Abstract:
Various treatments of shrimp pond bottom soil containing organic sludge were examined for the changes in pH, organic matter and removal efficiency of pathogenic bacteria (Vibrio and Pseudomonas). The experimental period was divided into 3 phases. In the first phase, shrimp pond bottom soil and pond organic sludge were placed in the experimental tanks and subjected to 15 days of five treatments and a control. The treatments included: (1) drying in sunlight and tilling, (2) drying in sunlight and tilling with lime, (3) drying in sunlight and addition of lime, (4) drying in sunlight and addition of probiotics and (5) drying in sunlight and tilling with probiotics. The control consisted only of drying in sunlight. In the first phase, pH of all treated soil and the control decreased significantly (P < 0.05) over the experimental period. Organic matter of the treated and control groups increased significantly (P < 0.05) from 1.76 ± 0.05% on day 0 to 4.33 ± 0.06% on day 15. Total heterotrophic bacteria (THB) declined significantly (P < 0.05) only in soil dried in sunlight, tilled with probiotics added (treatment 5). Vibrio species were completely eliminated within 6 days in all treatments. Pseudomonas counts decreased significantly (P < 0.05) over time in all groups. In the second phase, water from a 3-month-old shrimp pond and pond organic sludge from the post-harvested shrimp pond were added above the treated pond bottom soils and left for 10 days in order to simulate the second crop after termination of the first phase. To begin the third phase, water was drained and the pond bottom soils subjected again to the same treatments for a further 15 days. Soil pH declined significantly (P < 0.05) in all groups except treatment 2 over the experimental period. A significant increase (P < 0.05) in organic matter was observed at the end of the experiment in the third phase, with values of 4.17 ± 0.13% to 4.64 ± 0.04%. THB declined significantly (P < 0.05) in all groups over time. No Vibrio were found in any of the experimental tanks. In treatment 5, Pseudomonas was absent after day 9 of beginning the experiment in the third phase. In conclusion, drying in sunlight and tilling with probiotics were the best method for removal of Vibrio and Pseudomonas from shrimp pond bottom soil containing organic sludge.