Have a look: the high-quality compound fertilizer particles are consistent, without large or small lumps, and less powder. Red small potash fertilizer particles or white urea particles can be seen.
Second,rubbing: rub the compound fertilizer with your hands, leaving a layer of gray powder on your hands, and stickiness is a high-quality compound fertilizer.
Third,burning: Take a small amount of compound fertilizer and put it on the iron sheet and burn it in an open flame. The smell of ammonia indicates nitrogen, and the purple flame indicates potassium. The stronger the ammonia smell and the longer the purple flame is a high-quality compound fertilizer. On the contrary, it is inferior quality.
Forth,dissolution: High-quality compound fertilizer will dissolve in water, even if there is a small amount of precipitated powder, it is relatively small.