The implications of spatial variability in surface seal hydraulic resistance for infiltration in a mound and depression microtopography

Soil surface crusting has a major impact on water infiltration and erosion in many soils. Considerable progress has been made in describing crusting processes and in modelling the impact of crusting on infiltration. Most studies, however, have neglected the high spatial variability in crust characteristics observed in the field. The objective of this experiment was to determine the influence of runoff depth on infiltration rate in the presence of a surface seal varying in hydraulic characteristics with microtopography. The Blosseville silt loam has a low aggregate stability and forms crusts readily. The Villamblain silty clay loam has a greater aggregate stability due to its greater clay and organic matter contents, and it is more resistant to aggregate breakdown processes under rainfall. Samples of the soils were sieved to retain aggregates less than 2.0 cm and packed in 50×50×15 cm soil trays. The trays were surrounded by a 10 cm soil border to compensate for splash loss. After molding the surface into a mound and depression microtopography, the samples were subjected to simulated rainfall at an intensity of 22.8 mm h⁻¹. Hourly measurements of surface roughness showed that the original roughness was smoothed out due to the infilling of depressions by sediments detached from the mounds. For the final hour, runon was added to the top of the soil tray to increase the runoff rate and depth. For both soils, infiltration rate increased more than could be attributed to the increased ponding pressure head. The change in infiltration rate was particularly great for Villamblain. The measurements of hydraulic resistance showed that structural crusts had a lower hydraulic resistance than sedimentary crusts. They also showed that the crusts formed on Villamblain were of a lower hydraulic resistance than those of Blosseville. It appears that small changes in runoff depth can significantly increase infiltration rate when structural crusts of lower hydraulic resistance are inundated. The effect was less important in Blosseville which formed seals of relatively high hydraulic resistance everywhere. The results provide a suitable explanation for field observations of increasing infiltration rate with either increasing rainfall intensity or runoff rate. The results also have implications for the relationships between surface roughness, surface water storage, and infiltration.     

入渗水水质对土壤导水特性影响的试验研究

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。     

蓄水坑入渗表层土壤体积质量和饱和导水率的变化

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。     

Estimation and analysis of soil hydraulic properties through infiltration experiments: comparison of BEST and DL fitting methods

The BEST method (Beerkan estimation of soil transfer parameters through infiltration experiments) appears promising and easy to estimate not only saturated hydraulic conductivity but also water retention and hydraulic characteristics. However, few tests have been conducted to test the methodology. This study involved field BEST infiltration experiments for three layers (surface, 15 and 30 cm) for each of three soils with different soil textures under grassland. By comparing BEST with DL (differentiated linearization method), we found that the DL method did not produce a good estimate of the soil hydraulic properties and neither did it identify the transient flow state. The BEST method resulted in reasonable results and is therefore promising. However, with BEST we encountered some anomalies when calculating hydraulic properties in some cases with too few data points under the transient flow state. We show that the application of BEST field experiments requires a wide range of soil water content from initial to saturated states so as to include sufficient transient flow. The soil hydraulic properties determined using the BEST method showed contrasting characteristics between different soil textures with higher saturated hydraulic conductivity under coarse texture and lower values under loam textures, especially with highly compacted soils. Vertical variation in soil hydraulic properties was significant, and the surface layer had a lower saturated hydraulic conductivity partly caused by compaction (high bulk density) or by remnants of grass plants. Further research on the effects of compaction and grass plants on soil hydraulic properties is needed.     

河南省封丘县黄河背河洼地稻区水盐状况及其调控

黄河自河南孟津以下为地上河,沿两岸大堤外侧,形成宽约2-6公里,低于河床4-10米的背河洼地,是历来内涝和土壤盐溃化最为严重的地区,治理也很困难。近年来随着引黄灌溉事业的发展,不少地区种稻利用改良盐渍土,取得了很好的效果,但也有一些地区种稻以后,地下水矿化度虽只有0.5-1克/升,而土壤迅速返盐,稻田周围产生严重的土壤次生盐渍化。     

Measuring near‐saturated hydraulic conductivity of soils by quasi unit‐gradient percolation—1. Theory and numerical analysis

The saturated and near‐saturated hydraulic conductivity of soils, k_u, 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 k_u 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%.     

Effects of agricultural practices on hydraulic properties and water movement in soils in Brittany (France)

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.     

