Table 1.

Summarized references using single-frequency EC method in situ plant root research

Method	References	Plant	Growth substrate	Concern	Frequency range (Hz)	No. of plant
Single-frequency EC method	[18]	Maize	Hydroponics	Root number	1 k	15
	[19]	Maize	Pot Sand	Root wet weight, Root dry weight, Root length, Root surface area	800	24
	[20]	Carrot Sunflower Sunflower	Field Sand Sand	Root wet weight	1 k	113 15 15
	[21]	Carrot	Field	Root wet weight	1 k	92
	[22]	Tomoto	Hydroponics	Root dry weight	1 k	12
	[23]	Sunflower	Pot Sand	Root wet weight	1 k	12
	[24]	Acalypha	Hydroponics	Root wet weight	1 k	5
	[35]	Maize Maize	Pot vermiculite Field	Root wet weight Root wet weight	1 k	32 36
	[25]	Barley	Hydroponics	Root wet weight	1 k	16
	[26]	Barley	Pot chernozem	Root dry weight	1 k	67
	[36]	Bean	Pot Sand	Root dry weight, Root length, Root surface area	1 k	19
	[27, 28]	soybean	Pot perlite	Root dry weight, Shoot dry weight, Root/shoot ratio	1 k	40
	[29]	Maize Soybean	Pot chernozem	Root activity, SWC	1 k	30
	[30]	Wheat Soybean Maize	Pot Pumice or arenosol	Cadmium contamination, alkaline stress, drought, weed competition	1 k	12 20 10
	[31]	wheat	Pot Rhyolite and vermiculite	Salinity-alkalinity stress	1 k	20
	[32]	Cucumber Corn Soybean Wheat	Pot pumice, arenosol, chernozem, pumice	Salinity-alkalinity stress	1 k	30
	[33]	Stipa borysthenica Crepis rhoeadifolia	Sand Calcaric arenosol	Root activity, SWC	1 k	12
	[34]	Maize	Pot arenosol	Root dry weight, stem cross-sectional area	1 k	12