How to determine the pH value of soil in Kyushu spatial analysis
Soil pH determination is one of the common items in agricultural research. The pH value of soil not only reflects the existence and effectiveness of nutrients in soil, but also has a close relationship with its physical and chemical properties. This paper describes the current methods for determining soil pH in China and abroad, for reference only.
Dilute soil water or solution:
The soil pH measurement method requires the sample to be diluted using one of the following three liquids.
Water: Conductivity value is less than 0.2mS/m (at 25°C/77°F), pH is not lower than 5.6
? Potassium chloride solution: concentration 1mol / L
? Calcium chloride solution: concentration 0.01mol / L
Sample collection and processing:
? Collect the right amount of fresh soil and air dry in the room. The sample should be protected from direct sunlight and prevent the contamination of acid, alkali and other gases and dust.
• The sample can be dried in a dry box. Note: The set heating temperature of the oven should not exceed 40 ° C (104 ° F).
• Extract the appropriate amount of sample by quadruple method, remove impurities other than soil, and filter with a 0.84mm pore size test sieve.
Preparation of samples:
Soil pH determination methods in China and overseas have different requirements for sample preparation:
? Chinese standard: Weigh 10g (±0.1g) of the sample into a 50mL container, add 25mL of water (or solution), stir for 5 minutes, and then let stand for 1 to 3 hours.
International Standard: Weigh 10g (±0.1g) of the sample into a 100mL container, add 50mL of water (or solution), stir for 60 minutes, and then let stand for 1 to 3 hours.
pH measurement:
• Before performing soil pH measurement, you need to calibrate the meter. After calibration, place the prepared soil suspension on the stirrer and turn on the stirring function.
• Dip the pH electrode (with the temperature probe) into the sample solution and wait for the measured value to stabilize before recording the value.
Precautions:
• When calibrating, the temperature of the standard buffer should not be too different from the temperature of the sample solution, and the error should be controlled within 1 °C.
• The soil sample after screening should not be too thin, otherwise the effect will be measured.
• The sample liquid after the configuration must be precipitated for a sufficient period of time, otherwise the hydrogen ion distribution between the pH electrode diffusion layer and the free solution is affected.
• If the pH of the current water extract is less than 7, the pH of the soil should be determined using a salt extract by preparing a soil sample using potassium chloride or calcium chloride solution.
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