基于分形理论的马铃薯干燥过程水分输运特征分析

基于马铃薯内部结构的异质性和分布随机性,利用分形特性模拟了在干燥过程中的水分输运过程。结果发现结合收缩和分形现象的模型呈无收缩现象连续介质模型更接近实验值,且分形模型的内部压力分布没有出现像连续模型呈比例逐层下降的现象。包括收缩的分形模型与孔的连通性、孔隙率、面积分形维数和孔最小最大直径比值成正比,与迂曲分形维数和迂曲度成反比。     

北京市南水北调受水区垃圾场地下水污染预测

根据南水北调供水方案,南水北调进京10年后,受水区内垃圾场将会被地下水浸泡,如不采取防治措施,会对含水层水质造成严重污染。以北京西郊为研究区,利用Visual Modflow软件中的MODFLOW模块和MT3DMS模块分别建立了地下水水流模型和溶质运移模型,对研究区内污染物运移规律进行预测。预测结果表明,10a后氯离子(Cl-)、硝酸盐氮(NO2-3)和总硬度(THD)3种离子的最高浓度和被污染的面积均增大,预测结果可作为调整地下水开采与调蓄方案和垃圾场防渗规划设计的依据。     

横坡垄作下土壤湿润速率对褐土坡面侵蚀特征的影响

不同土壤湿润速率和侵蚀类型下团聚体破碎存在较大差异,进而诱发坡面侵蚀特征变化。横坡垄作特有的侵蚀过程可能改变土壤湿润速率对坡面侵蚀特征的影响效应。以褐土横垄为研究对象,基于室内模拟降雨试验,研究5个土壤湿润速率下(10、20、30、60、90 mm/h)不同侵蚀阶段的产流产沙和团聚体迁移规律。结果表明,细沟间阶段径流量随土壤湿润速率的增大而增加,而细沟阶段不同土壤湿润速率间的径流量无显著差异。2个阶段内,侵蚀量均随土壤湿润速率的增大而增加,与土壤湿润速率10 mm/h相比,20、30、60、90 mm/h速率下的侵蚀量分别显著增加25.16%~115.51%、95.02%~144.34%、151.03%~164.49%、249.42%~398.91%。细沟间阶段,土壤湿润速率的变化仅改变了产沙过程,而细沟阶段产流产沙过程均随土壤湿润速率发生了改变。主要迁移粒级-微团聚体流失所增加的细沟间和细沟侵蚀阶段分别主要来自2~5 mm和0.25~0.5 mm团聚体的破碎,而相应控制这2个粒级破碎的关键土壤湿润速率分别为20 mm/h和10 mm/h。不同阶段下迁移团聚体平均重量直径由大到小依次为细沟阶段、湿润处理后、细沟间阶段。     

设施条件下膜孔灌土壤水氮运移分布特性研究

在室内进行了模拟设施条件下膜孔灌灌施硝酸钾肥液试验,分析测定了灌后不同时间的土壤含水量和硝态氮质量分数。研究表明,土壤含水率和硝态氮质量分数随着灌后时间延长逐渐减小,土壤水分和硝态氮在灌后1d内存在明显减少现象,灌后5d土壤硝态氮反硝化作用加强;土壤含水率和硝态氮存在耦合现象,二者分布趋势基本相同,以膜孔中心为最大,远离膜孔中心逐渐减小。     

Fine-earth translocation by tillage in stony soils in the Guadalentin, south-east Spain: an investigation using caesium-134

Tillage erosion is increasingly recognised as an important soil erosion process on agricultural land. In view of its potential significance, there is a clear need to broaden the experimental database for the magnitude of tillage erosion to include a range of tillage implements and agricultural environments. The study discussed in this paper sought to address the need for such data by examining tillage erosion by a duckfoot chisel plough in stony soils on steep slopes in a semi-arid environment. Results of the investigation of coarse fraction (rock fragment) translocation by tillage in this environment have been presented elsewhere and the paper focuses on tillage translocation and erosion of the fine earth. Tillage translocation was measured at 10 sites, representing both upslope and downslope tillage by a duckfoot chisel plough on five different slopes, with tangents ranging from 0.02 to 0.41. A fine-earth tracer, comprising fine earth labelled with ¹³⁴Cs, was introduced into the plough layer before tillage. After a single pass of the plough, incremental samples of plough soil were excavated and sieved to separate the fine earth from the rock fragments. Translocation of the fine-earth tracer was established by analysing the ¹³⁴Cs content of the samples of fine earth. These data were used to establish translocation distances for each combination of slope and tillage direction. Translocation distances of the fine earth were not significantly different from translocation distances of the coarse fraction. For all sites, except uphill on the 0.41 slope, translocation distances were found to be linearly related to slope tangent. The soil flux due to tillage for each site was calculated using the translocation distance and the mass per unit area of the plough layer. For slopes with tangents <0.25, the relationship between soil flux and tangent was linear and the soil flux coefficient derived was 520–660 kg m⁻¹ per pass. This is much larger than the coefficients found in other studies and this high magnitude is attributed to the non-cohesive nature and high rock fragment content of the soil in this investigation. A second contrast with previous studies was found in non-linearity in the relationship between soil flux and tangent when steeper slopes were included. This was a product of variation in plough depth between the steepest slopes and the remainder of the study area. On the basis of the study it is suggested that an improved understanding of tillage erosion may be obtained by considering the dual processes of tillage detachment (mass per unit area of soil subject to tillage) and tillage displacement (equivalent to translocation distance per pass) in assessing, comparing and modelling tillage translocation. An improved model is proposed that recognises the complexity of soil redistribution by tillage, provides a framework for process-based investigation of the controls on tillage fluxes, and allows identification of potential self-limiting conditions for tillage erosion.     

