Land equivalent ratio

The Land Equivalent Ratio (LER) is a key agronomic index used to assess the land-use efficiency of intercropping systems by comparing their total yield to that of equivalent areas under sole cropping of the individual component crops at the same management level.^[1] It represents the relative land area required for monocultures to achieve the same combined output as the intercrop, thereby quantifying potential productivity gains from mixing crops.^[1] Originally conceptualized in earlier studies on crop mixtures dating back to the 1950s and 1960s, the LER was formally defined and popularized in 1980 to provide a standardized measure for evaluating intercropping advantages across diverse agricultural contexts.^[1] The LER is calculated as the sum of the partial land equivalent ratios for each crop in the mixture: LER = (Y_{ab} / Y_{sa}) + (Y_{ba} / Y_{sb}), where Y_{ab} is the yield of crop A in the intercrop, Y_{ba} is the yield of crop B in the intercrop, Y_{sb} is the sole-crop yield of B, and Y_{sa} is the sole-crop yield of A, all typically expressed per unit area.^[1] This formula assumes equal proportions of land allocation to each crop in the intercrop unless adjusted, and it relies on field trials to determine actual yields under comparable conditions.^[1] An "effective LER" variant can further refine the analysis by incorporating the farmer's desired yield proportions, ensuring the metric aligns with practical farming goals rather than equal outputs.^[1] When the LER exceeds 1, it indicates that the intercropping system is more land-efficient than monocultures, often due to complementary resource use such as light, water, and nutrients among crops, leading to higher overall productivity.^[1] Values below 1 suggest a disadvantage, while an LER of 1 implies no difference in land use efficiency.^[1] The metric has proven robust across various scales and management practices, making it a staple for research in sustainable agriculture, agroforestry, and crop diversification strategies aimed at enhancing food security and environmental resilience.^[2]

Background and Concepts

Definition

The land equivalent ratio (LER) is a metric used in agronomy to quantify the land use efficiency of intercropping systems relative to monocropping, representing the relative land area required under sole cropping to achieve the same total yield as obtained from the intercrop.^[1] It serves as an indicator of land productivity efficiency by comparing the performance of mixed cropping arrangements against separate cultivation of individual crops on dedicated land.^[3] Intercropping involves the simultaneous cultivation of two or more crop species on the same land, often in spatial or temporal arrangements that promote complementary resource utilization, in contrast to monocropping, which grows a single crop species across the entire area.^[1] The LER calculation relies on sole crop yield, defined as the productivity of a crop when grown alone under similar conditions, and intercrop yield, which is the productivity of each crop within the mixed system.^[3] These yields form the basis for assessing whether the intercropping arrangement enhances overall land productivity beyond what monocropping could achieve. The total LER is derived by summing partial LER values for each component crop in the intercrop, where a partial LER measures the relative contribution of an individual crop's intercrop yield compared to its sole crop yield.^[1] This summation provides a comprehensive evaluation of land productivity efficiency, with values greater than 1 indicating that intercropping requires less land than monocropping for equivalent production, thereby highlighting potential advantages in resource use.^[3]

