Effect of organic fertilizer on heterotrophs and autotrophs: implications for water quality management
1995
Qin, J | Culver, D A | Yu, N
Alfalfa meal as a source of organic fertilizer was used in a series of pond, enclosure and laboratory experiments to determine its effect on bacteria, algae and water quality. Bacteria and flagellate algae were increased, whereas nonflagellate algae were not significantly affected by organic loadings. Bacterial and algal turnover rates we re 1.9‐2.7 times daily and 0.18‐0.22 times daily at 20‐25ᵒC, respectively. Oxygen consumption rates were enhanced by increasing organic input or temperature. Dissolved oxygen in ponds with organic fertilizer was significantly lower than that in ponds without organic input. Because of low N and P content and high oxygen consumption, organic fertilizer alone is unlikely to provide adequate nutrients for algae and sufficient oxygen for fish. To stimulate the growth of food organisms for fish in aquaculture ponds, a combined use of inorganic and organic fertilizer is recommended, but the amount of organic fertilizer should be determined with care to avoid water quality deterioration. The amount of 10mg alfalfa 1⁻¹ wk⁻¹ is considered the upper safety limit for organic fertilization. The nitrogen and phosphorus ratio should be kept weekly at 20:1 by weight to promote the development of food organisms in ponds.
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