a	0.29 a	0.75 a	0.09 ab	0.10 a	0.19 a
	Pea	-	0.48 a	0.48 a	-	0.16 a	0.16 a
	SE	0.03	0.02	0.04	0.01	0.01	0.01
2022–2023	Barley	0.97 a	-	0.97 a	0.45 a	-	0.45 a
	Barley–Pea	0.32 b	0.80 a	1.12 a	0.06 b	0.07 a	0.13 b
	Triticale	1.12 a	-	1.12 a	0.39 a	-	0.39 a
	Triticale–Pea	0.41 b	0.76 a	1.17 a	0.08 b	0.06 a	0.15 b
	Pea	-	1.02 a	1.02 a	-	0.08 a	0.08 b
	SE	0.04	0.04	0.05	0.01	0.01	0.01

^Ϯ Within each year, means followed by different letters are significantly different according to the protected LSD test (α = 0.05). SE = standard error of the mean of cropping systems within each year.

) showed a clear advantage of the triticale–pea intercrop in 2020–2021, with a total value of 0.85 g MJ⁻¹, exceeding barley (0.58 g MJ⁻¹), triticale (0.55 g MJ⁻¹), barley–pea (0.53 g MJ⁻¹), and pea (0.33 g MJ⁻¹). On the other hand, in 2021–2022 and 2022–2023, total biomass RUE did not differ statistically among systems, with values ranging from 0.48 g MJ⁻¹ to 0.91 g MJ⁻¹ for the first year and 0.97 g MJ⁻¹ to 1.17 g MJ⁻¹ for the second year. For RUE, which is calculated based on grain yield, pea had the lowest values in 2020–2021 (0.12 g MJ⁻¹), while the cereal treatments had values between 0.22 and 0.34 g MJ⁻¹. No differences were detected in 2021–2022 across treatments, whereas in 2022–2023, barley and triticale monocultures displayed higher grain RUE (0.45 g MJ⁻¹ and 0.39 g MJ⁻¹, respectively) than barley–pea, triticale–pea, and pea (0.08 g MJ⁻¹–0.15 g MJ⁻¹). Overall, biomass RUE highlighted consistent advantages for the intercrops, especially for triticale–pea, while grain RUE was more variable across years, with the clear superiority of cereal monocultures in the 2022–2023 season and persistently lower values for pea.

3.7. Land Equivalent Ratio (LER)

The Land Equivalent Ratio (LER) values shown in

Table 8. Partial Land Equivalent Ratio (pLER) and total Land Equivalent Ratio (LER) across three consecutive growing seasons for five cropping systems used in the vineyard.

Growing Season	Cropping System	LER Based on Biomass			LER Based on Grain Yield
		Cereal	Legume	Total	Cereal	Legume	Total
2020–2021	Barley–Pea	0.39 a Ϯ	1.08 a	1.46 a	0.39 a	1.04 a	1.43 a
	Triticale–Pea	0.70 a	1.60 a	2.30 a	0.34 a	1.06 a	1.39 a
	SE	0.10	0.20	0.14	0.07	0.16	0.12
2021–2022	Barley–Pea	0.51 a	0.61 a	1.12 a	0.28 a	0.68 a	0.96 a
	Triticale–Pea	0.72 a	0.65 a	1.37 a	0.47 a	0.73 a	1.20 a
	SE	0.14	0.06	0.11	0.03	0.06	0.05
2022–2023	Barley–Pea	0.31 a	0.84 a	1.16 a	0.15 a	0.98 a	1.14 a
	Triticale–Pea	0.32 a	0.78 a	1.09 a	0.19 a	0.86 a	1.05 a
	SE	0.08	0.09	0.03	0.05	0.18	0.16

^Ϯ Within each year, means followed by different letters are significantly different according to the protected LSD test (α = 0.05). SE = standard error of the mean of cropping systems within each year.

indicate the efficiency of intercropping systems parallel to the respective monocrops in terms of biomass and grain yield. More specifically, in 2020–2021, the total LER calculated for biomass was higher for triticale–pea (2.30) than for barley–pea (1.46), indicating the stronger advantage of intercropping for biomass production. A similar pattern was observed in LER values based on grain yield, with barley–pea (1.43) slightly outperforming triticale–pea (1.39). Additionally, in 2021–2022, the LER values for both biomass and grain yield were generally lower than the previous year. Barley–pea had a total LER of 1.12 for biomass and 0.96 for grain yield, indicating a limited intercropping advantage. On the other hand, the triticale–pea intercrop exhibited better performance, with LER values of 1.37 for biomass and 1.20 for grain yield. In the final year of experimentation, LER values recorded a similar range to those of 2021–2022. The total biomass LER was 1.15 for barley–pea intercropping and 1.09 for triticale–pea treatment. However, LER values for grain yield were close to or slightly above 1, with barley–pea at 1.13 and triticale–pea at 1.05, suggesting that intercropping yields fluctuated in a similar range to that of the respective monocultures. In 2021–2022, both intercrops were in the top right quadrant, indicating that complementarity and cooperation outweighed the competition for the production of biomass, while in the other 2 experimental years, the mixtures were observed in top left quadrant, which indicates that pea outcompeted wheat (Figure 3a). In terms of grain yield, all mixtures, regardless of year, were observed in the top left quadrant, and, therefore, cereals were outcompeted by pea (Figure 3b). Overall, the LER values suggest that intercropping was generally beneficial, maintaining or even improving productivity compared to monoculture, particularly in the first year.

