The application of TDR in laboratory column experiments

An automated TDR system was used together with an automated tensiometer system in laboratory column experiments for the measurement of unsaturated hydraulic properties of soils. The laboratory experiments were a stationary flux (sprinkling infiltrometer) carried out with different fluxes, and a transient (evaporation) method. Simultaneous measurements of water content and pressure head give the water retention characteristic and enable the application of the instantaneous profile analysis for calculating the hydraulic conductivity. This direct analysis is compared with the traditional analysis methods normally used for the laboratory experiments. The application of automated measurement techniques and the use of TDR increases the speed of the measurements, generates more data points and requires less assumptions in the data analysis. Moreover, TDR measurements give insight in the flow process, including effects of hysteresis and heterogeneity within a sample. Performing the sprinkling infiltrometer and evaporation experiments on the same sample enables the determination of the unsaturated hydraulic conductivity at pressure heads ranging from −0.01 m to −6 m.     

SOILPAR 2.00: software to estimate soil hydrological parameters and functions

2 is a program for estimating soil parameters. It allows: (1) storing soil data in a georeferenced database, (2) computing estimates of soil hydrological parameters using 15 procedures, (3) comparing the estimates against measured data using both statistical indices and graphics, and (4) creating maps using the ESRI format. An interface to/from Excel and CropSyst is provided. Eleven methods estimate one or more of the following characteristics: soil water content at predefined soil matrix tension, saturated hydraulic conductivity, and bulk density. Three methods estimate the parameters of well-known soil water retention functions (Brooks-Corey, Hutson-Cass, van Genuchten), and one estimates both saturated soil hydraulic conductivity and the soil water retention curve parameters (Campbell). The software runs under Windows 98/NT/2000/XP and is freely downloadable via internet.     

Relations between pore-space and hydraulic properties in compacted beds of silty-loam aggregates

The aim of this study was to better understand features of the hydrodynamics of aggregated soil from experiments conducted on repacked soil samples. In the laboratory, aggregates 2 to 3 mm in diameter were prepared using a silty-loam material. These aggregates were wet to a water content close to their air-entry point value, and compacted to a predetermined bulk density. Two sets of samples were studied, with mean bulk density ranging between 1.0 and 1.6 Mg·m⁻³. Aggregates were extracted from samples of a first set, and their bulk density and water retention curve were determined. Water retention curve and unsaturated hydraulic conductivity of samples of a second set were determined using an instantaneous profile method. Experimental results were interpreted with respect to a functional pore-space classification. The water retention properties of the aggregates extracted from the samples were different, although differences in porosity between such aggregates were sometime too small to be measured. This was explained by a narrowing in the constrictions of intra-aggregate pores induced by compaction, even when this compaction was small. Discontinuities in the shape of the hydraulic properties of a loosely-compacted bed of aggregates were found. This was consistent with an independent desaturation of the inter- and intra-aggregate pores. However, unsaturated hydraulic conductivity of the loosely-compacted sample was affected by a small amount of water, which formed menisci between the aggregates close to the air entry point value of the aggregates. Soil hydraulic conductivity increased with the degree of compaction for a range of massbased water contents dryer than the water content at the air-entry point value of the aggregates. The influence of the contact surface between the aggregates on the unsaturated hydraulic conductivity of the samples was quantified, by assuming that water flows only through the aggregates. These experimental results are related to aspects of soil hydrodynamics, which are difficult to study in situ and difficult to predict with the existing models for the soil hydraulic properties.     

基于灰色关联法土壤水分垂直入渗影响因素研究

土壤水分入渗过程中主要受压力水头、土壤初始含水率、土壤容重、颗粒级配影响。基于一维垂直土柱积水入渗试验研究这些因素对入渗能力影响的主次关系,利用Green-Ampt与Philip入渗模型得到相应土壤入渗特性参数,采用灰色关联分析法研究四个因素对累积入渗量、饱和导水率、稳定入渗率、湿润锋面吸力、吸渗率的影响程度。结果表明,压力水头、土壤初始含水率、土壤容重、颗粒级配对累积入渗量、入渗率及Green-Ampt与Philip模型中物理参数有显著影响,各处理中饱和导水率与稳定入渗率间误差较小,吸渗率拟合值与利用湿润锋面吸力所得吸渗率计算值间相似程度较高,决定系数R2大于0.85;灰色关联分析结果表明,颗粒级配关联度均值r4最高为0.946 3,土壤容重、初始含水率其次,压力水头影响程度最小（r1=0.562 9）。总而言之,颗粒级配对土壤入渗特性影响起主导作用,该研究成果可为农业灌溉及水资源管理提供理论支撑。     

