Pond Bottom Management at Commercial Shrimp Farms in Chantaburi Province, Thailand

Most shrimp farmers in Chantaburi Province, Thailand, use water jets to dislodge sediment from empty pond bottoms, and wastewater is held for sedimentation before discharge into natural waters. Other pond bottom management practices used by a few farmers are sediment excavation, leave sediment but till entire pond bottom, and no mechanical treatment. All four methods of pond bottom treatment are followed by sun drying for 30 d. Soil organic carbon concentration in ponds following dry-out seldom exceeded 2%. Although shrimp production in 24 ponds supplied by the same source of water was negatively correlated with increasing soil organic carbon concentration (r = -0.582), this observation does not confirm a causative relationship. Moreover, in trials conducted at Burapha University, Chantaburi Campus, bottom soil organic matter concentration following dry-out differed little irrespective of treatment method. Lower soil moisture concentration revealed that dry-out was more complete with sediment removal than without, but better dry-out resulted in lower soil pH. Removal of sediment by excavation or flushing is expensive, and natural dry-out combined with liming and occasional sediment removal should be investigated as a less expensive and more environment-friendly alternative to removing sediment after each crop.