Simulation of the Dispersion of Pollutants Using two Approaches for the Case of a Low Source in the Sbl: Evaluation of Turbulence Parameterisations     

D. M. Moreira  J. C. Carvalho  A. G. Goulart  T. Tirabassi 《Water, air, and soil pollution》2005,161(1-4):285-297

An Eulerian model and a Lagrangian particle model are used to study the dispersion of a contaminant released from a low source in the Stable Boundary Layer (SBL) using two different turbulence parameterisations. The Eulerian model is based on the solution of the advection–diffusion equation by the Laplace transform technique. The Lagrangian model is based on a generalized form of the Langevin equation. The first parameterisation, Degrazia et al. (2000), is based on Taylor’s statistical diffusion theory and the observed spectral properties, supposes a linear combination between shear and buoyancy turbulence. The second, Hanna (1982), is based on observed spectral properties from Minnesota Planetary Boundary Layer (PBL) observations and is widely used in pollutant dispersion models. Considering that these simulations are in the SBL, the analysis of the results shows a reasonably good agreement between the values computed by the models against the experimental ones for the two turbulence parameterisations.  相似文献   

太湖地区水稻土中的β-葡糖苷酶活性   总被引：2，自引：0，他引：2  

WANG Xiao-Chang  LU Qin 《土壤圈》2006,16(1):118-124

The electrical conductivity （EC） of 1：5 soil-water extract （EC1：5） was studied utilizing path coefficient analysis. The study focused on revealing the main chemical factors contributing to EC of soil extracts and their relative importance. Results showed that the most important factors influencing the EC1：5 of coastal salt-affected soils were the concentration of salt in 1：5 soil-water extract （So）, Cl^-, and the sodium adsorption ratio （SAR）, while effects of pH, CO3^2-, HCO3^, soluble sodium percentage （SSP）, and sodium dianion ratio （SDR） were very weak. Though the direct path coefficients between EC1：5 and SO4^2- , Ca^2＋, Mg^2＋, K^＋, or Na^＋ were not high, influence of other chemical factors caused the coefficients to increase, making the summation of their direct and indirect path coefficients relatively high. Evidences showed that multiple regression relations between EC1：5 and most of the primary factors （So, Cl^-, and SAR） had sound reliability and very good accuracy.  相似文献   

Modeling nitrogen mineralization at surface and deep layers of sandy soils   总被引：1，自引：0，他引：1  

Nicolás Romano  Alfredo Bono 《Archives of Agronomy and Soil Science》2017,63(6):870-882

We evaluated potential soil nitrogen mineralization of 46 sandy fields of the Pampas for determining the contribution of deep layers to mineralization and modeling its trend in depth as a possible tool for improving current existing mineralization models based on surface data. Mineralization, total and mineral nitrogen decreased with depth. A potential model fitted well to these variables (R² = 0.95–0.99), but mineralization showed a more stratified profile. Consequently, the fraction of total nitrogen mineralized decreased with depth despite soils had constant texture across the profile. Potential mineralization to 1 m depth could be estimated using data from the 0–0.2-m soil layer and the average curvature of the potential model (R² = 0.60) or linear regression methods (R² = 0.71). Another estimation of potential mineralization could be performed by developing a pedotransfer function which used as predictors total nitrogen and depth (R² = 0.62), without the need of laboratory incubations. Our results showed that for sandy soils, deep nitrogen mineralization account for 40% of soil mineralization and can be assessed using surface data or the total nitrogen content of the soils. Because surface soil mineralization and whole profile mineralization were highly correlated, it is improbable that field mineralization modeling may be improved using deep data in these soils.  相似文献   

Pasting and Thermal Properties of Flours from Oat Lines with High and Typical Amounts of β‐Glucan     

Mirela Colleoni‐Sirghie  Jean‐Luc Jannink  Pamela J. White 《Cereal Chemistry》2004,81(6):686-692

