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1.
Daily matrix flow at 1-m depth in a volcanic ash soil was calculated during a period of one year using Darcy's law. Unsaturated hydraulic conductivity of undisturbed core samples could be expressed as a unique function of the soil water content. Hydraulic gradient obtained from soil water suction by a tensiometer installed at 90- and 110-cm depths, and hydraulic conductivity converted from the soil water content by time domain reflectometry (TDR) were monitored every 30 min throughout a year in a maize (Zea mays L.) Chinese cabbage (Brassica pekinensis Rupr.) field. The matrix flow obtained by this method was substituted for the water balance equation to estimate the bypass flow, and monthly and annual evapotranspiration. Annual rainfall in 1997 was 989 mm and evapotranspiration was estimated to be 730 mm. Net matrix flow at 1-m depth was 164 mm downward even though upward matrix flow occurred during half of the year. Downward flow determined by the water balance method exceeded the downward matrix flow during two heavy rain events in the year and the difference between the two flows was 63 mm, which was considered to correspond to a bypass flow. The bypass flow accounted for only 6.4% of the annual rainfall. Matrix flow was well monitored by the application of unsaturated Darcy's law in a field, and monthly evapotranspiration and bypass flow could be quantified by the introduction of the water balance equation. 相似文献
2.
Effects of agricultural practices on hydraulic properties and water movement in soils in Brittany (France) 总被引：2，自引：0，他引：2
Babacar Ndiaye Jrme Molnat Vincent Hallaire Chantal Gascuel Yannick Hamon 《Soil & Tillage Research》2007,93(2):251-263
The intensive agricultural use of soils in the Brittany region (western France) has increased the need for a better understanding of soil water dynamics. The aim of the present study is to compare quantitatively the differences produced by two agricultural practices on soil hydraulic properties (water retention curve and hydraulic conductivity) as well as the infiltration and drainage fluxes in the soils. This study was carried out on two experimental plots managed in the same way for 22 years. The two practices were continuous maize fertilized with mineral fertilizer, denoted as MX, and pasture within a ray-grass/maize rotation (3/1 year) with organic fertilization (pig slurry), denoted as PR. The study consisted of measuring soil physical properties in the laboratory and in the field, and estimating water infiltration in the soil of the two plots by recording water pressure heads after simulation of 2-h artificial rainfall with an intensity of 17 mm/h. We applied the van Genuchten model to describe the water retention and hydraulic conductivity curves (θ(h) and K(h)) for each soil horizon of the two plots. Hydrus-2D and ID softwares were used to construct a numerical model of water movement in the two soils. This model was used to quantify the infiltration rate, deep drainage and actual evaporation fluxes during the artificial rainfall experiment.The vertical influence of agricultural practices in both plots appears to be limited to the uppermost 35 cm. Deeper in the B horizon, there are only very slight differences in the hydraulic properties between the two plots. In the top soil horizons (H1–H5 and H6), the two soil properties mostly affected by practices are the hydraulic conductivity and the α parameter of the van Genuchten model. At the lowest pressure head studied here (−1.5 kPa), hydraulic conductivity in a given horizon differs by more than one order of magnitude between the two plots. The model reproduces quite satisfactorily the observed pressure heads in plot PR at all depths, in the rainy period as well as in the water redistribution period (efficiency >0.77). Results are less good for the MX plot, with efficiency ranging from 0.49 to 0.84 depending on the horizon. The different sources of simulation errors are identified and discussed. For the MX plot, the soil water movement model succeeds in reproducing the infiltration excess runoff observed in the field, allowing us to calculate that it accounts for 9% of the applied rainfall. No surface runoff or ponding appears in the PR plot during the artificial rainfall experiment. In the PR plot, the simulated deep drainage flux increases more rapidly than in the MX plot. The lower hydraulic conductivity in the top soil horizon of the MX plot compared with the PR plot appears to reduce the infiltration rate as well as the deep drainage flux. It also decreases the upward flow of water to the soil surface when the water content in the top soil layer is depleted by evaporation flux. The model simulation could be improved by a more precise representation of the soil structure, particularly the location, size and frequency of clods as well as the variability of hydraulic properties. However, we need to strike a balance between improving the quality of the simulation even further and the practical constraints and efforts involved in measuring the soil hydraulic properties. 相似文献
3.
