Intercropping of Cereals with Lentil: A New Strategy for Producing High-Quality Animal and Human Food

Abstract

Intercropping is an eco-friendly agricultural practice that can lead to increased productivity and improved resource efficiency. This two-year field study (2022–2023 and 2023–2024) aimed to evaluate the yield and quality (protein content) of lentil when intercropping with bread wheat (Yekora) and oat (Kassandra) under two spatial arrangements (1:1 alternate rows and mixed rows at a 50:50 seeding ratio) in northwestern Greece. A completely randomized design was applied with three replications. Differences were found between treatments regarding yield as well as protein content. Results showed that the highest total grain yield (2478.6 kg/ha) and land equivalent ratio (LER = 2.50) were recorded in the Yekora + Thessalia combination (alternate rows). Legume protein content remained consistently high (27–31%), while cereal protein content varied with genotype. Intercropping in alternate rows generally outperformed mixed sowing, indicating the importance of spatial arrangement in optimizing resource use. These findings suggest that properly designed cereal–lentil intercropping systems can enhance yield and quality while supporting sustainable agricultural practices. Intercropping of Yekora with lentil was superior compared to lentil and bread wheat monocultures and can be recommended as an alternative method for the production of human and animal food.

1. Introduction

The production of high-quality food for human and animal nutrition has become increasingly critical under the combined pressures of climate change, soil degradation, and global food insecurity. Intercropping—defined as the simultaneous cultivation of two or more crop species in the same field—has emerged as a sustainable and eco-efficient cropping strategy. This method optimizes the use of available resources, reduces dependence on external inputs, and enhances the stability and resilience of cropping systems [1]. Depending on the configuration, intercropping may include alternate row planting, mixed row sowing, strip cropping, or relay cropping. Among these, spatial arrangement plays a crucial role in determining the level of interspecific interaction and overall productivity. Cereal–legume intercropping is widely practiced in many agroecosystems, especially in rainfed and low-input environments, and it has many advantages, such as improvement of soil properties, weed and disease control [2], and resistance to lodging, an important characteristic for some cereals [3,4]. Legumes are of particular interest due to their dual role as high-protein food sources and natural nitrogen contributors via biological nitrogen fixation (BNF) through symbiosis with Rhizobium species [5,6]. Their inclusion in intercropping systems with cereals has been shown to reduce nitrogen fertilizer needs by up to 26% [7], while also enhancing phosphorus mobilization through root exudates [8]. Additionally, legumes contribute to improved soil structure, pest and disease suppression, and weed control [2,3]. Many studies have shown that long-term intercropping of legumes and cereals yields greater quantities and better nutritional quality compared to monocultures [5]. The intercropping system is relatively low-cost and more effective at increasing production, ensuring ecosystem sustainability compared to conventional farming and expensive technologies [9]. Therefore, these cultivation systems are suitable for low-input and organic farming systems.

Despite these advantages, intercropping systems face limitations related to competition for light, water, and nutrients, which may suppress one of the components—often the legume—depending on species and arrangement [9,10]. Such dynamics are influenced by morphological and physiological traits, such as plant height, root architecture, and growth rate. Understanding these interactions is essential to optimize combinations and spatial arrangements that minimize competition and maximize complementarity [11]. Several studies have demonstrated improved yield and resource-use efficiency under well-designed intercropping systems, such as lentil with barley or wheat [2,4,12,13,14]. However, comparative performance between cereal–lentil combinations remains underexplored, especially in Mediterranean environments.

Several indices such as land equivalent ratio (LER), relative crowding coefficient (K), competitive ratio (CR), aggressivity (A), actual yield loss (AYL), monetary advantage (MA), and intercropping advantage (IA) have been proposed to evaluate the competition and the economic advantage of intercropping [15]. The assessment of land-use efficiency and the overall performance of an intercropping system, in comparison with monoculture, can be accurately evaluated through the land equivalent ratio (LER) index.