Experimental oat lines high in β‐glucan (6–7.8%) and traditional lines (3.9–5.7% β‐glucan) were used to evaluate the effect of β‐glucan on pasting (by rapid viscoanalysis) and thermal properties (by differential scanning calorimetry) of oat flours. Significant correlations established between β‐glucan concentration and the pasting parameters after amylolysis demonstrated the role of β‐glucans in oat pasting. The relative decrease of peak viscosity (PV) observed after enzymatic removal of β‐glucans was correlated with β‐glucan concentration (r = 0.880, P < 0.010) and reconfirmed their contribution to pasting. A significant increase of PV with β‐glucan concentration obtained under conditions of either autolysis (deionized water used for dispersion) (r = 0.89, P < 0.010) or inhibition (silver nitrate solution used for dispersion) (r = 0.91, P < 0.001) might be explained by an increase in water retention capacity caused by the β‐glucans. Predictive models of β‐glucan concentration based on the whole pasting profile or selected profile regions were developed using partial least squares (PLS) regression.Prediction of β‐glucan based on the whole profile obtained in the silver nitrate solution was the most effective (r = 0.93, correlation coefficient of predicted vs. analyzed β‐glucans, P < 0.050). No correlations were observed between the thermal properties of oat flours and the β‐glucan concentration.  相似文献   

Evapotranspiration model selection for estimation of actual evaporation from bare soil,as required in annual potential groundwater recharge studies of a semi-arid foothill region     

Seyed Adib Banimahd  Ali Akbar Kamgar-Haghighi  Shahrokh Zand-Parsa 《Archives of Agronomy and Soil Science》2013,59(10):1455-1472

Improved evapotranspiration estimation is instrumental in annual potential recharge (Re) evaluations of semi-arid regions, in the context of the water balance approach. Complementary relationship areal evapotranspiration (CRAE) and advection–aridity (AA) and a general combination equation proposed by Granger and Gray (GG) were evaluated for the estimation of actual evaporation (E_a) from bare soil under occurrence of Re. Model capability was evaluated by utilizing data from lysimeter measurements during the hydrological years [(2011–2012) and (2012–2013)]. Measured parameters included soil moisture (SM), rainfall and related meteorological data and Re (lysimeter output). All models with original parameters performed poorly during 2011–2012 and 2012–2013, underestimating annual Re values. The 2011–2012 data were used for model calibration, considering annual E_a [criterion (I)] and cumulative E_a during the occurrence period of Re [criterion(II)]. The calibrated CRAE model [criterion (II)] produced the best simulation for E_a (NRMSE < 30%). The 2012–2013 data were used to validate the models, and the calibrated CRAE model produced acceptable results (NRMSE < 10%) in SM simulation (both criteria). But calibrated CRAE under criterion (II) provided the best estimation of annual Re (ΔQ < 6%). According to the results, CR models can produce acceptable estimation of annual Re, if initially calibrated utilizing criterion (II).  相似文献   

Digital mapping of cation exchange capacity using genetic programming and soil depth functions in Baneh region,Iran     

Ruhollah Taghizadeh-Mehrjardi 《Archives of Agronomy and Soil Science》2016,62(1):109-126

This study evaluates the performances of a combination of genetic programming and soil depth functions to map the three-dimensional distribution of cation exchange capacity (CEC) in a semiarid region located in Baneh region, Iran. Using the conditioned Latin hypercube sampling method, the locations of 188 soil profiles were selected, which were then sampled and analyzed. In general, results showed that equal-area quadratic splines had the highest R², 89%, in fitting the vertical CEC distribution compared to power and logarithmic functions with R² of 81% and 84%, respectively. Our findings indicated some auxiliary variables had more influence on the prediction of CEC. Normalized difference vegetation index (NDVI) had the highest correlation with CEC in the upper two layers. However, the most important auxiliary data for prediction of CEC in 30–60 cm and 60–100 cm were topographic wetness index and profile curvature, respectively. Validation of the predictive models at each depth interval resulted in R² values ranging from 66% (0–15 cm) to 19% (60–100 cm). Overall, results indicated the topsoil can be reasonably well predicted; however, the subsoil prediction needs to be improved. We can recommend the use of the developed methodology in mapping CEC in other parts in Iran.  相似文献   

