含残膜土壤水分特征曲线模型构建

Water characteristic curve model for soil with residual plastic film

农膜残留在土壤中累积后必然会改变土壤水动力学性能,导致土壤水分入渗能力下降,并严重影响土壤水和溶质运移。而土壤水分特征曲线是影响土壤水分和溶质运移的重要土壤水动力学参数,为了探索残膜对其影响机理,该文通过室内试验设置了5个不同残膜量(0、50、100、200、400 kg/hm2)处理,研究了残膜对土壤水分特征曲线的影响,构建了残膜条件下土壤水分特征曲线模型(soil water characteristic curve with residual plastic film,RPF-SWCC),并对其性能进行了评价。结果表明:随着土壤中残膜量增多,土壤保水能力逐渐呈降低趋势;且低吸力段(主要排大孔隙土壤水)的当量孔径体积占比增大,而高吸力段(主要排中小孔隙土壤水)的当量孔径体积占比则减小,其中400 kg/hm2残膜含量处理比无膜处理大孔隙当量孔径占比增大近20%。对RPF-SWCC模型参数估计,显示随残膜量增加土壤饱和含水率呈降低趋势,且RPF-SWCC模型拟合精度总体上高于van Genuchten(VG)、Brooks-Corey(BC)及Log normal distribution(LND)常用土壤水分特征曲线模型;对高残膜量处理,RPF-SWCC模型的均方根误差,几何平均数及决定系数R2均优于常用模型,且200、400 kg/hm2残膜含量处理RPF-SWCC模型的均方根误差比VG模型分别降低了24.3%和65.0%,可见构建的RPF-SWCC模型能较好地应用于含残膜土壤的水分特征曲线拟合。该研究可为农膜残留地区水分迁移模拟以及水肥高效利用提供理论依据和技术支撑。

The residual plastic film in soil inevitably affects soil hydrodynamic parameters, reducing the soil infiltration capacity, and seriously influences soil water and solute transport which is closely connected with soil water characteristic curve（SWCC）. In order to study the effects of different residual film amounts on soil water retention ability, 5 residual film treatments（0, 50, 100, 200, 400 kg/hm2） were conducted to measure SWCC based on the pressure plate extractor test; A new model of soil water characteristic curve with residual plastic film（RPF-SWCC） was constructed, and its performance was evaluated by parameters such as root mean square error（RMSE）, geometric mean（GMER） and coefficient of determination（R2）.The results showed that the ability of soil water retention decreased gradually with the increase of residual film amounts. The higher amount of residual plastic film would produce the lower soil moisture under the same suction condition, especially the high suction condition. For example, when the suction reached to its maximum（700 kP a）, the soil moisture of residual film treatment（400 kg/hm2） was only 79.58% of non-residual film treatment. With the increase of residual film, the equivalent aperture ratio was increased in the low suction stage（mainly draining soil water in large pore）. On the contrary, it was decreased in the high suction stage（mainly draining soil water in medium and small pore）. The equivalent aperture for large pores in the low suction stage was between 0.00300 and 0.15000 mm, and the equivalent aperture for medium and small pore in high suction stage was between 0.00043 and 0.00300 mm. When the residual film reached to 400 kg/hm2, the equivalent aperture ratio of the low suction stage increased by nearly 20% over the non-residual film treatment. In general, the SWCC fitting accuracy of van Genuchten（VG） and Log normal distribution（LND） model was higher than that of Brooks Corey（BC） model for the soil with residual film. VG model was more suitable for low residual film soil, and LND model was more suitable for high residual film soil. The RPF-SWCC model had a higher accuracy than van Genuchten（VG）, Brooks Corey and Log normal distribution model. The RMSE, GMER and R2 of the RPF-SWCC model were all better than the other models, and the RMSE for 2 high residual film treatments（200, 400 kg/hm2） were reduced 24.3% and 65.0%, respectively compared with the VG model; In addition, the parameters of RPF-SWCC model showed that the saturated soil water content decreased with the increase of residual plastic film, and the residual soil water content increased with the increase of residual plastic film. So, it can be concluded that RPF-SWCC model had better performance for fitting soil water characteristic curve with residual plastic film. The study can provide valuable information for development of soil water modeling and high efficient utilization of water and fertilizer in the residual plastic film area.