The present study was undertaken to evaluate the grain yield and protein content of lentil intercropped with bread wheat and oat under two spatial arrangements (alternate rows and mixed rows) and identify optimal genotype combinations in low-input systems for the production of food for human and animal consumption.

2. Materials and Methods

In the 2022–2023 and 2023–2024 growing seasons, experiments were conducted on the farm of the University of Western Macedonia in Florina, Greece (40°46′ N, 21°22′ E, 707 m asl), in a sandy loam soil with a pH of 6.3, organic matter content of 14.0 g kg⁻¹, N-NO₃ concentration of 100 mg kg⁻¹, P (Olsen) concentration of 50.3 mg kg⁻¹, K concentration of 308 mg kg⁻¹, and water holding capacity of 21.8% (0 to 30 cm depth). The plant materials used were cereals (oats, cultivar Kassandra, and bread wheat, cultivar Yekora) and legumes (lentil varieties, Thessaly and Elpida). A completely randomized design with three replications was used. The 3 different species were cropped either using monocropping or cereal–legume intercropping in all possible combinations between them. Therefore, a total of 36 experimental plots were created. The above-mentioned cultivars of the three species (wheat, oat, and lentil) were intercropped in two sowing systems (1:1 alternate lines and mixed sowing of the two species (wheat + lentil and oat + lentil) in the same line at 50:50 seeding ratio). Before sowing, basic fertilization was applied with the addition of diammonium phosphate (20-10-0) so that 80 and 40 kg ha⁻¹ of nitrogen and P₂O₅, respectively, were added into the soil. Sowing was performed by hand. Each experimental plot consisted of 6 lines that were 5 m long, of which the middle 4 were harvested. The sowing distances between the lines were 25 cm, while on the line, the sowing was continuous, and the dimensions of each experimental plot were 5 × 1.5 = 7.5 m². A two-meter corridor was left between replications. The crop was kept free of weeds by hand hoeing when necessary. During the growing season, the following morphological traits were measured: height and total height, blooming, number of fertile spikes or tassels per row (for cereals), and the number of pods per row (for lentil). Specifically, the height of the plants was measured in early April and one day before the harvest. Quantity parameters that were determined included the yield and quality parameters such as weight of 1000 seeds, hectoliter weight, LER (land equivalent ratio), aggressivity index (A), and competitive ratio (CR). When the LER value is less than one, intercropping negatively affects the growth and yield of the mixture species, indicating that resources are utilized more efficiently under monoculture. When the LER is equal to one, intercropping provides neither an advantage nor a disadvantage compared to monoculture. Conversely, when the LER exceeds one, it indicates that the mixtures perform better when intercropping than monocropping, reflecting a more efficient use of resources within the intercropping system [16].

Land equivalent ratio (LER) calculations were performed according to Dhima et al. 2007 [16]: LER = LER legume + LER cereal, where LER legume = YLi/YL and LER cereal = YCi/YC, from which YL and YC represent the yield of the legume and cereal, respectively, under monoculture, and YLi and YCi represent the yield of the legume and cereal under intercropping.

Aggressivity (A) indicates how greater the relative yield increase in the main crop (in our case, bread wheat and oat) is than that of the intercrop (with lentil) in the intercropping system. A positive value indicates that the cereal is the dominant species, while a negative value reflects legume dominance. When A is equal to zero, this indicates that both species are equally competitive. Aggressivity (A) calculations were performed according to Willey (1979) [17]:

Ac = (YCL/YC MONO × ZCL) − (YLC/YL mono × ZLC)

AL = (YLC/YL mono × ZLC) − (YCL/YC mono × ZCL)

• YCL: Yield of the cereal in the intercrop.
• YLC: Yield of the legume in the intercrop.
• YC mono: Yield of the cereal in monoculture.
• YL mono: Yield of the legume in monoculture.
• ZCL, ZLC: Sowing proportions of the cereal and the legume, respectively, in the intercrop (as a fraction of their full monoculture sowing rate).