Sampling soil and sediment depth profiles at a fine resolution with a new device for determining physical,chemical and biological properties: the Fine Increment Soil Collector (FISC)     

Lionel Mabit  Katrin Meusburger  Andra-Rada Iurian  Philip N. Owens  Arsenio Toloza  Christine Alewell 《Journal of Soils and Sediments》2014,14(3):630-636

Purpose

Many environmental investigations (empirical and modelling) and theories are based on reliable information on the depth distribution of physical, chemical and biological properties in soils and sediments. However, such depth profiles are not easy to determine using current approaches, and, consequently, new devices are needed that are able to sample soils and sediments at fine resolutions.

Materials and methods

We have designed an economic, portable, hand-operated surface soil/sediment sampler—the Fine Increment Soil Collector (FISC)—which allows for the close control of incremental soil/sediment sampling and for easy recovery of the material collected by a simple screw-thread extraction system. This innovative sampling system was developed originally for the beryllium-7 (⁷Be) approach in soil and sediment redistribution research. To ensure reliable estimates of soil erosion and sediment deposition from ⁷Be measurements, the depth distribution of this short-lived fallout radionuclide in soil/sediment at the resolution of millimetres is a crucial requirement. This major challenge of the ⁷Be approach can be met by using the FISC.

Results and discussion

We demonstrate the usefulness of the FISC by characterising the depth distribution of ⁷Be at increments of 2.5 mm for a soil reference site in Austria. The activity concentration of ⁷Be at the uppermost increment (0–2.5 mm) was ca. 14 Bq kg^?1 and displayed decreasing activity with depth. Using most conventional sampling devices (i.e. the scraper-plate system), the most accurate depth increment would have been 10 mm, and the activity concentration at the surface would have been considerably lower. Consequently, coarser sampling would have influenced estimates of ⁷Be-derived soil erosion and deposition. The potential application for other soil/sediment properties, such as nutrients (e.g. phosphorus), contaminants and carbon are also discussed.

Conclusions

By enabling soil and sediment profiles to be sampled at a depth resolution of millimetres, the FISC has the potential to provide key information when addressing several environmental and geoscientific issues, such as the precise depth distributions of soil/sediment nutrients, contaminants and biological properties.  相似文献   

Peak functions for modeling high resolution soil profile data   总被引：1，自引：0，他引：1  

D. Brenton Myers  Newell R. Kitchen  Randall J. Miles  Sabine Grunwald 《Geoderma》2011,166(1):74-83

Parametric and non-parametric depth functions have been used to estimate continuous soil profile properties. However, some soil properties, such as those seen in weathered loess, have anisotropic peak-shaped depth distributions. These distributions are poorly handled by common parametric functions. And while nonparametric functions can handle this data they lack meaningful parameters to describe physical phenomena in the depth distribution of a property such as a peak, an inflection point, or a gradient. The objective of this work is to introduce the use of asymmetric peak functions to model complex and anisotropic soil property depth profiles. These functions have the advantages of providing parameters, which quantify or describe pedogenic processes. We demonstrate the application of the Pearson Type IV (PIV) and the logistic power peak (LPP) functions to high resolution soil property depth profiles measured by diffuse reflectance spectroscopy in a claypan soil landscape of Northeastern Missouri, USA. Both peak functions successfully fit clay, silt, and pH data for an example soil profile from a summit landscape position (R² = 0.90 for pH and 0.98 for silt and clay). The LPP function was further demonstrated to fit clay depth distribution for a shoulder, backslope, footslope, and a depositional landscape position (R² = 0.98, 0.96, 0.96, 0.91). Relationships between the fitted parameters of these profiles were useful to describe landscape trends in their morphological features and show promise to continuously describe pedogenic processes in three dimensions. Peak functions are a useful companion to high-resolution soil profile data collected by sensors and their combined use may allow more intensive mapping and better explanation of soil landscape variability.  相似文献   

