**First, Combined Fertilizer Testing Method**
**Compound Fertilizer Nitrogen Test:**
**(a) Preparation:**
Ask the user to prepare concentrated sulfuric acid (98% analytical grade).
**(b) Determination Procedures:**
1. Weigh and grind 1.000 g of compound fertilizer into a small 50 ml bottle. Add 20 ml of distilled water to dissolve the fertilizer, then add 3 ml of concentrated sulfuric acid. Heat the mixture over low heat while shaking until the solution is reduced to about half. Remove from heat, let it cool, and transfer the solution to a 100 ml volumetric flask. Dilute to the mark with distilled water. Take 1 ml of this solution and dilute it again in another 100 ml volumetric flask with distilled water. This is the test solution.
2. Pipette 5 ml of distilled water into a clean beaker to prepare the blank solution.
3. Pipette 5 ml of the test solution into another clean beaker.
4. Pipette 5 ml of an 8 ppm ammonium nitrogen standard solution into another clean beaker.
5. Add 5 ml of phenol solution and 10 ml of sodium hypochlorite to each beaker, followed by 20 ml of distilled water. Shake well and let stand for 30 minutes.
6. Perform colorimetric measurement using the instrument as described in the manual.
**(c) Calculation of Results:**
Fertilizer nitrogen (%) = Instrument test value × 100/1 × 100/1 × 100/106
Where:
- The first two 100 represent sample pretreatment dilution factors.
- The first "1" refers to the weight of the sample.
- The second "1" refers to the volume taken.
- 100/106 converts ppm to percentage content.
**Compound Fertilizer Phosphorus Test:**
**(a) Preparation:**
1. Prepare citric acid leaching agent by dissolving one bag of citric acid in 200 ml of distilled water.
2. Prepare molybdenum sulfate anti-developer by dissolving 1.5 g of ascorbic acid in 100 ml of molybdenum sulfate solution. (Note: This solution should be prepared on the day of use.)
**(b) Test Steps:**
1. Weigh and grind 0.200 g of compound fertilizer into a flask or plastic bottle. Add 30 ml of citric acid leaching agent. Stir for 30 minutes, filter with medium-speed non-phosphorus filter paper. Pipette 1 ml of filtrate into a 100 ml volumetric flask and dilute to the mark with distilled water. This is the test solution.
2. Pipette 5 ml of distilled water into a clean beaker for the blank solution.
3. Pipette 5 ml of the test solution into another clean beaker.
4. Pipette 5 ml of a 2 ppm effective phosphorus standard solution into another clean beaker.
5. Add 5 ml of molybdenum sulfate anti-developer to each beaker, remove gas, add 40 ml of distilled water, and shake for 30 minutes.
6. Perform colorimetric measurement using the instrument as per the manual.
**(c) Calculation of Results:**
Fertilizer phosphorus content (P₂O₅%) = Measured solution content × 30/0.2 × 100/1 × 100/106 × 2.2913
Where:
- 30, 100 are dilution factors.
- 0.2 is the weight of the sample.
- 1 refers to the volume taken.
- 100/106 converts ppm to percentage.
- 2.2913 is the conversion factor from P to Pâ‚‚Oâ‚….
**Compound Fertilizer Potassium Test:**
**(a) Determination Procedures:**
1. Weigh and grind 0.500 g of compound fertilizer into a flask or plastic bottle. Add 30 ml of distilled water. Stir for 30 minutes, filter with medium-speed filter paper. Pipette 1 ml of filtrate into a 100 ml volumetric flask, dilute with water, add 1–2 drops of 10% sodium hydroxide, boil for 5 minutes, cool, and dilute to volume. This is the test solution.
2. Pipette 10 ml of distilled water into a clean beaker for the blank solution.
3. Pipette 10 ml of the test solution into another clean beaker.
4. Pipette 10 ml of a 20 ppm available potassium standard solution into another clean beaker.
5. Add 10 drops of disodium EDTA solution and 2 ml of formaldehyde solution to each beaker. Then add 2 ml of sodium tetraphenylborate solution and 40 ml of distilled water. Shake and let stand for 5–10 minutes.
6. Perform colorimetric measurement using the instrument as per the manual.
**(b) Calculation of Results:**
Fertilizer potassium content (K₂O%) = Measured solution content × 30/0.5 × 100/1 × 100/106 × 1.2046
Where:
- 30, 100 are dilution factors.
- 0.5 is the weight of the sample.
- 1 refers to the volume taken.
- 100/106 converts ppm to percentage.
- 1.2046 is the conversion factor from K to Kâ‚‚O.
**Second, Simple Fertilizer Testing Method**
**Nitrogen Fertilizer Test:**
**(a) Urea Test:**
The procedure is identical to that for compound fertilizer nitrogen, except that 0.2 g of sample is used instead of 1 g.
**(b) Other Simple Nitrogen Fertilizers:**
1. Prepare the test solution by weighing 1.000 g of sample into a 100 ml volumetric flask, dissolving in distilled water, and diluting to the mark. Take 1 ml of this solution and repeat the dilution process. This is the test solution.
2. Follow the same test process and calculation method as for compound fertilizer nitrogen.
**Phosphate Test:**
The method and calculation are the same as for compound fertilizer phosphorus.
**Potassium Test:**
1. Prepare the test solution by weighing 1.000 g of sample into a plastic bottle, adding 50 ml of distilled water, dissolving, and taking 1 ml of the solution to dilute in a 100 ml volumetric flask.
2. Follow the same test process and calculation as for compound fertilizer potassium.
**Hangzhou Top Instrument Co., Ltd.**
Room 806, Songdu Building, No. 69 Wangjiang Road, Hangzhou
Phone: 86062776
Fax: [Not provided]
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