The dataset comprises the field soil organic matter content as a percentage at three depth zones (roughly 0-10 cm, 10-20 cm and 20-30 cm), measured from bulk density soil samples taken within each 1metre x 1metre quadrat. Prior to measurement of bulk density all soil samples were dried at 105°C for 72 hours. A sub-sample was then taken and dried at 375°C for 16 hours to determine the percentage organic matter of dry soil. Sampling was conducted at six salt marsh sites at four spatial scales: 1 metre (the minimal sampling unit) nested within a hierarchy of increasing scales of 1-10 metres, 10-100 metres and 100-1000 metres. Three of the sites were in Morecambe Bay, North West England and three of the sites were in Essex, South East England. The Morecambe Bay samples were taken during the winter and summer of 2013. The Essex samples were taken during the winter, early spring and summer of 2013. This data was collected as part of Coastal Biodiversity and Ecosystem Service Sustainability (CBESS): NE/J015644/1. The project was funded with support from the Biodiversity and Ecosystem Service Sustainability (BESS) programme. BESS is a six-year programme (2011-2017) funded by the UK Natural Environment Research Council (NERC) and the Biotechnology and Biological Sciences Research Council (BBSRC) as part of the UK's living with Environmental Change (LWEC) programme. Full details about this dataset can be found at https://doi.org/10.5285/90457ba1-f291-4158-82dc-425d7cbb1ac5