Nitrogen and phosphorus cycling in shrimp ponds and the measures for sustainable management.

Six ponds of age 3 were selected 45 km north from Suzhou in the Tailake region, and research conducted on nitrogen and phosphorus cycling in P. vannanmei (Penaeus vannanme) ponds and M. nipponense (Macrobrachium nipponense) hatchery ponds under normal management. Two treatments each had three replications. The results confirmed that feed was the major path of nitrogen and phosphorus input, each accounted for 61.24% (193.81 kg ha(-1)) and 81.08% (45.20 kg ha(-1)) of the total nitrogen and phosphorus input for P. vannanme ponds; the values for M. nipponense ponds were 43.93% (86.31 kg ha(-1)) and 57.67% (14.61 kg ha(-1)), respectively. Water pumped into ponds contributed on average 83.57 kg ha(-1) nitrogen and 8.48 kg ha(-1) phosphorus for P. vannanmei ponds, and 87.48 kg ha(-1) nitrogen and 7.00 kg ha(-1) phosphorus for M. nipponense hatchery ponds. Shrimp harvest recovered 102.81 kg ha(-1) nitrogen (32.94% of the total nitrogen input) and 7.94 kg ha(-1) phosphorus (14.23% of the total phosphorus input) for P. vannanme ponds; and 43.94 kg ha(-1) nitrogen and 4.46 kg ha(-1) phosphorus for M. nipponense hatchery ponds. The sum of nitrogen losses through volatilization, denitrification and sedimentation was 173.62 and 122.39 kg ha(-1), 54.86% and 62.29% of the total nitrogen input for P. vannanme ponds and M. nipponense hatchery ponds, respectively. Sediment accumulated 41.46 and 14.63 kg ha(-1) phosphorus, 74.37% and 64.85% of the total phosphorus input for P. vannanm ponds and M. nipponense hatchery ponds. Draining and seeping caused 40.06 kg ha(-1) nitrogen (12.66% of total nitrogen input) and 6.36 kg ha(-1) phosphorus (11.40% of total phosphorus input) loss to the surrounding water from P. vannanme ponds in 114 days; 30.14 kg ha(-1) nitrogen (15.34% of the total input) and 4.45 kg ha(-1) phosphorus (17.57% of the total input) to channel water from M. nipponense hatchery ponds in 87 days, respectively. Countermeasures for sustainable pond management include improving feeds and feeding, sediment treatments, machine aerating, chemicals with no pollution, and integrated fish-shrimp cultivation. Management of water resources for pond and methods to reduce nitrogen and phosphorus loading into surrounding water from drainage are elucidated.