How deep is the soil studied - an analysis of four soil science journals

Background and aims Soil depth is a critical attribute of any soil, and determines rooting, moisture and nutrient storage, mineral reserve, anchorage, and a range of conditions that affect plant growth. We reviewed papers from four primary soil science journals and extracted how deep the soils were studied in those papers. Methods Soil depth was obtained over a 30-years period (1989-2019) from papers in: European Journal of Soil Science, Geoderma, Plant and Soil, and Soil Biology and Biochemistry. In total, 1146 papers were reviewed, and 37% (420 papers) included information on how deep the soil was studied. Results The number of papers that included soil depth increased from 31% in 1989 to 47% in 2019. The average soil depth studied was 27 cm, but it was 53 cm between 1989 and 1999, and 24 cm between 2004 and 2019. Most of the studies were from Europe, and 41% of the papers contained soil classification. Research that focused on soil mineralogy and technology tended to study soils to a greater depth (average 74 cm), whereas the depth in soil biology research was on average 18 cm. Over 80% of the soils were sampled by fixed depth and not by soil horizon. Conclusions Soil depth is lacking from about half of the papers in these four journals. The depth of the soil studied has halved in the past 30 years. Soil processes, soil properties, and microbial communities are depth-dependent, and for a more complete understanding, soils should be studied to a greater depth.