The impact of crop growth sub-model choice on simulated water and nitrogen balances

It is the aim of this study to analyse how different crop growth model routines affect the simulation of water flow and nitrogen transport of a crop rotation in agricultural fields. The model system Expert-N is briefly described and used to test the crop growth sub-models against data of a six-year field experiment on sandy soils. Expert-N is a modular soil–plant–atmosphere model system, which comprises different sub-models to simulate one-dimensional vertical transport of water, solute and heat in the unsaturated zone. It includes several sub-models to describe organic matter turnover and has three generic crop growth sub-models. The latter are derived from the crop models CERES, SPASS and SUCROS. Simulations were performed using the different sub-models for each of the cereal crops in the sugar beet, winter wheat, winter barley, winter rye crop rotation. Results show the impact of crop model choice on simulated water balances and turnover of C and N. It is concluded that the simulation of root growth and plant residue mineralisation needs some improvement.     

Simulating water and nitrogen behaviour in soils cropped with winter wheat

The SWATNIT model [26], predicting water and nitrogen transport in cropped soils, was evaluated on experimental data of winter wheat for different N treatments. The experiments were monitored at three different locations on different soil types in the Netherlands. Crop growth was simulated using the SUCROS model [11] which was integrated in the SWATNIT model. Both water and nitrogen stress were incorporated. Except for the soil hydraulic properties, all model parameters were taken from literature. The model performance was evaluated on its capability to predict soil moisture profiles, nitrate and ammonia profiles, the time course of simulated total dry matter production and LAI; and crop N-uptake. Results for the simulations of the soil moisture profile indicate that the soil hydraulic properties did not reflect the actual physical behaviour of the soil with respect to soil moisture. Good agreement is found between the measured and simulated nitrate and ammonia profiles. The simulation of the nitrate content of the top layer at Bouwing was improved by increasing the NH ₄ ⁺ -N-distribution coefficient thereby improving the simulation of the NH ₄ ⁺ -N-content in this layer. Deviations between simulated and measured nitrate concentrations also occurred in the bottom layers (60–100 cm) of the soil profile. The phreatic ground water might influence the nitrate concentrations in the bottom layers. Concerning crop growth modelling, improvements are needed with respect to the partitioning of total dry matter production over the different plant organs in function of the stress, the calculation of the nitrogen stress and the total nitrogen uptake of the crop through a better estimate of the N-demand of the different plant organs.     

WHNSIM — a soil nitrogen simulation model for Southern Germany

A one-dimensional deterministic soil nitrogen simulation model (WHNSIM) is presented. With the model the leaching of soil nitrate, its uptake by plant roots and the mineralization of soil organic nitrogen can be simulated. Basic elements of WHNSIM are differential equations that describe soil water, soil heat and soil solute transport. The equations are solved with a fully implicit finite difference method for a variety of boundary and initial conditions. With WHNSIM the soil nitrogen behavior of arable fields for one or more consecutive years can be described. The model has been calibrated for typical site conditions in Southern Germany. The main features of WHNSIM are discussed, some simulation results are also presented. For site conditions of Southern Germany the model appears to perform adequately.     

降雨蒸发条件下渗流区污染物迁移的数值模拟

采用溶质传递方程和水流动方程联立耦合进行数值求解,模拟土壤渗流区中有机污染物的垂直一维迁移过程。传递方程综合考虑气相扩散和液相的对流扩散过程,并且在水流动方程的边界条件中包含有降雨、蒸发的气候条件。数值模拟过程中将有机污染物苯作为研究对象,采用美国加州地区实际的土壤物性数据和气候条件,得到的模拟结果和Grifoll的研究结果基本一致。实验结果显示500 h污染物到达的深度近似为125 cm,2 000 h已经达到180 cm。另外,在模拟区域的不同深度设置数值模拟数据采集点,结果发现越接近不饱和区上表面的地方,受气候边界条件影响越大。     

Experimental and mathematical modeling of water regime and nitrate dynamics on zero tension plate lysimeters in soil influenced by high groundwater table

Unlike laboratory experiments, which are mostly performed under controlled conditions, lysimeter experiments generally simulate actual field conditions. This paper focuses on an efficiency of the zero tension plate lysimeters, which were implanted in silty-clay soils influenced by a high groundwater table. Measurements and following numerical simulations using the HYDRUS-2D model were performed separately for each of 4 years (2007–2010) to assess water flow and nitrate fluxes (applied as NPK or UREA fertilizer). Low efficiency of lysimeters during the vegetation period was mostly caused by high plant water demand and possible water diversion to the sides when the groundwater table was low. The HYDRUS-2D model was able in some degree to reproduce observed water and nitrate outflows. The water outflow through the lysimeter occurred when the groundwater table was high and greater rainfall events occurred. Water and solute diverged from the plate towards the dryer surrounding soil when groundwater table was low. Pressure head, water velocity and nitrate concentration distributions simulated around the lysimeter plate illustrated that the lysimeter plate had a significant impact on the water regime and nitrate behavior within the soil profile. The lysimeter plate also acted as a barrier for water flow and solute transport also.     