The hydrologic regimes of arable chernozems were simulated for two plots located within a watershed. For the last fifty years continuous corn monoculture was practiced in one plot, and permanent bare fallow was practiced in the other plot. Carbonates are detected from a depth of 140–160 cm under corn and from 70–80 cm under bare fallow. The objective of the simulation study was to test the validity of the hypothesis that the shallower depth to carbonates under bare fallow is related to carbonate rise due to changes in the hydrologic regime of bare soil compared to soil under vegetation. Mathematical modeling using the HYDRUS-1D software and the FAO56 method confirmed that the hydrologic regimes of arable chernozems within the two plots are different. The soil water content under bare fallow is generally higher than that under corn. The downward soil water fluxes for the two plots are comparable. The upward soil water fluxes under bare fallow significantly exceed those under corn and affect a thicker soil layer. The changes in the hydrologic regimes of chernozems under bare fallow favor the upward movement of carbonates through both the direct transfer by upward water fluxes and the diffusion of ions. 相似文献
4.
土壤饱和导水率是计算土壤剖面水通量以及设计灌溉和排水系统的重要参数,其测量准确与否直接影响各类水文和水动力学模型的预测精度。然而,现有土壤饱和导水率测定方法费时费力,给土壤水动力学研究工作带来了诸多不便。为此,该研究提出了一种基于线性源入流法与手机图像处理相结合的土壤饱和导水率快速测量方法。该方法首先利用手机拍照获取图像记录充分供水条件下线性水流在土壤表面扩散的过程,图像经处理后计算出土壤表面湿润面积及其随时间的变化关系,然后根据线性源入流法估算的土壤稳态入渗率来测得土壤饱和导水率,并与传统的定水头标准法测得的饱和导水率进行对比。结果表明：图像经畸变校正与二值化处理之后计算出栓皮栎林区土壤、油松林区土壤和砂壤土表面湿润面积与时间具有较好的幂指数关系,决定系数R2分别为0.994、0.995和0.998;在此基础上,采用线性源入流法测量栓皮栎林区土壤、油松林区土壤和砂壤土的稳态入渗率（即土壤饱和导水率）分别为23.40±1.21、23.86±1.83和22.99±2.26 mm/h,同时使用定水头标准法测量三种土样得到的饱和导水率分别为24.41±1.53、24.26±0.37和23.81±0.10 mm/h,与定水头标准法相比,该研究提出的土壤饱和导水率测量方法的相对误差分别为4.14%、1.64%和3.42%。可见,该研究提出的测定方法较为合理、简便、准确,可为获取土壤饱和导水率提供一种新的测量手段,后续研究会将该方法用于野外环境下土壤饱和导水率的原位测定,并验证该方法的准确性。 相似文献
5.
《Soil Use and Management》2018,34(3):370-379
The unsaturated soil hydraulic conductivity accounting for film flow is important for understanding soil hydrological and biological processes, especially in arid and semi‐arid regions. Recently, a theoretically based hydraulic conductivity model was developed to describe the hydraulic conductivity as a function of water content. We have used this model to compare seven soil water retention functions commonly used for predicting soil hydraulic conductivity due to film flow. A total of 30 soils, varying in basic properties, were selected from the Unsaturated Soil Hydraulic Database to evaluate the seven functions. The Webb method was applied to identify the critical soil matric potential (h c) below which thin film flow controls water movement. Soil hydraulic conductivity measurements at matric potential below h c were then used for curve fitting according to the seven functions. Slight differences were observed among the functions in predicting soil hydraulic conductivity due to film flow. Six of the seven functions in combination with the hydraulic conductivity model described the hydraulic conductivity due to film flow well, according to the terms of the coefficient of efficiency. The relatively poor performance of the one exception was due to the fact that the linear shape of the function made it less flexible at low matric potentials. In addition, the effect of textural class on its performance was substantial, showing a poorer fit for the sand soil compared with the loam and clay soils. These findings have important applications related to soil and water resources conservation especially in arid and semi‐arid regions. 相似文献
6.