推求土壤水分运动参数的简单入渗法──Ⅱ.实验验证

预报土壤中水分流动需要的土壤导水特性可通过观察水平土柱的入渗过程来确定,这一观测过程的分析是基于对Ｒｉｃｈａｒｄｓ方程求积分解。土壤水分特征曲线中的参数由观测的水平土柱和特征湿润长度和吸力为确定,非饱和土壤导水率由已确定的特征曲线中的参数和测定的饱和导水率导出。供试土壤有三种,它们的质地从砂壤到粘壤。由这种方法所确定的这三种土壤的水分特征曲线与实测的特征曲线符合良好,所确定的砂壤的非饱和导水率与实     

多因素作用下浑水入渗对土壤导水特性的影响

浑水土壤入渗具有复杂的上边界变化过程,其上边界导水能力的变化规律是研究浑水土壤入渗特性的重要基础。为研究浑水入渗形成致密层过程中导水率的变化情况,该研究进行了17组(9组正交试验处理,8组用于模型验证)浑水饱和土柱入渗试验,通过对试验结果进行多元回归构建多因素(浑水含沙率、黏粒含量及入渗时间)影响下砂土导水率动态模型;并结合浑水饱和土柱入渗特性进行合理假设,分别建立浑水砂壤土和粉壤土饱和土柱导水率动态模型并进行验证。结果表明:浑水含沙率、黏粒含量及入渗时间对砂土导水率影响极显著(P<0.01),入渗时间为砂土影响导水率变化的主要因素,其次为含沙率和黏粒含量;建立的砂土导水率动态模型决定系数为0.853,均方根误差为0.004 cm/min,表明该模型可客观反映各因素与导水率之间的关系;模型验证试验结果中均方根误差小于0.01 cm/min,相对误差绝对值均值小于7%,说明该导水率动态模型可靠性较高;砂壤土和粉壤土导水率动态模型决定系数分别为0.912和0.930,均方根误差分别为2×10^-3和5×10^-5 cm/min;模型验证中均方根...     

土壤层状质地对小流量地下滴灌灌水器特性的影响

以均质壤土（L）、均质砂土（S）、上砂下壤（SL）和壤土中有砂土夹层（LSL）4种土壤质地结构为对象,利用室内土箱试验,研究了土壤质地及其层状结构对灌水器流量的影响,估算了灌水器出口正压值。试验选用10 m水头压力下额定流量为1.1 L/h的地下滴灌专用灌水器。土壤为层状结构时,上层土壤厚度为20 cm,砂土夹层的厚度为10 cm。L、S、SL试验的灌水器埋深为15 cm;为了探讨灌水器埋深与土壤质地变化相对位置对灌水器性能的影响,LSL的灌水器埋深设计为15、25和35 cm。试验采用的工作压力为2、3、6和10 m水头。结果表明：灌水开始后,出口正压的迅速增大致使灌水器流量迅速减少,而后逐渐趋于稳定。灌水器流量随时间的变化可近似用幂函数表示。灌水器在土壤中的流量比在空气中的自由出流流量有所减小,灌水器自由出流流量越小,减小幅度越大。土壤层状质地对灌水器流量影响明显,一定压力下,灌水器在层状土壤中的流量小于在均质土壤中的流量,尤其当灌水器位于LSL的砂土夹层中时,流量比在均质壤土中减少13%,比自由出流流量减少20%。利用试验结果建立了地下滴灌灌水器流量与土壤饱和导水率、层状土壤结构、灌水器工作压力的经验关系,对各影响因子的敏感性分析结果表明,对地下滴灌灌水器流量影响最明显的是灌水器工作压力,其次是层状土壤结构,饱和导水率的影响较小。     

层状夹砂土柱室内积水入渗试验及模拟

为了研究夹砂层对入渗强度、湿润锋行进和沿程土壤含水率变化的影响,进行了室内层状夹砂土柱一维薄层积水入渗试验和相应情况下均质土柱的对照试验。结果表明,当湿润锋到达夹砂层上界面后,层状夹砂土柱的入渗过程与均质土入渗表现出明显不同。在湿润峰穿过夹砂层上界面时入渗率有较大波动,且最终进入稳渗阶段,其稳渗率明显小于同时刻均质土柱入渗率;当湿润锋穿过夹砂层后,夹砂层内的土壤含水率明显小于其饱和含水率。根据试验和分析,建立了针对层状夹砂土入渗的S-Green-Ampt模型,该模型可以较准确地反映层状夹砂土柱积水入渗的机     

不同含盐土壤圆盘入渗特征试验

不同含盐土壤水分入渗特征是获得准确的土壤水力参数的基础。该文通过圆盘入渗试验,分析了4种土壤在5个（-1、-3、-6、-9和-12 cm）负水头下的入渗特征。结果表明,随着水头的减小,4种土壤的吸湿率线性减小,稳定入渗率和非饱和导水率呈不同程度减小。随土壤含盐量增加稳定入渗率和导水率呈增大规律。根据实测资料确定了不同负水头下非饱和导水率的Gardner指数模型参数,为盐渍化土壤水力参数的确定提供理论参考。     

Evaporation and redistribution of salts in a silt loam soil as affected by tillage induced soil mulch

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.     