Increased Uptake of Chelated Copper Ions by Lolium perenne Attributed to Amplified Membrane and Endodermal Damage

The contributions of mechanisms by which chelators influence metal translocation to plant shoot tissues are analyzed using a combination of numerical modelling and physical experiments. The model distinguishes between apoplastic and symplastic pathways of water and solute movement. It also includes the barrier effects of the endodermis and plasma membrane. Simulations are used to assess transport pathways for free and chelated metals, identifying mechanisms involved in chelate-enhanced phytoextraction. Hypothesized transport mechanisms and parameters specific to amendment treatments are estimated, with simulated results compared to experimental data. Parameter values for each amendment treatment are estimated based on literature and experimental values, and used for model calibration and simulation of amendment influences on solute transport pathways and mechanisms. Modeling indicates that chelation alters the pathways for Cu transport. For free ions, Cu transport to leaf tissue can be described using purely apoplastic or transcellular pathways. For strong chelators (ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA)), transport by the purely apoplastic pathway is insufficient to represent measured Cu transport to leaf tissue. Consistent with experimental observations, increased membrane permeability is required for simulating translocation in EDTA and DTPA treatments. Increasing the membrane permeability is key to enhancing phytoextraction efficiency.     

Juglone Disrupts Root Plasma Membrane H+-ATPase Activity and Impairs Water Uptake, Root Respiration, and Growth in Soybean (Glycine max) and Corn (Zea mays)

Juglone is phytotoxic, but the mechanisms of growth inhibition have not been fully explained. Previous studies have proposed that disruption of electron transport functions in mitochondria and chloroplasts contribute to observed growth reduction in species exposed to juglone. In studies reported here, corn and soybean seedlings grown in nutrient solution amended with 10, 50, or 100 microM juglone showed significant decreases in root and shoot dry weights and lengths with increasing concentrations. However, no significant differences in leaf chlorophyll fluorescence or CO2-dependent leaf oxygen evolution were observed, even in seedlings that were visibly affected. Disruption of root oxygen uptake was positively correlated with increasing concentrations of juglone, suggesting that juglone may reach mitochondria in root cells. Water uptake and acid efflux also decreased for corn and soybean seedlings treated with juglone, suggesting that juglone may affect metabolism of root cells by disrupting root plasma membrane function. Therefore, the effect of juglone on H+-ATPase activity in corn and soybean root microsomes was tested. Juglone treatments from 10 to 1000 microM significantly reduced H+-ATPase activity compared to controls. This inhibition of H+-ATPase activity and observed reduction of water uptake offers a logical explanation for previously documented phytotoxicity of juglone. Impairment of this enzyme's activity could affect plant growth in a number of ways because proton-pumping in root cells drives essential plant processes such as solute uptake and, hence, water uptake.     

Numerical study of a permeable capsule under Stokes flows by the immersed interface method

A two-dimensional model to simulate the mass transfer of a permeable, deformable, and adhesive capsule flowing in a binary solution of a vessel is proposed using the immersed interface method (IIM). The fluid flow is governed by the full Navier–Stokes equations and the solute distribution is governed by the advection–diffusion equation. Mass transport across the capsule membrane is computed using the Kedem–Katchalsky equations while the adhesion between the capsule and the walls is introduced via a potential function. The model is first validated for the simple shear flow away from the substrate walls and then for capsule adhesion and deformation next to a substrate wall. It is next used to study solute transfer between the capsule and the vessel walls with and without a flow field. In the absence of a flow field, the results show that the transient of the solute transfer between the capsule and the vessel walls depends on the membrane diffusive permeability. In the presence of a Stokes flow field, behavior of the solute transfer seems to be fairly similar to that found for the stationary capsule for the same physical parameters. Moreover, the results suggest that the total solute transfer between the capsule and the vessel walls is enhanced when the capsule moves near to one wall. The increased adhesion strength between the capsule and walls would further increase the total solute transfer to the vessel walls although quite marginal.     

