Rhizon and Solu Systems for Soil pore Water Sampling
Soil Water Sampler Types
Soil Water Samplers. Inert samplers can extract small or larger volumes of (pore) water from soils and sediments in a simple, non-destructive and repeatable manner. Different soil water samplers, developed by i) Rhizosphere Research Products, and ii) Sentek can be used to sample water from both unsaturated and saturated soils, and the extract can be used to measure dissolved compounds such as salt / nutrients, dissolved organic carbon, dissolved gases, plant exudates incl. enzymes, or contaminants.
Rhizon Samplers, hold very small diameters and low dead volumes and are easy to handle. Several types of RRP Rhizons for small to medium soil pore water extraction are available:
- MicroRhizon Sampler & Accessories for use in Rhizonbox perforated rear panels,
- Rhizon Samplers for use in Rhizoboxes and Rhizonboxes (from top/side entry holes), and
- Rhizons for soil pore water sampling tasks in disturbed soils or particular well suited for sampling at depth (MacroRhizons).
Rhizon Sampler Accessories (syringes, vacuum vials) are listed below. Read below on characteristics of the Rhizon microfiltration membrane, and details on the sampling procedure. For continuous measurements of soil moisture content in larger diameter boxes, mesocosms, rhizotrons, and in the field, see soil moisture sensors.
Sentek SoluSampler, two types of robust, inert ceramic soil water samplers are available for large volume sampling in the field (Table 6). Read more on SoluSamplers.
MicroRhizon Sampler
MicroRhizons are mainly used in RhizonBoxes and Agar tests. They consist of two parts: a porous part (i.e. microfiltration membrane) of 8 mm with an outer diameter of 1 mm, and a PEEK tube (0.6*0.4 mm; 12 cm long) with a silicone connector that fits onto a syringe. The average pore size of the membrane is 0.15 µm, so no filtering of samples is required prior to analysis. The yield of MicroRhizons is up to 2 ml (depending on pore water availability). Because the MicroRhizon tubing is made of PEEK and a special adhesive, it can be steam sterilized. For MicroRhizons, any standard syringe with a "tip" and a wooden retainer can be used for sampling. The MicroRhizons and the syringe tip are connected by a "silicone connector" - i.e. a small piece of silicone tubing. Types for soil pore water sampling in RhizonBox back panels (RRP19.21.81), or with silicone sleeve (RRP19.21.83) for entry from the side of RhizonBoxes (4.5 mm holes) available.
| Models/Types | MicroRhizons and Accessories | OPEN |
Rhizon Samplers - SMS, MOM, CSS and Flex, MacroRhizons
Rhizon Samplers are used for (un-)disturbed soils (see types below), and are ideal to be positioned in Rhizoboxes and RhizonBoxes, pot experiments and the field. Rhizonboxes can be equipped with special 4.5 mm openings on the side wall(s) (e.g. at different depth) to insert CSS Rhizon samplers (diameter of 2.5 mm plus silicon sleeve to prevent leakage of water from the RhizonBox). They can be used to collect water from larger zones (length of porous parts: 5 cm or 10 cm) for analysing macro and micro elements, dissolved organic carbon (DOC), exudates and enzymes, and gases such as dissolved O2 or dissolved CO2. Using Rhizons with a 10 cm porous part, maximum yield of water is approximately 4 ml min-1. Rhizon Flex Samplers are particular suitable for sampling when installed in Rhizoboxes and Rhizonboxes during soil filling / set-up.
| Varieties | Rhizon Samplers | OPEN |
| Specifications | Rhizon Membrane Properties | OPEN |
| References | Rhizon Soil Water Samplers | OPEN |
Rhizon Sampler Types - Features
Rhizon SMS. For installation in disturbed soils, lab, greenhouse (pots, columns), and in upper layer in the field. For analysing macro elements, not suitable for analyzing metals and DOC. SS 316 strengthener wire (metal) can be bent permanently. Can be used in Rhizonboxes with restrictions (i.e. wait until soil contact is re-established).
