Continuous measurements of electrical conductivity in growing media using a modified suction probe: Initial calibration and potential usefulness

A electrical conductivity (EC) cell introduced into a porous ceramic cup wa s developed to continuously sample the solution and measure EC from differe nt growing media. Application of pressure head creates a continuous flow of solution from the growing media tested, into the ceramic cup, and through the EC cell. Continuous recording of the EC was achieved by connecting the EC meter to a data logger. Using two different pressure heads (-5 and -15 k Pa) allowed us to observe differences in the EC of the solution extracted t hat resulted from the different moisture retention of each growing media. A fter a maximum period of 24 h extracting the solution from different growin g media, EC values obtained with the probe were compared with those obtaine d using paste extracts, saturated with either deionized water or nutrient s olution. Results show EC values obtained using the probe with a -15 kPa pre ssure head were closer to values of EC measured in saturated extracts made with nutrient solution. Using a -5 kPa pressure head, EC values with probe were lower than those obtained by extracts done with nutrient solution, but higher than EC values from saturated extracts made with deionized water. S imultaneous measurements of matric tension and EC show the effect of pressu re heads applied in the probe on the water content of growing media. This t echnique is not destructive (the sampling of growing media is not necessary ) and it is possible to obtain EC measurements of solutions continuously. T his method of measuring water and salt content of the root environment has potential applications in the greenhouse production of pot plants. Measurem ents obtained with this method may lead to new information on nutrient upta ke by plants and the development of new strategies of managing fertility an d irrigation of horticultural crops.