Determination of Root Suction Force (1972)

The suction force of roots governs the uptake of water and essential nutrients by crops. Exploring this physiological metric enables a deeper understanding of plant-environment interactions. However, empirical field data on root suction force remained scarce due to the lack of an accurate, non-destructive methodology for peat-gley soils.

1. Development and Validation of a Field Method for Root Suction Force

The proposed method for determining root suction force was field-tested on peat-gley soil at the Polesian Experimental Peatland Station (Brest region). The experimental crops were barley and lupine.

To measure suction force using a refractometer, working sucrose solutions are prepared at approximately 1% concentration intervals. Lower and upper limits of the concentration gradient are established based on expected suction force ranges. The volume of each working solution depends on the number of treatments, requiring at least 10 ml each.

By placing 0.5 ml of each sucrose concentration into test tubes, a control scale and multiple experimental series (matching the number of test variants) are set up. Tubes are sealed with airtight rubber stoppers.

To facilitate layer-by-layer root sampling, a vertical polyethylene film was placed in the soil profile prior to sowing, restricting root spread in one direction. Throughout the growing season, the film was uncovered at newly designated spots, and root samples were collected at target depths within the active absorption zone (5–10 cm from root tips). If experimental conditions require strictly undisturbed natural soil horizons, root samples are collected directly from soil monoliths without sheets.

Each root sample is gently cleared of adhering peat particles using a soft brush, immersed in the working solution, and agitated to completely remove peat residues. Laboratory tests revealed that peat particles introduced into small volumes of sucrose solution dilute the medium with soil moisture. Washing roots in solutions identical in concentration to the test tube eliminates this error. Direct filtration of the test solution without preliminary washing, previously suggested in literature, was demonstrated to be unsuitable for peatlands.

Following washing, roots (approximately 8–10 segments of 1 cm each) are transferred into the test solution tubes. Samples are incubated for approximately one hour with periodic shaking. Refractometric readings are then taken and compared against control tubes. The solution whose concentration remains unaltered by root contact indicates an osmotic equilibrium equivalent to the root suction force. For intermediate readings, an interpolation curve is plotted.

2. Calibration Scale: Sucrose Concentrations and Osmotic Pressures

The operational correlation between sucrose solution concentration and developed osmotic pressure is summarized in Table 1.

3. Layer-by-Layer Measurements in Peat-Gley Soil

Root suction force measurements throughout the peat-gley profile revealed a direct dependence on layer moisture, reaching up to 8 atm in dry horizons. As a physiological rule, root suction force was lower than leaf suction force. In late July, lupine leaf suction force reached 4.6 atm, whereas roots at 10–20 cm depth registered 3.5 atm, at 40–50 cm — 3.0 atm, and at 70–80 cm — only 1.9 atm.

Depth variations strictly corresponded to profile moisture dynamics: on July 28, the topsoil layer (10–20 cm) experienced highest drying, while deep horizons (70–80 cm) remained well-hydrated. To extract water from dried topsoil, plants were forced to develop suction forces almost twice as high as those in deeper subsoil layers.

Under high relative humidity and overcast weather, root osmotic exchange with solutions proceeded more slowly, requiring extended incubation times.

4. Agroecological Significance for Polesian Land Reclamation

5. Original Article in Belarusian

6. References

1. Gusev N. A. Some Methods for Studying Plant Water Regimes. — Leningrad, 1960.
2. Slatyer R. O. Plant-Water Relationships. — Moscow, 1970.
3. Stankov N. Z., Ladonina T. P. // Herald of Agricultural Science. — 1971. — No. 8.