Purification effect of paddy field on fertile water from fish pond under different water management modes

Reasonable water use and suitable water management are beneficial to water environmental protection, in which it is one of the ways that utilize fertile water from fish pond to irrigate paddy field, by this disposal the nutrient in the water is absorbed by plants or adsorbed by soil meanwhile seepage from paddy field is decontaminated. Using test-pits with a relatively independent irrigation-drainage system, an experiment is carried out that paddy field is used for purifying fertile water from fish pond, the purification effect is studied under three water management modes which are intermittent irrigation and drainage, intermittent irrigation and continuous drainage, water balance between irrigation and drainage. The results showed :1) The paddy fields have a significant depurative effect on fertile water from fish pond under the three modes in water management, in terms of removal rate, of ammonium nitrogen (NH₄⁺-N) is better than that of nitrate nitrogen (NO₃^--N), of nitrogen, phosphorus is better than that of permanganate index (COM_Mn). 2) In light of water management, the removal rate under water balance between irrigation and drainage is lower than that of the others, the purification effect under this water management is associated with cycling speed of the fertile water, and has little to do with the seepage distance; under the intermittent irrigation, there is no obvious difference in removal rate for the some index of water quality (such as total nitrogen, total phosphorus and NH₄⁺-N) between the fertile water passing through 30 cm and 50 cm, and for NO₃^--N and COM_Mn the removal rate of the later is significantly better than that of the former. 3) The retainable time of the fertile water in paddy field has a certain effect on the nutrient removal efficiency, during growth stage of hybrid mid-season rice as long as the fertile water from fish pond - tays in paddy field for three days, the water quality could satisfy aquiculture.