According to

Table 9. Actual Yield Loss and relative Crowding Coefficient over three consecutive growing seasons for barley–pea and triticale–pea intercrops in the vineyard.

Growing Season	Cropping System	Actual Yield Loss Based on Biomass			Relative Crowding Coefficient Based on Biomass
		AYLCereal	AYLLegume	AYLtotal	KCereal	KLegume	Ktotal
2020–2021	Barley–Pea	0.55 a Ϯ	0.44 a	0.98 b	2.11 a	−0.02 a	−0.04 a
	Triticale–Pea	1.80 a	1.14 a	2.94 a	−2.08 a	4.83 a	−10.04 a
	SE	0.42	0.27	0.27	3.26	2.62	0.81
2021–2022	Barley–Pea	1.03 a	−0.18 a	0.84 a	4.62 a	−4.75 a	−21.94 a
	Triticale–Pea	1.87 a	−0.13 a	1.74 a	−0.31 a	0.77 a	−0.23 a
	SE	0.54	0.08	0.50	1.55	2.63	0.25
2022–2023	Barley–Pea	0.25 a	0.13 a	0.38 a	2.08 a	0.39 a	0.81 a
	Triticale–Pea	0.27 a	0.04 a	0.30 a	1.73 a	−0.07 a	−0.12 a
	SE	0.32	0.12	0.21	0.85	1.56	0.13

^Ϯ Within each year, means followed by different letters are significantly different according to the protected LSD test (α = 0.05). SE = standard error of the mean of cropping systems within each year.

, for all years of experimentation, the values of cereals’ AYL were positive, indicating the general benefit of cereals over legumes in crop mixtures. In 2020–2021, the AYL values indicate that intercropping resulted in a biomass gain for both cereals and legumes, with triticale–pea (2.94) showing a higher overall benefit than barley–pea (0.98). On the other hand, in 2021–2022, the AYL values of peas declined below 0, which shows a yield loss for the legume component of the intercrop, which was, however, compensated by the biomass yield of the cereal, resulting in a total AYL value above 0 (0.84 for barley–pea and 1.74 for triticale–pea). Equal to the first growing season, in 2022–2023, the AYL values of both cereals and legumes, as well as the total AYL of the plot, were above 0, with barley–pea recording a value of 0.38 and triticale–pea 0.30 showing intercropping benefits.

The Relative Crowding Coefficient (K) values for cereals suggest a competitive advantage of barley because, in all growing seasons, barley outcompetes pea in barley–pea intercropping, with a K value above 1 and higher than those of peas. For triticale–pea treatment, pea seems to perform better than triticale, as it has higher K values, especially across the first growing season. Only during 2022–2023 did triticale obtain a value above 1, but the total K plot was below 1, indicating the presence of moderate competition between the two intercropped species.

The LEC values for the first two years of experimentation were significantly above 0.25, indicating a productive and complementary intercropping system. More specifically, in both years, triticale–pea (1.12 for 2020–2021 and 0.47 for 2021–2022) was more effective in land utilization than barley–pea (0.42 for 2020–2021 and 0.31 for 2021–2022). On the contrary, during 2022–2023, barley–pea, with a 0.26 LEC value and triticale–pea with 0.25, were exactly at the lower bound of effective LEC in intercropping systems in terms of biomass yield (

Table 10. Land Equivalent Coefficient (LEC), System Productivity Index (SPI), and Percentage Yield Difference (PYD) across three consecutive growing seasons for two intercropping systems (barley–pea and triticale–pea) used in the vineyard.

Growing Season	Cropping System	LEC Based on Biomass	SPI Based on Biomass	PYD (%) Based on Biomass
2020–2021	Barley–Pea	0.42 b Ϯ	1134.52 a	46.32 a
	Triticale–Pea	1.12 a	1735.88 a	130.35 a
	SE	0.2	121.45	13.75
2021–2022	Barley–Pea	0.31 a	1159.32 a	12.05 a
	Triticale–Pea	0.47 a	1101.94 a	36.85 a
	SE	0.1	236.66	10.74
2022–2023	Barley–Pea	0.26 a	984.56 a	15.77 a
	Triticale–Pea	0.25 a	1051.36 a	9.42 a
	SE	0.1	61.819	3.20

^Ϯ Within each year, means followed by different letters are significantly different according to the protected LSD test (α = 0.05). SE = standard error of the mean of cropping systems within each year.