Hydraulic properties of a Walla Walla silt loam were significantly changed by 50 years or more of cultivation under either a wheat-peas rotation (tillage depth 30 cm) or a wheat-summerfallow rotation (tillage depth 15 cm) as compared with no cultivation. Soil pH was reduced to depths as great as 60 cm in the cultivated sites; dry bulk density was increased to depths as great as 40 cm. Expressions of these changes were greater in the wheat-peas rotation because tillage was deeper than in the wheat-summerfallow rotation. Small reductions in soil organic matter were also noted in the cultivated sites. In the 60- to 90-cm depth, all three sites had similar bulk density, pH, cation exchange capacity, soil texture, desorption water characteristic, and hydraulic conductivity. In the upper 40-cm layer the desorption water characteristic showed that cultivation produced more smaller pores at the expense of large pores; in the upper 30-cm layer of the cultivated soils hydraulic conductivity was reduced at least 10-fold for water potentials > −100 cm of H2O. Steady-state drainage profiles and associated assumptions suggest that long-term cultivation increased the hydraulic gradient in the upper 35 cm, and that the low saturated conductivity of the 0- to 15-cm layer had an overall drying effect on the 15- to 35-cm layer. In the cultivated soils increased runoff and denitrification in the plow layer should both be expected and water relations in the 15- to 35-cm layer should favor microorganisms sensitive to high water potentials. Simulations suggested that long-term cultivation decreased evaporation rates an estimated 40% and in wet soil, increased the drying time needed to attain optimum moisture for tillage. 相似文献
7.
Abstract. This study investigated the effect of the same volume of leaching water applied consecutively in either equal amounts or increasing amounts or decreasing amounts on the hydraulic conductivity of a saline sodic soil in 30 cm plastic columns in the laboratory. Gypsum was mixed with the surface 2–3 cm of soil. After leaching, the hydraulic conductivity was measured in each 10 cm depth of soil. Hydraulic conductivity decreased strongly ( P <0.05) with depth and the most effective method of applying the water was in gradually increasing amounts. 相似文献
8.
本文用一组张力计和中子水分计同步监测的剖面土水势和含水量的资料,通过零通量面法计算根层边界的水分通量;在剖面没有零通量面出现时,则用根层边界附近的土水势资料和预先测定的土壤导水率资料,通过达西公式计算其水流通量。结果表明,在水位较浅条件下,根层边界不仅有向上水流发生,而且在附近抽水灌溉引起水位急剧下降条件下,也有短期的向下水流发生,使深层土壤水分流出根层边界,对根系供水产生负的影响。 相似文献
9.
入渗水水质对土壤导水特性影响的试验研究 总被引：4，自引：2，他引：2
为探究不同入渗水水质对土壤导水特性的影响,采用圆盘负压入渗法进行试验研究,选取两种水质(蒸馏水和自来水)对黄壤和红壤进行4个压力水头(0,-3,-6,-9cm)下的圆盘入渗试验。结果表明,随着入渗水电导率的增大,土壤入渗率、吸渗率及导水率均随之增大,且红壤在不同电导率的入渗水作用下土壤吸渗率的变化差异显著(P0.05)。在低水头压力下,两种水质入渗条件下测得的土壤导水率差异显著(P0.05);在高水头压力下,两种水质入渗下测得土壤导水率差异不显著,表明入渗水水质对土壤导水率的影响主要发生在低压力水头下即在细孔隙下的导水特性上。两种土壤的大孔隙与中等孔隙对水流贡献率随入渗水电导率的增大而增大,而小孔隙对水流贡献率随入渗水电导率的增大而减小,入渗水水质对红壤土不同级别孔隙水流贡献率的影响显著(P0.05)。研究分析相关参数的变化有利于探讨野外试验时入渗水水质对试验结果的影响,对于正确认识农田水文过程、开发利用劣质水资源、提高农业灌溉灌水质量和灌水效率等具有重要意义。 相似文献
10.
