The nutrients in the fertile water from fish pond assimilated and utilized by paddy field

Abstract

Wastewater from aquiculture sometimes is called fertile water for plants because it contains useful ingredients such as nitrogen and phosphorus. In order to realize zero-discharge of wastewater from aquiculture, a field experiment was done that aquiculture water (fertile water for plants) from fish pond was applied to irrigate paddy field. The results showed that: 1) paddy field has an obvious effect on removal of some ingredients contained in irrigation water from fish pond, especially for NO₃^--N and TP. When aquiculture water stranded in the paddy field for more than 8 hours, the nutrient in it may be assimilated by paddy field 65.23% for TN, 71.97% for TP, 87.28% for NO₃^--N, 66.84% for NH₄⁺-N and 51.06% for COD_Mn. 2) when aquiculture water entered to the field and contacted with soil surface and plants, the various forms of nitrogen adsorbed is more than that of the TP and COD_Mn, in which the NH₄⁺-N and NO₃^--N adsorbed reach up to 49.92% and 41.78% respectively; when aquiculture water penetrates the soil, the absorption is 45.51% for TP, 35.63% for COD_Mn and 37.36% for NO₃^--N. 3) using fertile water from fish pond to irrigate paddy field, an output of rice may get to more than 9000 kg/hm² under 80% of the conventional fertilizer dosage which means fertilizer-saving 20% in contrast to the local conventional fertilizer use, and get to 7950 kg/hm² without fertilizer that undoubtedly is the most economical and friendly to environment.