Soil sampling equipment

Equipment for sampling and storage of (undisturbed) soil cores / soil rings, roots & soil pore water.

A critical step in obtaining accurate soil tests is to collect representative samples in situ. Typically, plots can be sampled in a simple random pattern across the field, taking at least 10-20 soil cores of equal size (depending on expected variability) at different depths. If you have distinct patterns in your plot, such as row-interrow in arable land or distance from trees in woodland, these will need to be taken into account. Alternatively, sampling transects can be established either to characterise a fairly homogeneous site or to follow known or expected changes in soil properties. Avoid or sample separately areas that are obviously very different from the site where you want to classify the soil - such as roads, eroded areas, pits and mounds, wet areas - or make these gradients part of your sampling design. If gradients are not part of your research question, plots with significant landscape or other differences can be divided into separate sampling areas. Differences may include soil type, slope, degree of erosion/soil compaction, drainage, land use history or other factors that may affect results. The more you know about your site before deciding on a sampling design, the better your design can avoid potential bias. If resources and site disturbance were not an issue (most are), then more samples means better means. In general, more intensive sampling should be used where detailed information on within plot variability is needed. This may include sampling some areas more intensively than others - to determine small scale variability.

Laboratory tests of soil physico-chemical or biological parameters are calibrated to specific depths or soil morphometric horizons (i.e. (specific type of) organic layer, mineral soil, etc.). It is therefore essential to sample at the appropriate depths or horizons, as a deeper or shallower core will give erroneous results. The sampling depth for most agricultural soils is usually the tillage depth, more skeletal (forest) soils are often sampled to a depth of about 30 cm. Where thick organic layers are present, it is often advisable to sample the mineral A horizon to a depth of at least 0-10 cm. The surface soil samples are usually used for conventional laboratory testing for carbon and nitrogen, pH, partial phosphorus, potassium and other nutrients (total or plant available). Deeper samples may be required when testing deep-rooted crops such as wheat and barley or trees. Ensure that surface litter, other organic layers and mineral soil layers are stored separately - plastic (freezer) bags are suitable for storage (best at 4°C; acceptable storage times vary widely with analyses - hours to a few weeks). Subsoil samples are often required to estimate available nitrogen and to determine C stocks. Both topsoil and subsoil samples are needed to reliably estimate the depth distribution of root systems, for example.

A stainless steel soil sampling probe / core soil sampler is the most commonly used tool in soil sampling. Particularly wider soil corer can provide a continuous soil core with minimal disturbance to the soil - that can be readily divided into various sampling depths / soil layers. Specific storage solutions are available to transport intact soil cores to the laboratory. Even if compression in larger diameter soil corers ist often small, it is good practice to determine the length of the sampled core (e.g. when extracted to in your storage container) and the depth of the sample hole. However, any soil compression has to be avoided for determining soil density - a vital parameter to get reliable stocks of e.g. carbon and nutrients. Thus specific soil ring samplers are often used horizontally in soil pit walls for soil density sampling - the shorter samples and thin-walled soil rings effectively minimise soil compaction. Vehicle mounted hydraulic probes are available and are the first choice for large agricultural trials where access to the sampling site is available and slope allows, but for most soil sampling campaigns manual soil corers are still the tool of choice. Other tools required for soil sampling include plastic sample bags (size to suit your sampling intervals, e.g. 3 or 6 L bags), a tape measure/ruler to determine potential compaction and a waterproof marker for labelling. If you are concerned about the markings coming off the bags, place a plastic tag with a pencil mark in each bag. For soil ring samplers, some soil/pallet knives are required to carefully remove excess soil from the top and bottom of the sample rings before storage. See the VSI soil corer manual for an examplary tools / packing lists for a soil sampling campaign.

• Amelung, W., Blume, H. P., Fleige, H., Horn, R., Kandeler, E., Kögel-Knabner, I., ... & Wilke, B. M. (2018). Scheffer/Schachtschabel Lehrbuch der Bodenkunde. Springer-Verlag.
• Carter, M. R., & Gregorich, E. G. (Eds.). (2007). Soil sampling and methods of analysis. CRC press.
• Cools, N., & De Vos, B. (2013). Forest Monitoring: Chapter 15. Forest Soil: Characterization, Sampling, Physical, and Chemical Analyses (Vol. 12). Elsevier.
• Franzen, D. W. and T. R. Peck (1995). "Field soil sampling density for variable rate fertilization." Journal of Production Agriculture 8(4): 568-574.
• Forster, J. (1995). Soil sampling, handling, storage and analysis. Methods in applied soil microbiology and biochemistry, Elsevier: 49-121.
• Gregorich, E. G. and M. R. Carter (2007). Soil sampling and methods of analysis, CRC press.
• Gross, C. D., & Harrison, R. B. (2018). Quantifying and comparing soil carbon stocks: Underestimation with the core sampling method. Soil Science Society of America Journal, 82(4), 949-959.
• Guo, M. (2009). "Soil sampling and methods of analysis." Journal of Environmental Quality 38(1): 375.
• Liu, S., et al. (2019). "Estimation of plot-level soil carbon stocks in China's forests using intensive soil sampling." Geoderma 348: 107-114.
• Ma, Y., Minasny, B., Malone, B. P., & Mcbratney, A. B. (2019). Pedology and digital soil mapping (DSM). European Journal of Soil Science, 70(2), 216-235.
• Nachtergaele, F., van Velthuizen, H., Verelst, L., Wiberg, D., Henry, M., Chiozza, F., ... & Tramberend, S. (2023). Harmonized World Soil Database version 2.0. Food and Agriculture Organization of the United Nations.
• Persson, L., & Bergström, L. (1991). Drilling method for collection of undisturbed soil monoliths. Soil Science Society of America Journal, 55(1), 285-287.
• Theocharopoulos, S., et al. (2001). "European soil sampling guidelines for soil pollution studies." Science of the Total Environment 264(1-2): 51-62.
• Van Groenigen, J. W., et al. (1999). "Constrained optimisation of soil sampling for minimisation of the kriging variance." Geoderma 87(3-4): 239-259.
• Veihmeyer, F. (1929). "An improved soil-sampling tube." Soil Science 27(2): 147-152.