Process simulation of desalination by electrodialysis of an aqueous solution containing a neutral solute

A model was developed to describe the desalination process of an aqueous solution consisting of a salt and a neutral solute using electrodialysis (ED). Under the assumption of plug flow in compartments, the ED process was analyzed in two-dimensional directions of the electric field and flow to get the differential equations of mass balance in the flow length. Then the transport equations of solutes and water through the membrane were deduced by the irreversible thermodynamics approach. Under the limited condition of uniform current density, the model composed of a first-order differential equation set was developed. While the model parameters such as transport coefficients, dimensions of ED equipment, operation conditions and characteristics of solutes are given, the model was solved by the numerical method. The variations of current density, concentrations of solutes and velocities in dilute and concentrated compartments vs. flow length can be simulated by the model. While there was no neutral solute, the model was used to simulate the desalination process of a salt solution. By comparing the ED experiments to the simulations, it is shown that the model is well suited to describe the actual desalination process. The effects of the initial values of variables in the model on the desalination process were simulated to attempt to construct the actual ED process; and the general simulation of desalination process can be realized by the model. While the effect of concentration polarization on the desalination process is reflected by the variation of membrane conductivity, the model was verified to describe the ED process successfully under low velocity.     

Modelling of the nitrogen cycle in farm land areas

The authors propose a method of modelling the cycles of water and nitrogen in the soil in order to simulate the drainage flow of water and the flow of leached nitrate, the main inputs into a model of transfer in aquifers. The processes of the N cycle included here are: mineralization, nitrification, ammonium adsorption-desorption, immobilization of N from ammonium and nitrate, N uptake by plants and leaching of nitrate. The results of a limited test of the model using data from Dutch experimental farms showed that, on the whole, measured and simulated values were in reasonably good agreement, in spite of the relative simplicity of the model. However, the simulations do not give detailed information concerning the dynamics of nitrogen in the various layers in the soil.     

Prediction of Equilibrium Partitioning of Nonpolar Organic Solutes in Water‐ Surfactant Systems by UNIFAC and COSMO‐RS Models

In the present study the potential of two thermodynamic‐based models (the group‐contribution UNIFAC model and the a priori predictive COSMO‐RS model) to predict solute partitioning in aqueous surfactant solutions is evaluated. In order to take into account the small size of micelles, the UNIFAC model was extended by the interfacial contribution based on the Gibbs‐Thompson equation. The applicability of the approach was successfully proved for the partitioning of nonpolar solutes (toluene, p‐xylene) in aqueous solutions of nonionic surfactants. The original COSMO‐RS model underestimates the concentration of the solute in the aqueous phase in the case of micellar systems since it does not account for the small size of micelles. At the same time, this model gives quantitative results for the octanol/water partition coefficients of both solutes under study leading to the conclusion that the affinity of both solutes to a certain solvent is well described. Thus, extending the COSMO‐RS by the interfacial term seems to be promising.     

A model to predict changes in soil moisture,NO3-N content and N uptake by wheat

A simulation model to predict fertilizer N behaviour in a soil-plant (wheat) system has been developed and tested. The model predicts components of field water balance (evaporation, transpiration, drainage and run-off) and changes in soil nitrogen amounts due to N transformations (urea hydrolysis, mineralization, nitrification and volatilization), N movement and plant N uptake using information on N transformation coefficients for the soil, atmospheric evaporative demand (E_pan), leaf area development and root growth characteristics of the crop. The model predicts N uptake by wheat through mass flow using a new simplified crop cover function. The coefficients of correlation between the measured and predicted N uptake by wheat grown under three different moisture regimes in the two years (1987–88 and 1988–89) approached unity. The computed amount of residual NO₃-N in the soil profile at wheat harvest matched well with the measured amount with a root mean square error of 13.7 percent. The close matching of the measured and model predicted components of nitrogen and water balances under three widely different set of irrigation treatments suggests of model's capabilities to help in on-farm N management both under irrigated and rainfed conditions.     

稀土浸出过程溶质传递的格子Boltzmann模拟

采用耦合传质的格子Boltzmann方法模拟风化壳淋积型稀土矿中稀土浸出的溶质传递过程,在验证模型有效性的前提下,获得了稀土矿填充孔隙中流体流动的速度分布和伴随流动过程的溶质浓度分布. 通过考察浸取流速对溶质传递过程的影响,得到最佳浸取流速,约为0.25~0.35 mm/s,使溶质传递效率最高. 浸取流速小于0.2 mm/s导致浸取周期过长、浸取剂消耗量大;浸取流速大于0.4 mm/s引起沟流,导致稀土不能有效地浸出. 此外,模拟所得传质舍伍德数Sh随雷诺数Re的变化关系与经验关系式吻合,表明提出的模型可用于预测稀土浸出过程的溶质传递规律.     

