1.？ Preparation of drugs
1) preparation of soil extractant: put a bag of soil combined extractant (invention patent number: 20110123020.4) powder into it.
In a 500 ml volumetric flask, add distilled water to constant volume.
2.？ Preparation of soil nutrient solution to be tested
Weigh 1.0g air-dried soil sample or1.0g fresh soil sample (1+water content), put it in a soil eluent bottle (triangular bottle or plastic bottle), and suck 20mL soil eluent with a straw. In the leaching bottle, pour a flat spoon of soil decolorizer (about 0.3g) into the leaching bottle, keep the temperature at 20-25℃, shake vigorously for 3 minutes, and then filter in a dry triangular bottle (the initial filtrate can be discarded when the triangular bottle is not dry), which is the effective nutrient solution of the soil to be tested. The solution can be used to determine ammonium nitrogen, nitrate nitrogen, available phosphorus and available potassium in soil.
[Note 1] The filtered solution to be tested should be covered at any time and determined as soon as possible. It is not advisable to leave it for a long time, otherwise it will easily cause ammonium nitrogen loss.
[Note 2] The ambient temperature has a certain influence on the determination, especially on phosphorus. When the room temperature is lower than 20-25℃, it is suggested to preheat the soil extract to 30℃ for later use. (the same below)
3.？ Determination of Ammonium Nitrogen in Soil
Suck the extractant separately with a straw? 2mL (blank), extractant? 2mL+ 1？ Drop soil nutrient mixed standard stock solution (standard use), soil solution to be tested? 2mL？ In three small test tubes, add:
Soil ammonium nitrogen 1? Reagent 4? be filled/suffused/brimming with
Soil ammonium nitrogen 2? Reagent 4? be filled/suffused/brimming with
Soil ammonium nitrogen 3? Reagent 4? be filled/suffused/brimming with
Shake well, after 5 minutes, transfer to a cuvette for determination:
① Turn the left wheel of the filter to set the value to 1, put the blank liquid into the light path, press the "Colorimetric" key, and the function number will be switched to 1, and press the "Adjust+"key or "Adjust-"key to make the instrument display 100%.
② Place the standard solution in the light path, press the "colorimetric" key, and the function number will be switched to 3. Press the adjustment key to make the instrument display 48.0.
(3) Place the liquid to be measured in the light path, and the instrument reading at this time is the content of ammonium nitrogen in the soil (mg/kg).
4.？ Determination of nitrate nitrogen in soil
Suck the extractant separately with a straw? 2mL (blank), extractant? 2mL+ 1？ Drop soil nutrient mixed standard stock solution (standard use), soil solution to be tested? 2mL？ In three small test tubes, add:
Nitrate nitrogen 1 reagent 4 drops (gradually added and shaken)
Nitrate nitrogen no 2 reagent 10 drop
Nitrate nitrogen No.3 reagent 1 drop (before use, shake it vigorously or take a hot water bath at 70℃ for 3 minutes and then shake it several times to make the precipitate fully suspended before use).
Shake it for one minute, let it stand for 15 minutes, then transfer it to a cuvette and measure it on a computer.
① Turn the left wheel of the filter to set the value to 2, put the blank solution into the light path, press the "Colorimetric" key, and the function number will be switched to 1, and press the "Adjust+"key or "Adjust-"key to make the instrument display 100%.
② Place the standard solution in the light path, press the "colorimetric" key, and the function number will be switched to 3. Press the adjustment key to make the instrument display 48.0.
(3) Place the liquid to be measured in the light path, and the instrument reading is the content of nitrate nitrogen in the soil (mg/kg).
[Note 1] Nitrate nitrogen rises and falls with water, mainly distributed in 0 ~ 40 cm soil layer. In order to make the test results more in line with the soil reality, it is suggested that the soil excavation depth should be 0 ~ 40 cm and the soil weight coefficient should be changed from 0. 15 to 0.3.
[Note 2] If reducing agent is added in the determination of soil hydrolyzed nitrogen, it is not necessary to determine nitrate nitrogen separately.
5.？ Determination of available phosphorus in soil
Suck the extractant separately with a straw? 2mL (blank), extractant? 2mL+ 1？ Drop soil nutrient mixed standard stock solution (standard use), soil solution to be tested? 2mL？ In three small test tubes, add:
4 drops of soil available phosphorus 1 reagent (shake slowly and carefully until there are no bubbles)
Soil available phosphorus 2? Reagent 4? be filled/suffused/brimming with
Soil available phosphorus 3? Reagent 1? be filled/suffused/brimming with
Shake well, let it stand for 10 minute, then transfer it to a colorimetric cup and measure it on a computer:
① Turn the left wheel of the filter, set the value to 6, put the blank solution into the light path, press the "Colorimetric" key, and the function number will be switched to 1, and press the "Adjust+"key or "Adjust-"key to make the instrument display 100%.
② Place the standard solution in the light path, press the "colorimetric" key, and the function number will be switched to 3. Press the adjustment key to make the instrument display 48.0.
(3) Place the liquid to be measured in the light path, and the instrument reading is the content of P2O5 in the soil (mg/kg).
(Note) When the room temperature is lower than 20℃, it is suggested to extend the reaction time before the reaction until the color of the solution is stable. The sign of color stability is that the reading is stable after standard adjustment, and there is no air bubble attached to the wall of the cuvette.
6.？ Determination of available potassium in soil
Suck the extractant separately with a straw? 2mL (blank), extractant? 2mL+ 1？ Drop soil nutrient mixed standard stock solution (standard use), soil solution to be tested? 2mL？ In three small test tubes, add:
Soil available potassium 1? Reagent 4? be filled/suffused/brimming with
Soil available potassium 2? Reagent 4? be filled/suffused/brimming with
Shake well, immediately transfer to a cuvette, and measure on a computer:
① Turn the left wheel of the filter, set the value to 6, put the blank solution into the light path, press the "Colorimetric" key, and the function number will be switched to 1, and press the "Adjust+"key or "Adjust-"key to make the instrument display 100%.
② Place the standard solution in the light path, press the "colorimetric" key, and the function number will be switched to 3. Press the adjustment key to make the instrument display a value of 200.0.
(3) Place the liquid to be measured in the light path, and the instrument reading at this time is the K2O content in the soil (mg/kg).