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Salt: a threat to the planet’s agricultural land

sòl salinitzat
Salt buildup from salt-laden water percolating to the surface and evaporating. (Source: Tim McCabe, USDA NRCS)

· IRTA researchers develop a globally pioneering methodology to quantify the impact of land use on a product’s life cycle

· Subsoil salinisation, made worse by the effects of climate change, now affects 20% of the planet’s cultivated land and threatens agricultural production

· Mitigating land degradation is a priority for both the United Nations and the European Union

The fields of Spain’s Ebro Delta produce around 90,000 tonnes of rice a year. In recent years, however, climate change has been compromising the crop’s production, forcing rice farmers to find new ways of tackling the high levels of local soil salinisation. According to the latest studies, climate change and subsidence have meant the Ebro Delta is sinking an average of three millimetres a year. That means sea levels are rising and invading the subsoil, leading to even greater salinisation in the phreatic zone.

The delta’s situation is not unique. As global sea levels rise, coastal areas are increasingly flooding with salty water that penetrates the soil and subsoil. Rainfall can help remove the salt, but increasingly frequent heatwaves and droughts lead to a rise in the use of phreatic zones to obtain fresh water for drinking and irrigation purposes, leading to even greater levels of soil salinisation.

All over the world, land is becoming a valuable and scarce resource. Its degradation is an especially serious problem in countries such as Spain, with its dry Mediterranean climate and land that has low levels of organic matter and textures that are prone to significant erosion. The long-term consequence of that is a loss of productivity, threatening both farmers’ livelihoods and the preservation of rural areas. Climate change’s progression also means any degradation is predicted to intensify.

Soil salinisation, which already affects 20% of cultivated land worldwide, presents new challenges for both agriculture and managing climate migration. Surprisingly, despite that risk, the issue had not previously been included in evaluation and quantification methods such as life cycle assessment (LCA), applied to large-scale environmental issues.

LCA is a methodological tool for measuring the environmental impact of all human activity – from harvesting an apple or manufacturing a car to undertaking a service such as painting a domestic wall – from raw material extraction to completion. The tool is based on collecting and analysing system inputs and outputs, from natural resources and emissions to waste and by-products. That work then provides quantitative data on the potential environmental impacts of those actions, allowing for strategies to be identified that will minimise or reduce those effects. LCA is particularly useful for comparing the impacts of two competing products and different versions of the same product to ascertain which one registers the fewest impacts (known as eco-design).

“Just 10 years ago, no one was focusing on soil; now, with climate change, that has changed,” says Montse Nuñez, a Beatriu de Pinós programme researcher at the IRTA, funded by the Government of Catalonia. In that regard, she highlights how the latest report from the United Nations’ Intergovernmental Panel on Climate Change (IPCC) focused on soil, and the subject is also part of the European Union’s forthcoming Horizon Europe 2021-2027 framework. 

“Well managed agricultural land can represent a significant carbon reservoir and have a ripple effect for the environment by providing improved nutrient retention for plants; reducing the need for irrigation water, pesticides and fertilisers; and guaranteeing long-term food production for future generations,” adds the researcher. “Agricultural land managed in harmony with the environment and integrated into the forest landscape also plays an extremely important role in maintaining biodiversity.”

Nuñez has developed a globally pioneering methodology, which was recently published in Environmental Science & Technology and which includes the impact of soil salinisation in LCA for food production. “For instance, we can look at the production life cycle of an apple by focusing wholly on the soil and analysing everything that happens. From transporting fertiliser to whether the land has had to be farmed to subsequently transporting the fruit for consumption, and how that process contributes to soil salinisation,” explains Nuñez.

Nuñez further elucidates on the apple production process. “The LCA methodology considers all of the variables within the process. If we take the example of apple sauce production, those variables would include extracting phosphorous, potassium and other minerals from mined land to make the glass for the packaging and the mineral fertiliser applied to the apple trees. As well as using up non-renewable resources, that leads to soil compaction caused by the mining equipment. Further variables include how farmers manage the fruit trees and the impact on soil and aquifers of the salts from irrigation water, along with the use of machinery, fertilisers and pesticides. Other impacts on the soil that may take place during the apple processing stage, the management of any organic waste and transportation would also be considered. “Our tool means we can evaluate environmental damage, such as the kilos of nitrogen from fertilisers that involuntarily enter natural ecosystems, the changes they provoke, and the affected or disappeared species,” says Nuñez. She also highlights how the open-access methodology can translate all impacts into the same units of measurement, allowing for a comparison between the effects of different human activities. “As such, we can both improve soil management and mitigate the effects of climate change,” concludes Nuñez.

REFERENCE ARTICLE: Nuñez, M. and Finkbeiner, M., A. Regionalised Life Cycle Assessment Model to Globally Assess the Environmental Implications of Soil Salinization in Irrigated Agriculture; Environmental Science & Technology 2020 54 (6), 3082-3090 DOI: 10.1021/acs.est.9b03334