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1.
W. R. Whalley L. J. Clark W. A. Take N. R. A. Bird P. K. Leech R. E. Cope & C. W. Watts 《European Journal of Soil Science》2007,58(1):18-25
The matric potential of soil water is probably the most useful assessment of soil water status. However, the water‐filled tensiometer (the benchmark instrument for measuring matric potential) typically only operates in the range 0 to ?85 kPa. In this paper, we report the development of a porous‐matrix sensor to measure matric potential in the approximate range ?50 to ?300 kPa. The sensor uses a dielectric probe to measure the water content of a ceramic material with known water retention characteristics. The calculation of matric potential takes into account hysteresis through the application of an appropriate model to measured wetting and drying loops. It is important that this model uses closed, rather than open, scanning loops. The calibrated sensors were tested in the field and the output compared with data from water‐filled tensiometers and dielectric measurements of soil water content. These comparisons indicated that conventional tensiometers gave stable but false readings of matric potential when soil dried to matric potentials more negative than ?80 kPa. The porous‐matrix sensors appeared to give reliable readings of matric potential in soil down to ?300 kPa and also responded appropriately to repeated wetting and drying. This porous‐matrix sensor has considerable potential to help understand plant responses to drying soil. 相似文献
2.
Abstract. This paper reports results from a four year study to investigate the suitability of porous ceramic cups to measure solute leaching on shallow chalk soils. Measurements were carried out in one field following surface applications of nitrate and bromide tracers and in two fields after only bromide was applied. Soil water samples were collected from porous cups at 30,60 and 90cm depth after every 25 mm of drainage, and soil samples from 0–30, 30–60 and 60–90 cm were collected monthly eachwinter. Soil matric suctions andvolumetric moisture content were measured in one winter. Leaching losses, measured with ceramic cups were compared with those measured by soil analysis. Porous cups installed in chalk at 60 and 90 cm depth were only able to collect samples regularly when soil matric suctions were less than 15 kPa. Water held at such low suctions is likely to move quickly through relatively large fissures in the chalk. The slow rate of equilibration between solute concentrations in water moving in macrofissures and those in water moving through micropores of the chalk matrix, means that porous cups may not provide good estimates of leaching losses if they are installed in chalk rock. 相似文献
3.
土体冻结过程中基质势与水分迁移及冻胀的关系 总被引：2，自引：0，他引：2
土体冻结过程中不同位置液态水的能量差引起了水分迁移与重分布,进而引发冻胀,关于势能差驱动下的冻土水分迁移问题一直由于技术手段的匮乏而没有完全解决。利用新近推出的可用于冻土水热研究的p F meter基质势传感器与5TM水分传感器,实时监测研究饱和青藏红黏土单向冻结过程中基质势-液态含水率-温度-含冰量-水分迁移量-冻胀变形之间在时间、空间上的耦合变化关系。结果表明:土体温度场变化引起内部液态水相变,打破了原有的能量平衡,试验结束后12~14 cm土样高处含水率最高达到55%,靠近冻融交界面处(10 cm)的未冻区含水率减小至25.8%,水分整体向冷端发生迁移;土体冻胀的快慢及冻胀量大小与水分迁移速率及数量具有线性关系;试验后土体内总含水率的分布与分凝冰透镜体的分布一致,已冻区液态含水率的分布与温度梯度近似成线性关系,未冻区液态含水率的分布与水分的迁移量有关,与温度梯度无关。此外,温度场对水分场的变化具有诱导作用但二者并不同步,当冻结速率减小到一定程度时水分才开始迁移,第10小时后温度场趋于稳定而水分迁移并未停止。研究成果揭示了土体单向冻结过程中液态水、基质势、温度等物理参数的动态变化过程及内在联系,为冻胀机制的研究以及冻胀模型的建立提供了试验基础。 相似文献
4.