).

As previously reported regarding LEC values, the System Productivity Index (SPI) was also higher in triticale–pea (1735.88) compared to barley–pea (1134.52) in 2020–2021, indicating greater productivity of this treatment, while in 2021–2022, the SPI values were similar for both systems (1159.32 for barley–pea and 1101.94 for triticale–pea), indicating comparable biomass production. A similar pattern was observed in 2022–2023, where SPI values were slightly lower than in previous years, with barley–pea (984.56) and triticale–pea (1051.36) showing similar levels of biomass yield.

The Percentage Yield Difference (PYD), which is calculated based on the biomass yield, was notably high for triticale–pea during the first two seasons, showing a significant advantage over barley–pea treatment. However, during 2021–2022, PYD values declined significantly from the previous year, with triticale–pea at 36.85% and barley–pea at 12.05%, suggesting a reduced intercropping advantage, while in 2022–2023, the barley–pea (15.77%) intercrop recorded a higher value of PYD than the triticale–pea (9.42%) intercrop, in contrast to previous years.

The CR values in

Table 11. Competitive Ratio (CR) and Aggressivity (A) across three consecutive growing seasons for two intercropping systems (barley–pea and triticale–pea) used in the vineyard based on biomass.

Growing Season	Cropping System	CR Based on Biomass		A Based on Biomass
		Cereal	Legume	Cereal	Legume
2020–2021	Barley–Pea	1.35 a Ϯ	3.02 a	0.11 a	−0.11 a
	Triticale–Pea	1.88 a	1.86 a	0.66 a	−0.66 a
	SE	0.41	0.22	0.65	0.65
2021–2022	Barley–Pea	2.72 a	3.05 a	1.21 a	−1.21 a
	Triticale–Pea	3.23 a	2.56 a	2.00 a	−2.00 a
	SE	0.64	0.22	0.60	0.60
2022–2023	Barley–Pea	1.41 a	4.30 a	0.13 a	−0.13 a
	Triticale–Pea	1.88 a	4.57 a	0.23 a	−0.23 a
	SE	0.75	0.36	0.43	0.43

^Ϯ Within each year, means followed by different letters are significantly different according to the protected LSD test (α = 0.05). SE = standard error of the mean of cropping systems within each year.

indicate pea’s competition over barley in barley–pea treatment, as it recorded higher values across all years based on biomass yield. On the other hand, in triticale–pea treatment, the competition was more balanced between the two species across the first year, as triticale had a CR value of 1.88 and pea 1.86; during 2021–2022, triticale (3.23) was more dominant over pea (2.56), but in the third season, pea became more competitive, as the CR for triticale was 1.88 while pea increased to 4.57.

Additionally, the Aggressivity index values show that both barley and triticale had a competitive advantage over pea, as they obtained higher values than legumes across all years. Especially in 2021–2022, the A values of barley were clearly higher (1.21) than pea (−1.21), and triticale showed an even stronger dominance (2.00) over pea (−2.00), suggesting that competition between cereals and pea intensified, potentially due to environmental factors. However, the Aggressivity Index values of the barley–pea treatment in 2020–2021 and 2022–2023 and triticale–pea treatment in 2022–2023 are close to 0, indicating the absence of competitive interactions among the two intercropped species of the mixture (Table 11).

In the first year, both crop mixtures exhibited positive AYL values for cereals and pea, indicating that intercropping was beneficial for both species compared to their respective sole crops (

Table 12. Actual Yield Loss (AYL) and Relative Crowding Coefficient (K) across three consecutive growing seasons for the two mixtures (barley–pea and triticale–pea) used in the vineyard.

Growing Season	Cropping System	AYL Based on Grain			K Based on Grain
		AYLCereal	AYLLegume	AYLtotal	KCereal	KLegume	Ktotal
2020–2021	Barley–Pea	0.57 a Ϯ	0.39 a	0.96 a	2.21 a	0.06 a	0.13 a
	Triticale–Pea	0.35 a	0.41 a	0.76 a	1.63 a	−1.58 a	−2.57 a
	SE	0.26	0.21	0.20	0.51	0.79
2021–2022	Barley–Pea	0.12 a	−0.09 a	0.03 b	1.20 a	−0.75 a	−0.90 a
	Triticale–Pea	0.88 a	−0.03 a	0.85 a	2.94 a	1.87 a	5.49 a
	SE	0.13	0.08	0.11	0.41	1.00
2022–2023	Barley–Pea	−0.39 a	0.31 a	−0.08 a	0.56 a	−0.81 a	−0.45 a
	Triticale–Pea	−0.23 a	0.14 a	−0.09 a	0.81 a	−1.37 a	−1.10 a
	SE	0.20	0.24	0.21	0.25	0.85

^Ϯ Within each year, means followed by different letters are significantly different according to the protected LSD test (α = 0.05). SE = standard error of the mean of cropping systems within each year.

