What are soil samples used for?
Based on the analysis of soil samples, statements regarding the soil quality, soil pollution, biological activity of the soil, the expected behavior of a soil and its suitability for a particular purpose are possible. Physical and chemical parameters can be determined based on the samples which give direct or indirect information on the specific question. The comparison of the parameters in various depths provides information on the soil stratification and also on the distribution of water and nutrients or pollutants in the soil, as well as the depth of anthropogenic influences.
Typical aims are:
- Receiving information about soil structure / the soil stratification
- Information on nutrient and humus content of a soil
- Information on occurrence, frequency, and activity of soil organisms including pests
- pH-value determination of the soil
- Determination of the particle size distribution for the basic characterization of a soil
- Determination of parameters of the water and air balance (for example pore volume, hydraulic and pneumatic conductivity, retention curve)
- Determination of mechanical soil parameters to evaluate the stability of the soil (e.g. pressure sensitivity or shearing resistance)
- Chemical analysis for the detection of harmful and hazardous substances in soil
The possibilities for the analysis of soil samples are very diverse. Accordingly diverse is the application range for soil sampling within the scientific and economical sector.
- Soil science incl. soil ecology
- Monitoring, evaluation and remediation of legacies of pollution
- Building sector
Challenges in soil sampling
For each type of soil investigation, the result of the examination can only be as good as the quality of the samples. However, the different questions and possibilities of investigation place different demands on a soil sample. The quality can therefore not be assessed generally, but depends on how well the necessary requirements are met. In general, however, the sample must be representative.
That means it should reflect the property to be analyzed in a manner typical of the site.
For this purpose the “location” needs to be defined precisely. For which scales should the obtained results be representative? From individual measuring points and soil profiles (plot scale) to the field scale and catchment scale (forests up to whole regions), planned investigation areas can have completely different dimensions. Inhomogeneities within this study area must be taken into account during samoling. Specifically, the sample size, number of samples, and the distribution of the sampling points within the study area depend on this.
Furthermore, the property to be investigated must be retained during the sampling. For pure mass considerations and chemical analyzes, only the constituent to be analyzed has to remain unaffected. The structure of the soil is not important. Disturbed soil samples are sufficient.However, interactions between the materials of the sampling devices (drills, storage vessels, etc.) and the substance to be investigated must be considered and avoided. The chemical properties of the material can be largely ignored for soil-physical investigations and questions on the water and air content. Here, however, it is crucial to maintain the soil structure during sampling and until examination. The soil sample must be obtained undisturbed.
The type of sampling and the tool used must be adapted to the question. We will be pleased to help you to find the right strategy for your application and to find the right sampling technology for this.
Which types of soil samples are there?
The following types of soil samples are distinguished:
Disturbed soil samples
The original stratification and structure of the soil is destroyed during removal. The representativeness of the material is the leading quality criterion.
This type of sampling is generally sufficient for chemical investigations, to determine the current water content and to determine the grain size distribution.
- Mixed samples: Soil material is retrieved with a shovel, a chisel or an auger (drill) and transferred into a transport vessel or a bag without taking into account the soil structure. Mixed samples can be taken over different depths or over larger areas in order to take account of the influence of inhomogeneities.
Undisturbed soil samples
The original stratification and structure of the soil is retained in the sample. The lowest possible influence on the soil structure during extraction is a decisive quality criterion.
This is particularly necessary for soil-physical investigations, as well as for investigations concerning the water and nutrient budget.
- Drilling core samples: removal of soil samples with drills while maintaining the stratification. Depending on the technology, the scale and quality of a soil drilling core sample can be very different. The soil structure can be influenced to some extent by the compaction, wall rubbing, shearing forces, etc., during sampling, so that the sample is no longer undisturbed. Material transfer can also lead to disturbances in the original layer sequence.
- Samples in sample rings: sampling of soil samples of specific volume with a substantial preservation of the soil structure. The soil samples are separated from the surrounding soil by means of a soil core sample ring driven into the soil and subsequently transported in the closed puncture cylinders as gently as possible. The volume of the driven ring leads to the compaction of the soil in the edge region. The lower the wall thickness of the sample ring and the greater the volume of the soil sample, the lower the influence of the compression. The rings are usually driven by a hammer into the ground. The resulting vibrations can lead to changes in the sample structure. For very dry, hard grounds, it is not possible to retrieve samples since the sampling ring can not be driven in.
- Cutted soil columns / Monoliths: removal of soil columns of specific diameter and specific length with minimal influence on the soil structure. Unlike sampling cylinders, the sampling vessel is not hammered into the ground. The soil column is cut free and the vessel takes it in without deformation. This way the compaction on the edges as well as the influence of the vibration caused by the driving impact on the structure is prevented. Further soil columns can be obtained in significantly larger scales than sample ring samples. It is also possible to take samples of very dry, hard soils..