Various Factors Limit Soil Carbon Storage Potential

Net zero emission targets can only be achieved by removing carbon dioxide from the atmosphere. Agroscope has modelled soil carbon storage, food production and agricultural greenhouse gas emission trends for Switzerland.

Over 90 countries – among them, Switzerland – have announced targets of net zero emissions by 2050. To reach this target, most of them will rely on the removal of carbon dioxide from the atmosphere to offset unavoidable or difficult-to-reduce emissions.

Soil carbon sequestration – defined as a net uptake of atmospheric carbon dioxide leading to increased organic carbon storage – is a quickly implementable, cost-efficient method for achieving this goal. Although carbon is not stored permanently in this way, natural carbon sinks such as afforestation and reforestation projects have a cooling effect on the atmosphere. Soil carbon storage is influenced by land use, crop types and duration of soil cover, as well as the use of organic fertiliser.

Carbon sequestration scenarios taking population growth into account

Adapting soil management to increase soil carbon sequestration can lead to co-benefits or trade-offs. Agroscope has set up a modelling framework for Switzerland that combines soil carbon sequestration, food production and agricultural greenhouse gas emissions. The connection with food production is crucial, since crop rotations and livestock numbers influence soil organic carbon stocks. In addition, carbon sequestration for 2020–2100 was modelled for three scenarios:

Basic scenario: Minimal changes in diet, production, import and export of food and feed. An estimated 43% growth in population by 2100 was taken into account in the model.

1. The cover crop scenario represents an enhanced use of this known soil protection method. Whenever the crop rotation permits, cover crops are planted. In addition, it was assumed that cover crop biomass can be increased slightly by more diverse, more productive mixtures.

2. Biochar scenario: Biochar produced from domestic resources which, however, were themselves produced outside of the system boundaries (i. e. from non-agricultural sources such as biomass from landscape maintenance).

3. Agroforestry-biochar scenario: Cultivation of additional biomass by means of fast-growing trees planted alongside agricultural fields and harvested for biochar production. To free up land for this, feed production on arable land was reduced, leading to additional changes in diet.

Soil carbon sequestration could decline rapidly after 2050

Limiting factors such as land and biomass availability or population growth may influence carbon sequestration and show that it will not be possible to maintain the latter in all of the studied scenarios from 2050 onwards. This information and the associated greenhouse gas emissions are crucial for planning net zero strategies, and underscore the importance of integrated assessments that account for the links between soil carbon storage and the food and feed system.

Population growth outweighs the storage effect in the most favourable scenario

Because of the increasing need for land for food production resulting from the forecasted growth in population, agroforestry land area will already be on a downward trend after 2030. In other words, even with the agroforestry-biochar scenario, which would take up the most CO₂, sequestration rates cannot be maintained as a result of the growing population.