Role of sediments in pond fertility
1990
Wirat Jiwyam
Two experiments on the effect of sediment on pond fertility and fish production (Nile tilapia, Oreochromis niloticus) were conducted. The first was a grow-out study and examined five types of bottom substrate. Five types of bottom substrate (detritus-removed, detritus-accumulated, topsoil, deepsoil and fishpond-mud) were placed in 15 rectangular concrete tanks. Fishpond-mud substrate gave the highest average chlorophyll a concentration (564 mg/cubic m) that obtained from last four weeks of culture period. The chlorophyll a concentration in the detritus-removed treatment was more constant (16 to 401 mg/cubic m) than in fishpond-mud substrate treatment (16 to 1609 mg/cubic m) which increased with the time. Fish production was also highest in the fishpond-mud substrate treatment. The effect of sedimented organic matter as a direct feed for Nile tilapia was indicated by 48.9 % higher net production from the detritus-accumulated treatment than detritus-removed treatment (983 vs 660 kg/ha/75 day). The second experiment of accumulation/release of nutrients was conducted on a laboratory-scale. All soil types accumulated phosphorus. This was indicated by increasing of phosphorus in composition of topsoil, deepsoil, and fishpond-mud which were equal to 0.01 %, 0.003 %, and 0.08 % respectively. All soil types acted as a source of nitrogen for the water column. This was indicated by decreasing of nitrogen from the compositions of topsoil, deepsoil, and fishpond-mud which were equal to 0.04 %, 0.003 %, 0.26 % respectively.
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