SPAC中的水分运动

本文对土壤-植物-大气连统体(SPAC)中水分运动的诸多方面,如非饱和土壤水分的导水参数,植物根系吸收土壤水分,植物根系中的水分运动.SPAC中的水流阻力及水容,土壤水分有效性动力学,滞后效应以及SPAC中水流的电模拟等.进行了介绍,评述和论述.     

土壤—植物系统中的瞬态流理论及电模拟的最新研究进展

对近几年在土壤一植物系统中瞬态流理论方面的研究成果，如电模拟模型，时间“常数”的变性，水容及相对重要性，水流阻力的大小及相对重要性，水流阻力的变性和水分运动的滞后效应等问题进行了介绍了综述。     

间歇降雨中土壤含水量分布及其对入渗的影响

通过室内土柱实验,研究了间歇性降雨事件中土壤剖面水分分布特征及其对入渗的影响.实验表明,积水发生时间与雨强和表层5 cm初始土壤含水量密切相关;前期累积入渗量越大.则土壤表面越容易发生积水;间歇入渗过程中,入渗还受间歇时间的影响,相邻入渗事件积水发生时间有提前的趋势.初始事件入渗速度较后续入渗大一个数量级;湿润锋运行速度存在明显的波动,在经历间歇期再分布后,湿润锋运动存在滞后效应,且波动作用较初始入渗更加显著.通过分析,认为土壤水入渗以运动波和扩散波的形式运动,两者交替起主要作用,土壤水分有随含水量升高以运动波传递,随含水量衰减以扩散波形式运动的趋势.     

水分胁迫对日光温室葡萄叶片生理变化及果实发育的影响

为探究鲜食日光温室葡萄高效节水生产的水分管理方式,选取日光温室6a生葡萄‘红地球’为试验材料,以充分灌溉为对照[CK,土壤含水率为75%～100%的田间持水率(θf)],分别在萌芽期、新梢生长期、开花坐果期、果实膨大期、着色成熟期设置土壤含水率为55%θf(其他4个生育期为75%～100%θf)的5个水分胁迫处理,调查叶片超氧化物歧化酶(SOD)活性及膜质过氧化物丙二醛(MDA)和脯氨酸(Pro)含量、果实纵横径、果实硬度、单粒重量和产量,研究日光温室葡萄叶片生理和果实产量对水分胁迫的响应机制。结果表明,在果实膨大期、着色成熟期施加水分胁迫均会显著降低葡萄叶片SOD活性和Pro含量,导致MDA含量大量积累,对叶片产生不利影响。在萌芽期、新梢生长期、开花坐果期进行水分胁迫对葡萄叶片SOD活性、Pro含量影响不大,但对叶片MDA含量的影响具有滞后效应。果实膨大期水分胁迫葡萄产量仅为14 830kg·hm–2,较CK和萌芽期、新梢生长期水分胁迫显著减产20%以上。因此,水分胁迫显著降低果实膨大期SOD活性及渗透调节物质含量,增加膜质过氧化物含量,并导致产量降低,该时期不宜进行亏水处理;生长前期的水分胁迫对葡萄叶片的生理和果实的影响不显著。     

极端干旱区不同水分条件下胡杨林生态耗水特征

以极端干旱区胡杨林为研究对象,探究不同水分条件下胡杨林土壤水分运动规律和胡杨生态耗水特征。结果表明:HYDRUS-1D模型对极端干旱区胡杨林土壤水分运动和蒸散发过程具有良好的模拟效果。不同水分条件下胡杨林土壤水分运动特征和生态耗水变化差异明显。随着下垫面水分条件趋于湿润,土壤水分含量和湿润锋入渗深度均出现增加,入渗深度分别达到100,120,150cm。下垫面水分条件改变导致土壤水分存蓄情况发生变化。下垫面水分补给增加的同时胡杨林蒸散发呈明显增加,其中植被蒸腾增加显著。随着水分条件逐渐湿润植被蒸腾占总蒸散比例由55%升至65%。研究显示,随着下垫面水分条件逐渐湿润,极端干旱区胡杨林生态耗水量逐渐增加,其中植物蒸腾消耗是造成水分耗散增加的主要原因。     

宁夏半湿润偏旱区农田水分运动及利用研究

通过长期定位试验,研究了宁夏半湿润偏旱区农田水分运动规律、主要作物对农田水分的利用、水分对作物生长的影响以及降水资源的利用。结果表明,春小麦水分入不敷出,干旱缺水及降水的季节变化是该区农业生产的主要限制因子,作物水分利用效率低影响了降水生产潜力的发挥,因而开发降水生产潜力是提高该区农业生产力的关键。     