Historical Development

The concept underlying the land equivalent ratio (LER), known as the relative yield total (RYT), emerged in the 1960s as a tool to quantify yield advantages in crop mixtures, with de Wit and van den Bergh introducing it in 1965 in their study on competition between herbage plants.^[4] The term LER and its formal framework were introduced in a seminal paper by R. Mead and R.W. Willey published in 1980. Titled "The Concept of a 'Land Equivalent Ratio' and Advantages in Yields from Intercropping," the work appeared in Experimental Agriculture and proposed LER as a standardized metric to compare the land area required for sole cropping versus intercropping to achieve equivalent yields, emphasizing its utility in evaluating resource use efficiency.^[1] This publication built on earlier discussions of intercropping productivity but provided the first rigorous framework for LER under that name, drawing from field experiments with cereal-legume mixtures.^[5] Following its introduction, LER saw early adoption in tropical agriculture research during the 1980s, particularly for assessing mixed cropping systems common in developing regions of Africa, Asia, and Latin America. Researchers at CGIAR centers, such as the International Institute of Tropical Agriculture (IITA) and the International Center for Tropical Agriculture (CIAT), applied LER to evaluate intercropping combinations like cassava-maize and rice-legume systems, demonstrating yield benefits over monocultures in resource-limited environments.^[6] This focus on tropical contexts aligned with global efforts to intensify smallholder farming without expanding land use, as evidenced in studies from Thailand and sub-Saharan Africa during the decade.^[7] By the 1990s, LER had evolved from a basic yield comparison tool into a key component of agroecological models, incorporating factors like temporal dynamics and environmental interactions to assess sustainable land management. The Food and Agriculture Organization (FAO) integrated LER into its frameworks for evaluating diversified cropping efficiency, highlighting its role in promoting agroecological practices that enhance overall system productivity.^[8] Similarly, CGIAR programs expanded its use in climate-resilient agriculture studies, where meta-analyses showed average LER values exceeding 1.0 in intercropped systems, underscoring advantages for food security in tropical zones.^[9]

Calculation and Interpretation

Formula

The land equivalent ratio (LER) is a dimensionless index used to quantify the land use efficiency of intercropping systems relative to monocultures. Its standard mathematical formulation for a two-crop system is given by

\text{LER} = \frac{Y_{ab}}{Y_{sa}} + \frac{Y_{ba}}{Y_{sb}},

where Y_{ab} represents the yield of crop A grown in the intercrop, Y_{ba} is the yield of crop B in the intercrop, Y_{sa} is the yield of crop A in monoculture, and Y_{sb} is the yield of crop B in monoculture.^[1] All yields must be measured in consistent units per unit land area, such as kilograms per hectare (kg/ha), to ensure comparability across cropping systems. The variables in the formula account for the proportional land shares implicitly through the yields obtained per unit area in each system; for instance, if crop A occupies a fraction p of the land in the intercrop, Y_{ab} reflects the total yield of A from that area, while Y_{sa} assumes full land use for A alone.^[1] This formulation derives from the conceptual basis of relative land area requirements: it calculates the total area of monoculture land needed to match the intercrop yields of each component crop, assuming equivalent land allocation in the monoculture comparisons for fairness.^[1] The approach builds on earlier work relating mixture productivity to sole crop equivalents, emphasizing total relative yield as a proxy for land productivity. For intercropping systems involving more than two crops, the LER extends additively as the sum of partial LERs for each component:

\text{LER} = \sum_{i=1}^{n} \frac{Y_i}{Y_{si}},

where n is the number of crops, Y_i is the intercrop yield of the i-th crop, and Y_{si} is its monoculture yield, maintaining the same unit consistency and relative land basis.^[1]

Example Calculation

To illustrate the application of the land equivalent ratio (LER), consider a typical example from maize-bean intercropping systems, where yields are measured in tons per hectare (t/ha). In this scenario, the intercrop maize yield is 3.2 t/ha, compared to a monocrop maize yield of 5.0 t/ha; the intercrop bean yield is 1.1 t/ha, compared to a monocrop bean yield of 1.8 t/ha.^[10] The computation begins with the partial LER for each crop, which represents the ratio of intercrop yield to monocrop yield:

Partial LER for maize: \frac{3.2}{5.0} = 0.64
Partial LER for bean: \frac{1.1}{1.8} \approx 0.61

The total LER is the sum of these partial values: $0.64 + 0.61 = 1.25.^[10] An LER greater than 1, such as 1.25 here, indicates a land use efficiency advantage, meaning the intercropping system produces the equivalent of 25% more land's worth of output compared to separate monocrops.^[10] Yield data input into the LER can vary depending on the intercropping design. In replacement intercropping, where the total plant density matches that of the monocrops (e.g., substituting rows or proportions), yields are compared directly on an area basis. In additive intercropping, where the density of one or both crops is increased beyond monocrop levels, the LER often reflects higher values due to the additional biomass, though competition may influence outcomes.