). The barley–pea system had a higher total AYL (0.96) than triticale–pea (0.76), suggesting a slightly greater overall yield advantage (

Table 13. Land Equivalent Coefficient (LEC), System Productivity Index (SPI), and Percentage Yield Difference (PYD) across three consecutive growing seasons for two mixtures (barley–pea and triticale–pea) used in the vineyard.

Growing Season	Cropping System	LEC Based on Grain	SPI Based on Grain	PYD (%) Based on Grain
2020–2021	Barley–Pea	0.40 a Ϯ	467.95 a	43.38 a
	Triticale–Pea	0.36 a	661.51 a	39.45 a
	SE	0.06	53.89	12.40
2021–2022	Barley–Pea	0.19 a	265.99 a	−3.87 a
	Triticale–Pea	0.34 a	279.52 a	19.64 a
	SE	0.03	52.28	4.98
2022–2023	Barley–Pea	0.15 a	442.81 a	13.61 a
	Triticale–Pea	0.16 a	389.84 b	4.98 a
	SE	0.03	92.15	15.75

^Ϯ Within each year, means followed by different letters are significantly different according to the protected LSD test (α = 0.05). SE = standard error of the mean of cropping systems within each year and growth stage.

). In the second growing season, total AYL values were again above 0, but that was due to the partial AYL of the cereals in the mixture, as AYL of pea was slightly negative, signifying that pea was not significantly benefitted from intercropping in this year and the total yield compensated from the cereals’ performance. The situation was exactly the opposite in the third growing season, where the total AYL was negative for both intercropping treatments, indicating a yield disadvantage for intercropping compared to monoculture. More specifically, the individual AYL values for cereals were negative (−0.39 for barley and −0.23 for triticale), implying that their yields were reduced under intercropping conditions. Conversely, pea in both systems had positive AYL values (0.31 for barley–pea and 0.14 for triticale–pea), suggesting that pea benefited from intercropping at the expense of cereals.

Regarding the Relative Crowding Coefficient (K) values based on grain yield, across the first two years, cereals showed a competitive advantage over pea, as they have values above 1, exhibiting a dominance in all treatments. Also, pea displayed lower K values than those of cereals, with the only exception being the triticale–pea intercropping of the second year, where pea had a K value lower than triticale, but above 1, resulting in a highly positive K total value (K = 5.49). On the other hand, in 2022–2023, the K values were below 1, both for the partials components of the intercropping systems (cereals or legume) and for the total relative Crowding Coefficient.

In the 2020–2021 season, both intercropping systems demonstrated Land Equivalent Coefficient values above 0.25, with barley–pea at 0.40 and triticale–pea at 0.36, suggesting beneficial intercropping interactions (Table 13). However, in the 2021–2022 season, LEC values differed between the two treatments, with barley–pea dropping below the 0.25 threshold (0.19), indicating weaker intercropping benefits in terms of grain yield, while triticale–pea maintained a relatively high LEC at 0.34. The decrease in LEC values also continued in the third year, where both intercropping systems exhibited values up to 0.16, suggesting weak interactions and possibly competition between species.

The SPI values seemed to be affected by environmental factors, as they display large variability from season to season according to Table 13. More specifically, in 2020–2021, triticale–pea treatment had a higher SPI value (661.51) compared to barley–pea (467.95), indicating that this system was more productive for grain yield, but in the 2021–2022 season, the SPI values for both systems were lower than in the previous one, with triticale–pea (279.52) showing only a slight advantage over barley–pea (265.99). On the other hand, during 2022–2023, the SPI values showed a different trend compared to previous years, with barley–pea treatment (442.81) outcompeting triticale–pea (389.84), changing the dynamics of the intercropping system.

As displayed in Table 12, PYD values were higher in barley–pea intercropping across the first (43.38%) and the third season (13.61%) compared to triticale–pea treatment (39.45% and 4.98%, respectively), suggesting, at the same time, that both intercropping systems provided a significant yield disadvantage in these growing seasons compared to the respective monocrops, with the slight superiority of triticale–pea.

The CR values over all experimental years were above 1 for both barley and triticale, with only the exception of barley’s CR in 2022–2023, which had a value of 0.60, which indicates that barley was less competitive in the barley–pea intercrop. Also, across all years, pea obtained higher CR values compared to cereals, meaning that pea outcompetes cereals in intercropping treatments (

Table 14. Competitive Ratio (CR) and Aggressivity (A) across three consecutive growing seasons for two intercropping systems (barley–pea and triticale–pea) used in the vineyard based on grain yield.

