首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 133 毫秒
1.
Knowledge of hydraulic properties is essential for understanding water movement in soil. However, very few data on these properties are available from the Loess Plateau of China. We determined the hydraulic properties of two silty loam soils on agricultural land at sites in Mizhi and Heyang in the region. Undisturbed soil cores were collected from seven layers to one meter depth to determine saturated hydraulic conductivity, soil water retention curves and unsaturated hydraulic conductivity (by the hot-air method). Additional field methods (internal drainage and Guelph permeameter) were applied at the Heyang site to compare differences between methods. Soil water retention curves were flatter at Mizhi than at Heyang. Water contents at saturation and wilting point (1500 kPa) were higher at Heyang than at Mizhi. However, unsaturated hydraulic conductivity was lower at Heyang than at Mizhi, with maximum differences of more than six orders of magnitude. Nevertheless, the two soils had similar saturated hydraulic conductivities of about 60 cm day− 1. Comparison between the methods showed that soil water retention curves obtained in the laboratory generally agreed well with the field data. Field-saturated conductivities had similar values to those obtained using the soil core method. Unsaturated hydraulic conductivities predicted by the Brooks–Corey model were closer to field data than corresponding values predicted by the van Genuchten model.  相似文献   

2.
The spatial variability of the saturated hydraulic conductivity (Ks) of a greenhouse banana plantation volcanic soil was investigated with three different permeameters: (a) the Philip-Dunne field permeameter, an easy to implement and low cost device; (b) the Guelph field permeameter; (c) the constant head laboratory permeameter. Ks was measured on a 14×5 array of 2.5 m×5 m rectangles at 0.15 m depth using the above three methods. Ks differences obtained with the different permeameters are explained in terms of flow dimensionality and elementary volume explored by the three methods. A sinusoidal spatial variation of Ks was coincident with the underlying alignment of banana plants on the field. This was explained in terms of soil disturbances, such as soil compaction, originated by management practices and tillage. Soil salinity showed some coincidence in space with the hydraulic conductivity, because of the irrigation system distribution, but a causal relationship between the two is however difficult to support. To discard the possibility of an artefact, the original 70 point mesh was doubled by intercalation of a second 14×5 grid, such that the laboratory Ks was finally determined on a 140 points 2.5 m×2.5 m square grid. Far from diluting such anisotropy this was further strengthened after inclusion of the new 70 points. The porosity (φ) determined on the same laboratory cores shows a similar sigmoid trend, thus pointing towards a plausible explanation for such variability. A power-law relationship was found between saturated hydraulic conductivity and porosity, Ksφn (r2=0.38), as stated by the Kozeny–Carman relation. A statistical reformulation of the Kozeny–Carman relation is proposed that both improved its predictability potential and allows comparisons between different representative volumes, or Ks data sets with different origin. Although the two-field methods: Guelph and Philip-Dunne, also follow a similar alignment trend, this is not so evident, suggesting that additional factors affect Ks measured in the field. Finally, geostatistical techniques such as cross correlograms estimation are used to further investigate this spatial dependence.  相似文献   

3.
Degradation of soil structure can lead to increased risk of run-off and soil erosion, and therefore, it is necessary to implement management practices that are more sustainable and will enhance and rehabilitate soils while increasing food production. The impact of small-grain rotations grown with legumes, fallow and continuously on total C (CT), labile C (CL), non-labile C (CNL), total N (NT), aggregation expressed as mean weight diameter (MWD) and infiltration determined as unsaturated hydraulic conductivity (Kunsat) were examined in a long-term rotation trial established in 1966 on a Black Earth (Pellic Vertisol) and a Red Clay (Chromic Vertisol) soil near Tamworth, in New South Wales, Australia. The results were compared with an adjacent uncropped pasture on each soil type. Cropping reduced all C fractions, NT, MWD and Kunsat on both soils, which were further degraded when long fallowing was included in the rotation. CL decreased by 70% with long fallow in the Red Clay and by 78% in the Black Earth compared with the adjacent pasture, while MWD decreased by 61% in the Red Clay and 91% in the Black Earth. Rotation of cereals with legumes resulted in smaller decreases in C fractions, NT, MWD and Kunsat when compared with pasture. Rotation with lucerne (Medicago sativa) resulted in 41% higher CL, 45% higher MWD and 87% higher Kunsat (10 mm tension) than long fallow on the Red Clay soil and 65, 126 and 43% higher on the Black Earth soil. There were strong positive correlations of soil C fractions and NT with MWD for both soil types. Similar significant relationships were found for all C fractions and NT with Kunsat (10 mm tension) for the Red Clay soil, but not for the Black Earth. Rotations with forage legumes can limit declines in C fractions, NT, MWD and Kunsat when cropping these soils and has potential to increase soil sustainability.  相似文献   

