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Study on Using Paddy Field to Improve the Quality of Pond Water

Author: ZhouYuan
Tutor: ZhuJianQiang; LiGu
School: Yangtze University
Course: Crop Cultivation and Farming System
Keywords: paddy fields pond culture seepage surface flow retention improvement
CLC: S271
Type: Master's thesis
Year: 2013
Downloads: 2
Quote: 0
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Abstract


As the rainfall plays an uneven distribution, the moist middle-eastern part of China and the south-western part which is rich in water resources can both incur drought years and drought period of intra-annual. Therefore, it is necessary to advocate water-saving no matter in arid and water-shortage areas or the areas which is relatively adequate for water resources. Another problem which cannot be ignored is that water environment continuously deteriorates under the new situation of fast development of economy and modernization process. While, the important reasons of water environment and quality deterioration are that the environment load of agricultural farming and planting. Thus, it is of great significance to exploit potentialities of water-saving environment protection of internal large-scale agriculture.Nowadays, under the situation of increasingly serious problem of water environment and pollution, it is imperative to implement cleaner production and ecological health of farming. Based on actual production characteristics of fishing and farming intercropping in southern plain lake area of China, the thesis breaks through the traditional method of the independent fishing and farming production and utilizes some related theories and methods such as Agronomy、Soil Science、Hydrology and Water Resource Science、Irrigation and Drainage Engineering and Pond Ecology, ect. It also based on test-pit simulation、pot experiment and moderate scale of farm-ditch-pond to research the purification effect of seepage and surface flow of paddy field in different water management ways and fertilization level on fertile water from fish pond in different culture level. It puts forward the technology of surface flow and seepage which is based on the loss of paddy nutrient of aquiculture water of paddy field purification, establishes the area of matching relationship between pond and field of purification of aquiculture water which is satisfied with requirements of healthy aquiculture water quality and circulation-water flow and identifies the optimum fertilization rate under the condition of using fertile water from fish pond to irrigate paddy field. It provides theoretical basis and technical support to pursue eco-friendly and material energy recycled fishing-faming combination production mode. The main research results are as follows:1) The nutrient content of the surface field water increases and then declines sharply after the application of basic fertilizer and tillering fertilizer. But the different two fertilizers would result in some differences of nutrient content variation trend. Though the dynamic monitoring of the nutrient content of surface field water after fertilization, it is known that nutrient content varies sharply and then tended to be stable a week after fertilizer. So in order to prevent the loss of fertilizer nutrients and the pollution of the pond, draining in3-5days after fertilization is prohibited (including subsurface drainage). After5days, it can control the drainage through low seepage intension should be controlled in3-5mm/d. A week after fertilization, taking advantage of paddy field to dispose surface flow properly can be considered to meet the requirements of the ecological health of farming on water quality.2) Under the management of intermittent irrigation and drainage, the purification effect of paddy field on fertile water from fish pond was related to its residence time and the thickness of the soil layer it went across. NH3-N, NO3--N, TN and TP are certain purified when irrigation water seepage just go through a10cm thickness of soil layer. Tests on booting and heading stages instructed that purification effects of paddy field on water remained unchanged when the seepage path was up to30cm. That is to say, increasing the thickness of soil layer to improve the removal efficiency is meaningless. For surface field water, the longer the residence time is the better the removal efficiency. While for its underground part, the residence time makes little difference. In addition, the effect of removing nitrogen and phosphorus at heading stage was larger than that of booting stage.3) Under the condition of intermittent irrigation and drainage, the longer the residence time of aquiculture water in the test-pits, the smaller the same seepage path of the DO value, while under the same residence condition, the greater the seepage path, the smaller the DO value. Under the condition of the balance of irrigation and drainage, when the seepage discharge is different, the oxygen consumption rate of water increases with the increase of seepage flow at a certain range. Beyond a certain range, the oxygen consumption rate decreases. While in the same level of the seepage discharge, the DO value of the water outlet significantly decreased.4) On a certain surface flow condition, the purification effect of paddy field on aquiculture water was related to its initial concentration and the higher concentration water was purified better. In other words, the surface flow of paddy field had a better effect on intensive aquiculture pond water than cage-free fishpond water.5) The purification effect of paddy field surface flow on all kinds of nutrient substance of aquiculture water