The competitive ratio (CR) quantifies the relative competitive ability of intercropped species. A CR value greater than 1 indicates that a species is more competitive, while a value below 1 suggests it is being suppressed.

CRwheat = (LERwheat/LERlentil) × (Zlentil/Zwheat)

CRlentil = (LERlentil/LERwheat) × (Zwheat/Zlentil)

where LERwheat, LERlentil are partial land equivalent ratios of wheat and lentil, respectively. Zwheat, Zlentil are proportions of wheat and lentil sown in the intercrop, relative to their full sole crop rates.

The harvesting of the four middle lines was carried out on 15 July 2023 and 10 July 2024 using a combine harvester. This was followed by determining the measurement of protein, ash, and moisture using a SpectraStar 2400–D (Unity Scientific, Milford, MA, USA) NIR (near-infrared spectrometer).

Statistical Analysis

All data were subjected to analysis of variance (ANOVA) to evaluate the effects of year, genotype, and spatial arrangement. Treatment means were compared using least significant difference (LSD) tests at the 5% probability level (p < 0.05). Mean comparisons are shown with different letters to indicate statistically significant differences.

3. Results

3.1. Grain Yield

The grain yield results across the two growing seasons (2022–2023 and 2023–2024) reveal important temporal and genotype variations in both cereals and lentil under intercropping systems. During the 2023–2024 season, cereal grain yield was significantly improved across most intercrop combinations, especially those involving Yekora. The genotype combination Yekora + Thessalia (separate rows) exhibited the highest yield, improving by approximately 91.6%, compared to the yield of the previous growing season (1294.1 kg/ha yield in 2022–2023 and 2478.6 kg/ha in 2023–2024). Similarly, the combination Yekora + Elpida (separate rows) showed improved yield from 1163.5 kg/ha (yield of 2022–2023) compared to 2038.5 kg/ha (yield of 2023–2024). These improved behaviors can be attributed to more favorable agroclimatic conditions in the period 2023–2024, which increased yields in all combinations and made the differences between the treatments more apparent (Figure 1 and Figure 2). Unlike cereals, legume yields remained stable or declined slightly between the two growing seasons, with the exception of the combination Yekora + Thessalia (separate rows), where the legume yield was higher in the second cultivation season (1371.9 kg/ha in 2022–2023 instead of 1745.6 kg/ha in 2023–2024). Across both cultivation seasons, separate row sowing consistently resulted in a significantly higher yield for both cereals and legumes compared to mixed sowing, demonstrating the positive effect of spatial arrangement on resource utilization and species performance in intercropping systems. These results underline the critical role of spatial arrangement in optimizing resource utilization and minimizing interspecific competition in intercropping systems. The combination of Yekora + Thessalia and Yekora + Elpida (alternate rows) emerged as the most productive concerning the total yield, suggesting its high potential for sustainable and efficient land use. Additionally, certain intercrops, particularly those involving Kassandra and Elpida, approached or exceeded the yield of their respective monocultures, highlighting the potential of specific genotype combinations for maximizing land-use efficiency.

3.2. Seed Quality

Protein content is a crucial quality trait in cereal–legume intercropping systems, reflecting not only nutritional value but also the physiological response of genotypes to interspecific interactions and environmental variation.

In both years, the combinations where Yekora was involved consistently showed the highest protein content among cereals, averaging over 12.5%, with small variations between seasons. In contrast, the combinations where Kassandra was involved had markedly lower cereal protein contents (4.6–5.1%), with no substantial differentiation in the second season, highlighting genotype-specific limitations in nitrogen assimilation or remobilization efficiency. Legume protein content remained consistently high across all combinations and both years, generally ranging from 27% to 31%. A minor decrease was observed in 2023–2024. The least affected combinations were Kassandra + Thessalia and Kassandra + Elpida, both in separate and mixed sowing, showing remarkable consistency between years.

