The Study On Drainage System For Reducing The Agricultural Non-point Source Pollution And Its Effects In Rice-based Irrigation Districts

Focuses on the problem of agricultural non-point source pollution in the rice-based irrigation districts in China,a drainage system with agricultural non-point source pollution prevention and treatment in rice-based irrigation districts and a researching experimentation basing on pollution-reducing effects of the system was established in the Qingshitan irrigation districts,Guilin,Guangxi Autonomous Region.The field experiment was set in Jianjiangtou test area with a completely constructed "two ways and four process" new type agricultural drainage system.Field observation in experiments aims at the ways and the processes in the operation of the system.At the same time,12 fields in Guilin irrigation experiment station was divided into 4 kinds of water-fertilizer operation mode,each has 3 repeat,to hold comparative trials.The results will be referenced during the process of confirming high-producing,water-saving and pollution-reducing water-fertilizer operation mode that are suitable for promotion and proving experiment results of Jianjiangtou test area.The main research contents and conclusions are as follows:(1)The construction of the drainage system with agricultural non-point source pollution prevention and treatment.The system was built by referring "two ways and four processes".The first ways is reducing pollution from the source,which includes saving water,reducing emission and reasonablely fertilization.We can name it as "water-fertilizer comprehensive regulation in paddy fields".The second way is reducing pollution during the drainage process.Firstly,the pollutions in drainage water were reduced in the field grassed waterways.Then it was carried and adjusted in small reservoirs and wetlands.Finally,the pollutions in drainage water were reduced in the ecological main ditch.(2)The technology of yield-growing,water-saving,drainage-decreasing and pollution-reducing and its effects.The research progress acquired from Jianjiangtou test area and irrigation experiment station in four years has proved the mode W2F2,includes intermittent irrigation and fertilize nitrogen fertilizer in four separated times,that are used in experiment station is the best water-fertilizer operation mode.It has the highest water productivity and 2.6%increasement on yield,37.7%irrigation water was saved,a 4.23%reduction in drainage water,a 27.1%reduction in TN,a 19.0%reduction in TN,which has excellent benefits.The W2F2 mode also has been validated in Jianjiangtou test area with relatively good results that the average nitrogen reduction rate in 2014-2016 is 15.1%and the phosphorus reduction rate is 11.2%.(3)The technology of using grassy waterways in paddy fields and its pollution-reducing effects.The grassy waterway in paddy fields has remarkable affects on reduction of nitrogen and phosphorus load in drainage water.It has a 15.56%reduction of TN load reduction and a 22.29%reduction of TP load reduction.Growing local plants which has pollution-reducing advantage in grassy waterways can finish not only financial goal but also pollution-controlled effects.(4)The technology of using small reservoirs and wetlands and its pollution-reducing effects.The small reservoirs and wetlands have prominent affects on reduction of nitrogen and phosphorus load in drainage water.It has a 23.81%reduction of TN load reduction and a 14.32%reduction of TP load reduction.Keeping a ratio of 1:14 small reservoirs and wetlands area to paddy field area is benefitial to utilizing wetlands' pollution-reducing effects.Optional hydraulic retention time and cleaning bottom mud in time ensure small reservoirs and wetlands to give play to better pollution-reduce.The usage of K-C*model to simulate the concentration of nitrogen and phosphorus in the import and export of wetland Validated the suitability of the model.(5)The technology of ecological main ditch and pollution-reducing effects.The ecological main ditch has a significant effect on the reduction of nitrogen and phosphorus load,with the reduction rate 7.14%of total nitrogen and 21.89%the total phosphorus.In the design of the ecological main ditch,the reasonable flow velocity,the size of the ecological ditch structure and the species and density of the ditch play important roles on the effect of the pollution reduction of the ecological ditch.(6)"Two ways and four processes" comprehensive pollution reduction effect of new Type farmland Water Conservancy System.The drainage water discharged from the paddy field continuously flow through the part of the system.The experiment show that the indicators of nitrogen and phosphorus emission load decrease along the way.The comprehensive purification effect is remarkable with the total nitrogen and total phosphorus load reduced by 52%and 55%respectively,suggesting that it is suitable for the application of rice irrigation in southern China.(7)The assessments of the ecological ditch on the reduction effects in plant varieties and in different density and the comprehensive benefits.Experiments and researches show that all 6 ecological ditches have remarkably reduction effects on TN and TP because of plants grown in ditches.The reduction rate of TN ranges from 15%to 44%and TP ranges from 11%to 32%.No.3 ditch,which represents grassy waterways,has a comprehensive benefits of 1096 Yuan and No.5 ditch,which represents ecological main ditch,has a comprehensive benefits of 1776 Yuan in designed plant density.The study notes the relation between reduction rate and roughness factor,increasing rate of ditch's water-crossing section and roughness factor,ditch's positive,negative and comprehensive benefits and roughness factor of No.3 ditch and No.5 ditch.It also mentions the approach to quantitative analyze positive,negative and comprehensive benefits of ecological ditches.(8)The popularization and application of the study progress.4 crop field areas have been set from early season rice's growth in 2015 to handle technology popularization and application,experimental observation.After early season rice's growth in 2016,the technology has been applied in large area in Qingshitan irrigation district,Guilin and 4 more large reservoir irrigation district's demonstration and extension area,which has achieved noteworthy water-saving,high-producing,pollution-reducing effects.The study also researched support system and planning layout for technology popularization and application in large area.