《Soil & Tillage Research》1987,9(1):65-77
Field experiments were conducted on a silty clay loam soil during 1980–1981 and 1981–1982 to study the effect of different soil management practices, such as zero cultivation (ZC), conventional cultivation (CC), CC + surface-applied pine needle mulch at a rate of 10 t ha−1 (CC + M), deep ploughing (DP) and inter-row compaction (IRC), on the soil hydro-thermal regime and root growth of wheat (Triticum aestivum L.). The soil of the experimental site is classified as Alfisol, Typic Hapludalf in which compact sub-surface layers are encountered. In the CC + M treatment, the soil water potential in the sub-surface layers remained higher in comparison to other treatments. In the DP treatment, the decrease in soil water potential was observed to greater depths in comparison to the remaining treatments. The soil water flux at 60-cm depth, calculated during 150–173 days of crop growth, was always upward in the CC + M treatment, at a rate varying from 0.2 to 1.16 cm day−1. In the other treatments, the flux at this depth was first downward then it became upward. The upward flux was highest under the DP treatment, followed by CC and CC + M and least under IRC and ZC treatments. The minimum temperature under CC + M treatment at 10-cm depth was raised by 4°C over the temperature under CC treatment (5°C). The rooting density and length in the CC + M treatment were the highest, followed by DP treatment, in comparison to the remaining treatments. 相似文献
11.
Soil water evaporation, redistribution of surface applied salts and unsaturated hydraulic conductivity were determined in field plots of a silt loam soil kept either untilled or tilled to a depth of 5 cm 2–3 days following irrigation. The hydraulic gradients measured were comparatively steeper and the zone of zero flux during drying occurred at greater depths in untilled than tilled soil. Tillage induced soil mulch reduced evaporation losses; its effectiveness, however, decreased during high external evaporative demand conditions. Some empirical relations to determine evaporation utilizing more easily accesible parameters, such as surface soil water content or suction and U.S. open-pan evaporation, were established for predictive purposes. Due to reduction in upward movement of water, shallow tillage resulted in decrease in upward movement of salts and thus, increased the efficiency of leaching during intermittent ponding. The empirical relationship describing the leaching process showed a net saving of 12.7% in water required to attain 70% removal of surface accumulated salts. Increase in unsaturated hydraulic conductivity of soil due to salinization was also observed. 相似文献
12.
灌溉方式对土壤水分运动参数的影响 总被引：1，自引：0，他引：1
通过实测和拟合的方法研究了不同灌溉方式对土壤饱和导水率及非饱和土壤水分运动参数的影响。结果表明:膜下滴灌明显改善了土壤导水性能,0-10 cm各土层土壤饱和导水率明显高于地面漫灌,并且两种灌溉方式下土壤饱和导水率都高于裸盐地;不同灌溉方式下,相同含水率所对应的非饱和导水率及非饱和扩散率均不同,0-100 cm各土层都表现为膜下滴灌>地面漫灌>裸盐地。膜下滴灌对土壤水分运动参数的影响,并不是由土壤质地、容重、温度、盐分等因素作用而引起,可能是由于膜下滴灌改变了土壤的团粒结构或土壤中盐分的离子组成而造成的。 相似文献
13.