4.
The level of compaction induced on cultivated fields through trafficking is strongly influenced by the prevailing soil-water status and, depending on the attendant soil degradation, vital soil hydraulic processes could be affected. Therefore, understanding the relationship between field soil-water status and the corresponding level of induced compaction for a given load is considered an imperative step toward a better control of the occurrence of traffic-induced field soil compaction. Pore size distribution, a fundamental and highly degradable soil property, was measured in a Rhodic Ferralsol, the most productive and extensively distributed soil in Western Cuba, to study the effects of three levels of soil compaction on soil water characteristic parameters. Soil bulk density and cone penetration index were used to measure compaction levels established by seven passes of a 10 Mg tractor at three soil-water statuses corresponding to the plastic (Fs), friable (Fc) and relatively dry soil (Ds) consistency states. Pore size distribution calculated from soil water characteristic curves was classified into three pore size categories on the basis of their hydraulic functioning: >50 μm (f>50 μm), 50–0.5 μm (f50–0.5 μm) and <0.5 μm (f<0.5 μm). The greatest compaction levels were attained in the Fs and Fc soil water treatments, and a significant contribution to compaction was attributed to the existing soil water states under which the soil compaction was accomplished. Average cone index (CI) values in the range of 2.93–3.70 MPa reflected the accumulation of f<0.5 μm pores, and incurred severe reductions in the volume of f>50 μm pores in the Fs and Fc treatments, while an average CI value of 1.69 MPa indicated increments in the volume of f50–0.5 μm in the Ds treatment. Despite the differential effects of soil compaction on the distribution of the different pore size categories, soil total porosity (fTotal) was not effective in reflecting treatment effects. Soil water desorption at the soil water potentials evaluated (0.0 to −15,000 cm H2O) was adversely affected in the f<0.5 μm dominated treatments; strong soil water retention was observed with the predominance of f<0.5 μm, as was confirmed by the high water content at plant wilting point. Based on these findings, the use of field capacity water content as the upper limit of plant available soil water was therefore considered inappropriate for compacted soils.  相似文献   

5.
Determining temporal changes in field-saturated hydraulic conductivity (Kfs) is important for understanding and modeling hydrological phenomena at the field scale. Little is known about temporal variability of Kfs values measured at permanent sampling points. In this investigation, the simplified falling head (SFH) technique was used for an approximately 2-year period to determine temporal changes in Kfs at 11 permanent sampling points established at the surface of a sandy loam soil. Additional Kfs measurements were obtained by the single-ring pressure infiltrometer (PI) technique to also compare the SFH and PI techniques. The lowest mean values of Kfs, M(Kfs), were detected in December and January (20.5 ≤ M(Kfs) ≤ 146.2 mm h−1), whereas higher results (190.5 ≤ M(Kfs) ≤ 951.9 mm h−1) were obtained in the other months of the year. The Kfs values were higher and less variable in the dry soil (θi ≤ 0.21 m3 m−3, M(Kfs) = 340.6 mm h−1, CV(Kfs) = 106%) than in the wet one (θi > 0.21 m3 m−3, M(Kfs) = 78.4 mm h−1, CV(Kfs) = 185%). Both wet and dry soil were less conductive at the end of the study period than at the beginning one but a more appreciable change was detected for the dry soil (Kfs decreasing by 83.4%) than for the wet one (Kfs decreasing by 63.0%). The simple SFH technique yielded Kfs results similar to the more laborious and time-consuming PI technique (i.e., mean values differing at the most by a factor of two). It was concluded that (i) the soil water content was an important factor affecting the Kfs results obtained in a relatively coarse-textured soil, (ii) the impact of time from the beginning of the experiment on the saturated hydraulic conductivity was larger for a repeated sampling of dry soil than of wet soil and (iii) the SFH technique yielded reliable Kfs results in a relatively short period of time without the need for extensive instrumentation or analytical methodology.  相似文献   

