农田排水改良盐渍化土壤效果与环境污染研究

Effect of Farmland Drainage on Improving Saline Soil and Environmental Pollution

为探讨河套灌区在农田排水过程中对盐渍化土壤的改良效果和环境污染的影响,于2019—2020年在河套灌区乌拉特灌域暗管排水综合试验区选择典型支渠灌溉控制区,针对作物各灌溉时期的水文过程、污染物的转化、迁移和汇集过程开展了系统试验。结果表明:利用DRAINMOD模型能较好地模拟农田排水量,模拟值与实测值相对误差(RE)为4.12%~13.44%、相关系数(R)为0.80~0.92、效率系数(NS)为0.82~0.90,均在误差范围内。利用马斯京根法对斗沟和支沟排水过程进行了演算,并在此基础上对NH_(4)^(+)、NO_(3)^(-)、还原性物质、盐分的迁移、转化和汇集过程进行了分析,排水过程和NH_(4)^(+)、NO_(3)^(-)、还原性物质、盐分浓度模拟结果与实测值较为一致,表明该方法能够在宏观上描述灌区不同排水组成所形成的环境污染过程。试验区主要污染物排放总量由大到小依次为还原性物质、NO_(3)^(-)、NH_(4)^(+),分别为349.47~363.10 kg、80.56~87.79 kg、6.79~7.18 kg。经过2年灌溉淋洗后,土壤脱盐率在土体中自上而下降低。暗管排水试验区0~20 cm土壤脱盐率为67.56%,较20~40 cm和40~100 cm分别高5.12、16.84个百分点;明沟排水试验区0~20 cm土壤脱盐率为34.54%,较20~40 cm和40~100 cm分别高12.90、15.58个百分点。淋洗之后土壤盐分由表聚型向均匀型变化,暗管排水和明沟排水在2020秋浇之后土壤电导率(EC)分别在2.20~2.63 dS/m、0.61~0.65 dS/m之间。试验区中度盐渍化土壤和盐土类型面积均有所下降,中度盐渍化土壤面积下降2.94个百分点,盐土面积下降29.42个百分点,非盐渍化土壤、轻度和中度盐渍化土壤分别增加2.94、8.83、20.59个百分点。盐土对试验区土壤脱盐率贡献最大,为126.78%。

In order to explore the improvement effect of salinized soil and the impact of environmental pollution on the process of farmland drainage in Hetao Irrigation District,a typical branch canal irrigation control area was selected in the Hetao Irrigation District Urad Irrigation Area subsurface drainage comprehensive experimental area from 2019 to 2020.Systematic experiments were carried out on the hydrological process,the transformation,migration and collection process of pollutants during each crop irrigation period.The results showed that the DRAINMOD model can better simulate farmland drainage.The relative error(RE)between the simulated value and the measured value was 4.12%~13.44%,the correlation coefficient(R)was 0.80~0.92,and the efficiency coefficient(NS)was 0.82~0.90,all within the error range.The drainage process of bucket ditch and branch ditch is calculated by using Muskingen method and on this basis,the migration,transformation and pooling processes of NH_(4)^(+),NO_(3)^(-),reducing substance and salinity were analyzed.The simulation results of the drainage process and the concentrations of NH_(4)^(+),NO_(3)^(-),reducing substance and salinity were in good agreement with the measured values,indicating that this method can macroscopically describe the environmental pollution process formed by different drainage components in the irrigation area.The total emissions of main pollutants in the test area was reducing substance,NO_(3)^(-) and NH_(4)^(+),in descending order,which were 349.47~363.10 kg,80.56~87.79 kg,and 6.79~7.18 kg,respectively.After two years of irrigation and leaching,the soil desalination rate was decreased from top to bottom in the soil.The soil desalination rate of the 0~20 cm soil in the dark pipe drainage test area was 67.56%,which was 5.12 and 16.84 percentage points higher than those of 20~40 cm and 40~100 cm,respectively;40~100 cm were 12.90 and 15.58 percentage points higher respectively.After leaching,the soil salinity was changed from the surface accumulation type to the uniform type,and the soil EC values of the concealed pipe drainage and the open ditch drainage were between 2.20~2.63 dS/m and 0.61~0.65 dS/m after the autumn irrigation of 2020.The areas of moderately salinized soil and saline soil types in the experimental area were decreased,the area of moderately salinized soil was decreased by 2.94 percentage points,and the area of saline soil was decreased by 29.42 percentage points.Non-saline soil,lightly and severely salinized soil increased by 2.94,8.83 and 20.59 percentage points,respectively.Saline soil contributed the most to the soil desalination rate in the experimental area,which was 126.77%.