Growing Season	Cropping System	CR Based on Grain Yield		A Based on Grain Yield
		Cereal	Legume	Cereal	Legume
2020–2021	Barley–Pea	1.33 a Ϯ	3.26 a	0.18 a	−0.18 a
	Triticale–Pea	1.13 a	3.11 a	−0.05 a	0.05 a
	SE	0.38	0.43	0.44	0.44
2021–2022	Barley–Pea	1.48 a	4.14 a	0.21 a	−0.21 a
	Triticale–Pea	2.01 a	2.78 a	0.91 a	−0.91 a
	SE	0.27	0.22	0.18	0.18
2022–2023	Barley–Pea	0.60 a	7.81 a	−0.70 a	0.70 a
	Triticale–Pea	1.12 a	6.60 a	−0.37 a	0.37 a
	SE	0.46	1.94	0.39	0.39

^Ϯ Within each year, means followed by different letters are significantly different according to the protected LSD test (α = 0.05). SE = standard error of the mean of cropping systems within each year.

).

The Aggressivity (A) values reveal that, among the cereals, barley had a slightly positive dominance over pea in the first (0.18), while across the second growing season, both barley and triticale outcompeted the legume (0.21 and 0.91, respectively). In 2022–2023, pea became dominant in the combinations with barley or triticale, suggesting that the increased competitiveness of pea is likely due to environmental conditions or resource availability, which may have affected the legume component (Table 14).

4. Discussion

4.1. Leaf Area Index (LAI)

Across seasons and growth stages, the barley–pea and triticale–pea mixtures consistently exhibited higher or earlier peaks in leaf area index (LAI), up to 180% greater than those observed in the corresponding sole crops. These results support the hypothesis that structural complementarity within mixed canopies enhances the fraction of intercepted photosynthetically active radiation and thereby fosters the development and growth of intercropped species [52,53]. In cereal–legume intercropping systems, temporal niche differentiation constitutes a principal mechanism underlying the increased capture of PAR and the enhancement of Radiation Use Efficiency [54], particularly under Mediterranean conditions, where water and nitrogen (N) availability are frequently limited [24,55]. The cultivation of two species in the same place can result in a better canopy cover, as shown by the increase in the LAI in our results. The two species differentiate in their canopy structure, resulting in an aboveground complementarity, enhancing light interception. This canopy structure covers and shades the soil, moderating the vineyard microclimate and reducing evapotranspiration and thermal stress on the vine root zone [1,3]. Similarly, in an intercropping system in an olive grove, the mixtures obtained higher LAI values [17]. The variability in LAI values over the years was mainly due to the abnormal distribution of rainfall, especially during the critical period of stem elongation in 2023, resulting in accelerated plant senescence (Figure 2).

4.2. Plant Height

Plants were taller in most mixtures in comparison with their respective monocultures, and especially for triticale. However, peas were taller in monocultures compared to intercropping treatments. This can be attributed to the fact that plants grown at higher densities are exposed to competition for light during the early vegetative stages and grow higher and faster to access more sunlight [56,57]. Also, in a mixture of cereals with legumes, cereals take up more soil N, and legumes are dependent on symbiotic N fixation. Therefore, legumes spend more resources and more carbohydrates to support N fixation, and their growth in height is limited, especially when soil N status is low [58,59]. Also field experiments [17,52,60] and modeling approaches [55] show that light interception and nitrogen dynamics affect plant growth, and also that cereals dominate the upper canopy and that legume height reaches a plateau much earlier. Moreover, several approaches can reduce the extent that one species grows more than the other, such as sowing ratio, date of sowing, and cultivar selection [61,62].

4.3. Leaf Greenness Index (SPAD)

Cereals in intercropping systems with pea showed higher SPAD values compared to monocultures in most treatments, and especially with barley, as it was 14% in 2023. This is probably because, during intercropping, cereals take more N from the soil [63]. However, pea had similar values for SPAD in intercropping and monocropping conditions, probably because of N₂ fixation [29,63]. Cereals frequently dominate in taking up soil N early in the season and having higher leaf greenness in cereals, especially during low N supply levels in soil or water stress, making legumes, when they are grown in intercropping systems, rely on N₂ fixation [31,63]. This mechanism was more obvious during the 2023 growing season, as the reduced rainfall limited soil nitrogen mineralization and transport, conditions that typically restrict nitrogen uptake [54]. Consequently, while cereal monocultures affected negatively from both water and nitrogen stress, leading to lower chlorophyll content, the intercropped cereals maintained higher leaf greenness, demonstrating that cereal–legume mixtures offer greater physiological resilience under water-limited Mediterranean conditions [28,49].