轻质土壤水分特征曲线估计的简便方法 总被引：5，自引：0，他引：5
以黄淮海平原封丘地区的潮土和风沙土为研究对象,根据大量的土壤基本物理性质和土壤持水数据,利用多元逐步回归分析方法,建立了轻质土壤在不同基质势下土壤含水量(θ)的传递函数模型,并进行了模型验证。结果表明,利用轻质土壤的基本物理性质估计其水分特征曲线是一种简便可行的方法,并且,在回归方程中,增加-30kPa含水量项可提高-30kPa以上土壤含水量的估计精度;增加-1500kPa含水量项可以明显提高-100kPa至-1500kPa间土壤含水量的估计精度。 相似文献
5.
6.
P. Ilnicki 《植物养料与土壤学杂志》1982,145(4):363-374
Soil water hysteresis in organic soils In 20 undisturbed samples of peat, muck, peaty soil and humic sand, the hysteresis of the moisture characteristic by soil suction from 0 to –9,8 kPa and from 0 to –29,4 kPa was measured. The greatest hysteresis was found in peat. Suction values from –1 to –3 kPa caused differences of 0,076 cm3/cm3 in water content during drying and wetting. In muck with low ash content and in humic sand the hysteresis was smaller. In peaty soil and muck with high ash content (> 40 %) it diminished to twice or three times lower values in comparison with those in peat. In organic soils the hysteresis decreases clearly by soil suction higher than –6 kPa. Repetition of drying and wetting gave a diminution (ca. 30 %) of the hysteresis loop in peat and displaces it towards the field of lower water content. The hysteresis of muck did not change considerably. The change of the porosity structure (pore ϕ > 30 μm) during the repetition of drying and wetting indicate that some soil shrinkage has occured. 相似文献
7.
The question of whether the response of earthworms to soil moisture is governed by their reaction to soil wetness (moisture content) or to soil water energy (matric suction) was examined in two species of earthworm using moisture gradients in three contrasting soil types with clay contents varying from 4 to 39%. Gravimetric moisture gradients ranging over 5–30% were established in horizontal cores comprising 12 or 14 sections containing loosely packed soil. Earthworms were introduced to each section at the beginning of each experiment. The earthworms moved from sections containing dry soil into adjacent sections containing moister soil. Clear effects were evident after 6 h but these became more obvious after 96 h. For the earthworm Aporrectodea rosea, the threshold soil mositure level at which earthworms were induced to move away from dry soil was a matric suction of about 300 kPa (pF 3.4) and was independent of soil type. In contrast, for A. trapezoides, the threshold soil moisture varied with soil type (sandy loam 15 kPa, loam 25 kPa, clay 300 kPa). We conclude that, for the earthworm A. rosea, matric suction and not water content of soil provided the cue by which the earthworm recognized dry soil. For A. trapezoides, there was an interaction between matric suction and soil type in which the response of A. trapezoides to soil moisture varied with soil texture and the threshold for avoidance of dry soil ranged from a matric suction of 300 kPa (20% w/w) in clay to 15 kPa (10% w/w) in sandy loam. 相似文献
8.
Determination of hydraulic parameters to estimate water movement and water storage in undisturbed soil. A comparison of field and laboratory methods. The soil moisture characteristics and the unsaturated conductivity were measured under field and laboratory conditions. In an undisturbed soil monolith in continous connection with the underlying loess-soil-layer 60 tensiometer and a neutronprobe-accestube were used respectively to determine the matric potential and water content changes during a transient drainage experiment. Within the matric potential range of 0 to approximately ?50 to ?100 mbar the soil moisture characteristics determined in the laboratory and in the field are substantially different. When the matric potential is more negative than ?100 mbar the slope of these curves and hence the specific moisture capacities are relatively well comparable. The field-measured conductivity functions differ considerably from those values which were either measured under lab-conditions or computed from the soil moisture characteristics data. The conductivities are expressed as a function of the matric potential which is possibly the major reason for these remarkable differences. However, the changes in water content in this dense silty clay loam are too small to express the unsaturated conductivity as a function of the absolute water content. The most serious problems in extrapolating the results of the less time consuming laborcalculation methods to field conditions arise in that range of matric potentials where water movement is significant. 相似文献
9.