保护性耕作对潮土物理性质的影响

为了研究保护性耕作对土壤物理性质的影响,以黄淮海平原典型潮土区小麦—玉米轮作系统的长期定位试验为基础,探讨不同耕作方式与秸秆还田处理下土壤容重、饱和导水率、紧实度、含水量的变化。结果表明,0~20 cm土层,土壤容重、土壤紧实度随着翻耕频率的减少而增加,每两年翻耕一次(CNTW2T)和每四年翻耕一次(CNTW4T)的土壤紧实度比长期免耕分别降低了40%、17%,土壤紧实度与土层深度呈显著正相关;保护性耕作改变土壤导水性能,随着免耕年限的增加,土壤饱和导水率显著降低;少免耕土壤含水量比传统翻耕高0.77%~3.01%。秸秆覆盖能显著降低土壤紧实度,改良土壤压实状况,提高土壤饱和导水率,减少土壤水分蒸发,从而改善土壤保水能力。免耕有利于土壤蓄水保墒,但长期免耕易导致土壤压实,不利于作物生长,少耕(CNTW2T、CNTW4T)既可改善土壤导水、保水性能,又可减少土壤压实,因此在黄淮海平原实施少耕与秸秆还田相结合的保护性耕作有利于改良土壤物理性质,提高土壤保水能力。     

Hydraulic conductivity measurements of the spatial variability of a loamy soil

The spatial variability of the parameters K_fs and α of the exponential form of the hydraulic conductivity given by K(ψ)=K_fs exp (αψ) where ψ is the water pressure head in the soil has been examined on a bare agricultural soil, by performing surface infiltration measurements with the Guelph Pressure Infiltromer. Thirty two measurements were made at each node of a 4 m × 8 m grid. Both the early-time transient and steady-state flow rates, for three hydraulic heads (6, 16 and 25.5 cm) imposed at the soil surface have been analyzed. It is shown that the best estimates of the field-saturated hydraulic conductivity, K_fs and of the alpha parameter (α) are given by calculations based on the steady-state regime simultaneously applied to the three heads. The results indicate that both, K_fs and α are better described by a lognormal than a normal distribution. They also show that the parameters are autocorrelated up to about 25 m and to 20 m respectively and negatively spatially correlated together within a distance of 24 m. These findings tend to invalidate some assumptions classically used in the stochastic models of unsaturated water flow in porous materials.     

负水头灌溉对温室番茄植株蒸腾规律影响的研究

利用Flow32茎流计分别测定负水头灌溉和常规灌溉方式下的番茄植株蒸腾速率,探讨负水头灌溉方式对番茄植株蒸腾影响及植株蒸腾速率与太阳辐射强度之间的关系,同时分析了负水头灌溉下植株一天不同时刻耗水量差异和负水头灌溉对水分利用效率的影响。试验结果表明,负水头灌溉下的番茄植株蒸腾速率要大于常规漫灌,但有着相同的变化趋势,植株的蒸腾速率主要受太阳辐射强度的影响;负水头灌溉方式能为作物适时适量提供水分,且有效地减少无效地表蒸发和地下深层渗漏,提高了作物的水分利用效率。     

A comparison of near-saturated hydraulic properties measured in small cores and large monoliths in a clay soil

The effect of measurement scale on hydraulic properties close to saturation was investigated in a clay soil. Results from measurements on undisturbed “standard” small soil core samples were compared with results from three large intact soil monolith samples which were assumed to reflect natural soil hydraulic behaviour. An intermediate sample size, which was used to characterize soil water retention relations (θ(ψ)) in each layer in the intact monoliths, was obtained by cutting the intact monoliths in three layers. The small cores were subsequently sampled from the cut monoliths so that all measurements were made on the same soil material. Measurements of θ(ψ) and saturated hydraulic conductivity (K_s) were compared, as well as the exponential relationships between K_s and macroporosity (ϕ_ma), the latter derived from the θ(ψ) data for small cores and from specific yields for intact monoliths. Between soil water pressure heads of −60 cm and −15 cm the small core data and the cut monolith data showed similar θ(ψ) relations, whereas they diverged closer to saturation. When comparing K_s and ϕ_ma, small core data were correlated with the intact monolith data although the small cores had smaller values. Thus, the “standard” small cores can satisfactorily predict the investigated soil hydraulic properties for a natural soil at pressure heads equal or less than −15 cm, but they may be in error, especially in soils with macropores, in the pressure head range −15 cm to saturation, i.e. in the largest macropores.     

