Predicting near surface (0-20 cm) high resolution (2 cm) soil organic carbon and soil property depth profiles

Soil biogeochemical cycling is concentrated at the soil surface. In many climates the 0-20 cm soil depth is the most dynamic. This paper examines and reports on near surface SOC (0 – 20 cm) depth increment sampled soil data for a range of climates and soils from across Australia. Soil sampling was undertaken by a scraper plate apparatus that extracts soil at 2 cm depth increments over a 1000cm 2 area providing a relatively large sample that integrates over a larger area than commonly used soil cores. Maximum depth of samples was 20 cm. There is a global lack of data examining soil properties at shallow depths and at relatively high resolution. The findings demonstrate that SOC has the highest concentration in the top 0-4 cm with concentration regularly decreasing down the profile and that each sampled site displayed a unique SOC depth distribution. A power function provided the best fit to the data. Each site examined had a unique SOC depth pattern. There was no consistent relationship with SOC and clay content. For some sites SOC was significantly related with clay (p<0.05) while others having no relationship with clay down the profile (p>0.05). A general rule was found where a site with a clay content of >20% had a relationship with SOC down the profile. At sites with clay content <20% there was no significant relationship with soil texture. At all sites there was a significant relationship between SOC and soil Electrical Conductivity (1:5 soil:water method) suggesting a capacity to predict soil properties in the examined environments. Soil texture cannot predict SOC depth distribution while EC was found to have predictive potential.