This manuscript is published as SOIL Letters publication as it provides a timely and important contribution, formulating six fundamental principles for the robust study of soil carbon saturation. This is an important topic in research on soil carbon and its role in climate change mitigation which should be of interest to the wider geoscience community.

As consumers demand to know more about the provenance of their food and the impact its production has on the environment, it is timely to consider the role that the supply chains of companies play in protecting soils from degradation. Soil degradation is increasingly considered as a commercial risk in supply chains, with soil quality a priority objective in retail-sector sustainability efforts. Many products and services rely on soils, and loss of productivity can be a significant risk. This interesting paper examines how soil sustainability features in accreditation schemes used by major food retailers and the potential influence these might have for soil protection. As many organizations and companies across different sectors are attempting to apply robust sustainability standards, it makes a timely contribution. It addresses four key questions: (i) To what extent are companies considering soil sustainability as part of their sustainability strategy? (ii) Do sustainability standards that companies use have a potentially meaningful impact on soil protection, and does that impact affect standards' market penetration? (iii) Are schemes that emphasize the environment more likely to have a stronger soil-related impact? (iv) What are companies' practical considerations in their application of soil protection criteria in voluntary sustainability standards?

This is one of the first surveys of soil fungal diversity across land uses at the national scale.