局部灌水条件下不同根区在作物吸水中的作用

采用分根装置,在均匀灌水、固定部分根区灌水和根系分区交替灌水3种方式下,分期测定玉米的耗水量、两个1/2根区及整个根区的土—根系统水分传导与土壤含水量,研究各个根区在作物水分吸收中的作用。结果表明,3种灌水方式下,玉米耗水量与全部根区和灌水区土-根系统水分传导间均存在密切的正相关关系。均匀灌水条件下,1/2根区水分传导约占全部根区水分传导的一半;固定灌水条件下,灌水区占全部根区水分传导的比例远大于非灌水区,与全部根区接近。交替灌水条件下,两个根区对全部根区水分传导的贡献呈交替变化,其非灌水区占全部根区水分传导的比例较之固定灌水明显增大。全部根区土-根系统水分传导与灌水区土壤含水量明显相关,灌水区土壤含水量决定了整株作物的水分吸收情况。交替灌水的非灌水区从土壤到根系仍有一定的水分传输作用,而固定灌水的非灌水区使全部根区的土—根系统水分传导降低。     

不同干扰对城市绿化用地土壤物理性质的影响

为了解压实对城市新建绿地土壤物理性质的影响,以西安植物园新园区为研究对象,依据土壤压实程度的不同以及地表植被的差异进行区域划分,对不同区域内的土壤分层采样,并进行土壤容重、孔隙状况、水分常数等物理性质的测定。结果表明：随着压实程度的增加,土壤各层次间的发生规律发生了改变,土壤出现退化现象。研究区域内的土壤容重偏高,平均值为1.52 g/cm³;土壤总孔隙度、通气孔隙度、土壤含水量、田间持水量、土壤饱和导水率明显偏低,平均值分别为44.71%、12.81%、15.46%、20.77%、20.7 mm/h。土壤容重与总孔隙度、通气孔隙度、田间持水量、自然含水量、饱和导水率之间呈极显著的负相关;通气孔隙度与饱和导水率、自然含水量、田间持水量之间均呈现显著的正相关。压实对各层土壤物理性质的影响表现为表层土>浅层土>深层土,人为践踏产生的压实只影响到表层土壤。     

聚丙烯酰胺对天津滨海吹填土导水性能的影响研究

为改善滨海吹填土的导水性能,加速吹填土的淋洗排盐,通过室内土柱试验,研究了不同浓度聚丙烯酰胺(PAM)溶液施用对滨海吹填土入渗性能和淋盐能力的影响,结果表明：与对照处理相比,0.05、0.2、0.3、0.6、1.2、2.4 g/L PAM溶液施用均能有效改善滨海吹填土土壤结构,显著提升吹填土导水性能和淋洗脱盐能力,降低吹填土pH,增加土壤水分含量。淋洗初期,PAM施用浓度越高,吹填土入渗速率越大,随时间的延长,入渗速率降低;出水稳定后,0.6 g/L PAM处理入渗速率最大,达0.059 cm/h,为对照的1.64倍;淋洗267 h后,施用PAM处理土壤含盐量均低于1.0 g/kg,为非盐渍土,0.6 g/L处理最低,仅为0.32 g/kg,而对照处理含盐量为4.82 g/kg,属于重度盐渍土。可得出结论对于天津滨海吹填土,300万分子量的阴离子型PAM最佳施用浓度为0.6 g/L。     

Distribution Characteristics and Prediction of Equilibrium Moisture of Non saturated Clay Subgrade

