Urea is white spherical in appearance, with total nitrogen content ≥46% and low hygroscopicity, which is between ammonium sulfate and ammonium nitrate. With the increase of temperature, its hygroscopicity increases. Urea is easily soluble in water and liquid ammonia. When pure urea is heated to near the melting point under normal pressure, it begins to show instability, resulting in condensation reaction and biuret, which loses its fertilizer effect on crops. If you put a clean iron piece on the fire and put urea particles on it, you can see that urea melts and volatilizes quickly, and at the same time, a small amount of white smoke comes out with the smell of ammonia.
(2) ammonium sulfate.
Agricultural ammonium sulfate is a white or light-colored by-product, with light yellow or gray crystals, and its nitrogen content is ≥ 20.8% (Grade II). Ammonium sulfate has little hygroscopicity and is easily soluble in water. Its aqueous solution is acidic and reacts with alkaline substances to release ammonia. When ammonium sulfate is heated on a fire, it can be seen that it melts slowly, accompanied by ammonia and sulfur dioxide.
(3) ammonium nitrate.
The appearance of ammonium nitrate is white, without visible impurities, and the agricultural products are allowed to be yellowish. Total nitrogen content ≥ 34.4% (Grade II). Ammonium nitrate has strong hygroscopicity and caking property. When the temperature changes, its aqueous solution will recrystallize, which is very sensitive to heat. A large amount of ammonium nitrate is easily decomposed by heating, which can cause combustion (explosion in severe cases), accompanied by white smoke, which can smell ammonia, and the aqueous solution is acidic.
(4) ammonium chloride.
Ammonium chloride is a white crystal. Agricultural products are allowed to be yellowish, and the nitrogen content is 22.5% ~ 25%. Soluble in water, with the increase of temperature, the solubility in water increased significantly. The aqueous solution is acidic, and ammonium chloride has strong water absorption and is easy to agglomerate. When a small amount of ammonium chloride is heated on a fire, it can smell a strong pungent smell accompanied by white smoke. Ammonium chloride will melt quickly and disappear completely, and the unmelted part will turn yellow during melting.
(5) Ammonium bicarbonate for agriculture.
Appearance is white or light gray crystal, with ammonia smell, nitrogen content ≥ 16.8% (secondary), strong hygroscopicity, easy to dissolve in water, and weak acid in water solubility. When simply identifying ammonium bicarbonate, you can rub a small amount of samples with your fingers and smell strong ammonia.
(6) calcium superphosphate.
The appearance is dark gray, off-white, etc. And there are many tiny pores in the loose powder block, commonly known as "honeycomb eyes". Effective phosphorus pentoxide content ≥ 12% (qualified product), slightly acidic, belonging to acidic fertilizer, sensitive to the action of alkali, and easy to lose fertilizer efficiency. Part of it can be dissolved in water, and the aqueous solution is acidic. Under normal circumstances, the hygroscopicity is small. If the air humidity reaches above 80%, it will absorb moisture and form lumps. It is unstable when heated, so it smells slightly smoky and sour.
(7) calcium magnesium phosphate fertilizer.
The appearance is grayish white, grayish green or grayish black powder, which looks very fine. Under the irradiation of sunlight, you can generally see broken glass-like objects shining. Phosphorus pentoxide content ≥ 12% (qualified product), insoluble in water, not easy to run off, not absorbing moisture, non-toxic and non-corrosive, and will not change when heated in fire.
(8) compound fertilizer.
Appearance should be grayish brown or grayish white granular products, without visible mechanical impurities. Some compound fertilizers contain urea with white granular crystals, which are not completely crushed, or urea exists alone in compound fertilizers as complete granular crystals. The total nutrient of low-concentration compound fertilizer is more than or equal to 25%, the total nutrient of medium-concentration compound fertilizer is more than or equal to 30%, and the total nutrient of high-concentration compound fertilizer is more than or equal to 40%, in which the single nutrient content shall not be less than 4%. Compound fertilizer has slight hygroscopicity. Compound fertilizer particles are easy to be crushed after absorbing moisture, which is non-toxic, tasteless and non-corrosive, and can only be partially dissolved in water. When the commonly used compound fertilizer is heated on the flame, white smoke can be seen and ammonia can be smelled, and it cannot be completely melted.
(9) Agricultural zinc sulfate.
Needle crystals with white or slightly colored appearance. The zinc content of zinc sulfate heptahydrate should be ≥2 1.8%. Zinc sulfate is soluble in water, and its aqueous solution is acidic.
(10) potassium dihydrogen phosphate.
The appearance is white crystal. The content of agricultural potassium dihydrogen phosphate should be ≥92%. Potassium dihydrogen phosphate is soluble in water, and its aqueous solution is acidic.