4.4. Yield Components

Yield component responses in intercropping systems are frequently compensatory rather than additive [64]. Competition between component species may reduce one or more yield components—for instance, spikes per plant or seeds per spike in cereals and pods per plant or seeds per pod in legumes—but the overall productivity of the intercrop can be maintained or even enhanced through more efficient resource capture [38,65]. In the present study, cereal yield components remained stable across treatments, probably due to the cereals’ faster initial growth rate and deeper roots, which allowed for better soil moisture and nitrogen capture during the vegetative stages [27]. On the other hand, pea yield components were negatively affected by intercropping, particularly during the first two years. This reduction was likely driven by the shading effect of the taller cereal companion, which limited pod filling [17]. Similar patterns have been widely documented in Mediterranean cereal–legume mixtures, where cereals tend to dominate yield formation, while legume’s performance is often constrained during reproductive stages under dry spring conditions [38,66].

4.5. Dry Biomass and Grain Yield

In contrast to yield component responses, the mixtures consistently outperformed the respective monocultures in total biomass production across all years, with the triticale–pea intercrop achieving the highest dry matter yield, reaching up to 11.63 t ha⁻¹. Although cereal biomass in the mixtures was reduced due to interspecific competition, the overall yield advantage relative to monocultures reflects compensatory and complementary interactions in light and nitrogen capture [52,63]. Similar results have been stated by Lithourgidis et al. [67] and Dhima et al. [38], who observed increased dry matter production in cereal–legume intercrops—such as vetch–cereal mixtures—across Greece and southern Europe, where mixed canopies enhanced biomass accumulation compared to sole legumes. The underlying mechanisms include greater leaf area index (LAI), complementary rooting systems between component species, and reduced soil evaporation within inter-row spaces [52,53,58]. In 2022, higher rainfall during February and March may have helped early vegetative growth, especially for cereals, which can be more competitive compared to legumes in capturing soil resources [58]. On the other hand, in 2023, peas were favored compared to the other years, probably due to higher temperatures in December and January, which resulted in reduced cold stress and an earlier vegetative growth for the pea.

Grain yield was influenced by the year, and it showed considerable variation, as in 2021, where the uppermost grain yield was reported in triticale monoculture, while in the intercropping treatments, cereals showed a lower yield; however, legumes contributed to the enhancement in the total grain yield of the intercropping system. Also, during the second year (2022), the highest grain yield was found in barley, and there was no difference among the different treatments. Following the third year, the grain yield was low, despite the fact that biomass yield was high in pea, and this can be because grain set was affected by the weather conditions. Water and heat stress can reduce grain set and final grain yield, especially in legumes [68,69,70,71]. Meta-analyses and simulation studies indicate that cereal–legume mixtures can provide a more efficient use of resources and often stabilize or increase grain yield [72], although the magnitude of this effect depends on factors such as the sowing ratio and timing, nitrogen availability, and seasonal water and temperature stress [31,62,73].

4.6. Water Use Efficiency (WUE)

The intercropping treatments showed higher WUE by up to 60% compared to pea monocultures, being close to cereal’s WUE in the different growing seasons. Moreover, similar results were concluded in other studies from Mediterranean countries, as when there is canopy cover, there is a reduction in water loss from the soils, increasing WUE [46,74,75]. Climatic conditions also affected WUE over the years. In the warmer 2023 growing season, the intercrop canopy helped conserve moisture, allowing for the mixtures to maintain high WUE, while the barley monocrop was more affected by water deficit. In contrast, in the wetter 2022 season, especially during February and March, water was a less limiting factor, and monocultures performed equally as well as the intercrops (Figure 2). Furthermore, Abad et al. [1,2] reported that legume-based cover crops in vineyards can improve soil function by enhancing nitrogen status and water infiltration. Although temporary water competition may occur around veraison, it can often be mitigated through timely crop harvest and appropriate management practices—patterns that were also evident in the present experiments.

4.7. Radiation Use Efficiency (RUE)

The consistently high biomass Radiation Use Efficiency (RUE) observed in the mixtures—particularly in the triticale–pea combination—highlights the complementary effects arising from the canopy structural diversity of intercrops, which enhances the leaf area index (LAI) and consequently improves radiation interception [54,55,57]. In seasons when treatment differences were no longer statistically significant (2021–2022 and 2022–2023), RUE values were likely influenced by light interception saturation and environmental constraints such as water or heat stress, which negatively affected photosynthetic efficiency in the second and third experimental years [76,77]. Mixtures obtained higher LAI values, especially in 2021–2022 and 2023–2024 (Table 1), when there were higher temperatures and rainfall in the early vegetative growth stages (Figure 2), which could have resulted in shading. As observed, the RUE of cereal was lower in the intercrops compared to the sole crops, probably due to shading from legumes and the reduction in cereal biomass in intercrops (Table 5).