The space distribution characteristics of equilibrium moisture of non saturated clay subgrade were surveyed along the road cross section by the in situ and laboratory tests. Based on the basic theory of unsaturated soil mechanics, matric suctions of soil samples with different kinds of moisture condition were determined and the soil water characteristic curve model was calibrated to reflect a single valued function relationship between water content and matric suction of clay soils. Combining the above results, an estimation method of the equilibrium moisture of the unsaturated clay subgrade outside the affected zone of atmospheric precipitation/evaporation was established. The results show that the atmospheric precipitation/evaporation has significant effect on moisture condition of the subgrade soil located in the upper part of the subgrade near the central reserve and hard shoulders. However, equilibrium moisture of subgrade soil outside the affected zone of atmospheric precipitation/evaporation is mainly controlled by the impact of the groundwater table. Fredlund & Xing model can be used to characterize the relationship between the unsaturated clay soil moisture and matric suction, and the fitting results of model parameters have high reliability. A consistency between the predictive results and the experimental data shows the presented model is accurate and credible.     

不同改良材料对粘质盐土物理性状和棉花产量的影响

为了研究不同类型的改良材料对滨海粘质盐土物理性状的改良效果,在黄河三角洲滨海粘质盐土区进行田间试验,设置了泥沙用量为20、40 t/hm~2,3种硅藻泥用量为1.5、3.0、4.5 t/hm~2和对照试验,探讨不同改良材料与用量对土壤容重、孔隙状况、饱和导水率、土壤水盐分布以及对棉花生长和产量的影响。研究结果表明:在0~20 cm表层土壤中,不同处理的土壤容重和总孔隙度无显著差异;与对照相比,3个硅藻泥处理的大孔隙数量比分别降低0.51%、2.53%和4.75%,土壤饱和导水率降低1.18%、15.88%、22.65%,土壤含盐量降低62.76%、72.01%和75.76%(P0.05),棉花产量降低2.8%、5.0%、11.1%;2个泥沙处理的大孔隙数量比分别增加了17.75%和37.09%,土壤饱和导水率增加17.94%、60.29%(P0.01),土壤含盐量降低23.17%、25.08%(P0.05),棉花产量增加11.1%、16.7%。引黄泥沙有效改善土壤质地和孔隙状况,增加土壤饱和导水率,适宜改良粘质盐土的物理性状。硅藻泥不适用粘质盐土物理性状的改良。因此,改良粘质盐土的关键是选择增加土壤大孔隙数量、比例,提高土壤饱和导水率的材料。     

Matric Suction Effect on Shear Strength of Roadbed Unsaturated Soil

A study which focuses on the role of matric suction in the stress strength of roadbed unsaturated soil was presented. Two types of tests were described, namely, the suction controlled shear test and microstructure scanned test. For the former, four sub tests were conducted under different suction and net normal stress conditions. And two unsaturated soil samples that belong to the same type but with different water contents were scanned. In contrast with clay soil, the corresponding results show that the strength of silty sand soil does not always increase as matric suction increases or soil water content decreases; there exists a peak contributed by matric suction that acts on soil stress strength. The main reason for this kind of phenomenon is due to the typical microstructure of this type of soil and the various types of pore water retention. Additionally, the state of stress in which soil sample meets can also exerts important influence on soil strength.     

不同耗水强度下节水灌溉稻田土壤含水率与非饱和土层厚度关系研究

为了探索基于土壤非饱和层厚度指导水稻节水灌溉的可能性,研究节水灌溉稻田土壤含水率与非饱和土层厚度的关系非常必要。本文通过设计盆栽试验,针对不同耗水强度开展连续观测,根据实时观测的土壤含水率与非饱和土层厚度,建立起两者之间的定量关系。结果表明：稻田日耗水强度越大,其非饱和土层厚度随时间增加的速率越大,达到最大值所需的时间越短。非饱和土层随时间增加时对应的土壤含水率则随时间下降,两者之间成负相关关系。通过建立土壤含水率与非饱和土层厚度的二次抛物线关系,结果显示将非饱和土层厚度作为水分控制指标指导灌溉精度高、切实可行。最后,将土壤含水率与非饱和土层厚度关系曲线运用到水稻控制灌溉的实践中,推算出土壤含水量下限对应的非饱和土层厚度值,确定以非饱和土层厚度为指标的控制灌溉方法,为黑龙江地区水稻节水灌溉管理技术提供参考,为下一步的水分运动模型率定及模拟更多土质和更多耗水情形下的土壤水分提供依据。     

Calculation Method of Hydraulic Characteristics for Direct-Return Chilled Water System

