Fish pond fertilization in summer
I. Characteristics of fertilizer changes in summer fish ponds
1, the pool water nitrogen content increased. June-August is the main growing season for fish. Due to the large amount of feeds fed, fish excrement and residual bait are increased. At this time, the water temperature is high, and the oxidative decomposition rate of organic matter is accelerated. Fish excrement, biological carcass and residual bait in the pond are oxidized and decomposed in water to produce a large amount of nitrogenous substances. According to the determination, the effective nitrogen content of the pond water is usually 0.5-2 mg/L, and the maximum can reach 4 mg/L. In particular, in precision cultured fish ponds, the nitrogen sources are already abundant during the main growing season of fish. Moreover, about 60% of available nitrogen in refined fish ponds exists in the form of total ammonium in summer, and part of total ammonium is responsible for fishes. Non-ionic ammonia, which is toxic to other aquatic organisms, can directly or indirectly affect fish growth. It can be seen that the effective nitrogen in the water during the main growth season of fishes increases with the increase of feed amount, so there is no need to apply inorganic nitrogen with high nitrogen content or organic nitrogen fertilizer with large oxygen consumption.
2, phosphorus reduction. In summer, the content of available phosphorus in pond water is very low. The main reason is that phosphorus easily forms insoluble phosphate with calcium ions in water, and it is easily adsorbed and fixed by colloidal substances in pond mud and water to form plants that cannot be used. Ineffective phosphorus. In the fish growth season, due to the consumption of phytoplankton, the available phosphorus content in the water is reduced, generally below 0.01 mg/l.
3. The proportion of nitrogen and phosphorus is seriously imbalanced. It has been determined that the ratio of available nitrogen and available phosphorus in the refined culture ponds is preferably 35:1 to 50:1, and the current general culture ponds greatly exceed this ratio, resulting in apparent “phosphorus hunger†of algae in water. phenomenon. Therefore, the content of available phosphorus in water is the main limiting factor for the growth of phytoplankton. Due to the lack of available phosphorus in the water, a large amount of available nitrogen is not fully utilized and is wasted. Therefore, application of inorganic phosphate fertilizer in the main growth season of fish can increase the effective phosphorus content in the water, adjust the ratio of available nitrogen and available phosphorus, make full use of the available nitrogen in the refined culture pond, promote the growth of phytoplankton, and increase the productivity of the pond.
Second, the clever application of phosphate fertilizer to phosphorus nitrogen
1, phosphorus method, time, number and frequency. Phosphate should be first dissolved in water, fully dissolved, select sunny day 9-10 when Quanchiposa. Sprinkling methods and requirements are the same as the methods used to splash soymilk during fry cultivation, such as spraying machines. Sprinkling concentration: 5ppm of calcium dihydrogen phosphate or superphosphate 10ppm. Since the upper and lower layers of the pond are not easily convective, the upper layer of water-soluble phosphate fertilizer can maintain a relatively high concentration, and the phytoplankton also begin to concentrate on the upper layer of the pool. This is the reason that the “phosphorus-starved†algae have special characteristics of absorbing and storing phosphorus. The utilization rate of water-soluble phosphate fertilizer is greatly increased, and it is usually splashed every 15 days from May to September.
2, attention. Do not stir the pool on the day after splashing (including pulling nets, adding water, and starting aerators at noon, etc.) to prolong the time for the suspension of water-soluble phosphate fertilizers in the water and reduce the absorption and fixation of phosphorus by the pond sludge. Usually 3-5 days after the application of phosphate fertilizer, the peak of phytoplankton in the pool will appear, the biomass will increase significantly, and the ammonia nitrogen content will drop. At this time, according to the requirements of water quality management, new water should be added properly to prevent the water from being over-concentrated.
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