Characterization of transport across cellulose acetate membranes in the presence of strong solute–membrane interactions

Certain organic solutes, including phenol, undergo anomalous enrichment when hyperfiltered through cellulose acetate membranes: the solute concentration is higher in the permeate than in the feed solution. A number of existing theoretical approaches describing hyperfiltration phenomena are presented and their merits and limitations upon application to the transport of phenol discussed. A new two-parameter transport relationship is derived based on an extension of the solution–diffusion model. The enrichment, or negative solute rejection by the membrane, is predicted to occur whenever the pressure-induced solute permeation velocity exceeds that of water. By acknowledging and incorporating the effect of pressure on the chemical potential of the solute, the present extended solution–diffusion model relationship successfully describes hyperfiltration data of phenol in homogeneous and asymmetric cellulose acetate membranes provided the contribution of convective flow to the overall solute transport is insignificant. In addition to the transport parameters of the extended solution–diffusion model, the transport parameters of the phenomenological, Kedem–Spiegler, and combined viscous flow–frictional relationship are evaluated from hyperfiltration data obtained with 0.05 and 0.1 wt % phenol feed solutions and homogeneous cellulose acetate membranes of different acetyl content.     

矿井水脱盐过程中卷式反渗透膜性能的数值模拟研究

为了更好地研究矿井水中无机盐组分对于反渗透过程产水、结垢及脱盐效果的影响,以内蒙古某煤矿矿井水水质组分作为进水水质条件,采用计算流体力学（CFD）模拟单支商用标准8寸卷式反渗透膜元件（陶氏BW30-400）内部的传质以及局部浓差极化的分布,预测实际运行情况下微溶盐结垢的风险。进水通道采用以阿基米德螺旋曲线为卷制轨迹的几何模型。无机盐的混盐作用通过混盐渗透压模型模拟。从全尺度卷式反渗透膜元件的模拟结果可以看出,卷式反渗透膜内的水流主要以轴向流速为主,沿切向阿基米德螺旋线的流速较低,对整体盐度分布的影响较小（<1%）,可以忽略不计,在后续模拟中采用简化模拟单元或几何模型或网格。在模拟操作条件下,卷式膜元件的浓水网产生的水头损失占整体水头损失约86%,为卷式膜元件中的主要水头损失来源。在没有安装浓水网的进水流道中最高Na₂SO₄浓度位于元件浓水出口处,高达3594 mg/L,约为有浓水网情况下的1.8倍。而且有浓水网的进水流道内,浓差极化现象主要发生在浓水网背水侧局部区域,影响范围较小。该模型模拟得到的产水量与实测产水量做对比,误差小于5%,同时模拟结果也接近ROSA9.1模拟数据（误差<4.4%）,因此可以对卷式反渗透膜的无机盐脱盐过程进行较精确的模拟仿真。与商业设计软件如ROSA（反渗透系统分析）相比,其只提供产水和浓水中的盐浓度信息,本文开发的模型可以提供浓度极化的特征信息,加深了对卷式反渗透膜在不同位置的潜在结垢风险的理解。     

The Allelochemical Sorgoleone Inhibits Root H+-ATPase and Water Uptake

Sorghum plants inhibit the growth of some adjacent species. Root exudates from grain sorghum (Sorghum bicolor), consisting primarily of the quinone sorgoleone, are phytotoxic to several plant species, yet the mechanisms of growth inhibition remain to be fully explained. Disruption of electron transport functions in isolated mitochondria and chloroplasts has been reported as one explanation for growth inhibition. In the studies reported here, however, soybean seedlings grown in nutrient solution with 10, 50, or 100 microM sorgoleone showed no disruption of photosynthesis, as measured by leaf fluorescence and oxygen evolution, yet their mean leaf surface area was less when grown in 100 microM sorgoleone. Furthermore, in the presence of these same concentrations of sorgoleone, decreased nutrient solution use by soybean seedlings and decreased H+-ATPase activity in corn root microsomal membranes were observed. This suggests that impairment of essential plant processes, such as solute and water uptake, driven by proton-pumping across the root cell plasmalemma should also be considered as a mechanism contributing to observed plant growth inhibition by sorgoleone.     

PEM燃料电池中质子交换膜内水和质子的迁移特性

质子交换膜的水含量及水和质子的迁移对PEM燃料电池的性能具有重要影响.提出了一个稳态两相流数学模型,用以研究质子交换膜中的水迁移和水含量及其与质子传递阻力的关系.模型耦合了连续方程、动量守恒方程、物料守恒方程和水在质子交换膜中的传递方程.通过与实验数据对比,验证了模型的有效性.分析模拟结果发现,当电流密度相同时,沿气体流动方向,质子交换膜中水的电渗拉力系数、反扩散系数和水力渗透系数逐步增大,而水的净迁移系数逐步减小;同时,质子交换膜的含水量增加,质子传递阻力逐步下降;增大电池的操作压力,电渗拉力系数、反扩散系数、水力渗透系数、水净迁移系数和质子膜的含水量增加,而质子传递阻力下降,使燃料电池的性能得到了提高.