The findings suggest that legumes maintain a high protein profile regardless of the cereal mixture or planting season, reaffirming their value as a protein source in intercropping. In contrast, cereal protein content is more genotype-dependent and sensitive to both competition and seasonal factors. As can be seen from the diagrams concerning the protein content, this was not affected by the different climatic conditions prevailing in the two growing seasons and the same profile was more or less maintained (Figure 3 and Figure 4).

3.3. Competition Indices

The land equivalent ratio (LER) is a widely accepted index to evaluate the advantage of intercropping over monocropping. Across both growing seasons, most intercrop combinations recorded LER values greater than 1, showing a clear advantage of intercropping over monocropping systems. However, temporal variation in LER values reflects genotype–genotype interactions and potentially varying environmental conditions. The highest LER was observed in Yekora + Thessalia (separate rows) in the 2023–2024 growing season (2.50) higher value compared to the previous season (1.73). This suggests highly effective interspecific cooperation and minimal competitiveness under the climatic conditions of the period 2023–2024. Very high LER values were recorded in both cultivation seasons in the mixtures Yekora + Elpida (separate rows) and Kassandra + Elpida (separate rows), further confirming the superiority of these combinations. The mixed sowing systems (e.g., Kassandra + Thessalia mixed rows) showed consistently lower LER values over the two years (remained at 0.90), underscoring that the sowing system critically influences intercrop efficiency (Figure 5).

The overall increased LER value in 2023–2024 for most combinations reflects improved complementarity between cereal and legume components. The consistent superiority of sowing in alternate rows over mixed sowing highlights the importance of reduced competition for achieving success between crops (Figure 6).

In both growing seasons, most combinations showed positive aggressivity values for cereals, confirming that cereals generally dominated legumes in the intercropping systems. Legumes showed negative aggression values in almost all combinations, indicating their reduced competitive ability compared to cereals. Of particular interest are the values of the aggressivity index (A) in the combination Kassandra + Elpida (mixed sowing). In 2022–2023, legumes exhibited positive aggression (A = 0.3188), while in 2023–2024, this was reversed with cereals gaining dominance (A = 0.0395). This suggests variation in competitive ability per year, possibly due to changes in growth conditions or biomass distribution of the two species. The results suggest that, although cereals consistently demonstrate dominance in most combinations, their competitive advantage can be moderated by both environmental factors and management practices (e.g., row arrangement). The overall decrease in cereal aggressivity in the 2023–2024 growing season suggests more balanced interspecific interactions, possibly due to improved coexistence or changes in crop vigor (Figure 7).

4. Discussion

The production of high-quality and high-nutrient food for human and animal nutrition is becoming increasingly important in the face of climate change and the food crisis. Intercropping is a new strategy, a credible and ecologically friendly proposal for overcoming these problems. The sowing of one or more crops simultaneously or sequentially [18] in alternating rows, or mixtures on the same row, within the same agricultural plot during the same growing season [1] limits the use of external inputs [18] because of intercropping advantages such as better nitrogen utilization, increased soil fertility, pest and disease control, efficient competition with weeds, and optimization of the utilization of available resources. On the other hand, competition between the two species involved in the intercropping system can reduce the overall yield, while at the same time, it often gives an advantage to the cereals in the mixture with legumes. Cereals are the most important source of concentrated carbohydrates, while legumes are a reliable source of protein, and because of their rapid growth and ability to fix nitrogen, have become an important rotation crop in sustainable and organic agriculture. The findings of this two-year field study confirm that cereal–lentil intercropping, particularly under alternate row arrangements, enhances productivity and resource-use efficiency compared to monocultures. However, the performance of different genotype combinations varied substantially, reflecting complex interactions between species, spatial configuration, and seasonal conditions.