Effect of Application of Surfactants on Hydraulic Properties of Soils

This study explores the effect of surfactants, commonly found in detergents, on the hydraulic properties of soils. The soil properties examined included hydraulic conductivity, infiltration characteristics, and effective suction at the wetting front, capillary rise and soil penetrability. Two agricultural soils—a loam and a sandy loam, and three surfactants—one anionic surfactant (Sulphonic) and two non-ionic surfactants (Rexol and Rexonic), were used in the study. Changes in hydraulic properties with the application of surfactants were compared with properties obtained with deionised water (control). The results showed that Sulphonic, the anionic surfactant, had a significant effect on hydraulic properties of both soils. Applications of Sulphonic caused decreases in the capillary rise and penetrability, and an increase in the solid–liquid contact angle, shape factor and sorptivity. Except for a slight decrease in hydraulic conductivity resulting from the application of Rexol, the non-ionic surfactants did not reveal significant impact on the hydraulic characteristics of test soils.     

Simultaneous transport of surface salts and water through unsaturated soils during infiltration and redistribution

Abstract

Certain concepts regarding the simultaneous transport of surface ‐salts and water under transient unsaturated flow conditions vere verified for three soils using laboratory soil columns. Treatments included different water application rates (i.e., continuous ponding and controlled rates) and different initial soil water contents. Calcium chloride, spread on the soil surface to simulate a salt‐affected soil or broadcasting of a fertilizer (or other additive), was leached with chloride free water (0.01 N CaSO₄). Salt and water profiles were determined by destructive sampling at 2 cm depth intervals at two stages: (i) immediately following infiltration and (ii) after Batching infiltration plus redistribution time.

Immediately following infiltration as well as after matching infiltration and redistribution time, chloride was leached more efficiently and to relatively deeper depths with slower than with faster rates of water application only in sandy and sandy loam soils. The results, thus, show that slower rates of water application nay not increase leaching efficiency over faster rates in heavy‐textured and sodic soils with very poor permeability. Regardless of water application rate, initial soil water content, redistribution time and soil type, salt front (i.e., salt peak) did not coincide with the water front but lagged behind it by a few to several centimetres. That is to say that salt peak did not occur at a depth above which total soil water storage in the profile equalled cumulative infiltration. The higher the initial soil water content, the deeper and more complete was the displacement of chloride during infiltration for a given quantity of water applied at different rates. This trend was not modified during post‐irrigation period in sandy soil, but it was entirely reversed in sandy loam soil.     

聚丙烯酰胺施用对碱土和非碱土水力传导度的影响

聚丙烯酰胺（PAM）可增加土壤结构的稳定性，但它对土壤水力传导能力的影响尚不清楚。通过室内土柱淋洗试验，研究了PAM施用量和施用方式对不同碱度土壤饱和水力传导度的影响。PAM施用量为0、1／5000、1／2000和1／1000（PAM与于土重之比），施用方式为混合施用和表面覆盖施用，土壤为碱土和非碱土两种。试验结果显示，在未施用PAM的条件下，非碱土水力传导度大于碱土。PAM混合施用显著地减小了土壤的稳定水力传导度，但它对碱土的影响程度大于对非碱土的影响。PAM覆盖施用降低了非碱土的稳定水力传导度；但碱土的稳定水力传导度随PAM施用量的增加先减小后增大。为了维持良好的土壤水力传导性能，应尽可能地减小PAM的施用量，或在非碱土地上采用混合施用而在碱土地上采用地表覆盖的施用方式。     