宁夏半湿润偏旱区农田水分运动及利用研究

通过长期定位试验,研究了宁夏半湿润偏旱区农田水分运动规律、主要作物对农田水分的利用、水分对作物生长的影响以及降水资源的利用。结果表明,春小麦水分入不数出,干旱缺水及降水的季节变化是该区农业生产的主要限制因子,作物水分利用效率低影响了降水生产潜力的发挥,因而开发降水生产潜力是提高该区农业生产力的关键。     

地下水浅埋区重度盐碱地覆膜咸水滴灌水盐动态试验研究

通过在高垄埋设水银负压计,研究土壤水势动态,并在枸杞不同生育期对潜水位以上各土层盐分进行取样分析,研究土壤盐分周年动态变化,为地下水浅埋区重度盐碱地改良利用提供理论依据。结果表明,在覆膜滴灌一个灌溉周期内,土壤水分运动始终为自滴头下方饱和区持续径向向外扩散;雨季降雨使水分从土壤剖面整体向下运动,随着潜水位的升高水分运动逐渐减弱,转为自垄中部向垄坡方向运动。盐分运动受水分运动影响明显,周年盐分动态可以分为春季强烈蒸发—积盐阶段、灌溉淋洗—稳定阶段、雨季淋溶—脱盐阶段、秋季蒸发—积盐阶段和冬季相对稳定阶段五个阶段。剖面土壤电导率(EC1∶5)均值从1.64 dS m-1增长至1.69 dS m-1,土壤未明显积盐,但盐分在剖面分布的周年变化表明滴灌灌溉调控了水分盐分在土壤中的分布,为作物根系生长提供了良好的土壤环境条件。因此,地下水浅埋区重度盐碱地可以通过高垄覆膜咸水滴灌技术加以利用。     

基于CT图像的土壤孔隙结构三维重建及水力学性质预测

为了更好地了解土壤孔隙结构对水分运动过程的影响机制,该文利用黄淮海平原原状潮土CT扫描图像,通过数字图像分析和计算机重建技术对孔隙结构进行三维重建,根据图像分析获得的孔隙大小分布和连通性等形态学参数建立了用于描述孔隙尺度结构特征对水分运动影响机制的网络模型,据此预测了样本尺度(样本体积为385.84cm3)的土壤水力学性质。结果表明,模型预测的水力学性质和实测值基本吻合,变化趋势基本一致,二者的决定系数达0.94以上。结果表明相关网络模型可以较好地模拟孔隙尺度的水分运动过程,可用于预测土壤的非饱和水力学性质。     

土壤有机质含量对土壤水动力学参数的影响

通过测定并分析不同有机质含量的壤质土样的饱和导水率,水分特征曲线,水分扩散率及几个水分常数,阐明了土壤有机质含量与水动力学参数的关系,从动力学角度探讨了有机质影响水分运动的机理。     

ANALYSIS OF ONE-DIMENSIONAL STEADY FLOW IN CONSTRAINED SWELLING SOILS

The relation between the steady-state flow rate in horizontal columns of swelling soils and the pressure difference applied across the ends is derived for small flow rates. The slope of the curve representing the relationship at zero flow rate gives the value of the hydraulic conductivity corresponding to the initial water content (and hence to the average water content). The result is valid for hysteretic systems. The curves are concave to the pressure axis for published moisture characteristics. However, they can be convex for characteristics of a form that has not been reported but which does not violate known physical laws. A particular hydraulic conductivity/water content relationship leads to linear curves.     

Laboratory equipment and calculation procedure to rapidly determine hysteresis of some soil hydrophysical properties under nonsteady flow conditions

Laboratory equipment was developed to measure nonsteady water potential and water content profiles in soil columns, with a high resolution in time and space. Moisture content was monitored using TDR-miniprobes and water potential was measured with microtensiometers. Gradients were applied by controlling the water potential at the bottom of the soil column during adsorption and desorption with the aid of a ceramic plate. The described experimental setup was designed specifically to determine effects of hysteresis on the water content/water potential and water potential/hydraulic conductivity relationships in undisturbed soil samples. In addition, an algorithm to process the data and to calculate the above mentioned relationships is presented. The algorithm includes the smoothing of data with Bezier functions before the calculation of the moisture retention curves and the conductivity functions. Results obtained from an albic E-horizon of a silty Luvisol are presented exemplarily to demonstrate the applicability of the proposed method in studying hysteresis effects.     