6.
Ferralsols under native vegetation have a weak to moderate macrostructure and a well-developed microstructure corresponding to subrounded microaggregates that are usually 80 to 300 μm in size. The aim of this study was to analyze how the hydraulic properties of a clay Ferralsol were affected by a change of structure when the native vegetation is cleared for pasture. We studied the macrostructure in the field and microstructure in scanning electron microscopy. The water retention properties were determined by using pressure cell equipment. We determined the saturated hydraulic conductivity, Ks, by applying a constant hydraulic head to saturated core samples, and the unsaturated hydraulic conductivity, K(Ψ), by applying the evaporation method to undisturbed core samples. Results showed a significant decrease in the water retained at −1 and −10 hPa from 0- to 40-cm-depth when the native vegetation is cleared for pasture. That decrease in the water retained was related to a smaller development of microaggregation and greater proportion of microaggregates in close packing. For smaller water potential, there was no difference of water retained at every depth between native vegetation and pasture. Pedotransfer functions established earlier for Brazilian Ferralsols and using clay content as single predictor gave pretty good results but the precision of the estimation decreased when the water potential increased. This decrease in the precision was related to the lack of predictor taking structure into account. Ks and K(Ψ) showed an upward trend with depth under native vegetation and pasture. Except at 0–7-cm depth between the Brachiaria clumps in the pasture where smaller Ks and K(Ψ) than at the other depth was recorded whatever land use, we did not record any significant difference of Ks and K(Ψ) at every depth between native vegetation and pasture. The upward trend shown by the hydraulic conductivity with depth was related to the increase in the development of microaggregation with depth.  相似文献   

7.
黄河三角洲滨海盐渍土饱和导水率的研究   总被引：3，自引：1，他引：3  
白冰  陈效民  秦淑平 《土壤通报》2005,36(3):321-323
通过对黄河三角洲滨海盐渍土饱和导水率的研究, 结果表明: 原状土的饱和导水率随着土壤剖面深度的增加呈现出表土层高、中间土层低、底土层又升高的趋势; 扰动土与原状土的饱和导水率差异较大, 土壤饱和导水率与土壤容重呈负相关、而与孔隙度、结构系数、团聚度等均呈正相关。原状土的饱和导水率能反映田间水分运动以及孔隙状况, 对研究土壤水量平衡和水土保持有重要的意义。扰动土的饱和导水率对于土壤理化性质的理论研究有一定参考价值。  相似文献   

8.
For many centuries manure application to the soil has been common practice. Organic amendments and fertiliser applications can increase crop yields and soil organic matter (SOM). However, the long-term impacts on soil physical fertility are often neglected. This study was carried out on the Broadbalk Wheat Experiment at Rothamsted, UK, established in 1843 on an Aquic/Typic Paleudalf soil. Application of farmyard manure (FYM), N fertiliser and wheat straw on total organic C (CT), labile C (CL) and non-labile C (CNL), total N (NT), mean weight diameter (MWD) and unsaturated hydraulic conductivity (Kunsat) were studied on wheat (Triticum aestivum) and adjacent woodland and pasture areas. Manure additions, N fertiliser and straw incorporation increased all C fractions, particularly the CL fraction. The addition of 35 t ha−1 year−1 of FYM increased CT to 2.5 times that of the control (no fertiliser) treatment and CL to 5 times that of the control. With highest N application and straw returned, CT increased by 1.3 times and CL by 1.5 times that of the control treatment. There were linear relationships between rate of N fertiliser applied and all C fractions, with the rate of increase almost double with straw than straw removed. Manure application improved MWD, as did high N fertiliser additions with straw returned. Application of N fertiliser only increased MWD and Kunsat (at 10 mm tension) if straw was returned, while the addition of manure resulted in decreased Kunsat. The highest Kunsat rate was on the high N fertiliser, straw returned treatments. The uncropped areas all had high soil structural stability. Similar relationships occurred between all C fractions and NT and MWD for the high C soils, but relationships were much stronger with CL than the other C fractions in the low C soils. These results showed that soils with low C concentration are more reliant on CL for structural stability.  相似文献   