Rhizon MOM. For installation in disturbed soils etc. as for SMS. For analysing macro and micro elements, dissolved gases and DOC. MOM samplers have a tip with a bulb (2.8 mm) and need several hours or days to achieve a good contact between soil and sampler. Strengthener is a glass fibre wire. Can be used in Rhizonboxes with restrictions (i.e. wait until soil contact is re-established). See Rhizon Sampler Accessories.
| Models/Types | Rhizon types SMS and MOM | OPEN |
Rhizon CSS. For direct sampling in cores, undisturbed soils and Rhizonboxes (with silicon sleeves, from side). For analysing macro and micro elements incl. metals, dissolved gases and DOC. CSS samplers have a flat tip (2.5 mm) of the diameter of the porous part. The direct contact between the soil and the porous part makes CSS samplers suitable for immediate sampling - when inserted e.g. through the side holes of Rhizonboxes. Strengthener is a 10-15 cm glass fibre wire. The porous membrane (5 or 10 cm in length) should be fully inserted into the soil and must be at least 0.5 cm away from the outside. 1st choice for Rhizonbox sampling from the side; immediate sampling.
Rhizon Flex. For disturbed soils or positioned during the filling of Rhizo(n)boxes (from the side holes OR top) or pots. For analysing macro and micro elements similar to CSS. In contrast to CSS, the strengthener is a nylon wire, and the long tube length makes it easy to install them at the intended soil depth and from the top of Rhizoboxes. Good choice for Rhizobox sampling when installed during set-up. See Rhizon Sampler Accessories.
| Models/Types | Rhizon types CSS and Flex | OPEN |
MacroRhizon. For field research & placement at depth. For analysing macro and micro elements incl. metals, dissolved gases and DOC. They have a porous membrane (9 cm) with an outer diameter of 4.5 mm and a pore size of 0.15 µm. MacroRhizons are only available with female luer lock, suitable for creating a vacuum with syringes. Four lengths available are 0 (=direct sampling), 30, 60, and 90 cm tube length. Can also be used in large (i.e. >3 cm deep) Rhizoboxes and Rhizotrons. See below for notes on the installation of MacroRhizons.
| Models/Types | MacroRhizon Samplers | OPEN |
Rhizon Sampler - Accessories
What accessories do you need for sampling? This depends on the type of Rhizon ... read more on how to do sampling / soil water manipulation with Rhizons below. All available accessories are listed here. We are happy to suggest required accessories if you describe your use case to us.
| Models/Types | Rhizon Accessories | OPEN |
Soil Solution Sampling / Manipulation with MicroRhizons & Rhizons
For sampling rhizosphere pore water, you need a (Micro-)Rhizon sampler and accessories to create a (partial) vacuum (see images below).
- MicroRhizon samplers need a syringe with tip and a silicone connector
- Rhizon samplers with a female luer lock need a syringe + retainer (OR a male-male luer connector and a vacuum tube)
- Rhizon samplers with a male luer lock need a needle and a vacuum tube (evacuated vial), (OR a female-female luer connector and a syringe)
- What is the difference? Continue reading
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The advantage of vacuum vials is that the sample does not come into contact with air. The advantage of needles/syringes is that the vacuum can be easily restored by pulling back the plunger. However, male-to-male and female-to-female luer connectors are available to easily "correct" your initial choice of sampler luers later. If you use syringes to create a vacuum, wooden retainers can be used to block the plunger -which keeps the vacuum. If you use vacuum vials, you can buy them pre-evacuated or prepare them cost-effectively using the Vacuum Vial Evacuator EV-101. Simply connect a needle to the male Luer lock on Rhizon samplers (or use a female-to-female connector) and insert it through the septa of the vacuum tube.
If you cannot extract soil water, you may have forgotten to remove the (blue or red) protective cap from the Rhizon before use. Please check and try again. If the protective cap is already off you may have to wait a little longer. The porous membranes of any (Micro-)Rhizon samplers must be completely wet before you can apply vacuum.
If you are interested in testing the response of specific roots or rhizosphere compartments to changes in the soil environment (e.g. salts, heavy metals or other pollutants, dissolved carbon, etc.), you may consider using (micro)rhizons to inject a solution into the soil (next to a specific root or soil region) instead - or use RhizonIrrigators for setting specific irrigation treatments by passive suction or active outflow.