Applications

Intercropping Systems

Intercropping systems commonly employ the land equivalent ratio (LER) to assess the efficiency of combining crops, particularly in cereal-legume pairings such as maize and beans or cowpea, where legumes fix nitrogen to complement cereal demands.^[11] In row intercropping, crops are planted in alternating strips, such as 1:1 or 2:2 row configurations of maize and cowpea, allowing spatial separation to minimize competition, while mixed intercropping involves within-row planting of both species for intimate association and enhanced resource sharing.^[11] Relay cropping, exemplified by cowpea sown into standing sorghum fields, extends the growing season and leverages temporal niche differentiation to boost overall productivity, with LER values exceeding 1 across manure application rates in smallholder setups.^[12] In tropical smallholder farms of sub-Saharan Africa, LER evaluates intercropping performance under variable soil fertility and moisture, revealing yield advantages; for instance, maize-cowpea systems in northern Ghana's Guinea savanna achieved LERs of 1.14 to 1.81, highest in low-fertility fields with within-row arrangements.^[11] Similarly, meta-analyses of African intercropping trials report average LERs of 1.45 for maize-legume combinations, ranging from 1.2 to 1.5, demonstrating 20-50% land savings compared to sole cropping.^[13] In Mozambique's sandy soils, maize-cowpea intercropping yielded LERs of 1.51 for straw and up to 1.91 for grain, outperforming monocultures by improving nutrient access.^[14] LER guides planting density optimization by quantifying trade-offs in intercropping configurations; for example, within-row maize-cowpea at balanced densities maximizes LER above 1.5 in nutrient-poor sites, informing farmers to adjust ratios for reduced competition and higher total output.^[11] Unlike the relative yield total (RYT), which assesses yield advantages based on unit area and population density, LER specifically emphasizes the relative land area required to achieve equivalent yields, highlighting spatial efficiency in diverse systems.^[15]

Sustainable Agriculture and Agroecology

In agroecology, the land equivalent ratio (LER) serves as a key metric for evaluating the efficiency of polyculture systems, where it quantifies land use advantages by comparing combined yields from diverse crop mixtures to equivalent monocultures, often revealing enhanced resource utilization such as water, nutrients, and sunlight.^[8] This approach supports biodiversity assessment by highlighting how polycultures foster ecological synergies, such as improved soil health and pest regulation, which contribute to overall system resilience compared to monocultures.^[16] The Food and Agriculture Organization (FAO) promotes LER within its agroecology framework to advance climate-resilient farming practices, emphasizing its role in integrating crops, trees, and livestock to minimize external inputs and bolster adaptation to environmental stresses like drought.^[8] Modern applications of LER extend to agroforestry, particularly in tree-crop systems, where values exceeding 1.3 demonstrate superior productivity; for instance, walnut-cereal intercroppings in Mediterranean climates achieve LERs of 1.3 to 1.6, reflecting efficient land use while providing additional ecosystem services like shade and soil stabilization.^[17] Post-2000, LER has informed policy impacts in carbon sequestration models, as agroforestry systems with high LERs—such as silvoarable schemes yielding 1.0 to 1.4—enhance soil carbon storage and align with incentives for sustainable land management under frameworks like the European Union's Common Agricultural Policy.^[18] Research trends underscore LER's value through meta-analyses, including a 2016 study on cereal-legume mixtures that reported a median LER of 1.16 across diverse management practices, indicating consistent land efficiency gains when legumes are sown earlier or densities are optimized to balance competitive interactions.^[19] A 2024 study further demonstrated that legume intercropping improves long-term productivity and soil carbon storage, with systems requiring on average 19% less land than monocultures.^[20]

