Table 1.
Details of studies (plant species, growth medium, and electrical frequency at which capacitance was determined) and parameters obtained for linear relationships between capacitance and root system size
| Publication | Plant species | Growth medium | Frequency | R2 values | n | |||
|---|---|---|---|---|---|---|---|---|
| (kHz) | FM | DM | RL | SA | ||||
| Chloupek (1972) | Zea mays | Sand (container) | 0.8 | 0.736 | 0.728 | 0.731 | 0.663 | 24 |
| Allium cepa | Sand (container) | 1 | 0.566 | 0.545 | nd | 0.529 | 14 | |
| Helianthus annuus | Sand (container) | 5 | 0.916 | 0.897 | 0.92 | nd | 15 | |
| Avena sativa | Clay soil (container) | 5 | 0.566 | 0.464 | nd | nd | 15 | |
| Helianthus annuus | Clay soil (container) | 5 | 0.692 | 0.432 | nd | nd | 10 | |
| Brassica napus | Not specified | 0.081 | nd | nd | nd | 18 | ||
| Chloupek (1977) | Daucus carota | Loam soil (field)* | 1 | 0.514 | 113 | |||
| Helianthus annuus ** | Sand | 1 | 0.549, 0.554 | 15 | ||||
| Helianthus annuus *** | Sand | 1 | 0.523, 0.543, 0.566 | 15 | ||||
| Kendall et al. (1982) | Trifolium pratense | Solution | 1 | 0.672 | 21 | |||
| Medicago sativa | Silt loam soil (field*) | 1 | 0.436 | 20 | ||||
| Dalton (1995) | Solanum lycopersicum | Solution | 1 | 0.877 | 12 | |||
| van Beem et al. (1998) | Zea mays 35 d **** | Vermiculite | 1 | 0.85 | 32 | |||
| Zea mays 70 d **** | Vermiculite | 1 | 0.27 | 32 | ||||
| Zea mays 56 d **** | Loam soil (field) | 1 | 0.41, 0.53 | 36 | ||||
| Ozier-Lafontaine and Bajazet (2005) | Amaranthus tricolor | Solution | 1 | 0.937 | 5 | |||
| Solanum lycopersicum | Solution | 1 | 0.987 | 11 | ||||
| Solanum lycopersicum | Clay loam soil (container) | 1 | 0.829 | 15 | ||||
| Preston et al. (2004) | Populus deltoides × Populus nigra | Potting compost (container) | 1 | 0.866 | 0.895 | 33 | ||
| Rajkai et al. (2005) | Helianthus annuus | Sandy soil (container) | 1 | 0.832 (needle), 0.921 (clamp) | 12 | |||
| McBride et al. (2008) | Zea mays (exp. 1, 4 genotypes) | Turface, porous granular medium (container) | 1 | 0.779, 0.647 | 30, 30 | |||
| 0.823, 0.364 | 30, 30 | |||||||
| Zea mays (exp. 2, 4 genotypes) | Turface | 1 | 0.761, 0.846, | 30, 30 | ||||
| 0.646, 0.726 | 30, 30 | |||||||
| Bengough et al. (2009) | Triticum aestivum (35 genotypes) | Gravel-sand mix (containers) | 1 | 0.753 | 67 | |||
| Tsukahara et al. (2009) | Prunus persica | Soil (field) | 1 | 0.897 | 0.896 | 27 | ||
| Pyrus pyrifolia (on Pyrus betulaefolia rootstock) | Soil (container) | 1 | 0.806 | 18 | ||||
| Pitre et al. (2010) | Salix viminalis × Salix schwerinii | Soil (pots), sandy soil (field) | 1 | 0.81, 0.49 | 16, 8 | |||
| Chloupek et al. (2010) | Daucus carota | Soil (field) | 1 | 0.525 | 92 | |||
*Final harvest date only (several previous harvest dates gave poorer correlations, possibly a result of dry soil.
**Capacitance was measured first with several, and then with only one, electrode in soil.
***Capacitance was measured with one electrode in soil at 5, 10, and 15cm from the plant.
****Combined data from eight genotypes in vermiculite, six in field.
FM, fresh mass; DM, dry mass; RL, root length; SA, surface area; n, number of replicates.