In contrast, grain RUE showed greater variability than biomass RUE, as the with cereal monocultures were the highest in 2022–2023, while pea was consistently low. This can be explained as cereals form grains with the significant remobilization of carbohydrates from leaves to grains, and the harvest index in cereals is much higher than in legumes [78,79,80,81]. Also, the weather conditions and the treatments can affect RUE [78,79,80,81]. Therefore, grain legumes are more affected by water and heat stress at anthesis and grain set, resulting in lower pod and seed set, with a lower seed filling period and lower harvest index [82,83]. Moreover, water and heat stress cause lower grain RUE, despite the fact that biomass accumulation remains adequate.

In conclusion, the RUE of biomass increased under intercropping treatments; however, the RUE for grain requires careful management practices that can ensure reproductive growth and higher grain yield through sowing ratios, fertilization, and harvesting time [84,85,86].

4.8. Land Equivalent Ratio (LER)

The Land Equivalent Ratio (LER) exceeded 1.0 in most treatments, apart from the barley–pea intercrop, which reached an LER of 0.96. These results indicate that the intercropping systems generally conferred a significant advantage over monocultures [17,52,87]. Variability in LER was influenced also by the climatic conditions during each growing season. Specifically, in the dry season of 2021, facilitation probably occurred among the intercropped species, resulting in the highest LER values, while in 2022, the sufficient early rainfall allowed for monocultures to grow well, reducing the benefit of intercropping [29]. Similarly, biomass production was consistently higher than grain yield, suggesting that the reproductive stage is more sensitive to environmental conditions than vegetative growth, ultimately leading to a reduction in harvest index [75,88]. This was more obvious during 2023, when the heavy rains during the reproductive stage negatively affected grain setting, confirming that grain yield is much more sensitive to environmental factors than vegetative biomass [82,88]. Comparable findings have been reported in other intercropping systems, where LER values typically exceeded 1.0, and the magnitude of the LER response was influenced by crop species, cultivar choice, and the management practices that shaped competitive interactions among component crops [17,38,39,89,90].

4.9. Intercrop Indices: Actual Yield Loss (AYL), Relative Crowding Coefficient (K), Land Equivalent Coefficient (LEC), System Productivity Index (SPI), and Percentage Yield Difference (PYD), Competitive Ratio (CR), and Aggressivity (A) Based on Biomass and Grain Yield

All intercrop combinations showed an advantage according to the AYL index, with consistently positive AYL values. These results indicate that the intercropping systems exhibited complementarity and facilitation in their use of environmental resources [55]. Among the two components of the mixtures, cereals consistently displayed higher AYL values than pea, suggesting that cereals benefited more from intercropping [17,38,89]. The response of the cereals to the treatments is probably because cereals are better acclimated to the Mediterranean conditions and they can more efficiently utilize the available soil water and N [91]. A similar tendency was observed in the second season: peas grew more slowly than cereals from January to March due to lower temperatures, which favored the cereals better adapted to cold conditions and therefore able to outcompete peas during the early growth stages. On the other hand, in 2023, the lower AYL values can be attributed to the excessive rainfall recorded during the reproductive stages (April–June). These probably induced lodging and fungal diseases within the dense intercropped canopies [17,38], while precipitation during anthesis affected pollination and seed set [54]. Consequently, the reproductive advantage of the mixtures was limited compared to previous seasons. Moreover, the total AYL based on grain yield was positive during the first two experimental years, indicating a clear intercrop advantage, but became negative in the third year, likely due to peas outcompeting cereals, a pattern not seen previously.

In this study, the K values for both biomass and grain were generally either negative or greater than 1. Higher K values indicate that a species achieves similar yields in both intercrops and monocrops, whereas negative K values indicate higher yields in intercrops than in monocrops [91]. However, these coefficients are significantly dependent on the climatic conditions. In the 2021 season, when water was limited, the positive K values were due to facilitative interactions between companion plants, which are essential under drought stress [52]. Conversely, in the 2023 season, the abundant rainfall shifted the interaction to light competition interactions among species. Dense canopies probably increased interspecific competition for photosynthetically active radiation, altering the Crowding Coefficient compared to the dry years [17,38]. Several treatments showed complementary or facilitative interactions between species, contributing to the yield advantages observed in the intercrops. Pea exhibited negative K values, indicating facilitation and higher yields in intercrops compared with monocrops. Similar outcomes have been found in other experiments, in which triticale–pea and barley–pea intercrops produced higher yields than their respective monocrops [39,92].

The Land Equivalent Coefficient (LEC) was used to assess intercropping performance, and values exceeding the threshold of 0.25 indicate that both species contribute significantly to the intercrop [44]. In the present study, several treatments and growing seasons produced LEC values greater than 0.25, demonstrating that intercrop yields approached or surpassed those of the corresponding monocrops. Furthermore, under stress conditions—such as competition from vines, which impose additional pressure on annual crops due to their shallow root systems—complementarity and facilitation between species became more pronounced, in line with the Stress Gradient Hypothesis (SGH) [93]. Only in the third year and in terms of grain yield were the values of LEC below 0.25. Grain setting is more sensitive to environmental stress than vegetative growth [82,88], and heavy rain during the reproductive stage negatively affected grain yield for the cereals in the intercrops. This resulted in less balanced mixtures in terms of grain yield, since cereals were negatively affected and obtained lower pLER values.