Evaluation of similar-media scaling and a one-parameter model for estimating the soil water characteristic 总被引：2，自引：0，他引：2
Two simple methods for estimating the soil water characteristic curve from saturated soil water content, or even just the soil bulk density, plus one other measured point on the curve (such as the water content at a matric potential of –33 kPa) were evaluated. A similar-media scaling approach and the one-parameter model of Gregson et al. were compared for eight diverse soils from within the USA. The scaling method also requires knowledge of one complete curve to serve as a reference. The one-parameter model was extended to include the residual water content, and the soils were divided into three textural groups for the analysis. Visual comparison of the calculated vs. measured soil water content for both methods showed less scatter in the relationship to the 1:1 line, concomitant with smaller calculated error terms, for the one-parameter model. These results demonstrate that the one-parameter model is better than similar-media scaling in estimating soil water content. 相似文献
10.
为优化土壤水分传感器的埋设位置,该文针对宁夏日光温室滴灌黄瓜田间的土壤水分传感器埋设位置进行优化试验,确定出最佳埋设深度和宽度。利用最小二乘法对澳大利亚生产的MP406土壤水分传感器进行标定,得到水分利用效率的拟合值与实测值的相关性系数为0.9906。设计了多路数据自动采集监测与灌溉系统,可同时获取不同处理的18个水分传感器数据,通过远程客户端实时下载和监控水分数据并实现自动灌溉,通过远程手机短信监控功能,进行手机短信命令控制一个或多个处理的实时灌溉,系统可同时测量不同处理的灌水量。计算水分利用效率和产量,分析传感器水分数据的差异和相关系数,确定出土壤水分传感器在宁夏日光温室滴灌黄瓜田间的最佳埋设深度和宽度位置,该研究方法为确定土壤水分传感器的埋设深度及宽度提供可行的参考方案。 相似文献
11.
In saline soils under semi-arid climate, low matric and osmotic potential are the main stressors for microbes. But little is known about the impact of water potential (sum of matric and osmotic potential) and substrate composition on microbial activity and biomass in field collected saline soils. Three sandy loam soils with electrical conductivity of the saturated soil extract (ECe) 3.8, 11 and 21 dS m?1 (hereafter referred to EC3.8, EC11 and EC21) were kept at optimal water content for 14 days. After this pre-incubation, the soils were either left at optimal water content or dried to achieve water potentials of ?2.33, ?2.82, ?3.04 and ?4.04 MPa. Then, the soils were amended with 20 g?kg?1 pea or wheat residue to increase nutrient supply. Carbon dioxide emission was measured over 14 days; microbial biomass C was measured at the end of the experiment. Cumulative respiration decreased with decreasing water potential and was significantly (P?<?0.05) lower in soils at water potential ?4 MPa than in soils at optimal water content. The effect of residue type on the response of cumulative respiration was inconsistent; with residue type having no effect in the saline soils (EC11 and EC21) whereas in the non-saline soil (EC3.8), the decrease in respiration with decreasing water potential was less with wheat than with pea residue. At a given water potential, the absolute and relative (in percentage of optimal water content) cumulative respiration was lower in the saline soils than in the non-saline soil. This can be explained by the lower osmotic potential and the smaller microbial biomass in the saline soils. However, even at a similar osmotic potential, cumulative respiration was higher in the non-saline soil. It can be concluded that high salt concentrations in the soil solution strongly reduce microbial activity even if the water content is relatively high. The stronger relative decrease in microbial activity in the saline soils at a given osmotic potential compared to the non-saline soil suggests that the small biomass in saline soils is less able to tolerate low osmotic potential. Hence, drying of soil will have a stronger negative effect on microbial activity in saline than in non-saline soils. 相似文献
12.