小碎石与细土混合介质的导水特性 总被引：3，自引：1，他引：3
含碎石土壤的导水性质研究有利于这种多孔介质水分运动的模拟。本文采用室内定水头法和离心机法分别测定两种质地土壤(壤土、黏壤土)和三种岩性小粒径(2~10 mm)碎石构成的土石混合介质的饱和导水率和水分特征曲线,采用van Genuchten-Mualem模型计算各土石介质的非饱和导水率,分析碎石对土壤导水能力的影响。试验结果显示,风化程度低的碎石对黏壤土具有明显的增大饱和导水率的作用,且碎石含量愈高,增加的效果愈明显;而风化程度高的碎石对土壤结构无明显的改善作用,且对黏壤土具有减小饱和导水率的作用。风化程度低碎石介质的非饱和导水率随土壤水吸力的增加呈现了先大于土壤和土石介质的后迅速减小到低于土壤和土石介质的变化过程。风化程度低的河卵石和风化程度高的粉泥页岩碎屑分别构成的土石介质的非饱和导水率较土壤的低,而风化程度中等的片麻状花岗岩碎块构成的土石介质的非饱和导水率较土壤的高。近饱和状态下,碎石含量高的土石介质的非饱和导水率也相应的高,而较大的土壤水吸力下,土石介质的非饱和导水率呈现随碎石含量的增大而减小变化趋势。试验结论可为含碎石土壤水分平衡研究提供参考。 相似文献
14.
Hydraulic characteristics of Basalt saprolites Frequent erosion leads to shallow soils in which underlying saprolites become root space. Until now only few data are available on the water balance and the hydraulic properties of saprolites, therefore saprolites in Basalt and in comparison a ferrallitic soil sediment were investigated in undisturbed samples (steel cylinders, large coated monoliths). Pore size distribution and unsaturated hydraulic conductivity were measured and calculated. Clefting causes a high saturated hydraulic conductivity. Already in the range of pF 1.8 the unsaturated hydraulic conductivity decreases considerably. Despite of large total pore volumes and considerable volumes of moderately adherent water (pF 2.5–4.2) the supply to plants is restricted, depending on the degree of rooting. The drainage of saprolites may often be underestimated, the contribution in water supply to plants is often overrated. 相似文献
15.
The saturated and near‐saturated hydraulic conductivity of soils, ku, is a sensitive indicator of soil structure and a key parameter for solute transport and soil aeration. In this contribution, we present and numerically investigate a double‐disk method to determine ku in the laboratory by steady‐state percolation at different suction steps. Tension infiltration of water takes place at the top of a soil column through a porous disk with a smaller diameter than the soil sample. This leaves part of the soil surface open and ensures a proper soil ventilation. Drainage takes place at the base through a porous disk with the full diameter of the soil column at exactly the same tension as applied to the top boundary. Since the infiltration area is less than the percolation area, the water flow diverges and the equality of steady flow rate and hydraulic conductivity, which characterizes the standard unit‐gradient experiment, is no longer valid. To develop a general relationship between observed steady flow rate and unsaturated hydraulic conductivity, the experiment was simulated with the Richards‐equation solver HYDRUS 2D/3D, for twelve different soil classes. We found for tensions in the range 1 cm < 10 cm, an infiltration disk diameter of 4.5 cm diameter and a sample diameter of 8 cm diameter that the flux rate at any given tension was about 0.7 times the respective hydraulic conductivity, with an error of less than 10%. 相似文献
16.
E.G. YOUNGS 《European Journal of Soil Science》1982,33(1):3-12
Hydraulic conductivity profiles of saturated composite porous columns were obtained in two ways: first, from measurements of the hydraulic potential profiles with uniform vertical flow; and second, by making use of a potential theorem concerning the flow between sources and sinks, from measurements of the hydraulic potential difference between the ponded surface and the base when the flow was intercepted in turn by successive drains located at intervals down the column. Both techniques gave the same results. The hydraulic conductivity profile of a structurally unstable column changed significantly with time, suggesting that such measurements might be used to monitor soil structural changes and root development in lysimeter studies. 相似文献
17.
Sarkar et al. (this issue) proposed a laboratory measurement method for obtaining the hydraulic conductivity of soil at near‐saturated moisture conditions, bridging the gap between measurements that can be obtained with the evaporation method in the medium dry region, and measurements of the saturated conductivity by traditional methods. The method is based on a tension infiltration on a limited part of the surface of a soil sample and drainage of the sample at the same tension, leading to a divergent flow field. Despite equal tensions at top and bottom of the sample (“unit gradient”), the water flux in the sample is smaller than the corresponding value of the soil hydraulic conductivity at the applied tension. From numerical analysis of the flow problem, they concluded that unsaturated conductivity can be obtained with an accuracy of 10% for all texture classes of the USDA soil texture triangle. In this paper, we test the methodology for three different soil types using an appropriate apparatus. The results match well with independent saturated conductivity measurements on the wet side, and with unsaturated conductivity measurements in the medium moisture range that were obtained with the evaporation method. 相似文献
18.