Installation of MacroRhizons
MacroRhizons are only available with a female Luer lock, suitable for creating a vacuum with syringes. It is recommended that the MacroRhizons be installed horizontally in a soil profile wall (direct), or drilled / cored soil hole at an angle of 30 to 45°. This will prevent rainwater from running along the PVC pipe and directly into the membrane.
- Want to know more about MicroRhizon installation in the field? Continue reading
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An installation tool (19.21.51) is available for placing the MacroRhizons in any hole larger than ~2 cm in diameter and up to ~85 cm deep. Select MacroRhizons of appropriate length (direct, 30, 60, 90 cm). Install in profile wall (direct) or core the soil to the depth where the top end of the 9 cm sampling membrane will be placed, then use the installation tool to create a small (4 mm) hole for insertion of the MacroRhizon membrane section, allowing the sampler to fit tightly in largely undisturbed soil. Backfill the hole above, preferably to approximate the soil profile pattern. Make sure the Luer lock remains clean. For best results, it is recommended to wait 2–3 weeks before sampling; if there is no rain, consider watering the area at the beginning to allow the soil to settle tightly around the sampler. A vacuum for sampling can only be applied when the membrane is wet! You may consider installing MacroRhizons in parallel with Minirhizotron tubes - this will allow you to characterize soil water patterns at different depths along the rooting profile. Drill and Drop soil moisture probes, or access tube-based soil moisture EnviroScan sensors, can provide complementary information on spatial and temporal soil water dynamics.
Sentek Solu Soil Solution Sampler
Sentek SoluSampler, a large soil solution sampler, a lysimeter cup that draws water from the surrounding soil and stores it in an inert ceramic cup for collection and analysis. The large sample cups are ideal for accurate, site-specific analysis of soil water properties such as salinity and nitrate content. Suitable for installation at various depths and field conditions (i.a. high / low flow types for different textured soils). With a rugged and durable design, the SoluSamplers are most suitable for field applications and large sample volumes.
| Models/Types | Sentek SoluSampler | OPEN |
| References | Sentek SoluSampler | OPEN |
Solu Water Sampler - Installation, USe
Samples of soil pore water are extracted from the ceramic cup using a large syringe. See the description below and the SoluSampler Manual above (pdf) for more details on installation and operation.
- Want to know more about SoluSampler installation and sampling procedure? Continue reading
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- Select Solu Sampler type: high or low flow according to texture/soil moisture.
- Core / drill a hole (c. 40 mm diameter), and to required depth. Keep soil for back-filling.
- Wet SoluSamplers. Attach to installation tool for greater depth.
- Insert SoluSampler with tube protruding from the surface (keep stopcock clean).
- Prepare a slurry (sieved, sampled soil & water). Preferably use soil from the installation depths soil profile to mix the slurry.
- Pour the slurry into the hole to ensure good soil contact, up to 1-2 cm above the SoluSampler. Add some soil, gently tap. Add a 1:1 mixture of sand and betonite to seal the hole and act as a hydraulic barrier.
- Fill in the remaining soil to the surface. Allow the Solu Sampler to settle / wet.
Generally, it takes about two weeks after installation for the SoluSampler to provide a representative soil water sample. During this two-week period, discard two or more extracted samples to avoid unrepresentative samples.
Sampling:
- Vacuum is created using a large syringe (60 ml). Connect the syringe to the stopcock. Create vacuum (potentially using several cycles), close stopcock.
- Vacuum is maintained for at least 4 hours. During this time: Soil water is drawn through the ceramic cup and stored in the unit.
- After this time, water can be extracted with a (clean) syringe.
- After drawing out the soil water, the Sentek SoluSampler should not remain under vacuum conditions until the next time it is used. Consider the long-term effects of bacterial/fungal growth on nutrient analysis; chemical sterilization may be required for extended SoluSampler incubation times but consider effects on soil microbiome, etc.
Analysis of the collected soil water can be carried out by:
- Portable Electrical Conductivity (EC) meter (in the field)
- Nitrate strips (in the field)
- A wide range of laboratory analysis
Ex situ Root and Soil Observation Systems allow using Rhizon samplers in replicated root and rhizosphere studies, see Rhizoboxes or dedicated Rhizonboxes (for direct insertion of MicroRhizons).