4.1. Yield Variation and Spatial Arrangement

Combinations such as Yekora + Thessalia and Yekora + Elpida in alternate rows consistently yielded the highest total grain production and LER values (up to 2.50), indicating strong interspecific complementarity. In contrast, combinations under mixed sowing (e.g., Kassandra + Thessalia) displayed LER values below 1, signifying inefficient resource use and competitive suppression, especially of lentils. These outcomes underscore the importance of spatial separation, which reduces direct competition and allows for more efficient light, water, and nutrient utilization, as also reported by Tosti et al. (2023) [19] and Koskey et al. (2022) [2]. Finally, Raza et al. (2023) [20] studied low inputs cereal–legume systems and concluded that spatial arrangement plays a decisive role in balancing competition and complementarity.

Despite the general advantage of alternate rows, not all combinations benefited equally. For instance, the performance of Kassandra + Elpida, even in alternate rows, was moderate, suggesting that genotype compatibility also plays a decisive role. This supports findings from Michalitsis et al. (2024) [21], Hoang et al. (2024) [22], and Demie et al. (2022) [23] who emphasized the importance of cultivar selection in intercropping systems.

4.2. Physiological Mechanisms and Competitive Dynamics

The dominance of cereals, as reflected in the positive values of the aggressivity and CR indices, can be attributed to morphological traits such as greater plant height, faster early growth, and dense canopy structure, which enable cereals to outcompete legumes for light. In combinations involving Yekora, this effect was more pronounced due to its tall and vigorous growth habit. Similarly, Ross et al. (2005) [24] attributed the reduced yield of legumes in intercropping with cereals to the greater height of cereals and their resulting increased competition for light. Bijarnia et al. (2024) [25] attributed the higher competitiveness of baby corn in intercropping with cowpea to its faster growth rate, taller canopy, and more extensive root system. Interestingly, while cereal yield generally increased in the second cultivation season, likely due to favorable weather conditions, legume yield either remained stable or slightly declined in most combinations. This observation is consistent with findings by Lorenzetti et al. (2024) [26], who reported that cereals tend to benefit more from improved climatic conditions in intercrops, while legumes may suffer from increased shading or below-ground competition, especially when grown with highly competitive wheat genotypes. Both studies observed that cereals generally exhibited higher competitiveness over legumes, as indicated by positive aggressivity and competitive ratio (CR) indices.

Below-ground competition also played a role. Lentils, with shallower and less aggressive root systems, may have been disadvantaged in mixed rows where cereal roots competed for limited soil nutrients and water. Additionally, the lack of spatial separation in mixed sowing reduces the niche differentiation that typically underpins successful intercropping.

Though not directly measured in this study, root exudate interactions and mycorrhizal symbiosis could also influence competitive balance. Previous studies (e.g., Duchene et al. 2017) [27] suggest that legumes can facilitate nutrient access for cereals via rhizosphere processes, particularly when root zones are spatially distinct. Future studies incorporating rhizobox trials or isotopic tracing could clarify these mechanisms.

4.3. Protein Content and Nutrient Allocation

Legume protein content remained consistently high across treatments (27–31%), highlighting their physiological stability and suitability for nutritional enhancement in intercropping systems. In contrast, cereal protein content was more sensitive to genotype, with Yekora outperforming Kassandra regardless of spatial arrangement. These differences may reflect variation in nitrogen uptake efficiency and allocation patterns. As suggested by Koskey et al. (2022) [2], cereals with enhanced N-use efficiency contribute more positively to the nutritional quality of intercrops. Similarly, Zingale et al. (2023) [28] found that intercropping durum wheat with legumes not only enhanced yield but also improved grain amino acid composition. This is in agreement with our own observations, especially in systems including lentil, which retained its high protein levels while contributing to protein enrichment in cereals. In a broader context, Chimonyo et al. (2023) [29] reviewed intercropping across sub-Saharan Africa and emphasized its contribution to protein output per hectare. Their focus on nutritional efficiency per unit area reinforces the use of land equivalent ratio (LER) as a meaningful indicator. Our findings, with LER values consistently exceeding 2.0, support this approach and confirm the efficiency of intercropping in maximizing both land use and protein production.