Oxidation of methane in the rhizosphere of rice plants

Oxidation of CH₄ in the rhizosphere of rice plants was quantified using (1) methyl fluoride, a specific inhibitor of CH₄ oxidation, and (2) measuring changes in plant-mediated CH₄ emission after incubation under air, N₂, or 40% O₂. No significant rhizospheric CH₄ oxidation was observed from rice plants in the ripening stage. CH₄ emission from rice plants 1 week before panicle initiation increased by 40% if CH₄ oxidation in the rhizosphere was blocked. The growth stage of the rice plant is an important factor determining the rhizospheric CH₄ oxidation. Fluctuation of rhizospheric CH₄ oxidation during the growing season may help to explain the observed seasonal CH₄ emission patterns in field studies. Measurements from four rice varieties showed that one variety, Pokkali, had higher rhizospheric CH₄ oxidation. This was probably because Pokkali was in an earlier growth stage than the other three varieties. Both in the early and in the late growth stages, incubation under N₂ caused a much stronger CH₄ flux than inhibition of CH₄ oxidation alone. Apparently, N₂ incubation not only blocked CH₄ oxidation but also stimulated methanogenesis in the rhizosphere. Incubation under a higher O₂ atmosphere (40% O₂) than ambient air decreased the CH₄ flux, suggesting that increasing the oxidation of the rice rhizosphere may help in reducing CH₄ fluxes from rice agriculture. The O₂ pressure in the rhizosphere is an important factor that reduces the plant-mediated CH₄ flux. However, inhibition of methanogenesis in the rhizosphere may contribute more to CH₄ flux reduction than rhizospheric CH₄ oxidation.     

地下滴灌土壤水运动和溶质运移的数学模型及验证

以非饱和土壤水运动理论和多孔介质中溶质运移的对流－弥散理论为基础，建立了地下滴灌条件下描述地埋点源土壤水运动和溶质运移的数学模型。模型中对滴头边界进行了简化，并对其可行性进行了检验。模拟计算结果得到室内试验资料验证。该模型可用来描述地下滴灌土壤水、肥运动和分布规律，以便为地下滴灌系统的合理设计提供理论依据。     

种植作物条件下粉砂壤质土壤水盐运移的数值模拟研究

利用大型水盐运动模拟土柱研究了在田间气候作用下作物 (小麦 玉米连茬种植 )生长对土壤水盐运移的影响。研究并建立了土壤水盐运移的数学模型 ,就模型所需的饱和导水率、水力传导度、水分特征曲线、水动力弥散系数进行了室内外测定 ,并对数学模型进行了数值求解。对四个土柱的模拟结果与实测结果进行了数据分析和对比。结果表明 :数值模拟结果和实测数据比较 ,除个别点有一定偏离之外 ,模拟计算结果与实测值拟合效果比较理想 ,说明该模型用于模拟种植作物条件下粉砂壤质土壤的水盐运移是实际可行的。     

蒸发条件下粘土层对土壤水和溶质运移影响的模拟

以土壤水和溶质运移的动力学原理为基础 ,采用数值模拟方法 ,研究了在浅层地下水和蒸发条件下含有粘土层土壤的水和Cl-的运移状况 ,重点探讨了两种粘土的层位和层厚对水和Cl-运移影响的差别及原因。研究结果表明 ,粘土层对土壤的水和溶质运移影响的程度 ,与层状土壤中该粘土及其组合土壤的水力学性质有关。本文模拟的重粘土 (简称Y粘土 )与轻壤土所组成的层状土壤 ,其基本情况为 ,随粘土层层位的升高和层厚加大 ,土壤水分蒸发和地下水补给速率降低 ,Cl-积累减少。而轻粘土 (简称R粘土 )与轻壤土所组成的层状土壤 ,由于它们的导水率曲线在压力水头h约 - 10 0 0cm处相交 ,当h低于此值时 ,R粘土的导水率就大于轻壤土的。因此 ,蒸发、补给速率和Cl-积累强度出现以顶位最高 ,甚至高于均质轻壤土 ,其次为底位 ,最低为中部层位的现象。在蒸发条件下Cl-在剖面中的积聚部位主要是土表。粘土层的存在 ,起到了阻滞作用 ,而阻滞程度则与该粘土水力学性质、层位、厚度和地下水埋深有关     

土壤溶质运移参数估计图解方法

基于土壤中溶质运移的对流 弥散方程 (CDE)提出了溶质运移参数估计的图解方法。根据土柱溶质运移“穿透曲线”(BTC)数据计算通量浓度随时间变化 (dc/dt)。应用绘图软件 ,例如MicrosoftExcel,绘制出t1 5dc/dt和dc/dt相对于时间的变化曲线。这两条曲线都是单峰曲线 ,并被用于估计CDE中延迟因子(R)和弥散系数 (D0 )。设计算例和穿透实验数据被用于校正图解法估计参数的精度和稳定性。参数估计的稳定性由估计参数对它们平均值的标准差评价 ;参数的估计精度与CXTFIT法和等斜率法比较。结果表明图解法具有较高的精度和较好的稳定性 ,特别是对于运移参数R的估值。图解法是一个确定性方法 ,它具备确定性方法中估计参数唯一性特点 ,克服了统计方法中需要给定参数初值的缺点。因此 ,这个方法是土壤溶质运移参数估计的可选方法之一。