土壤系统中溶质运移研究博士研究生：石 辉学科、专业：土壤学研究方向：土壤溶质运移导 师：邵明安研究员为了满足日益增长的人口对粮食的需求，农用化学物质被广泛使用，这些物质可通过各种渠道进入土壤，因此研究土壤中农用化学物质的迁移、转化对于防止环境污染和促进农业持续发展有着重要的意义。

本文在对土壤溶质运移理论分析的基础上，采用土柱实验、田间实验以及计算机模拟研究土壤系统中溶质的运移过程，得到以下主要结论：1．通过分析土壤溶质运移与化学色谱之间的相似性，利用化学色谱理论分析了土壤溶质穿透曲线的形状，以及塔板理论模拟溶质运移的穿透曲线。

发现穿透曲线的形状主要由溶质在固体土粒与溶液中浓度的吸附等温线来决定，对于凸型分配函数，表现为前缘陡峭、后缘“拖尾”的“拖尾”型穿透曲线；对于凹型分配函数，表现为前缘“伸舌”、后缘陡峭的“伸舌”型穿透曲线。

对于非反应型溶质理论上应当保持对称的高斯型穿透曲线，但在实际土壤中由于不动水体的存在，穿透曲线也表现出前缘陡峭、后缘拖尾的“拖尾”型穿透曲线。

根据塔板理论认为土柱由理想形态的一系列小塔板所组成，忽略弥散作用，利用质量守恒定律可得到描述溶质运移的塔板模型]21)2e x p (21[210N M M e r f c N N M M e r f c c c ++-= （1）该模型与溶质运移的CDE 方程解具有一定的相似性，但由于忽略了弥散作用，其估计 浓度低于CDE 方程。

2．研究表明，在一般情况解析解第二项的贡献较小（<4%），可以省略。

对CDE 方程 省略第二项后的解析解进行了详细分析，通过误差函数的逆运算得到下述公式D utx Ce arcerf t 2)21(-=- （2） 对于穿透曲线则有tD uD L22-=ξ （3）这样可利用ζ与t 线形关系的斜率、截距估计CDE 参数D 、R 值。

实验结果证实该方 法与常用CXTFIT 拟合结果一致。

当Ce 按照边界层定义一个固定值时，式（2）则为边界 层与时间的关系。

对于边界层，定义其相对浓度为3‰时拟合参数与CXTFIT 结果一致。

测定穿透曲线费时费力，由式（2）可利用任意两个时刻的Ce （x 1，t 1），Ce （x 2，t 2）估计参 数。

3．对薄层土壤溶质运移的可动水体与不可动水体模型进行了研究。

发现对于薄层土壤 在忽略弥散的作用下，其溶质运移穿透可用式（4）表示VV e e C C )1)(1()1(0)1(1φξφφξξξ+--+--+=- （4） 式（4）表明，可将薄层土壤溶质运移分为二个阶段。

初始阶段，由于ξ和V 较小，式（4）的第一项较小，因而对浓度影响不大；而在后期阶段，第二项的数值变小，浓度主要由第一项决定，但第二项数值减小的幅度较慢。

用土柱实验进行了验证。

4．研究了田间NO 3-N 的时空变化。

发现NO 3-N 在垂直方向上可分为0-60cm ， 60-140cm ，140-200cm 三个层次，层次间NO 3-N 的含量达到显著差异。

在水平方向上，NO 3-N 的变异远远大于土壤水分的变异。

NO 3-N 随时间的变化主要表现在气候因素对其的影响。

随着降雨量的增加，0-60cm 土层中的NO 3-N 表现出减少趋势；而60-140cm 在降雨量小于50mm 时随降雨量的增加NO 3-N 含量增加，而大于50mm 时随降雨量的增加而减少；140-200cm NO 3-N 基本不变。

这可能有在低降雨量的情况下将上层NO 3-N 淋溶进入中层，引起中层的NO 3-N 增加；而降雨量大时，降雨可将NO 3-N 淋入下层，导致中层NO 3-N 降低。

NO 3-N 的产生与温度关系密切，随温度的增加，0-60 cm 土层的NO 3-N 增加，而下两层则变化平缓。

这主要由于NO 3-N 在表层产生，随温度增加，硝化作用增强，NO 3-N 生成增加；而土壤下层，土壤温度本身变化较小且非NO 3-N 的主要生成区，因而随温度变化较小。

5．关于土壤溶质运移的研究，主要是在饱和条件下进行的，但实际化学物质是在非饱和情况下运移的，与土壤水分运动存在耦合。

本文介绍了土壤水分、溶质耦合运动的基本方程，所采用土壤水分、基质势、导水率关系以及所采用的边界、初始条件，模拟非饱和土壤的水分、溶质耦合运动。

模拟结果表明，水分的湿溶锋与溶质锋在非饱和情况下并不重合。

在对田间情况进行简化后，模拟田间NO 3-N 与水分运动情况，结果在趋势上与实测值具有相似性，但由于土壤的非均质性、边界条件的选择等因素使预测值与测定值存在一定的偏差。

