This method is applicable to compound fertilizers made by chemical methods or compound fertilizers made from nitrogen, phosphorus, and potassium fertilizers through secondary processing.

Grind the sample and pass it through100Number sieve (aperture)0.15mm）. The grinding operation should be carried out quickly to avoid water loss or moisture absorption during the grinding process, and to prevent the sample from overheating. Mix the sample thoroughly and place it in a sealed wide mouthed bottle. After placing the sample, there should be some space left in the bottle. Seal and label (sample name, sample preparation date, sample maker).