Interestingly, high cereal aggressivity was often associated with reduced legume yield and quality, confirming the trade-off between dominance and interspecies balance. Therefore, selecting cereal cultivars with moderate competitive ability (e.g., Kassandra) may be beneficial for achieving more equitable resource partitioning.

4.4. Broader Agronomic and Ecological Considerations

While this study emphasized productivity, intercropping also offers significant environmental and economic benefits. Legume inclusion can reduce the need for synthetic nitrogen fertilizers by up to 25–30%, lowering production costs and mitigating greenhouse gas emissions. Furthermore, spatial arrangements that promote complementarity may enhance soil carbon sequestration, improve microbial diversity, and suppress weeds and pests—benefits widely acknowledged but not yet quantified in this study.

Economically, intercropping may improve land-use efficiency, reduce input costs, and stabilize yields under climatic stress, but the absence of cost–benefit analyses or market valuation in this study limits firm conclusions on adoption potential. Future work should integrate economic modeling to assess profitability under different genotype–management combinations.

4.5. Comparison with Other Intercropping Systems

Our results support the superiority of alternate row sowing in cereal–legume systems, in line with studies on lentil with barley [19], wheat with faba bean [20], maize with soybean [30], and faba bean with barley [31]. However, this contrasts with findings by Gennatos and Lazaridou (2021) [32], who observed higher forage yield in mixed sowing of barley with forage peas. These contrasting outcomes highlight that intercropping performance is highly context-specific, influenced by crop purpose (grain vs. forage), species traits, and local conditions. In addition, the sowing in separate rows is considered as an alternate technique in order to overcome the competition of two species for nutrients and light and avoid a reduction in the cereal or legume yield [33].

5. Conclusions

This study highlights the potential of lentil–cereal intercropping under Mediterranean rainfed conditions. The combination of genotype selection with alternate row sowing improved both yield and protein content. Yekora bread wheat combined with Thessalia lentils was particularly effective, demonstrating enhanced yield, resource efficiency, and reduced competition. Intercropping, when strategically designed, can contribute to more sustainable and productive agroecosystems.

This two-year field study demonstrated that intercropping lentil with bread wheat or oat, particularly in alternate row configurations, significantly improved grain yield, land-use efficiency, and protein content stability, compared to monoculture systems. The most productive combinations were Yekora + Thessalia and Yekora + Elpida in alternate rows, reflecting efficient resource use and strong interspecific complementarity.

Legumes maintained stable and high protein levels across all treatments and seasons, affirming their value as reliable protein contributors in intercropping systems. Meanwhile, cereal protein content varied by genotype: Yekora consistently achieved >12.5%, while Kassandra remained below 5%, highlighting the importance of cereal cultivar selection.

Among the intercropping configurations tested, alternate row sowing emerged as the most effective, reducing interspecific competition and supporting mutual crop benefits. Conversely, mixed sowing often resulted in suppressed legume performance, lower LER values (<1.0 in some cases), and cereal dominance, particularly when involving competitive genotypes such as Yekora.

A different behavior was observed between the two growing seasons in terms of yield, but not in terms of protein content, due to the different climatic conditions that prevailed. The less favorable conditions of the first cultivation period reduced yields and also the differences between the various combinations used.

These results emphasize that spatial arrangement and genotype compatibility are critical to the success of cereal–legume intercropping systems. The findings support the adoption of such systems as a sustainable intensification strategy, especially under low-input conditions typical of Mediterranean-type environments.

Further research should focus on the following:

• Quantifying the environmental benefits of intercropping (e.g., reduced fertilizer use, soil health improvement).
• Incorporating economic evaluation (e.g., cost–benefit ratios, net returns).
• Exploring below-ground interactions (e.g., mycorrhizal symbiosis, nitrogen transfer mechanisms).
• Evaluating multi-season and multi-location performance to support wider adoption.