Advantages and Limitations

Benefits

The land equivalent ratio (LER) serves as a key indicator of land efficiency in intercropping systems, where values greater than 1 demonstrate overyielding compared to monocultures, signifying improved utilization of resources such as light, water, and nutrients.^[21] For instance, a meta-analysis of 934 experiments found an average LER of 1.23 for grain yields, equivalent to 19% land savings relative to sole cropping, alongside enhanced nitrogen use efficiency (total output index of 1.11).^[21] This overyielding arises from complementary resource capture among crop species, allowing for higher total productivity per unit area without proportional increases in inputs.^[22] In practical terms, LER analysis aids farmers in resource-poor settings by identifying intercropping combinations that maximize output per hectare, thereby promoting food security through increased and diversified production.^[21] Systems with LER > 1 can produce equivalent yields on less land, reducing pressure on arable areas and supporting smallholder livelihoods in regions with limited farmland.^[23] Additionally, by encouraging crop diversification, LER-guided practices help mitigate risks from environmental variability, such as drought, while enhancing overall system resilience.^[21] Intercropping informed by LER also supports diversification strategies that reduce pest risks, as mixed systems disrupt pest lifecycles and habitats more effectively than monocultures.^[24] This biodiversity-driven pest suppression contributes to stable yields without heavy reliance on chemical controls, aligning with sustainable agriculture goals.^[24] Empirical studies consistently link higher LER values to improved economic returns in mixed systems, with land savings often ranging from 16% to 50%.^[22]^[23] For example, in Cameroon, maize-legume intercropping achieved LERs up to 1.93, correlating with benefit-cost ratios of 3.5, outperforming monocropping economically.^[23] Similarly, maize-okra intercropping in Nigeria yielded LERs of 1.89–1.96 and gross monetary returns up to ₦26,850 per hectare, demonstrating profitability gains of 35% over sole cropping at optimal densities.^[25] These findings underscore LER's role in quantifying the financial viability of intercropping for enhanced farmer income.^[23]

Assumptions and Criticisms

The land equivalent ratio (LER) relies on several key assumptions to facilitate comparisons between intercropping and monocropping systems. It presupposes equal soil quality and management practices across both systems, including identical levels of inputs such as fertilizers, water, and pest control, to ensure that any observed yield differences stem solely from cropping arrangement rather than environmental or agronomic variations.^[26] Additionally, LER assumes that yields for intercropped and sole-cropped species are measured at equivalent stages of maturity or harvest timing, allowing for direct comparability of productivity under standardized conditions. The metric further ignores non-land factors, such as differences in labor requirements, machinery use, or overall management complexity, which may be higher in intercropping due to the need for synchronized planting and harvesting of multiple species.^[26] Criticisms of LER highlight its sensitivity to the choice of monocrop baselines, particularly in systems with uneven competition between species, where variations in planting densities or spacings can distort the ratio's interpretation of land use efficiency.^[2] For instance, reliance on mean monocrop yields from experimental sites as a reference may overlook site-specific conditions, leading to inflated or underestimated advantages in heterogeneous environments.^[26] Another major critique is LER's overemphasis on total yield as a proxy for efficiency, without incorporating crop quality, nutritional value, or economic returns, which can result in misleading assessments when intercropped species have differing market values or production costs. This focus on biomass alone also fails to capture absolute productivity levels, as a high LER does not guarantee superior overall output compared to monocropping.^[26] To address LER's shortcomings, particularly in competitive intercropping systems where LER values fall below 1, complementary indices such as the relative crowding coefficient (RCC) and aggressiveness (A) are often employed. These metrics provide deeper insights into interspecific competition dynamics; for example, RCC quantifies the relative dominance of one species over another in resource capture, while A measures the relative yield depression or advantage of each crop compared to its monocrop performance.^[27] Such alternatives help interpret cases of yield disadvantage by revealing underlying competitive interactions that LER alone may obscure.^[27]