Vegetated buffer zones (BZs) between arable fields and bodies of water are commonly established to reduce erosion and run‐off of particle‐bound nutrients. Functioning of a BZ depends on soil structure, as it is important for water infiltration. Therefore, it is vital to understand how varying management practices affect soils of BZs. We studied the structural and hydraulic properties of three differently managed BZs established in a boreal Vertic Stagnic Cambisol (clay, 51%). The three management practices for vegetation were as follows: natural with no treatment, harvested yearly and grazed by cattle. We used bulk density and macroporosity, together with a pore geometry index (air permeability per unit air‐filled porosity), to describe the soil structural properties. Hydraulic properties were measured at different length scales by means of an aggregate sorptivity test, saturated hydraulic conductivity of the core samples and field‐saturated hydraulic conductivity. Vegetation management markedly affected the physical properties in the top 5 cm of the soil. Properties were least favourable for infiltration at the grazed site, with the greatest bulk density, least macroporosity and hydraulic conductivity or greatest pore tortuosity. In general, spatial variation in zones with restricted and good hydraulic conductivity together with reduced aggregate sorptivity in the deeper horizons made the soil prone to preferential flow when initially dry. Prolonged wetness, on the other hand, reduced saturated hydraulic conductivity significantly, resulting in surface run‐off. Harvesting was considered the best management practice due to its inherent capacity for reducing the soil nutrient content and because it has minor implications for soil physical properties. 相似文献
19.
表层土壤体积质量和导水率是影响土壤入渗及水分运动的重要物理参数。该文采用土壤切片技术和数字图像分析技术,分析了蓄水坑灌条件下入渗水头对砂壤土表层土壤体积质量的影响,进行了不同入渗水头、土壤体积质量对砂壤土表层土壤饱和导水率的试验研究,并对蓄水坑侧向水平入渗湿润锋变化的试验结果与数值模拟结果进行对比分析。结果表明：该研究试验条件下（土壤体积质量为1.345 g/cm3）,入渗水头对土壤体积质量和表层土壤饱和导水率有较明显的影响。随着入渗水头的增大,其作用下的表层土壤体积质量趋于增大,土壤结构趋于密实,表层土壤的饱和导水率趋于减小;表层土壤饱和导水率与入渗水头和土壤体积质量之间呈乘幂关系,且表层土壤饱和导水率对土壤体积质量的变化较为敏感,当土壤体积质量达到某一程度时（1.466 g/cm3）,入渗水头对表层土壤饱和导水率的影响甚微。研究成果揭示了入渗水头影响蓄水坑土壤入渗的微观机制,为进一步研究蓄水坑灌法提供了理论依据。 相似文献
20.
M. J. KOOISTRA R. MIEDEMA J. H. M. WÖSTEN J. VERSLUIS J. BOUMA 《European Journal of Soil Science》1987,38(4):553-563
Computer simulation of the soil water regime was used to calculate moisture deficits for Pleistocene and fluvial Holocene clay soils for a 30-year period. Hydraulic conductivity (K-h) and moisture retention (h-θ) data were derived for major horizons in both soils as well as functions to characterize bypass flow and effects of horizontal planar voids on upward unsaturated flow of water from the water-table to the root zone. Calculated moisture deficits in Holocene soils occurred earlier during the year and were more pronounced during the summer period. Differences between the two soils could be attributed to more pronounced formation of horizontal planar voids in the Holocene soil, which was associated with more pronounced swelling and shrinkage of the undisturbed soil material. The relatively low swelling and shrinkage of the undisturbed Pleistocene soil material was attributed to very dense packing of the elementary soil particles. 相似文献