is varied. Various forms of nitrogen are removed better than phosphorus. The removal efficiency of NO2-N is always at the highest level. Apart from absorbing nutrient substances like N、P, etc, the surface flow have certain improvement effects on CODMn. chlorophyll a、turbidity、suspended solids, etc. 6) The removal rate of paddy field surface flow on the nutrient substances of aquiculture has a close relationship with nutrient content (the initial concentration), flow path、irrigation and drainage flow(the surface flow) and fertilization level. The removal rate of TN and NO3--N is in direct proportion to the initial concentration, flow path and fertilization level, and it is inverse proportion to the flow; TP is direct proportion to the flow path and fertilization level, and it is inverse proportion to the initial concentration and flow rate; NH3-N and NO2--N is direct proportion to the flow path, and it is inverse proportion to the initial concentration and flow, it has nothing to do with fertilization level. Under the condition of constant surface flow, the removal rate of paddy field surface flow on the nutrient substances of water has significant binary relationship with nutrient content of irrigation water(the initial concentration) and flow path. For intensive aquiculture pond, in addition to the removal rate of NO2--N is negatively related to the initial concentration and positively related to the flow path, the removal rate of the rest of the indicators are positively correlated with initial concentration and flow path. For cage-free fishpond, in addition to the removal rate of TN and No2-N which are positively correlated with initial concentration and flow path, the removal rate of the rest is similar to the NO2--N which is under the condition of intensive aquiculture pond. Whether the correlativity has relationship with culture mode remains to do further research. Although the correlation of removal rate nutrient content and flow path is slightly different, the effect of flow path on the removal rate is always the biggest, and it is far greater than the initial concentration. So in the use of paddy field surface flow to water purification can be controlled through flow path initially.7) In the use of paddy surface flow for water purification, the effect of flow rate on removal rate is to be paid more attention. Due to surface flow greatly increases the circulation-water flow, and it can through increasing flow path appropriately to improve the single-pass removal rate. So under the situation of satisfying circulation-water flow, it can shorten the working time of pump with large flow circulation mode.8) The trophic state index of pond aquiculture water which is through paddy surface flow circulation are improved to a certain extent, but the trophic status index of quiet water is still in severe eutrophic condition and it showed an increasingly trend as time goes by. The nutrition status index of circular pond has certain improved after circulation, but then it has a tendency to pick up. In order to ensure favourable water circulations of circular aquiculture pond, the water must be circulated and the water circulation rate must be controlled well each time. According to the results of the tests in nearly three years, it can preliminarily determine that the aquiculture pond circulates once every7-10days and each water circulation rate hold10%~20%of all the water amount of the pond.9) Using paddy surface flow purifies fertile water from fish pond, the area of paddy field matched of the cage-free fishpond is far less than the intensive aquiculture pond. The area of paddy field decreases with the increase of the circulation-water flow, but it must consider the impact of "flowing water" growing on rice growth while increasing the circulation-water flow. In addition, the removal rate decreases with the larger flow. In order to achieve the dual effect of water purification and grain harvest, it can finally find the best combination of flow rate, removal rate and growth of rice.10) The retention of paddy field has a good purification effect on aquiculture water. As the recovery rate of aquiculture water which is purified by it is low. So that the area of paddy used is large. Due to the less circulating water quantity and the DO value of subsurface seepage flow decreases, the retention of paddy is replaced surface flow generally. It is better to combine surface flow, seepage and retention to purify aquiculture water.11) The effect of paddy surface flow on DO value of aquiculture water(the functions of oxygen enrichment or oxygen consumption) has relationship with culture mode、the types of paddy field and soil texture, etc. It has the function of oxygen enrichment to intensive aquiculture pond and the oxygen consumption to cage-free fishpond.12) Using the fertile water from fish pond to irrigate,80%of conventional fertilizer application is more appropriate. Just spraying proper foliar fertilizer at the period of nutrition peak can ensure higher rice production.The results of the above research combine pond culture with production of paddy field with the water as a link and turn aquiculture wastewater into irrigation fertile water for paddy field. It is benefit for improving the quality of pond water and material recycling, realizing the zero-discharge of wastewater from fish pond and providing effective methods and new ways for the controlled agriculture non-point source pollution.

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CLC: > Agricultural Sciences > Agricultural Engineering > Irrigation and water conservancy > Agricultural hydrology
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