NY/T 1121.2-2006 Soil Testing Part 2: Determination of Soil pH NY/T1121.2-2006 Standard Download Decompression Password: www.bzxz.net

ICS13.080.05
Agricultural Industry Standard of the People's Republic of China
NY/T1121.2—2006
Soil Testing
Part 2: Method for determination of soil pH
Soil Testing
Part 2: Method for determination of soil pH2006-07-10 Issued
2006-10-01 Implementation
Ministry of Agriculture of the People's Republic of China
NY/T1121 "Soil Testing" is a series of standards, including the following parts: Part 1: Collection, processing and storage of soil samples Part 2: Determination of soil pH
Part 3: Determination of soil mechanical composition
Part 4: Determination of soil bulk density
Part 5: Determination of cation exchange capacity of calcareous soils Part 6: Determination of soil organic matter
Part 7: Determination of available phosphorus in acidic soils Part 8: Soil fill Determination of Available Boron
Part 9: Determination of Available Molybdenum in Soil
Part 10: Determination of Total Mercury in Soil
Part 11: Determination of Total Arsenic in Soil
Part 12: Determination of Total Chromium in Soil
Part 13: Determination of Exchangeable Calcium and Magnesium in Soil Part 14: Determination of Available Sulfur in Soil
Part 15: Determination of Available Silicon in Soil
Part 16: Determination of Total Water-soluble Salt in Soil Part 17: Determination of Chloride Ion Content in Soil-Part 18: Determination of Sulfate Ion Content in Soil This part is Part 2 of NY/T1121.
This part is proposed and managed by the Ministry of Agriculture of the People's Republic of China. NY/T1121.2—2006
The drafting units of this part: National Agricultural Technology Extension Service Center, Institute of Agricultural Resources and Agricultural Zoning of Chinese Academy of Agricultural Sciences, Shanghai Agricultural Technology Extension Service Center, Jiangxi Province Soil and Fertilizer Technology Extension Station. The main drafters of this part: Tian Youguo, Xin Jingshu, Ren Yi, Long Huaiyu, Zhu En, Zheng Lei. I
1 Scope of application
Soil testing
Part 2: Determination of soil pH
This part is applicable to the determination of pH of various soils. 2 Determination principle
NY/T1121.2—2006
When H glass electrode and calomel electrode are inserted into soil suspension, a battery reaction is formed, and a potential difference is generated between the two. Since the potential of the reference electrode is fixed, the size of the potential difference is determined by the activity of hydrogen ions in the test solution, and its negative logarithm is pH, which is directly read on the pH meter. bzxz.net
3 Instruments and equipment
3.1 Acidity meter
3.2 pH glass electrode-saturated calomel electrode or pH composite electrode3.3 Stirrer
4 Reagents and solutions
4.1 Potassium hydrogen phthalate
4.2 Disodium hydrogen phosphate
4.3 Borax (NazBO-10H0)
4.4 Potassium chloride
4.5 PH4.01 (25C) standard buffer solution
Weigh 10.21 g of potassium hydrogen phthalate that has been dried at 110℃~120℃ for 2h~3h, dissolve it in water, transfer it into a 1L volumetric flask, make up to volume with water, and store it in a plastic bottle.
4.6 pH 6.87 (25℃) standard buffer solution Weigh 3.53g of disodium hydrogen phosphate and 3.39g of potassium dihydrogen phosphate that have been dried at 110C~130℃ for 2h~3h, dissolve in water, transfer to a 1L volumetric flask, adjust to volume with water, and store in a plastic bottle. 4.7 pH 9.18 (25℃) standard buffer solution Weigh 3.80g of borax (NaBO10HO) that has been balanced and dissolve in CO2-free water, transfer to a 1L volumetric flask, adjust to volume with water, and store in a plastic bottle.
4.8 Balancing of borax
Put borax in a desiccator containing saturated aqueous solution of sucrose and salt for two stacks of night. 4.9 Remove 00% distilled water
5 Analysis steps
5.1 Instrument calibration
Adjust the instrument temperature compensator to the same temperature value of the test solution and standard buffer solution. Insert the electrode into the standard buffer solution of pH 4.01 and adjust the instrument so that the pH value of the standard solution is consistent with the instrument indication value. Remove the electrode, rinse with water, dry with filter paper, insert it into the H6.87 standard 1
NY/T1121.2—2006
Ai Chong solution, check the instrument reading, and allow an absolute difference of 0.1PH unit between the two standard solutions. Repeat several times until the instrument is stable. If it exceeds the specified allowable difference, check whether there is a problem with the instrument electrode or standard solution. When the instrument is calibrated correctly, it can be used for sample measurement. 5.2 Determination of soil water immersion pH
a) Weigh 10g (accurate to 0.01g) of air-dried sample that has passed through a 2mm aperture sieve into 50mL high-grade flask, add 25mL of water to remove CO (soil-liquid ratio is 1:2.5), stir with a stirrer for 1min to fully disperse the soil particles, and then measure after leaving it for 30min. Insert the electrode into the sample suspension (note that the lower part of the glass electrode bulb is located at the soil-liquid interface, and the calomel electrode is inserted into the upper clear liquid), gently turn the burner to remove the water film of the electrode, promote rapid balance, let it stand for a while, press the reading switch, and record the pH value when the reading is stable. Release the reading switch, take out the electrode, wash it with water, and use a filter paper strip to absorb the water before measuring the second sample. After measuring 5 to 6 samples, the positioning needs to be checked with a standard solution. 6 Expression of analysis results
When measuring pH with an acidity meter, the pH can be read directly without calculation. 7 Precision
The absolute difference allowed by repeated test results: neutral and acidic soils ≤0.1pH unit, alkaline soil ≤0.2pH unit. 8 Precautions
Long-term storage glass electrodes that are not used need to be soaked in water for 24 hours to activate them before use. Temporarily unused electrodes can be soaked in water. When not used for a long time, they should be kept dry. When the surface of the glass electrode is contaminated, it needs to be treated. The cavity of the calomel electrode should be filled with saturated potassium chloride solution. There should be a small amount of potassium oxide crystals at room temperature, but potassium chloride crystals should not be too much to prevent blocking the passage between the collector and the measured solution. There should be no bubbles between the inner electrode and the bulb of the glass electrode, and between the inner electrode and the multi-ceramic end core of the calomel electrode.
The position of the electrode in the suspension has an impact on the measurement result. It is required to insert the calomel electrode into the upper clear liquid and try to avoid contact with the mud.
Shaking the beaker during pH reading will cause the reading to be low. It should be left to stand for a while after shaking before reading. Avoid acid and alkali vapor intrusion during operation. The standard solution can generally be stored for 1 to 2 months at room temperature, and the shelf life can be extended in a 4℃ refrigerator. Do not pour the used standard solution back into the original solution for mixing. If turbidity or precipitation is found, it cannot be used again. Temperature affects the electrode potential and the ionization balance of water. During the measurement, the temperature compensator should be used to adjust it to be consistent with the temperature of the standard buffer solution and the test solution. The pH of the standard solution changes slightly with temperature. When calibrating the instrument, refer to Table 1. Table 1 pH changes of H buffer solutions at different temperatures
Standard solution 4.01
Standard solution 6.87
Standard solution 9.18
Standard solution 4.01
Table 1 (continued)
Standard solution 6.87
NY/T 1121.2—2006
Standard solution 9.18
After continuously measuring samples with pH>7.5, it is recommended to soak the glass electrode in 0.1mol/L hydrochloric acid solution to prevent the electrode from responding slowly due to alkali.
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