The Soil Footprint: A new indicator to measure the impact of agriculture on soil erosion

A team of researchers from the Department of Agronomy at the University of Córdoba has taken a decisive step in the fight against soil degradation by introducing an innovative concept: the soil footprint.

Led by Andrés Peñuela, Vanesa García Gamero and Tom Vanwalleghem, they have developed a method for calculating and comparing the impact of different crops on agricultural soil loss. This new tool is essential for raising awareness among producers and consumers of the seriousness of soil erosion and the importance of protecting this vital resource.

Their work is based on the idea that just as concepts such as the carbon footprint or water footprint have raised awareness of the environmental impact of the products we consume, the soil footprint could do the same for soil erosion. The researchers’ main aim is to simplify the communication of this issue, a threat that has been largely overlooked but which has significant implications for the future of agriculture and global food security.

What is the Soil Footprint?

The soil footprint is an indicator that measures the impact of a crop on agricultural soil loss, or how much soil is eroded in the process of growing a particular food. It is calculated by dividing the erosion rate by the crop yield, giving a figure that indicates how much soil is lost per unit of food produced.

This concept, proposed by the research team, aims to provide a clearer understanding of the problem of soil erosion. The simplicity of the formula – erosion divided by productivity – makes it applicable and understandable to both experts and the general public.

The value of the Soil Footprint lies in its ability to quantify, compare and communicate the impact of different crops on soil. For the first time, we can measure how much land is eroded over time depending on the type of crop – essential information for developing sustainable agricultural management strategies.

How is the Soil Footprint Measured?

The formula behind the Soil footprint may be straightforward, but its implications are far-reaching. It is measured using two key factors:

• Soil erosion rate (t/ha/year): This is the amount of soil that is lost due to factors such as wind, rain or inappropriate farming practices.
• Crop yield (t/ha/year): This measures the amount of food or product harvested from one hectare of land in a year.

The ratio of these two elements provides a measure of how much a crop contributes to soil erosion relative to its yield. For example, if a hectare of olive trees causes 8 tonnes of soil loss and yields only 1.9 tonnes of olives, the soil footprint would be around 4.2 tonnes of soil loss per tonne of product.
Using this method, the team at the University of Córdoba analysed the top 10 crops in Spain and ranked which were more sustainable in terms of soil conservation and which caused more erosion relative to their yield. This type of tool is crucial for identifying crops that need urgent intervention to reduce their impact on soil erosion.

Olive cultivation: A serious case of ecological footprinting

Among the crops surveyed, olive stands out as having the highest soil footprint in Spain. This is largely due to the fact that olive groves, especially in southern Spain, are often located on steep slopes, making them highly susceptible to erosion. More than 52% of the olive-growing area in southern Spain is classified as being at high or very high risk of soil erosion. Although olives are an economic powerhouse for the country, their cultivation results in significant soil loss compared to their yield.

However, the researchers stress that the problem is not only due to the nature of the crop, but also to the climatic conditions, agricultural practices and topography of the regions where it is grown. Implementing sustainable land management practices, such as the use of cover crops, could drastically reduce soil erosion in olive groves without compromising productivity.

Crop comparison: Winners and losers of soil sustainability

In their study, the researchers ranked Spain’s main crops according to their soil footprint. While olives, cherries and wheat topped the list as having the highest soil footprints, other crops such as onions, potatoes and oranges had the lowest soil footprints. This means that these latter crops result in less soil loss relative to the amount of food they produce, making them more sustainable choices for soil conservation.

The analysis also identified the most problematic regions in the country. The province of Jaén (Andalusian region), home to the largest area of olive groves, had the highest concentration of severe soil erosion, highlighting the need for immediate intervention in agricultural management.

Soil Footprint influencing factors

Several factors influence the impact of crops on soil erosion:

• Climatic conditions: Rainfall intensity, storm frequency and temperature all play a role in the rate of erosion.
• Topography: Steep slopes increase water run-off and therefore soil erosion.
• Agricultural practices: Techniques such as intensive ploughing or excessive use of herbicides exacerbate soil erosion, while sustainable practices such as no-till farming and cover crops can significantly reduce the rate of soil loss.

Strategies for reducing the land footprint

Reducing the land footprint is an urgent task and a challenge for global agriculture. The solutions require a collective effort involving farmers, scientists, policy makers and consumers. Some of the most effective soil conservation strategies include:

• Cover crops: Planting vegetation between main crops helps protect the soil from rain and wind erosion.
• No-till farming: This practice avoids the use of traditional ploughing, preserves the natural structure of the soil and reduces erosion.
• Crop rotation: Alternating different types of crops can improve soil health and prevent excessive erosion.
• Sustainable agricultural policies: Governments need to implement policies that encourage sustainable farming practices and penalise activities that degrade the soil.

The role of consumers in soil protection

Just as consumers have become more aware of their carbon and water footprints, they have the power to influence the reduction of the soil footprint. Demand for sustainably produced products can encourage farmers and the food industry to adopt soil-friendly practices.

The researchers suggest that in the future, food products could carry a soil footprint label, similar to eco-labels, to help consumers make informed choices that support soil conservation.

Conclusion

The introduction of the concept of the Soil Footprint by researchers at the University of Córdoba marks a turning point in how we understand the environmental impact of agriculture. By measuring how much soil is lost in relation to crop yields, this indicator highlights the urgent need to protect soil as a finite and essential resource.

The challenge of reducing the soil footprint lies not only with farmers and policymakers, but also with consumers, who can play a key role by demanding products that respect the soil and support sustainable farming practices.