Recycling of fishpond waste for rice cultivation in the Cuu Long delta, Vietnam

摘要

Catfish (Pangasianodon hypophthalmus) production has expanded to over one million tonnes in 2007 from ponds that cover about 5,000 ha in the Cuu Long delta, Vietnam. From these ponds, large quantities of liquid and solid waste are discharged to waterways without treatment. Consequently, the pollution of canals or rivers by loading of fishpond waste, rich in nutrients (especially nitrogen, phosphorus and potassium) has emerged as a major concern. A survey in the dry season 2007 of 16 paired fields showed that rice yield in 8 paddies receiving waste from fishpond was 1 t/ha higher than in another 8 paddies that did not use wastes. A field experiment was conducted in the wet season 2007 using three doses of solid wastes (1, 2 and 3 tonne/ha) in combination with 1/3 or 2/3 of the recommended inorganic fertiliser rate (60N-17P-24K in kg/ha). Rice yields were more or less the same in all treatments, suggesting that the fishpond waste replaced 1/3 to 2/3 of the fertiliser normally applied. Another experiment was carried out using liquid waste from fishponds for irrigating i-ice together with inorganic fertilisers at 2/3 of the recommended farmer dosage. Rice yields were also the same in all treatments. These results confirmed that solid and liquid wastes from fishponds can be recycled for rice culture to mitigate pollution of waterway and reduce fertiliser costs.