Rational Fertilization of Fish Ponds and Methods for Applying Nitrogen Fertilizer in Rice-Fish Paddy Fields

Fertilizing fish ponds is one of the main techniques for regulating the aquatic environment of ponds and cultivating natural fish food organisms. If the water is too lean, the fish raised will almost always have big heads, small tails, thin backs and little flesh; using too much fertilizer will degrade water quality, not only affecting fish growth but even causing mass fish deaths. Therefore, rational fertilization of fish ponds should pay attention to the following points:

① Determine the amount of fertilizer based on the fertility of the pond water

It is generally believed that normal pond water transparency should be 25-30 cm, and the water should be tea-brown, green-brown, yellow-brown and oil-blue in color. If the transparency is too great and the water is too pale, this indicates that the water is relatively lean, and the amount and frequency of fertilization should be increased;

② Chemical fertilizers need to be dissolved in water first

Chemical fertilizers have the characteristics of quick fertilizer effect and short duration, so they are mostly used as topdressing in high-temperature seasons. Generally, they are first dissolved in water and then splashed on. If spread directly, fish that accidentally eat the fertilizer granules will suffer poisoning and die. Generally, topdressing is applied 1-2 times a month, using 5-7.5 kg each time per 667 sq m;

③ Organic fertilizers need to be fully fermented

Unfermented organic fertilizer, because it contains many pathogenic organisms, will cause fish diseases, and also because organic matter consumes a large amount of oxygen during decomposition, it easily causes oxygen deficiency and fish deaths in fish ponds;

④ The fertilizer ratio must be reasonable

Fertilization of fish ponds should be reasonably supplemented according to the degree of deficiency of various nutrients in the water. For example, if the water in some fish ponds is clear and lean, organic fertilizer should be applied together with chemical fertilizer when fertilizing. Generally, the ratio of manure to chemical fertilizer is 4:1, and they are separately mixed with water and then splashed together;

⑤ Fertilize rationally according to the weather and the activity of the fish

When the weather is muggy or there is continuous rain, apply less or no fertilizer; when the fish do not feed actively or are sick, it is best not to fertilize, so as to avoid causing fish deaths.

Appendix: How to apply nitrogen fertilizer in rice-fish paddy fields? 

Raising fish at the same time as planting rice in paddy fields is called “rice-fish farming”. Rational application of nitrogen fertilizer in rice-fish paddy fields not only benefits rice but also has a good effect on fish growth. When applying nitrogen fertilizer in rice-fish paddy fields, choosing a suitable type of nitrogen fertilizer is crucial. Ammonium bicarbonate in chemical fertilizers is somewhat toxic to fish, so it is best used as a base fertilizer, and fish fry should be released one week after application. For topdressing with nitrogen fertilizer, urea and ammonium sulfate are generally suitable. Use 7.5-10 kg of urea per 66/sq m, and the amount of ammonium sulfate should be doubled. If ammonium bicarbonate must be used, it should be applied in small amounts several times. When topdressing, first drain the field water shallow, drive the fish into fish ditches or fish pits, and then deepen the field water after fertilization; in this way there is no effect on the fish. In addition, applying barnyard manure as topdressing not only serves as fish bait but also provides a good fertilizer source for rice, achieving two goals at once.