In order to optimize design and operation, it is necessary to calculate accurately hydraulic characteristics large central air-conditioning systems. Simplified Model can not be applied to hydraulic calculation of large pipe network topological structure for its large calculation error. Taking into account the regulating characteristics of terminal branch temperature regulating valve, a direct-return chilled water system is studied, an accurate mathematical model of pipe network hydraulic characteristics has been established and a computer logic algorithm with virtual flow has been given. A direct-return pipe network with ten AHU branches is used as simulation calculation object, the pipe network supply-return water pressure difference is calculated, and also the temperature regulating valve opening and actual flow of each branch are calculated in the condition of different supply-return water pressure difference. The calculated results accord with the natural characteristics of high pressure difference unbalanced for direct-return pipe network. The calculation method can ensure calculation convergence.     

Analysis of Water Supply of Plants Under Saline Soil Conditions and Conclusions for Research on Crop Salt Tolerance

Abstract In the dry areas of the world there is an increasing pressure to apply low quality brackish waters for plant irrigation (agriculture, horticulture, landscape greening). Consequently there is a demand to improve salt tolerance of conventional crops and to develop adequate irrigation techniques too. The efforts in the past decades to approach the understanding of salt stress mechanism by focusing on biochemical and physiological research were disappointing with respect to progress for crop growth and yields under saline soil conditions. However, it is generally agreed by all disciplines involved in research for crop salt tolerance that under saline soils conditions the reduced water supply of crops is the most critical growth factor. The paper presents some model calculations and field investigations that demonstrate the effect of root water uptake on the salinity of the root surrounding soil fraction (rhizospheric soil). It is shown that root hair length and rhizospheric soil volumes are factors most relevant for understanding crop salt tolerance, when growing in soils. It is postulated that short root hairs contribute to a lower salt tolerance (onions), whereas long root hairs enhance water uptake from saline soils and crop salt tolerance (rape). As interactions between roots and soil contribute to the salt tolerance of crops under field conditions, it is doubtful that selection for salt tolerant varieties and breeding for salt tolerance under conditions of water and flow culture experiments is very efficient. Breeding for more salt-tolerant crops and brackish irrigation techniques should consider root morphology and soil/root contact zone.     

上海市杨浦区公园、道路绿地土壤物理性状及电导率分析

为了给土壤改良治理提供数据支撑,笔者采用环刀法测定杨浦区公园和道路绿地的土壤物理性质,使用便携式土壤水分测量仪测定电导率,使用便携式渗透仪现场观测土壤导水率。结果表明：杨浦区土壤电导率略高于标准值0.05 mS/cm3,土壤通气性不良,土壤非毛管孔隙度比城市园林绿化种植要求低5.88%。道路绿地土壤容重比标准高0.03 g/cm3、土壤总孔隙度比城市园林绿化种植最理想的标准低2.42%,公园绿地符合标准。道路绿地土壤含水量与持水能力均显著低于公园绿地。及时翻松地表土壤,通过堆积树皮、凋落叶增大土壤中腐殖质含量,降低土壤紧实度;加强日常养护管理,防止人为因素的破坏干扰;植物绿化种植过程中,从使植物群落结构丰富多样等方面入手改良土壤质量。     

种棉改良对粘质盐土物理性状及水盐动态的影响

为了研究棉花种植对滨海粘质盐土物理性状及水盐动态的影响,笔者在黄河三角洲滨海粘质盐化潮土区进行田间试验,设置了连续种棉改良3年和盐碱荒地2种不同处理,探讨种棉改良对土壤容重、饱和导水率和不同条件下土壤水盐动态的影响。结果表明:与盐碱荒地相比,种棉改良后0~20 cm土层的土壤容重降低了15%(P0.01),土壤饱和导水率增加了89.23%(P0.05)。在春季蒸发条件下,0~20、20~40、40~60、60~80、80~100 cm 5个土层中,种棉改良的土壤含盐量比盐碱荒地分别降低了52.07%、55.17%、55.23%、53.78%和47.43%。种棉改良还增加了少量降雨对土壤盐分的淋溶,有效抑制表层土壤盐分积累,使棉花生育期内的土壤耕作层含盐量低于3 g/kg,保证了棉花不同时期的正常生长,是盐碱荒地改良和高效利用的有效途径之一。