9.
Manure is a source of plant nutrients and can make a valuable contribution to soil organic matter (SOM). Two experimental sites were studied on a Halpic Phaeozem soil near Bad Lauchstadt in Germany. The first experiment, called the static experiment, commenced in 1902. The impact of fresh farmyard manure (FYM) (0, 20 and 30 t ha−1 2 year−1) combined with P, K and N fertiliser application on total organic C (CT), labile C (CL), non-labile C (CNL), total N (NT), mean weight diameter (MWD) and unsaturated hydraulic conductivity (Kunsat) was investigated. The second experiment commenced in 1984 and investigated the effect of extreme rates of fresh FYM applications (0, 50, 100 and 200 t ha−1 year−1) and cropping, or a continuous tilled fallow on the same soil properties. At both sites a nearby grassland site served as a reference. On the static experiment, FYM application increased all C fractions, particularly CL, where application of 30 t ha−1 2 year−1 increased CL by 70% compared with no FYM application. Fertiliser additions to the static experiment had a positive influence on C fractions while NT increased from both FYM and fertiliser application. MWD increased as a result of FYM application, but did not reach that of the grassland site. Both fertiliser and FYM application increased Kunsat (10 mm tension) on the static experiment. In the second experiment application of 200 t ha−1 year−1 of FYM increased concentrations of CL by 173% and of CNL by 80%, compared with no FYM application to make them equivalent to, or greater than the grassland site. A continuously tilled fallow resulted in significant decreases in all C fractions, NT and MWD compared with the cropped site, while Kunsat (10 mm tension) was increased on the 0 and 50 t ha−1 year−1 treatments as a result of a recent tillage. There was no difference in Kunsat between the cropped and the continuous tilled fallow at FYM applications of 100 and 200 t ha−1 year−1. There were similar significant positive correlations of all C fractions and NT with MWD on both experimental sites but the relationships were much stronger on the extreme FYM experiment. Weaker relationships of C fractions and NT with Kunsat (10 mm tension) occurred for the static experimental site but these were not significant for the extreme FYM experimental site. The strongest relationship between C fractions and Kunsat was with CL. This research has shown that applications of FYM can increase SOM and improve soil physical fertility. However, the potential risk of very high rates of FYM on the environment need to be taken into consideration, especially since the application of organic materials to soils is likely to increase in the future.  相似文献   

10.
Deep mouldboard ploughing to a depth of 0.45 m, gypsum (5 t ha−1) and double cropping wheat (Triticum aestivum) with a summer forage crop were applied individually, and in combination, to modify a hardsetting red-brown earth (Alfisol) used for flood-irrigated wheat production. The effects of these treatments upon water infiltration, storage and intake during irrigations, application efficiency, and depletion between irrigations were measured. Gypsum markedly increased saturated hydraulic conductivity (Ks) immediately after being applied in June 1984 but not in 1985. Mouldboard ploughing and double cropping had little effect on Ks. All Ks values were less than 0.5 m day−1. Plant available water content (PAWC) was increased by gypsum application and mouldboard ploughing after the initial irrigation in 1984, and by the three main treatments in 1985. The order in which the main treatments increased PAWC was: gypsum>mouldboard ploughing>double cropping. Water applied and water intake during irrigations were increased by mouldboard ploughing and gypsum during the first irrigation in 1984 by as much as 60 mm. Thereafter mouldboard ploughing, gypsum and double cropping had little effect on water intake, and only gypsum increased the amount of water applied in 1985. The ratio of water intake to water applied during irrigations (application efficiency) was increased by mouldboard ploughing to 59% in 1984; no treatment had values greater than 40% during 1985. Water depletion was significantly increased by mouldboard ploughing in 1984 and by gypsum and double cropping in 1985. Few significant interactions were found between the three main treatments, each of which would improve soil-water relations for crop growth, although the effect of mouldboard ploughing on soil-water relations declined after the first year. Despite substantial improvements after 2 years in some treatments, soil hydraulic properties were inadequate for optimal irrigated cropping.  相似文献   

