Lime is commonly used by farmers and is applied at 200–300 kg/ha as an initial dose, irrespective of the pH level. This is followed by the application of cow dung (the most common animal manure used) by most farmers at an initial dosage of 2 000–3 000 kg/ha. In addition to cow dung, inorganic fertilizers such as urea and superphosphate are also commonly used. Organic compost (Figure 6) is used by some farmers to improve plankton productivity. Following the initial dose and after stocking the seed, farmers in most parts of the country resort to regular fertilization with organic manures and inorganic fertilizers.
The amounts used are based on the fertility level of the water, which is estimated by visual observation coupled with theexperience of the farmer. The application of organic manures (Figure 7) can be up to 20 tonnes per ha, or more in the case of farmers in Andhra Pradesh; coupled with a higher level of application of inorganic fertilizers such as urea and superphosphate, the combined level of all the inorganic fertilizers used could be more than 1 000 kg/ha. Farmers in Andhra Pradesh have developed these application levels based on practical experience, and thus studies are needed to ascertain the impact of these fertilizers on fish growth (such studies can help to determine the optimal level of fertilization and reduce nutrient input costs).
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