研究了滴灌灌溉频率和土壤水势对马铃薯生长和水分利用效率的影响。研究结果表明，滴灌灌溉频率和土壤水势对土壤水分的分布有很大影响，灌水频率越低，灌水前的表层土壤干燥的范围越大，灌水后的土壤湿润范围越大；控制滴头下面20 cm处土壤水势明显影响到50 cm深度以上的土壤水势，20 cm深度处土壤水势越高，50 cm深度范围内的平均土壤水势越高；土壤表面土壤水势越低，以滴头为中心形成的干燥范围越大。当土壤基质势低于-45 kPa时，马铃薯的块茎膨大率会迅速下降，总产量、商品薯产量和水分利用效率高低顺序为：-25 kPa>-35 kPa>-15 kPa>-45 kPa>-55 kPa。不同灌溉频率下马铃薯的总产量、商品薯产量和水分利用效率的高低顺序为：1天1次>2天1次>3天1次>4天1次>6天1次>8天1次。就华北地区而言，采用滴灌对马铃薯进行灌溉，土壤基质势以-25 kPa左右为好，灌水频率以每天1次最优。 相似文献
13.
用毛细吸渗原理快速测量土壤田间持水量的研究 总被引：18，自引：8，他引：18
田间持水量是衡量田间土壤保持水分能力的重要指标，视为对作物有效的土壤水分的上限，对农田灌溉和作物水分管理具有十分重要意义。该研究提出了能快速测量土壤田间持水量的新型毛细吸渗法。该方法以田间持水量为无地下水影响下土壤基质所能吸持的最大含水量为物理基础，设计了一套满足田间持水量要求的实验方法、装置和程序，采用5种不同土壤测量了其田间持水量，并与用威尔科克斯法测量得到的田间持水量进行了对比。结果表明：所提出的新型测量方法，无论是基本原理还是室内试验均可行。与威尔科克斯法相比，其测量值略微偏小；两种测量值相关性很好，相差约为9％，产生这种现象的原因主要是土壤的吸湿过程与脱湿过程中土壤含水率的滞后所致。与传统的测量方法相比，该方法可大大缩短测量时间，具有利用前景。 相似文献
14.
利用基于轴平移技术的Geo-Expert高级型应力相关土-水特征曲线压力板仪研究不同覆土压力(0、40、100、200 k Pa)对南阳膨胀土土水特征曲线(soil-water characteristic curve,SWCC)的影响;并对提出的考虑土体变形及多孔隙分布形态的双应力变量广义SWCC表征方程进行如下试验验证:1)不同覆土压力下微多孔隙分布形态的南阳膨胀土侧限固结试验及脱湿试验SWCC验证;2)零净法向应力状态双孔隙尺度硅藻土双峰SWCC试验验证;3)不同净围压状态下单孔隙尺度韩国残积土SWCC试验验证;4)多应力路径下法国Bapaume黄土,不同初始干密度下日本Edosaki砂土在脱湿-吸湿过程SWCC试验验证;并比较分析新方程与van Genuchten方程及Fredlund等方程的差异性。结果表明:1)覆土压力会显著改变膨胀土结构及孔隙通道,进而改变SWCC边界效应区、过渡区形态;也改变了双重孔隙尺度土壤的进气值;第1个波峰SWCC进气值均在1 k Pa左右;相比于零覆土压力试样,40、100、200 k Pa覆土压力试样第2个波峰SWCC进气值分别高4.74、17.58、67.23 k Pa;2)未考虑净法向应力影响的单应力状态多峰SWCC、考虑侧限双应力状态多峰SWCC、各向同性净法向应力单峰SWCC、不同脱湿-吸湿路径SWCC及不同初始干密度的SWCC试验拟合曲线均表明,双应力广义SWCC具有包容复杂影响因素的能力;3)新方程能够利用至少3个土-水数据即可拟合出具有较高的精度的整条SWCC。研究为定量描述土壤的持水、渗透及强度特性提供参考。 相似文献
15.