11.
Soil puddling in advance of rice (Oryza sativa L.) transplanting disperses surface aggregates and generates compaction at depth. As a management scheme for rice, puddling is typically considered advantageous for maximizing resource availability and yield. However, some experimental findings suggest a conflict between edaphic conditions created by this establishment technique and the performance of subsequent non-rice crops like wheat (Triticum aestivum L.). At a site in the mid-hills region of Nepal on a silt loam soil with vertic characteristics, we compared the impact of six rice tillage (surface tillage—T1, shank subsoiler—T2, shank subsoiler + moldboard plough—T3) and establishment (soil puddling + transplanting—TPR, direct seeding—DSR) combinations on soil physical properties over two cycles of the rice–wheat rotation. For the rice season, 0–20 cm saturated hydraulic conductivity (Ksat) in the DSR plots was 2.6 and 4.3 times higher than their TPR counterparts in the first (Y1) and second (Y2) years, respectively (TPR-Y1 = 93 mm day−1, DSR-Y1 = 241 mm day−1, TPR-Y2 = 133 mm day−1, DSR-Y2 = 582 mm day−1), whereas tillage method did not significantly influence Ksat in this soil layer. The impact of rice establishment method was reflected in higher TPR bulk densities in the 5–10 (DSR = 1.19 g cm−3, TPR = 1.24 g cm−3) and 10–15 cm (DSR = 1.24 g cm−3, TPR = 1.29 g cm−3) depth increments in the wet season. Although none of the treatments significantly influenced the position or thickness of the plough sole, penetration resistance profiles suggest that vertical fractures with reduced soil strength were created within the pan region by deep tillage (T2 and T3), although these features were not associated with higher hydraulic conductivities from 20 to 50 cm. As the soils dried at the end of the rice season, crack propagation in the deep tilled plots (T2 and T3) was more pervasive. During the wheat season, comparable bulk density profiles and soil moisture retention characteristics across the treatments suggest that many of the edaphic changes induced by contrasting rice tillage and establishment practices did not persist in the self-mulching, vertic soils at our site. Conversely, significant increases in Ksat among the DSR plots from Y1 to Y2 (Y1 = 241 mm day−1, Y2 = 582 mm day−1) imply a temporal element to soil structural regeneration with adoption of direct seeding.  相似文献   

12.
可耕种坡地的土壤水力参数非均质性变化   总被引：3，自引：0，他引：3  
The spatial variations of the soil hydraulic properties were mainly considered in vertical direction. The objectives of this study were to measure water-retention curves, θ（ψ）, and unsaturated hydraulic conductivity functions, K（ψ）, of the soils sampled at different slope positions in three directions, namely, in vertical direction, along the slope and along the contour, and to determine the effects of sampling direction and slope position of two soil catenas. At the upper slope positions, the surface soils （0-10 cm） sampled in the vertical direction had a lower soil water content, 0, at a certain soil water potential （-1 500 kPa 〈 ψ 〈 -10 kPa） and had the greatest unsaturated hydraulic conductivity, K, at ψ 〉 -10 kPa. At the lower slope positions, K at ψ〉 -10 kPa was smaller in the vertical direction than in the direction along the slope. The deep soils （100 110 cm） had similar soil hydraulic properties in all the three directions. The anisotropic variations of the hydraulic properties of the surface soils were ascribed to the effects of natural wetting and drying cycles on the structural heterogeneity. These results suggested that the anisotropy of soil hydraulic properties might be significant in influencing soil water movement along the slope and need to be considered in modeling.  相似文献   

13.
Detailed information of the variability of soil properties and processes in space and time is presented for a dark red latosol (Alfisol) of the county of Piracicaba, S.P., Brazil. Data were collected on 25 plots along a 125 m transect during the years 1989–1991, and consisted of the soil water content θ in the 0–150 cm soil layer and the water pressure heads h at 135 and 165 cm depths. These raw data were used to characterize variabilities in space and time using classical statistics and in a second step to analyse the difficulties in calculating soil water storage, soil hydraulic conductivities, hydraulic gradients, soil water fluxes and water balances. In general, there was a great variability of hydraulic properties and processes, which is fairly constant in time in the case of basic data like soil water content and potential, but not in the case of calculated data like hydraulic conductivities and gradients, and soil water flux densities. A discussion is presented of the difficulties of using Darcy's equation to estimate soil water flux densities due to the exponential K(θ) and K(h) relationships of the hydraulic conductivity K, and of the influence of variability in space and time on the establishment of water balance components.  相似文献   

