What Is Land Equivalent Ratio?
The Land Equivalent Ratio (LER) is a metric used primarily in agricultural economics and resource allocation to assess the effectiveness of growing multiple crops simultaneously on the same plot of land, a practice known as intercropping, compared to growing them separately in monoculture. It quantifies the relative land area required under sole cropping to achieve the same yield as obtained from an intercropped system. Essentially, Land Equivalent Ratio provides a standardized way to determine if a mixed-cropping system is more efficient in its use of land than a single-crop system. The Food and Agriculture Organization (FAO) defines LER as "the ratio of the area under sole cropping to the area under intercropping needed to give equal amounts of yield at the same management level."9
History and Origin
The concept of evaluating the efficiency of mixed cropping systems has roots in early agricultural research. However, the specific formalization of the Land Equivalent Ratio as a widely accepted index is often attributed to the work of R. Mead and R.W. Willey, who published "The Concept of a 'Land Equivalent Ratio' and Advantages in Yields from Intercropping" in Experimental Agriculture in 1980.8 This seminal paper provided a clear methodology for calculating LER, offering a robust tool for researchers and farmers to quantify the advantages in efficiency gained from intercropping practices. Before this, similar concepts, such as the "relative yield total" (RYT), were proposed by de Wit and van den Bergh in 1965.7 The development of LER provided a more refined and widely adoptable measure for assessing productivity gains in mixed-cropping systems.
Key Takeaways
- The Land Equivalent Ratio (LER) measures the land efficiency of intercropping systems compared to monoculture.
- An LER greater than 1 indicates a yield advantage from intercropping, meaning less land is needed for the same total output.
- LER is calculated as the sum of the ratios of intercropped yields to sole-crop yields for each component crop.
- It serves as a crucial tool for promoting sustainability and maximizing land productivity in agriculture.
- Limitations include assumptions about equivalent management levels and the potential for not fully accounting for varying crop values or production costs.
Formula and Calculation
The Land Equivalent Ratio (LER) is calculated by summing the individual LERs of each crop grown in the intercropping system. The formula for LER with (m) different crops is:
Where:
- (LER) = Land Equivalent Ratio
- (IY_i) = Yield of the (i^{th}) crop when grown in an intercropped system
- (SY_i) = Yield of the (i^{th}) crop when grown as a sole crop (monoculture) on the same land area
- (m) = Total number of crops in the intercropping system
This formula allows for the direct comparison of combined yields from an intercropped field against what those individual crops would produce if grown separately on equivalent land areas, highlighting the overall land use optimization.
Interpreting the Land Equivalent Ratio
The interpretation of the Land Equivalent Ratio is straightforward and provides critical insights into the economic efficiency of intercropping.
- LER > 1: An LER greater than 1 indicates that the intercropping system is more efficient than sole cropping. For example, an LER of 1.2 suggests that 20% less land is required under the intercropping system to produce the same total yield as if the crops were grown separately. This signifies a land-use advantage, implying better utilization of environmental resources like light, water, and nutrients, or a positive interaction between the crops, leading to greater overall output from a given area. This can be seen as a form of comparative advantage in land use.6
- LER = 1: An LER equal to 1 suggests that the intercropping system provides no land-use advantage or disadvantage compared to sole cropping. The same total yield could be obtained by growing the crops separately.
- LER < 1: An LER less than 1 indicates that the intercropping system is less efficient than sole cropping. This means that more land would be required under the intercropping system to achieve the same total yield as in monoculture. This could be due to strong competition between the intercropped species, leading to reduced yields for one or both crops.
Hypothetical Example
Imagine a farmer is considering intercropping corn and beans. To calculate the Land Equivalent Ratio, they first need data on the yields of each crop when grown in monoculture and when intercropped.
