At Svartberget Research Station, an ongoing soil project, investigating soil organic carbon and nitrogen, uses plastic balls added to the soil pit to estimate pit volume.
Soil is a major component of the terrestrial carbon cycle. Thus, monitoring temporal change in Soil Organic Carbon (SOC) and Nitrogen (SON) stock isrequired to close the ecosystem mass balance of these elements and to assess the role of terrestrial ecosystems in the global carbon cycle.
In an on-going project, with the aim to monitor the SOC and SON stocks within the target area of the Eddy Covariance (EC) flux tower at Svartberget soil samples have been collected and prepared. The project involves organizing student field assistants working on the project, collecting soil samples in the field, photographing the soil pit, setting up a soil drying lab, liaising with the central laboratory and following the protocol to process the soil samples (i.e., labelling, drying, sample weighing, separation of soil stones and vegetation).
The SOC and SON stocks for the first meter (0 to 100 cm) of the soil profile is determined from measurements of soil organic carbon and nitrogen content as well as bulk density of the soil. The SOC and SON content is analysed by a central laboratory, while the station team measures the soil density.
Johan Westin, Experiment Group Leader at the Unit for Field-based Forest Research, offers some practical advice about the technique used for pit volume,
“Have you ever taken on the task to estimate the bulk density of all of what you have dug up from a 1 m deep pit in a spruce forest in northern Scandinavia? In theory, it is easy. Just dig a rectangular shaped pit on the flat soil down to a one meter. Measure width and length. Weigh everything that you have dug up. Move on to next pit.
In reality though, there are stones, rocks, roots, sand, clay and so on. The pit seldom has a regular shape so the task to measure the volume is suddenly not so easy. This may be the point where all the hours you have spent with your children in a “bollhav” (ball pit) somewhere suddenly pays off. Buy balls and bring the “bollhav” to the field (leave the kids at home), fill the pit with the balls and count the number of balls. Calculate the pit volume. Move on to next pit. It’s a colourful approach.”