The System Productivity Index (SPI) for the intercropping systems had similar values over the three growing seasons, indicating that the productivity of the systems was stable and was not affected by environmental variability [94]. A similar tendency was found for the Percentage Yield Difference (PYD) of the triticale–pea intercrop in 2020–2021, which also had the highest LEC values. These data indicate that when an intercropping system is well balanced, the competition among the various species is minimized and there is an enhancement in the complementarity and facilitation between the component species [95]. However, in the final two years of this study, the SPI and LEC values declined relative to the first year. This reduction in productivity could be because of the lower rainfall, which led to reduced soil water availability and increased competition for soil nitrogen [58]. The triticale–pea mixture displayed an LEC value below 0.25, indicating an unbalanced intercrop, which corresponds to the lowest PYD among all combinations. These results highlight the significance of careful species consideration in crop mixtures, as differences in growth patterns, maturity, and morphology strongly influence competitive interactions within mixtures [96,97].

The Competitive Ratio for pea was higher than that of barley in all years within the barley–pea intercrop, indicating that pea was the dominant species in this mixture. In contrast, in the triticale–pea intercrop, triticale was dominant in the first year, but was suppressed in the subsequent two years. This difference between mixtures likely reflects the lower competitiveness of barley due to its shorter plant height and, therefore, was negatively affected by the shading of the peas. In the first year, peas were shorter than the other years, and this could have resulted in less shading, especially of the triticale plants, which are taller than barley. It is probable that, in the first-year, triticale overcame competition for sunlight from peas, and outcompeted them belowground, obtaining higher soil N resources. This shift changed the following year when peas grew taller, shading the cereals and therefore resulting in higher competition [29]. Similar observations have been stated in other experiments, where pea often outcompetes the cereal component of the mixture [17,97].

The variability observed in the LEC, SPI, and PYD indices corresponded closely with the Aggressivity (A) values. In the first two years, cereals dominated grain yield, as reflected by their positive A values. Furthermore, for biomass, A values for pea were negative across all years, indicating that the cereal component remained the dominant species. Similar patterns have been reported in other intercrops, such as oat–common vetch mixtures, where A values were above 0 for oat and negative for vetch across different sowing densities [44]. These findings underline the strong influence of environmental conditions on species performance and highlight the importance of careful species selection to enhance the productivity and balance of intercropping systems [61,96,97,98,99].

4.10. Potential Impacts on Soil Organic Carbon, N Cycling, and Microbial Activity

Beyond immediate crop performance, vineyard intercropping promotes sustainable intensification by enhancing soil health and providing ecosystem services. Spatiotemporal diversification in these systems facilitates carbon sequestration by increasing soil organic carbon (SOC) and promoting higher microbial diversity and stability. Furthermore, the optimization of nitrogen cycling through the inclusion of legumes allows for a significant reduction in synthetic fertilizers. This reduction can mitigate nitrous oxide (N₂O) emissions by 18–23%, reducing environmental degradation [100]. The effectiveness of these vineyard intercropping systems can be further optimized through spatiotemporal diversification strategies designed to decrease interspecific competition [101]. Restructuring canopy architecture understory species could enhance photosynthetically active radiation (PAR) interception and improve the microclimate conditions like temperature and humidity. Such management practices foster complementarity, increasing the Land Equivalent Ratio (LER) and ultimately strengthening the overall resilience and sustainability of Mediterranean vineyard agroecosystems [100,101].

5. Conclusions

Intercropping systems involving cereals and legumes have been widely studied in field experiments; however, their performance in more complex agroecosystems such as vineyards has received far less attention. The present study demonstrates that triticale–pea and barley–pea intercrops can be successfully integrated into vineyard systems, with triticale–pea showing better productivity, contributing to higher biomass as well as improved environmental resource use efficiency under Mediterranean conditions, especially compared to monocropping under stressful conditions. Although cereals tend to be more competitive than pea within these mixtures, pea performance can be enhanced using appropriate management practices, including adjusted seed ratios and optimized harvest timing. The intercropping indices used in this study provide valuable insights into species interactions and confirm that intercropping offers significant land use advantages and greater resilience across variable and stressful environmental conditions, while monocultures performed similarly mainly in favorable seasons. Overall, we emphasize the significance of careful species selection, strategic mixture design, and effective management techniques for maintaining high productivity and enhancing the sustainability of cereal–legume intercrops in Mediterranean vineyard environments.