Modeling and correction of soil penetration resistance for varying soil water content 总被引：1，自引：0，他引：1
For this study penetration resistance (PR) was measured within the profiles of four Oxisols for a wide range of water contents (θ) and bulk densities. Obtained data were utilized to parameterize 23 previously applied regression models. The most promising models were selected to illustrate effects of soil texture on PR. Finally, a new correction method based on normalization of PR with θ corresponding to a matric potential of − 10 kPa was introduced. Evaluation of texture effects revealed that for very wet soils PR was lowest, but increased with clay content. PR at − 1500 kPa exhibited a maximum at clay content of 35% and at − 10 kPa PR was least affected by texture. From all regression models three- and two-parametric exponential and power functions yielded closest matches to measured data. The proposed correction significantly dampened the influence of θ on PR, which allows better comparison for a specific soil or among different soils. 相似文献
16.
Jrg Bachmann 《植物养料与土壤学杂志》1998,161(2):147-155
Measurement and simulation of nonisothermal moisture movement in water-repellent mineral soils Water repellency often occurs in surface soil horizons, where the temperature may have a significant effect on water movement. Relatively few studies have been conducted to measure the effect of temperature gradients on hydraulic processes in water-repellent soils. The objective of this paper is to analyze the simultaneous impact of hydraulic and thermal gradients on water movement in unsaturated soils. Four sandy soils with organic matter contents between 1.0 and 2.4 percent were used in a laboratory column experiment. The soils had similar particle size distribution and contact angles between 25 and 111 degrees. The water repellency was measured with the “sessile drop method”. The experiments were conducted with open laboratory soil columns. A ceramic plate was placed at the upper end of the soil column to allow water movement from a reservoir, the lower end was closed. The matric potential of ?175 hPa at the upper part of the column was held constant. Simultaneously a constant temperature gradient of approximatly 1.1 °C/cm was applied during the nonisothermal runs. Hydraulic properties of the four soils were determined sequentially at different temperatures (5, 20 and 38°C). The time dependent volumetric water content, matric potential and temperature were measured at five positions in the column. It was found that after steady state was established the water content and matric potential profiles of the four soils differed considerably. A computer code based on the theory of Philip and De Vries (1957) was developed to simulate water and heat transport. For three soils with contact angles of 25–35, 93–108 and 109–111 degrees, respectively, the model performed well when the theoretically calculated thermal vapor difivisivity, DTV, was multiplied by a factor between two and three. For the slightly water repellent soil with a contact angle between 45 and 83 degrees, however, this factor was about seven to eight. This factor could be the result of a combined impact of the moderate water repellency and the micromorphology of the humic substance. 相似文献
17.
基于近邻传播算法的茶园土壤墒情传感器布局优化 总被引：1，自引：0，他引：1
针对节水灌溉的土壤墒情传感器布局问题,提出了基于近邻传播算法(affinity propagation,AP聚类算法)的优化布局策略。策略在保证茶园传感网络全覆盖的基础上,实时采集试验区各节点的土壤墒情数据,构建节点土壤含水率的相似度矩阵,并迭代计算各节点的吸引度和归属度值,得出聚类数和聚类中心。结果表明,采用AP聚类算法对试验区域传感器进行优化布局,优化了传感器数量和位置,使传感器数量由25个减少到2个。在试验区随机采集土壤相对含水率,经验证,聚类中心节点的土壤相对含水率与试验区平均值相近,相对偏差近为0.76%,表明聚类中心节点的土壤墒情数据具有代表性。该方法有效降低了数据的冗余度,节约了系统成本。 相似文献
18.
干旱区盐碱地滴灌土壤基质势对土壤盐分分布的影 总被引：2，自引：3，他引：2
该文通过田间试验研究覆膜滴灌条件下土壤基质势对土壤盐分分布的影响.试验设3个水平的土壤基质势处理:-5 kPa(S1),-15 kPa(S2)和-25 kPa(S3),每个处理重复3次,按随机区组布置.试验结果表明:垄作覆膜滴灌条件下各盐分离子的迁移和分布特性不同.Na< 和Cl-.易被灌溉水淋洗,主要分布在湿润体的边缘,在滴头附近含量最低,远离滴头含量逐渐增大,土壤基质势越高,淋洗效果越明显,离子含量和土壤总盐量呈线性相关.Mg2 、Ca2 、HCO3含量受土壤基质势影响较小,在土壤剖面分布相对均匀,离了含量和土壤总盐量之间没有明显相关关系.盐渍化土壤中总盐分的淋洗主要受到作物播种时第一次大水量灌溉和苗期阶段较高土壤基质势控制的灌溉影响,作物生育中后期不同土壤基质势处理对土壤总盐分的淋洗影响较小.该研究结果对盐碱地水盐调控和灌溉制度的制定具有理论意义和应用价值. 相似文献
19.
