Intercropping legumes and cereals: best practices and long-term benefits

Intercropping legumes and cereals (wheat or barley) is a regenerative agronomic practice designed to increase overall productivity, boost soil fertility, and lower environmental impact. By leveraging the biological nitrogen fixation of legumes, this approach optimizes resource use—light, water, and nutrients—while curbing weed pressure and erosion. Proper planning (moderate seeding rates, timely undersowing, and selective herbicide management) ensures balanced crop development and minimizes lodging risk.

Intercropping between legumes and cereals (in this case, wheat or barley) is an regenerative agronomic practice aimed at:

• increasing productivity
• improving soil fertility
• reducing environmental impact.

Below is a technical overview of how to effectively plan and manage this strategy, highlighting its benefits and challenges.

Agronomic Rationale: Why Introduce Legumes?

Legumes (e.g., protein pea, vetch, clover, faba bean) are well-known for their ability to perform biological nitrogen fixation (BNF). Symbiotic bacteria (e.g., Rhizobium spp., Bradyrhizobium spp.) in their root nodules capture atmospheric nitrogen and make it available to both the host plant and, to some extent, the surrounding soil ecosystem. In the medium and long term, this results in:

1. Reduced need for synthetic nitrogen fertilizers (lower costs and less pollution).
2. Improved soil fertility through the addition of organic matter and the structural benefits of legume roots, which enhance soil porosity and aggregate stability.
3. Increased biodiversity, as the presence of two (or more) cultivated species promotes ecological diversification, with positive effects on pests, diseases, and weeds.

Which Legume Species Should Be Selected?

Among the legumes commonly intercropped with cereals, vetch (Vicia sativa and Vicia villosa) plays a prominent role. This crop is particularly valued for its high nitrogen-fixing capacity and vigorous vegetative growth, making it highly effective in competing with weeds. The abundant biomass production of vetch contributes to soil structure improvement. However, its medium-to-long growth cycle makes it more sensitive to water scarcity, particularly in warm climates where careful irrigation management or conservation practices like mulching and reduced tillage are essential to prevent water and heat stress.

Another promising option is protein pea (Pisum sativum subsp. arvense). This species is often cultivated for its high-protein grain, primarily for livestock feed. While its root system contributes to soil fertility, it is relatively sensitive to waterlogging and therefore requires well-drained soils. In its early growth stages, protein pea produces less biomass than vetch, potentially providing less effective weed suppression.

Faba bean (Vicia faba var. minor), widely used in Mediterranean regions, has a deep root system that improves soil structure and aeration, fostering beneficial soil microorganisms. It tolerates cooler climates well but is sensitive to high thermal stress during flowering, which can impair pod formation. Despite this, when properly managed, faba bean fixes substantial amounts of nitrogen, reducing the need for synthetic fertilizers.

Finally, clovers (Trifolium spp.), including species such as Trifolium repens, incarnatum, and alexandrinum, offer diverse growth habits. Clovers are particularly effective at covering the soil, helping to suppress weeds and maintain moisture in the upper soil layers. However, many annual summer clovers are poorly adapted to high temperatures, which can limit their performance in regions with thermal stress during critical growth or pre-flowering phases.

Planning and Sowing Strategies

Intercropping between winter cereals and legumes requires meticulous planning to ensure optimal development of both crops while avoiding issues such as lodging or inadequate soil coverage.

Initially, cereals (e.g., wheat or barley) are sown in autumn at moderate seeding rates. Over-seeding should be avoided as it may lead to lodging in spring, which reduces light penetration to the soil and hampers the successful establishment of undersown legumes.

The second step involves sowing legumes in late winter, during the cereal's tillering phase. Given the small seed size of most legumes used in intercropping (e.g., vetch or clover), it is recommended to use a fertilizer spreader capable of accurately distributing 30–50 kg/ha of seed. To achieve even seed distribution, the spacing between passes should be narrower than for standard fertilizer applications.

Following the legume sowing, an operation with a tine harrow can be performed to incorporate the seeds into the soil while simultaneously controlling early-stage weeds. Alternatively, a conventional cereal seed drill may be used, ensuring that the legume seeds are not buried deeper than 1 cm to promote uniform establishment across the field.

Once the emergence phase is complete, cereal management continues as in conventional systems. Fertilization and disease control strategies are applied, bearing in mind that selective herbicides may be necessary for effective weed control. Herbicides should be carefully chosen to avoid damage to the legume crop.

Finally, at maturity, cereals are harvested. A medium-low cutting height is recommended, and straw should be removed from the field to enhance light availability for the legume, allowing it to grow further and outcompete summer weeds.

Practical example of intercropping implemented at Horta S.r.l.

1. February – Legume seeds are broadcast-sown into wheat fields to initiate their germination early without interfering with the emergence and tillering of the cereal.
2. Late March – At the end of the wheat tillering phase, clover is also introduced. This ensures a diversified ground cover, reducing the risk of direct competition between species while maintaining good crop density.
3. Early June – The legume begins to develop, but the strong competition from wheat for light and water limits its excessive growth. This creates a dynamic balance between the two species, with the legume remaining in optimal conditions to continue its vegetative phase.
4. Harvest Phase – During wheat harvesting, legume seeds are sown again, taking advantage of the harvest operation to distribute the seeds with minimal additional effort.
5. July – After the wheat harvest, the legume quickly expands across the field cleared of the cereal, effectively occupying the space and reducing the emergence of weeds. In the surrounding untreated areas, however, a significant presence of weeds is observed.
6. August – In the absence of sown legumes, harvested wheat fields are quickly colonized by weeds, leading to negative consequences for agronomic management and soil quality. Conversely, in fields where legumes were introduced, the cover remains functional and contributes to soil regeneration.

Long-Term Benefits and Final Considerations

Intercropping provides a range of benefits that enhance both productivity and environmental sustainability. From an agronomic perspective, one of its key advantages is the overall productivity increase, as mixed crops exploit available resources—light, water, nutrients, and carbon dioxide—more effectively. The complementary use of resources by species with different phenological and root characteristics minimizes intraspecific competition and leads to higher biomass production compared to monoculture.

In terms of resource conservation and soil management, intercropping reduces soil erosion and runoff through more intensive and continuous ground cover. This minimizes nutrient loss, improves soil structure, and enhances water use efficiency. The inclusion of legumes in intercrop systems further boosts soil fertility: their nitrogen-fixing ability decreases reliance on chemical fertilizers, delivering economic and environmental benefits.

Intercropping also improves ecological resilience. More diverse cropping systems offer natural insurance against climatic and pest-related challenges. The presence of species with varying growth cycles disrupts pest and pathogen life cycles while supporting a more abundant population of pollinators and beneficial insects. Consequently, farmers can reduce pesticide usage and adopt a more balanced, sustainable management approach.

Finally, in terms of environmental sustainability, intercropping reduces carbon footprints by lowering the need for chemical fertilizers and enhancing carbon sequestration through diverse crop residues. This virtuous cycle enhances the overall health of the agroecosystem, ensuring the long-term productivity and sustainability of cultivated lands for future generations.

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