14.
Tillage management can affect crop growth by altering the pore size distribution, pore geometry and hydraulic properties of soil. In the present communication, the effect of different tillage management viz., conventional tillage (CT), minimum tillage (MT) and zero-tillage (ZT) and different crop rotations viz. [(soybean–wheat (S–W), soybean–lentil (S–L) and soybean–pea (S–P)] on pore size distribution and soil hydraulic conductivities [saturated hydraulic conductivity (Ksat) and unsaturated hydraulic conductivity {k(h)}] of a sandy clay loam soil was studied after 4 years prior to the experiment. Soil cores were collected after 4 year of the experiment at an interval of 75 mm up to 300 mm soil depth for measuring soil bulk density, soil water retention constant (b), pore size distribution, Ksat and k(h). Nine pressure levels (from 2 to 1500 kPa) were used to calculate pore size distribution and k(h). It was observed that b values at all the studied soil depths were higher under ZT than those observed under CT irrespective of the crop rotations. The values of soil bulk density observed under ZT were higher in 0–75 mm soil depth in all the crop rotations. But, among the crop rotations, soils under S–P and S–L rotations showed relatively lower bulk density values than S–W rotation. Average values of the volume fraction of total porosity with pores <7.5 μm in diameter (effective pores for retaining plant available water) were 0.557, 0.636 and 0.628 m3 m−3 under CT, MT and ZT; and 0.592, 0.610 and 0.626 m3 m−3 under S–W, S–L and S–P, respectively. In contrast, the average values of the volume fraction of total porosity with pores >150 μm in diameter (pores draining freely with gravity) were 0.124, 0.096 and 0.095 m3 m−3 under CT, MT and ZT; and 0.110, 0.104 and 0.101 m3 m−3 under S–W, S–L and S–P, respectively. Saturated hydraulic conductivity values in all the studied soil depths were significantly greater under ZT than those under CT (range from 300 to 344 mm day−1). The observed k(h) values at 0–75 mm soil depth under ZT were significantly higher than those computed under CT at all the suction levels, except at −10, −100 and −400 kPa suction. Among the crop rotations, S–P rotation recorded significantly higher k(h) values than those under S–W and S–L rotations up to −40 kPa suction. The interaction effects of tillage and crop rotations affecting the k(h) values were found significant at all the soil water suctions. Both S–L and S–P rotations resulted in better soil water retention and transmission properties under ZT.  相似文献   

15.
Porosity and soil water properties of Caribbean volcanic ash soils   总被引：6，自引：0，他引：6  
Abstract. Volcanic ash soils are generally recognized as soils with excellent and stable physical properties. Here we characterized the porosity and water properties of volcanic ash Andosols and Nitisols from Guadeloupe in contrasting banana systems: (1) perennial crop without mechanization, (2) mechanized and regularly replanted crop. Desiccation from 1 kPa to 1550 kPa moisture tension leads to significant shrinkage in the Andosol, representing a 50% reduction of the void space. The clayey Nitisol exhibited limited shrinkage. Soil clods from the mechanized plots had a significantly smaller macroporosity than that from perennial plots. The soil hydraulic conductivity was also drastically reduced in the compacted layers of the mechanized plots. However, Nitisols appeared to be less affected than Andosols. Laboratory compression tests showed that both soils were susceptible to compaction at soil moisture close to field capacity. The shrinkage properties of the Andosol were due to microaggregation of non-crystalline components upon drying. The relative stability of the macroporosity in the Nitisol was probably related to the presence of stable microaggregates made of halloysite and iron oxide. Two major processes promote soil structure degradation in the Andosol under mechanized banana cropping, surface desiccation and soil compaction. They are both induced by repeated tillage after clearing.  相似文献   

16.
崩岗不同土层土壤水力学特性差异性分析   总被引：1，自引：0，他引：1  
为研究崩岗不同土层土壤水力学特性的差异性,采用离心法测定不同土层土壤水分特征曲线,筛选出适合的土壤水分特征曲线拟合模型,结合统计模型,推求土壤的当量孔径分布、比水容量、非饱和导水率和扩散率,分析崩岗不同土层土壤水力学参数的变化规律。结果表明,崩岗土层从红土层到砂土层的变化过程中,土壤质地由黏土向砂土变化;Fredlund&Xing模型对崩岗土壤土水特征曲线拟合效果最好;参数θs、α、n随着质地变黏重逐渐减小;随着土层深度的增加,土壤的持水性能降低;土壤比水容量、非饱和导水率和扩散率受土壤质地和基质吸力的共同影响。在低吸力阶段,3个指标随基质吸力变化比较平缓,砂土层土壤比水容量和非饱和导水率最大,扩散率最小;而在高吸力阶段,砂土层土壤的这些指标降低较快,且低于其他土层,各层土壤间导水率和扩散率差异随着基质吸力的增加而增大。  相似文献   

