How to choose diammonium and compound fertilizer reasonably
WENZHOU DIYE VALVE&FITTINGS CO.,LTD , https://www.diye-valve.com
June 29 07:39:24, 2025
Ms. Tian from Donggang City, Liaoning Province asked: A small plot of rice was planted in Datian for breeding purposes. Only 12 kg of diammonium phosphate was applied per mu, but the seedlings turned yellow. What could be the cause, and what should she do?
A: Yellowing of the seedlings is likely due to a lack of nutrients, particularly nitrogen deficiency. In the nursery stage, the soil should be rich in organic matter, and fertilizer application should be higher than in the field. The amount of fertilizer Ms. Tian used may not be sufficient, especially in terms of nitrogen and potassium. Since no organic fertilizer was added, trace elements might also be lacking. It is recommended that she apply 10 kg of urea per acre or a mix of ammonium sulfate, ammonium bicarbonate, and 5–10 kg of potassium sulfate. If symptoms like leaf spot disease appear, she can spray zinc sulfate or a multi-microelement solution as instructed.
Mr. Wu from Jiansanjiang Farm in Heilongjiang asked: Previously, when planting soybeans, diammonium phosphate worked well, but now it doesn’t seem to have any effect. Is there a problem with the fertilizer?
A: It’s not the fertilizer itself that’s at fault, but rather improper usage. Newly developed land usually has higher fertility, so diammonium phosphate was sufficient before. However, after years of use, soil fertility has declined, and simply applying diammonium may not provide enough nitrogen and potassium. It’s still possible to use diammonium, but it's important to add appropriate amounts of nitrogen and potassium fertilizers and avoid over-application.
Ms. Li from Nanyang City, Henan Province asked: When buying compound fertilizer, solubility is important, but people often overlook the nutrient ratio. What are the differences in solubility among different types of fertilizers?
A: Generally, chemical fertilizers dissolve quickly in water, which gives them a faster effect — this is one of their main advantages. Among them, nitrogen fertilizers are the most soluble, followed by potassium, while phosphate fertilizers vary in solubility, ranging from highly soluble to poorly soluble. The solubility of compound fertilizers depends on their composition and production process. The higher the proportion of nitrogen and potassium, the more easily they dissolve.
Ms. Guo from Wuhu City, Anhui Province asked: When transplanting greenhouse melons, she used high-tower granulated compound fertilizer with an NPK ratio of 30:5:5, but the lower leaves were burned. Could this be fake fertilizer?
A: No, it's not fake. Leaf burn is caused by improper application. High-tower granulated compound fertilizer contains a lot of urea, which dissolves quickly and can easily burn young plants. It should be applied away from the roots or mixed thoroughly into the soil. Also, ensure proper ventilation to prevent ammonia toxicity, which can lead to leaf or flower burn.
Mr. Lan from Dezhou City, Shandong Province asked: Greenhouse cucumbers are being fertilized with general-purpose compound fertilizer, but the fertilizer doesn't dissolve, and the seedlings aren't growing well. Why is that?
A: It's because the wrong type of fertilizer is being used. A high-nitrogen, high-potassium compound fertilizer would be more suitable. This type of fertilizer dissolves well in water and has a nutrient ratio that suits the growth stage of cucumbers. It should be dissolved in water before application and mixed into the soil during trenching.
Mr. Zhao from Weishi County, Henan Province asked: How can solanaceous vegetables grow well in winter?
A: For winter-growing solanaceous crops, selecting well-draining bed soil and applying adequate base fertilizer is essential. Ensuring good heat retention helps seedlings grow strong and fast, which is key to preventing diseases like blight and rickets. To treat fungal issues, you can use 30% carbendazim (3–4 ml per 3 liters of water) or 64% phosphorous acid (120–170 g per 50 kg of water). For aphids, pyrethroid insecticides or acetamiprid can be used. Overwatering often causes yellowing, so monitoring soil moisture is crucial.
Mr. Zhang from Huainan County, Anhui Province asked: Which is better between urea and ammonium-based nitrogen fertilizers?
A: The effectiveness of each depends on how they are used. Urea has a high concentration and needs 3–5 days to convert into ammonium nitrogen under microbial action. Before that, it’s hard for plants to absorb it and it’s easily leached. So, don’t apply too much at once, and avoid flooding immediately after. Ammonium-based fertilizers can volatilize easily in calcareous soils or when mixed with alkaline substances, so they should be applied deep and covered afterward.
Mr. Zhou from Jingzhou City, Hubei Province asked: Why is calcium superphosphate acidic? Can it be used as a foliar fertilizer?
A: Calcium superphosphate is produced by reacting phosphate rock with sulfuric acid, and it contains a small amount of free acid, making it slightly acidic. However, since it is water-soluble and the free acid content is strictly controlled, it can be safely used as a foliar fertilizer. For example, spraying 1–3% solution on wheat, corn, or rice, and 0.5% on cotton, tomatoes, cucumbers, etc., can improve yield and quality. The best time to spray is during the late growth stage or before and after flowering.
(Senior Consultant of Sinofert Company, Professor Wang Xingren from China Agricultural University)
Farmers Daily
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