Determination of Soil Conductivity
Soil conductivity (soil conductivity) refers to the ability of the soil to conduct electricity, which is expressed by measuring the conductivity of the soil extract. The unit of measurement result is expressed in mS/m (ie 10μS/cm). When the measurement result is greater than or equal to 100mS/m (ie 1000μS/cm), three significant digits are retained; when the measurement result is less than 100mS/m, it is retained to one decimal place.
Soil conductivity is the sum of anions and cations in the soil extract, which represents the salt content of the soil. Measuring soil electrical conductivity can directly reflect the content of soil mixed salt, which is of great significance for determining the difference in the temporal and spatial distribution of various field parameters, and thus lays the foundation for the popularization of modern precision agriculture based on information and knowledge.
The national standard HJ 802-2016 "Electrode Method for the Determination of Soil Electrical Conductivity" gives a method for the determination of soil electrical conductivity. It is required to take natural air-dried soil samples and add water at a ratio of 1:5 (m/V) (the conductivity is not Above 0.2mS/m, that is 2μS/cm), shake and extract at 20℃±1℃, and then measure the conductivity of the extracted solution at 25℃±1℃ with a Conductivity Meter. It should be noted that when the conductivity of the extracted solution of the soil to be tested is less than 1mS/m (that is, 10μS/cm), carbon dioxide and ammonia in the air have a greater impact on the measurement of conductivity. Operate in a closed small space. Can eliminate or reduce its interference.
Sample prepare---Calibration---Sample prepare--- Measurement
● Collect, prepare and store samples in accordance with the relevant regulations of HJ/T 166.
● Configure conductivity standard solution or use commercially available conductivity standard solution
● Use conductivity standard solution to calibrate the conductivity meter
● Weigh 20.00 g of soil sample into a 250 ml shaker bottle, add 100 ml water at 20°C±1°C, cap the bottle, place it on a reciprocating horizontal constant temperature shaker, and shake at 20°C±1°C for 30 minutes. After standing for 30 minutes, filter or centrifuge, and collect the extract in a 100 ml beaker for testing.
● Make blank samples in the same steps
● Rinse the electrode several times with water, and then rinse the electrode with the extraction solution to be tested. Insert the electrode into the extraction solution to be tested, and correct the temperature to 25℃±1℃ in accordance with the requirements of the instruction manual of the conductivity meter, and measure the conductivity of the soil extraction solution. Read the conductivity value directly from the conductivity meter, and record the temperature of the extract at the same time.
● The same procedure is used to test the blank sample. The blank conductivity value should not exceed 1mS/m (ie 10μS/cm). Otherwise, you should find the reason and re-measure.
● Record the measurement results.