17.
A stochastic approach to simulate water flow in a macroporous soil   总被引：1，自引：0，他引：1  
  相似文献   

18.
Soil erodibilty during concentrated flow (Kc) and critical flow shear stress (τcr), both reflecting the soil's resistance to erosion by concentrated runoff, are important input parameters in many physically-based soil erosion models. Field data on the spatial and temporal variability of these parameters is limited but crucial for accurate prediction of soil loss by rill or gully erosion. In this study, the temporal variations in Kc and τcr for a winter wheat field on a silt loam soil under three different tillage practices (conventional ploughing, CP; shallow non-inversion tillage, ST; deep non-inversion tillage, DT) in the Belgian Loess Belt were monitored during one growing season. Undisturbed topsoil samples (0.003 m3) were taken every three weeks and subjected to five different flow shear stresses (τ = 4–45 Pa) in a laboratory flume to simulate soil detachment by concentrated flow. To explain the observed variation, relevant soil and environmental parameters were measured at the time of sampling. Results indicated that after two years of conservation tillage, Kc(CP) > Kc(DT) > Kc(ST). Kc values can be up to 10 times smaller for ST compared to CP but differences strongly vary over time, with an increasing difference with decreasing soil moisture content. The beneficial effects of no-tillage are not reflected in τcr. Kc values vary from 0.006 to 0.05 sm−1 for CP and from 0.0008 to 0.01 sm−1 for ST over time. Temporal variations in Kc can be mainly explained by variations in soil moisture content but consolidation effects, root growth, residue decomposition and the presence of microbiotic soil crusts as well play a role. τcr values increase with increasing soil shear strength but Kc seems more appropriate to represent the temporal variability in soil erosion resistance during concentrated flow. The large intra-seasonal variations in Kc, which are shown to be at least equally important as differences between different soil types reported in literature, demonstrate the importance of incorporating temporal variability in soil erosion resistance when modelling soil erosion by concentrated flow.  相似文献   

19.
Soil degradation processes may be of various kinds, including soil compaction. The present study was carried out with the objective of assessing the sensitivity of agricultural or recently abandoned soils in Maputo province of Mozambique to compaction. The assessment is based on the maximum of bulk density attained using the Proctor test (MBD).

In this study the soil texture is expressed by silt plus clay (S + C) or clay (C). The relations between the soil texture and MBD, and between soil texture and critical water content (CWC—soil water at which MBD is attained) were determined. Selected soils range from 10 to 74% of S + C and 9 to 60% of C.

The results suggest there is a relationship between the considered parameters, being that between S + C and MBD or CWC, the best. For MBD the relationship is represented by two quadratic equations with the boundary in between these being a S + C value of 25% and C value of 20%.

Based on the obtained results, one can conclude that the selected parameters may be a useful basis for estimation of the sensitivity to compaction of the Maputo province's soils. It is recommended that similar studies be carried out for soils under forest land and for soil of other provinces to establish the national physical degradation hazard as a function of soil parameters determined routinely and at low cost. The suggested parameters are texture and soil organic matter (SOM).  相似文献   


20.
The effects of conservation tillage (CT) systems on crop production and erosion control have been well documented, but limited information is available concerning the effects of different CT systems on the hydraulic properties of layered soils. The effects of three CT treatments: chisel (CH), no-tillage (NT) and till-plant (TP) as compared with conventional modlboard plowing (CN) were investigated on a Griswold silt loam soil (Typic Argiudoll), formed in loess overlaying glacial till. Hydraulic properties were determined in situ. In addition, hydraulic conductivity was determined in the laboratory where more detailed hydraulic conductivity changes were monitored for the lower soil moisture tension range near soil saturation.

At or near saturation, there was no difference in hydraulic properties for all four tillage treatments. For example, mean saturated hydraulic conductivities (from laboratory determination) were 25.5, 25.1, 24.2 and 22.8 cm day−1 for CN, CH, TP and NT, respectively. However under unsaturated conditions, tillage treatments and soil layering (discontinuity between surface loess and glacial till beneath) affected hydraulic properties. In situ hydraulic conductivity (K) ranked CH>CN = NT = TP for the 0.32–0.33 m3 m−3 moisture content range. There were no differences in K for all treatments at other moisture ranges considered and at moisture contents 0.31 m3 m−3, in situ specific moisture capacity was, however, significantly lower in NT than in the other three treatments. Throughout the 20-day free drainage period for in situ K determination, the effect of layering is exhibited by the mean K values at the 50-cm depth being higher than those at 25 cm. There were negligible treatment-block interaction effects on the hydraulic properties as the soil became drier. Spatial variability in hydraulic properties was also noted for all treatments and soil depths considered.  相似文献   


设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号