What fertilizer is used as an iron source in soilless culture?
Combining organic and inorganic fertilizers. Farmyard manure is an organic fertilizer; it has a complete range of nutrients and a long-lasting fertilizing effect. Chemical fertilizer is an inorganic fertilizer; it has a single nutrient, a relatively high content, and takes effect quickly. By applying organic and inorganic fertilizers together, they complement each other's strengths, and the fertilizing effect can be greatly improved. For example, combining human and livestock manure with ammonium chloride, superphosphate, ammonium chloride...
In the early days of soilless culture development, the iron source used was inorganic salts such as ferrous sulfate and ferric chloride. Ferric chloride has a molecular weight of 270.30 and contains 20.66% iron; it appears as yellow-brown or orange-yellow lumpy crystals, has a slight hydrochloric acid odor, is highly deliquescent in air, and is easily soluble in water. Ferrous sulfate, commonly known as green vitriol, can supply iron and sulfur and contains 20.09% iron; it is a blue-green crystal, unstable in nature, and readily loses water and oxidizes into brown ferric sulfate. It is even less stable under high temperature and strong light or in the presence of alkaline substances.Because ferrous sulfate is a by-product of some industries, it has a wide range of sources and is cheap. It is an important iron source for soilless culture crops and is also a raw material for making other iron fertilizers such as ferrous ammonium sulfate and chelated iron. Because inorganic iron salts such as ferric chloride and ferrous sulfate readily become iron phosphate or iron hydroxide precipitates and lose effectiveness when alkalinity is high, and may even be oxidized into basic salt precipitates under neutral conditions, while low-valence ferrous sulfate is easily oxidized by oxygen in the air into high-valence iron and loses effectiveness, often causing iron deficiency in plants. Later, the iron salts used in cultivation were changed to organic acid iron, such as ferric citrate and ferric tartrate. Although these compounds are somewhat better in availability than ferric chloride and ferrous sulfate, they themselves are very unstable, so their effects are also not ideal. With the development of modern chemical science, it became clear that organic compounds capable of forming chelate rings can be used to react with iron, or chelated iron. This type of chelated iron used as an iron source in soilless culture nutrient solutions has a very good effect, so it is now used to replace the initially used inorganic iron salts and organic acid iron. Iron chelate is a light brown or dark brown powdery substance. In soilless culture nutrient solutions, iron can form a stable compound and can maintain effectiveness for a relatively long time. Iron chelates mainly include disodium ethylenediaminetetraacetate iron, disodium diethylenetriaminepentaacetate iron, and many others. Because disodium ethylenediaminetetraacetate iron is cheap and has relatively good stability, the most commonly used at present is disodium ethylenediaminetetraacetate iron. When preparing it, first dissolve ferrous sulfate and disodium ethylenediaminetetraacetate iron separately, then mix them together for chelation before use.