Monoculture Yields:
- Corn (sole crop): 5,000 kg per hectare
- Beans (sole crop): 1,500 kg per hectare
Intercropped Yields (from 1 hectare of intercropped land):
- Corn (intercropped): 3,500 kg per hectare
- Beans (intercropped): 1,000 kg per hectare
Now, let's calculate the individual LERs for each crop:
- LER (Corn) = (Intercropped Corn Yield) / (Sole Corn Yield) = 3,500 kg / 5,000 kg = 0.70
- LER (Beans) = (Intercropped Beans Yield) / (Sole Beans Yield) = 1,000 kg / 1,500 kg = 0.67
Finally, sum the individual LERs to get the total Land Equivalent Ratio:
- Total LER = LER (Corn) + LER (Beans) = 0.70 + 0.67 = 1.37
In this hypothetical example, the Land Equivalent Ratio of 1.37 indicates that the intercropping system is 37% more efficient in terms of land use than growing corn and beans separately. This means that to achieve the same total output, the intercropped system requires 37% less land than if the crops were cultivated individually. This insight could influence a farmer's investment decisions regarding planting strategies.
Practical Applications
The Land Equivalent Ratio has numerous practical applications across various domains, particularly within agriculture and related resource management fields. It is a vital tool for:
- Agricultural Research and Development: Researchers use LER to evaluate the performance of different intercropping systems, identifying crop combinations and spatial arrangements that maximize land use efficiency and productivity. Studies frequently employ LER to demonstrate yield advantages of multi-crop farms over sole-crop farms.5
- Farm Management and Financial Planning: Farmers can use LER to make informed decisions about cropping patterns, optimizing their limited land resources to increase overall output and potential income. It helps assess the profitability of intercropping versus monoculture, as seen in analyses of maize and soybean intercropping in dryland agroecosystems.4
- Sustainable Agriculture and Sustainability Initiatives: LER is a key indicator for promoting sustainable farming practices. By demonstrating that less land is needed to produce the same amount of food, intercropping, guided by LER, supports efforts to reduce agricultural expansion and its environmental footprint.
- Supply Chain Planning: For industries reliant on agricultural products, understanding the land optimization potential through LER can inform sourcing strategies and forecasts, contributing to more stable and efficient supply chains.
- Policy Making: Government agencies and non-governmental organizations involved in food security and land use planning can utilize LER data to formulate policies that encourage efficient and sustainable agricultural practices, particularly in regions with high population density or limited arable land.
Limitations and Criticisms
While the Land Equivalent Ratio is a widely used and robust indicator of yield advantage in multi-crop systems, it does have certain limitations and has faced criticisms. One major critique is that LER typically assumes the same level of management for both intercropping and monocropping systems, which may not always be realistic in practice.3 Intercropping often involves more complex management, potentially requiring different labor inputs, pest control strategies, or nutrient management, which are not directly reflected in the LER calculation.
Another drawback is that LER does not inherently account for differences in the market value or economic significance of the component crops. An intercropping system might have a high LER, indicating efficient land use, but if one of the crops has a very low market value, the overall economic benefit to the farmer might be less attractive. Some studies have noted that LER often considers only direct costs and benefits, potentially overlooking indirect and social costs and benefits associated with different farming systems.2 Furthermore, LER focuses solely on yield and does not directly incorporate other factors important for farmers, such as production risk management or specific grower preferences. Researchers have also highlighted issues with how certain formulas derived from LER, such as land use efficiency (LUE), have been miscited or incorrectly applied in some studies.1
Land Equivalent Ratio vs. Relative Yield Total
The Land Equivalent Ratio (LER) and Relative Yield Total (RYT) are closely related concepts used to evaluate the efficiency of intercropping systems. In essence, LER is the modern and more commonly used term for what was previously or is sometimes still referred to as RYT.
The Relative Yield Total (RYT) was introduced earlier as a measure of the biological advantage of mixed cropping systems. Like LER, it is calculated by summing the relative yields of each component crop, where the relative yield of a crop is its yield in the mixture divided by its yield in monoculture. Therefore, the formula and interpretation are identical to that of the Land Equivalent Ratio. The key distinction lies more in historical terminology and common usage. While RYT laid the groundwork, the Land Equivalent Ratio became the more formalized and widely adopted index, particularly following its comprehensive treatment by Mead and Willey. Both terms aim to quantify whether a given area of land under a mixed-cropping system produces more total output than the same area of land under sole crops, thereby reflecting the efficiency of land use.