关键词：溶质运移 塔板理论 对流——弥散方程（CDE ） 可动与不可动水体模型（MIM ） NO 3-N 水分与溶质耦合运动Solute Transport in SoilsIn order to meet the demand for food of the increasing population, agri-chemicals are widely used. Agri-chemicals enter soils by many ways, solute transport and its transfer in soils have great significance for prevention of environmental pollution and maintenance of sustainable agriculture. In this paper, based on theoretical analysis of solute transport in soils, soil column experiment, and field experiment and computer simulation technique were used to study solute transport in soils. Meanwhile, a method for fertilization application localized compaction dime, which can prevent leaching of N fertilizer and improve fertilizer use efficiency, was presented. This is an example of application for the theoretical achievements of solute transport. The results are as the fellows.1.By analyzing the similarity between solute transport in soil and chromatography in chemistry, shapes of Breakthrough Curve (BTC) and simulation soil solute transport by using chromatography were conducted. The shape of BTC is mainly determined by adsorption isotherm between soil solid particle and soil solution. For convex function, there is “pulling tail ” BTC that the front part of BTC is high and steep and the rear part of BTC is “pulling tail ”. For concave function, there is “stretching tongue ” BTC that the front part of BTC is “stretching tongue ” and the rear part of BTC is high and steep. For non-reactive solute, BTC is “pulling tail ” type because there is immobile water in field soils. According to the plate theory, the soil column was formed by a series plates and the plate model is obtained by neglecting dispersion:]21)2exp(21[210N M M erfc N N M M erfc c c ++-= (1)This model has same tendency as the analytical solution of CDE, but the estimation result was less accurate than CDE due to neglecting dispersion.rge amount of research indicated that under normal condition, the contribution of the second term of analytical solution of CDE is relatively small (<4%) and then can be neglected. For the analytical solution of neglecting the second term, the following formula can be acquired through inverse operation of the error functionD ut x Ce arcerf t 2)21(-=- (2 ) For BTC, which ist D u D L 22-=ξ (3 ) So the parameters of D and R can be estimated by the slope and intercept of linear relationship between ξ and t . The estimated parameters from experimental result by intercept method were similar as by CXTFIT method. When the relative concentration Ce was defined as a constant for a boundary layer, Eq.(2) shows the relationship between the position of boundary layer x and time t .When Ce was defined as 3‰ in the boundary layer, the results were as same as CXTFIT. Meanwhile, the parameters of CDE can be estimated by any two point Ce(xl, tl) and Ce(x2, t2) through Eq.(2).3. Solute transport using MIM model in a thin-layer soil was carried out and the results showed that the effluent concentration can be expressed by Eq.(4) of dispersion is neglectingVV e e C C )1)(1()1(0)1(1φξφφξξξ+--+--+=- （4） Eq.(4) indicated that solute transport in a thin-layer soil can be divided into two stags. At the initial stage, ξand V was relatively small. So that the first term is small and it has little contribution to effluent concentration. In the second stage, the value of second term becomes smaller; the first term is dominant.4. The temporal and spatial variability of NO 3-N in field condition was studied. The results showed that the change of NO 3-N with depth could be divided into three layers, i.e. 0-60cm, 60-140cm, and 140-200cm. For the horizontal level, variation of NO 3-N is much larger than that of soil moisture. Changes of NO 3-N content with time mainly reflect the effect of climate. NO 3-N content in 0-60cm decreased with the increase of rainfall. In 60-140cm, NO 3-N increased when precipitation was less than 50mm but decreased when precipitation was greater than 50mm. NO 3-N in 140-200cm has little variation. The reasons are under the condition of smaller rainfall, NO 3-N in the upper layer is leached into the middle layer, thus NO 3-N in the middle layer is increased. When the rainfall is larger, the NO 3-N in the middle is leached into lower layer, so the amount in middle layer becomes smaller. The NO 3-N content was closely related with temperature. With the increase of temperature, NO 3-N in 0-60cm layer is increased, but other layers have small change. NO 3-N is formed mainly in top layer; nitrification is enhanced with the increase of temperature, thus NO 3-N content in upper layer raised. Between two lower layers, the change of temperature is small, so relative varieties of NO 3-N are very little,5. Most solute transport in soils was studied in a saturated condition, but agri-chemicalstransport often happened in unsaturated condition. Solute transport usually couples with soil water movement. Based on the mechanism of soil moisture and solute transport, and relationship among soil moisture, matric potential and hydraulic conductivity, the movement of soil moisture coupling with solute was simulated for specified boundary and initial conditions. The results showed that the wetting front was not coinciding with the solute front. After simplifying rainfall condition, the simulation results of NO 3-N and soil moisture showed same change trends as measurement but there existed some deviation because of soil nonhomogenity and boundary condition.Keywords: Solute transport, Plate theory, Convection-dispersion equation (CDE), Mobile and immobile model (MIM), NO 3-N, Temporal and spatial variety, Movement of soil moisture coupled with solute transport。