Effects of compaction on soil surface water repellency

Water repellency can reduce the infiltration capacity of soils over timescales similar to those of precipitation events. Compaction can also reduce infiltration capacity by decreasing soil hydraulic conductivity, but the effect of compaction on soil water repellency is unknown. This study explores the effect of compaction on the wettability of water repellent soil. Three air‐dry (water content ～4 g 100 g^?1) silt loam samples of contrasting wettability (non‐repellent, strongly and severely water repellent) were homogenized and subjected to various pressures in the range 0–1570 kPa in an odeometer for 24 h. Following removal, sample surface water repellency was reassessed using the water drop penetration time method and surface roughness using white light interferometry. An increase in compaction pressure caused a significant reduction in soil surface water repellency, which in turn increases the soil's initial infiltration capacity. The difference in surface roughness of soils compacted at the lowest and highest pressures was significant (at P > 0.2) suggesting an increase in the contact area between sessile water drops and soil surfaces was providing increased opportunities for surface wetting mechanisms to proceed. This suggests that compaction of a water repellent soil may lead to an increased rate of surface wetting, which is a precursor to successful infiltration of water into bulk soil. Although there may be a reduction in soil conductivity upon compaction, the more rapid initiation of infiltration may, in some circumstances, lead to an overall increase in the proportion of rain or irrigation water infiltrating water repellent soil, rather than contributing to surface run‐off or evaporation.     

Effect of Continuous Rice–Wheat Rotation on Soil Properties from Four Agro‐ecosystems of Indian Punjab

In Indian Punjab, rice–wheat is a dominant cropping system in four agro‐ecosystems, namely undulating subregion (zone 1), Piedmont alluvial plains (zone 2), central alluvial plains (zone 3), and southwestern alluvial plains (zone 4), varying in rainfall and temperature. Static and temporal variabilities in soil physical and chemical properties prevail because of alluvial parent material, management/tillage operations, and duration of rice–wheat rotation. A detailed survey was undertaken to study the long‐term effect of rice–wheat rotation on soil physical (soil separates, bulk density, modulus of rupture, saturated and unsaturated hydraulic conductivities, soil water content, and suction relations) and chemical (organic carbon, pH, electrical conductivity) properties of different textured soils (sandy clay loam, loam, clay loam, and silty clay loam) in these four zones of Punjab. Soil samples (of 0‐ to 30‐cm depth) from 45 sites were collected during 2006 and were analyzed for physical and chemical properties. The results showed that sand content and pH increased whereas silt and organic carbon decreased significantly from zones 1 to 4. Compared to other textures, significantly greater organic carbon, modulus of rupture, and pH in silty clay loam; greater bulk density in clay loam, and greater saturated hydraulic conductivity in sandy clay loam were observed. Irrespective of zone and soil texture, in the subsurface soil, there was a hard pan at 15–22.5 cm deep, which had high soil bulk density, modulus of rupture, more silt and clay contents (by 3–5%) and less organic carbon and hydraulic conductivity than the surface (0–15 cm) layer. These properties deteriorated with fineness of the soil texture and less organic carbon content. Continuous rice–wheat cropping had a deleterious effect on many soil properties. Many of these soils would benefit from the addition of organic matter, and crop yields may also be affected by the distinct hardpan that exists between 15 and 22.5 cm deep.     

Characterizing the soil moisture regime of a Typic Haplohumod

The saturated hydraulic conductivities (K_sat) of 22 spodic horizons with and without a thin iron pan, were measured in situ with a new technique, using large, carved-out columns, encased in gypsum. Measured infiltration rates and pressure heads above and below the spodic horizons allowed calculation of K_sat, which averaged 8 cm d^?1. Flow rates averaged 32 cm d^?1, however, due to a hydraulic head gradient across the spodic horizon of 4 cm cm^?1. Occurrence of a thin iron pan in the spodic horizon did not affect its K_sat-value. The measured high flow rates exclude the occurrence of perched watertables. Lateral flow of water, forming surface ponds in local depressions, was due to surface runoff, rather than to lateral movement of perched water: surface ponding of water occurred also in soils in which the spodic horizon had been mixed by tillage.     

土柱尺寸对扰动黏壤土饱和导水率的影响

土壤饱和导水率Ks是最基本的水力参数之一,而已知实验室内其值的确定受土柱尺寸的影响.以关中的塿土为研究对象,在室内,采用定水头法,研究5～30 cm内6个不同土柱尺寸对扰动黏壤土Ka测定的影响.结果表明：随着时间的延伸,Ks逐渐减小,其值最初降幅较大,其后趋于稳定,且在5 ～ 30 cm土柱直径范围内,Ks随着土柱直径的变大,扰动黏壤土的Ks递增,二者线性相关,y=0.000 4x＋0.003 7（R2=0.965 1）.研究结果可为测定Ks合理测定时间段及合理尺寸的选择提供参考.