Effective stresses in unsaturated soils and their applicability in the theory of critical state soil mechanics

Cricital state soil mechanics, which expresses relationships between deformation and effective stresses, has not yet been established for unsaturated soils. Effective stresses in unsaturated soils are not only complicated functions of the applied stress and the pore-water pressure, but are also hysteretic. Furthermore, they cannot yet be determined independently, because present theories are inadequate, and they must be obtained by the less satisfying method of comparing the deformation of unsaturated and saturated soils subjected to similar stress paths. The paper discusses the further measurements that need to be made to validate the extension of critical state soil mechanics to unsaturated soils, and concludes that unless the effect of hysteresis proves to be small, the theory may be too difficult, if not impossible, to apply quantitatively.     

Water repellency of organic growing media related to hysteretic water retention properties

With respect to soils, most growing media can exhibit hysteresis during drying/wetting cycles, which greatly affects their hydraulic properties. In the case of organic substrates, hydrophobicity during desiccation could be considered as one of the main factors leading to hysteretic behaviour. The purpose of this study was to estimate the influence of changes in wettability on the water retention properties, θ(ψ), of peat and pine bark during a drying/wetting cycle. Major differences in the hydraulic behaviour of the two organic materials studied were observed. For peat, hysteresis was found in the water retention curve (21%) and also in the contact angle/water potential relationship, (α(ψ), 20%), whereas in pine bark, this phenomenon was less pronounced in the water retention curve (10%) and even more limited in the α(ψ) curve (> 5%). Water retention hysteresis was successfully modelled using a modified van Genuchten‐Durner approach (VG_α model), which took into account the local hydrophobicity of each poral domain of the porous media, regardless of the extent of hysteresis. Incorporating the parameters of the VG_α water retention model into a α(ψ) equation to characterize overall or average changes in the hydrophobicity of the material during desiccation resulted in values very similar to those of the contact angles calculated with the capillary rise method. These results indicate that water retention properties of these organic substrates are strongly influenced by hydrophobicity.     

初始浓度对六氯苯在土壤中的吸附-解吸的影响及解吸

Adsorption and desorption are important processes that influence the transport, transformation, and bioavailability of hexachlorobenzene (HCB) in soils. To examine the adsorption-desorption characteristics of HCB, equilibrium batch experiments were carried out using two soils (red soil and paddy soil) with different initial HCB concentrations (0.25, 0.50, 0.75, 1.00, 1.50, 2.50, 3.50, and 5.00 mg L^-1) by using 0.01 mol L^-1 calcium chloride as the background solution. The successive desorption experiments (48, 96, 144, 192, and 240 h) were conducted after each adsorption equilibrium experiment. The results revealed that adsorption and desorption isotherms of HCB on two soils were nonlinear, which can be best described by the Freundlich equation with the square of the correlation coefficient (r²) ranging from 0.97 to 0.99. Desorption of HCB from the two soils exhibited hysteresis at all HCB concentrations because the Freundlich desorption coefficients were always higher than the Freundlich adsorption coefficients. The hysteretic effect was enhanced with increasing initial HCB concentration, and positive hysteresis was observed at different concentrations.     

THE MEASUREMENT OF SOIL-WATER HYSTERETIC RELATIONSHIPS ON A SOIL MONOLITH

Soil water properties of an undisturbed uniform soil monolith were studied under laboratory conditions. Water content, hydraulic conductivity and soil water suction were measured simultaneously on a full cycle starting from saturation, drying to a small water content and then wetting until saturation was reached again. The results showed clearly the hysteretic nature of the relations between water content and suction and between hydraulic conductivity and suction, but not between hydraulic conductivity and water content.     

砂壤质褐土饱和导水率与物理性质的多尺度关系——小波分析法

正确估算土壤水力特性是准确了解土壤水分运动和溶质运移过程的前提。土壤水力特性具有明显的空间变异特征,由于其空间异质性是各种物理、化学和生物过程(如生物活动、耕作、地形、土壤侵蚀)在不同尺度下综合作用的产物,导致其变异     

负水头条件下的土壤水分垂直一维入渗特性研究

通过室内模拟试验研究了3种土壤在不同负水头条件下的土壤水分垂直一维入渗特性,并基于Brooks-Corey模型,结合非饱和土壤水动力学方程,推导分析了负水头条件下土壤水分垂直一维入渗时累积入渗量、入渗率、湿润锋以及入渗时间之间的理论关系,并利用入渗试验资料检验了这些变量关系。同时,验证了Philip入渗公式在负水头条件下的适用性。研究结果表明:这些理论关系可以很好地描述负水头条件下的土壤水分垂直一维入渗特性。