Equations to compensate for the temperature effect on readings from dielectric Decagon MPS‐2 and MPS‐6 water potential sensors in soils
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下载免费PDF全文 Dielectric sensors use electrical permittivity as a proxy for water content. They determine permittivity by using sensor‐type‐specific techniques and calibration functions, and relate it to a volumetric water content. Water potential sensors then translate the water content into a potential based on the sensor‐specific moisture characteristic curve. Dielectric readings are affected by temperature, which may distort hydraulically‐induced changes in soil water content. Methods for the removal of spurious temperature effects are lacking for dielectric water potential sensors. With this study, we aimed to fill this knowledge gap for the dielectric Decagon MPS‐2 and MPS‐6 water potential sensors. We first determined the temperature effect on MPS readings with laboratory experiments in which temperature was cycled between 4 and 26°C in different soil types. We then fitted single empirical equations that compensated for the temperature effect on MPS readings. Finally, we validated temperature‐compensated MPS soil water potentials, and therefore the equations, in a multi‐year field study in two forest soils where hourly data from three sensor models were available, i.e., from MPS‐2, MPS‐6, and a heat capacity sensor (ecoTech pF‐Meter) that is not sensitive to temperature effects. The temperature fluctuation experiments showed that the strongest temperature effects on MPS readings occur under dry conditions and that the MPS sensors themselves are largely responsible for these effects. Likewise, the field‐based validation showed that the MPS readings were highly affected by temperature under dry conditions. Applying a temperature compensation to these readings, using the equations from the temperature fluctuation experiments, resulted in strong correlations near the 1:1 line between data from the MPS and pF‐Meter sensors. Therefore, we recommend using the equations to remove spurious temperature effects from MPS‐2 and MPS‐6 readings in non‐saline soils with water potentials between –100 and –2000 kPa (at 22°C) and temperatures between 4 and 26°C. 相似文献
20.
《Communications in Soil Science and Plant Analysis》2012,43(3-4):377-388
Abstract Porous plates or cups are commonly used to collect soil solution samples in field studies or from intact soil columns. Some commonly used materials for porous plates may adsorb soil solution constituents such as phosphorus (P). An alternative to using a porous plate is to use a membrane filter with a known pore size and bubble point. The objective of this study was to evaluate the utility of polyethersulfone membranes (pore size 0.45 µm and bubble point >200 kPa) to extract soil solution from in situ soils and intact soil columns for phosphate analysis. In situ soil solution samplers were constructed from modified reusable polysulfone membrane filter holders equipped with polyethersulfone membranes (47 mm diameter). A ?10 kPa vacuum was maintained in the samplers, which enabled soil solution collection at soil water potentials of 0 to ?4 kPa in loamy sand, 0 to ?10 kPa in sandy loam, and 0 to ?12 kPa in sandy clay loam soils. In a laboratory study, soil solution samplers continued to hold a vacuum to ?77 kPa soil water potential. Soil solution samplers were further evaluated in a field study at 45‐, 90‐, and 135‐cm depths in two soils. Samplers operated with relatively few difficulties for the first 12 months of field evaluation. Membranes apparently dried during periods of low soil water potential but increases in soil moisture were sufficient to rewet the membrane. Sampler failures in the field increased during 13–18 months because aged vacuum tubing and root interferences with samplers at 45 cm. Improvements in sampler design may improve the durability for implementation in long‐term field experiments. Membrane filters worked near flawlessly to maintain unsaturated conditions in intact soil columns. The filter units facilitated easy collection of soil water from the intact soil columns without altering the chemical composition of the percolate. 相似文献