Determination of soil pH
Soil pH is one of the most important basic properties of soil. The availability of essential nutrients for most crops is related to the pH of the soil. Therefore, understanding the pH status of soil is important for understanding the effectiveness of soil nutrients and recommending fertilization. . While measuring soil nutrients, soil pH measurement is also an indispensable indicator. First, the method principle Soil pH measurement methods can be roughly divided into two major categories of potentiometric and colorimetric methods, with the progress of analytical instruments, the soil laboratory basically uses the potentiometric method, potentiometric method is accurate, fast, convenient, etc. advantage. The potentiometric method is used in the ASI method. The basic principle is that when a pH meter is used to measure the pH of the soil suspension, the potential difference is generated due to the difference in the activity of the solution H+ ion inside and outside the glass electrode, that is: Third, the operation steps (a) instrument calibration with standard buffer to check the pH time, must use two different pH buffer, one for pH4.01, one for pH6.87, or one for pH6.87, one for pH9. 18, depending on the pH of the soil to be measured, it is preferable to use this pH close to the soil. During the test, first insert the electrode into a buffer, turn on the power, after adjusting the zero point and temperature compensation, set the baffle to the pH level and use the “positioning†adjustment knob to adjust the reading to the pH of the standard buffer. This adjustment is Electrode asymmetric potential, after a buffer correction, if the electrode is intact or the instrument has been working under normal conditions, the allowable deviation should be within 0.02 (pH 7.000.02) when checking with the second buffer. If there is a large deviation, the electrodes must be replaced and the instrument must be checked. Liothyronine Sodium,Anabolic Steroids Powders ,High Quality Bimatoprost Testosterone Raw Powders Co., Ltd. , http://www.nsrawpowders.com
Where: a1 is the H+ ion activity of the solution in the glass electrode, and the value is fixed.
A2 is the H+ ion activity of the solution outside the glass electrode, ie, the activity of H+ in the solution to be tested.
It can be seen from the above equation that the potential difference between the inside and outside of the glass electrode is determined only by the activity of H+ in the test solution, and the negative logarithm value is the pH. The pH of the solution can be read directly from the pH meter by switching on the pH meter.
Second, reagent preparation
1. pH 4.01 Standard Buffer Solution Weigh 10.21g of potassium hydrogen phthalate (KHC8H4O4, analytical grade) dried at 105°C in a 1000ml volumetric flask, and dissolve to volume after dissolution.
2. pH6.87 Standard Buffer Solution Weigh out 3.39g of potassium dihydrogen phosphate (KH2PO4, analytical grade) dried at 50°C in a 1000ml volumetric flask and dissolve to volume after dissolution.
3. The pH9.18 Standard Buffer Solution Weigh 3.39g of borax (Na2B4O710H2O, analytical grade) in a 1000ml volumetric flask and dissolve to volume after calibration.
(b) Determination of soil pH Sample sample to take 10 ml soil sample into the sample cup, add 25 ml boiling water after cooling with the extract liquid adder, stir in the blender for 10min, place for 30min, and then use The pH meter measures the pH. Reading the reading directly is the soil pH.