Maintaining valuable soils

May 9, 2018, Swiss National Science Foundation
Construction inside and outside the construction zone is leading to a loss of valuable soil and its functions. Credit: Swiss National Science Foundation

Each year almost one thousand hectares of cultivated land continue to be lost, thereby wiping out numerous services delivered by the soil, such as filtering water and storing carbon, which are central for our society's wellbeing. The National Research Programme "Sustainable Use of Soil as a Resource" (NRP 68) is suggesting ways in which spatial planning can be structured so that this loss remains as small as possible. First and foremost, soil quality should play a larger role in spatial planning decision-making.

Between 1985 and 2009, 85,000 hectares, or five percent of the cultivated land available in 1985, was lost, mainly in the Swiss Central Plateau and valley floors. Recent land-use statistics indicate that this loss has continued at a slightly reduced rate over the last few years. Although the revision of the Spatial Planning Act (SPA) has alleviated the situation with regard to rezoning, a large amount of land is still being consumed by infrastructure and building construction outside the official building zones. Along with this, we forfeit the numerous soil functions – such as its fertility, its ability to store carbon and also to retain and filter water.

Considering soil quality when weighing up interests

Although the Spatial Planning Act requires land to be used economically, existing legislation does not give cultivated land sufficient protection. Compared to other areas worth protecting such as marshland and forests, fewer specific legal conservation goals exist for cultivated land. One exception is that of crop rotation areas, which make up around one third of all agricultural land. The remaining two thirds of cultivated land is scarcely considered when weighing up interests. Furthermore, when ring-fencing crop rotation areas, only agricultural productivity is relevant: other soil functions, such as filtration or its role as a habitat, tend to be disregarded. But it is precisely these aspects that sustainable spatial planning must include when weighing up interests. Added to this, most current construction activity is taking place on highly productive agricultural land: due to their historical development, existing settlements are often surrounded by high-quality soil. Expanding construction activity in the immediate vicinity of settlements therefore leads to a significant loss of high-quality soil in many cases.

Thresholds for the loss of soil quality

Soil index points make it possible to control the use of high-quality soil by settlement developments. Credit: Swiss National Science Foundation

Until now, there has been a shortage of suitable instruments for practicably including in planning decisions. Researchers from the National Research Programme "Sustainable Use of Soil as a Resource" (NRP 68) have therefore developed the concept of soil index points that makes soil quality tangible. For example, it provides information on the question of where construction work or rezoning would be associated with the least impact on soil quality. "Such a system can be used to maintain soil quality in the long term," explains Adrienne Grêt-Regamey of ETH Zurich. "At a cantonal level, we could define a threshold that represents the maximum tolerable consumption of soil index points. Using this as a quota would enable us to control consumption in terms of soil quality." Experience gained in Stuttgart has shown that the loss of high-quality soil can be reduced using tools such as this.

Achieving a sustainable soil policy

Figure 2: Room for manoeuvre for construction usage in the commune of Uster (ZH). Credit: Swiss National Science Foundation

Other NRP 68 researchers are also highlighting the importance of available cultivated land and its quality. "Anticipated population growth and climate change in particular represent major challenges for the sustainable use of soil," declares Felix Walter of Ecoplan. "Because soil is not a renewable resource, there is no way of avoiding restrictions in the long term." We therefore not only need to take action in farming and forestry, but also in other policy areas such as settlement and infrastructure development, and we need to make targeted efforts with regard to communication. Based on an overview of possible initiatives, Felix Walter is therefore highlighting ways of achieving a sustainable soil policy. Alongside effective measures in spatial planning, agriculture and forestry, such a strategy also requires improved soil mapping, an intensive awareness campaign, close collaboration between the various parties involved in soil protection and , and a high degree of commitment on the part of political bodies at the federal, cantonal and local level.

We do not have much time in which to take effective measures towards a sustainable soil policy. "Time is of the essence," stresses Adrienne Grêt-Regamey. "Our analyses show that the window of opportunity for protecting today's soil quality is extremely small." We therefore need to further develop the necessary foundations without delay. For example, in order to use soil index points, we need in-depth pilot studies, which NRP 68 is no longer able to carry out. "The forthcoming second revision of the Spatial Planning Act provides an opportunity to incorporate quality more firmly into legislation."

Figure 3: Inter-communal cooperation has the potential to reduce the loss of soil quality resulting from new construction schemes. Example: Greifensee region (Canton of Zurich). Credit: Swiss National Science Foundation

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