The Longitudinal Dispersion Coefficient of Soils as Related to the Variability of Local Permeability   总被引：1，自引：0，他引：1  

C. A. Aggelopoulos  C. D. Tsakiroglou 《Water, air, and soil pollution》2007,185(1-4):223-237

Solute (NaCl) miscible displacement experiments are performed on long disturbed soil columns to determine the hydrodynamic longitudinal dispersion coefficient and correlate it with the variability of the local permeability. The solute concentration, averaged over several cross-sections along the soil column, is monitored by measuring the electrical resistance between rod electrodes. The measured solute concentration breakthrough curves are fitted simultaneously with the one-region and two-region analytical models of the 1-D advection–dispersion equation to estimate the longitudinal dispersion coefficient, D _L, as a function of Peclet number, Pe, for common groundwater flow velocities (2?<?Pe?<?50). Macroscopic simulations of miscible displacement in 2-D porous media described by a periodic permeability field with low, moderate and high variability are employed to evaluate the predictability of the one-region and two-region models, and the sensitivity of the dispersion coefficients and flow velocities estimated from soil column displacement tests to the variance of local permeability. When the variability of the local permeability becomes high, the one-region model fails, while the two-region model is capable of reproducing satisfactorily the breakthrough curves, and providing reliable values of dispersion coefficients. The two mean pore velocities estimated by the two-region model represent, on average, a fast and a slow mean velocity of the dispersion front, whereas their difference is a measure of the transient evolution of the width of the equi-concentration dispersion front.  相似文献   

Characterization of field‐scale dryland salinity with depth by quasi‐3d inversion of DUALEM‐1 data          下载免费PDF全文

J. Huang  T. Kilminster  E. G. Barrett‐Lennard  J. Triantafilis 《Soil Use and Management》2017,33(2):205-215

To understand the limitations of saline soil and determine best management practices, simple methods need to be developed to determine the salinity distribution in a soil profile and map this variation across the landscape. Using a field study in southwestern Australia, we describe a method to map this distribution in three dimensions using a DUALEM‐1 instrument and the EM4Soil inversion software. We identified suitable parameters to invert the apparent electrical conductivity (EC_a – mS/m) data acquired with a DUALEM‐1, by comparing the estimates of true electrical conductivity (σ – mS/m) derived from electromagnetic conductivity images (EMCI) to values of soil electrical conductivity of a soil‐paste extract (EC_e) which exhibited large ranges at 0–0.25 (32.4 dS/m), 0.25–0.50 (18.6 dS/m) and 0.50–0.75 m (17.6 dS/m). We developed EMCI using EM4Soil and the quasi‐3d (q‐3d), cumulative function (CF) forward modelling and S2 inversion algorithm with a damping factor (λ) of 0.07. Using a cross‐validation approach, where we removed one in 15 of the calibration locations and predicted EC_e, the prediction was shown to have high accuracy (RMSE = 2.24 dS/m), small bias (ME = ?0.03 dS/m) and large Lin's concordance (0.94). The results were similar to those from linear regression models between EC_a and EC_e for each depth of interest but were slightly less accurate (2.26 dS/m). We conclude that the q‐3d inversion was more efficient and allowed for estimates of EC_e to be made at any depth. The method can be applied elsewhere to map soil salinity in three dimensions.  相似文献   

Ion transport through unsaturated soils: field experiments and regional simulations     

T. Kumke  T. Streck  & J. Richter 《European Journal of Soil Science》2002,53(1):57-70

This paper describes the movement of anions and cations through soils at the regional scale using block‐scale and regional simulations of one‐dimensional ion transport through cultivated soils. The simulations were based on field experiments in a region of about 10 km² in Lower Saxony, Germany. Transport was modelled with the convection–dispersion equation, and the cation exchange was described using the Gapon equation. We evaluated the spatial variation of cation exchange parameters, obtained estimates valid at the block scale, and simulated the one‐dimensional transport of anions and cations. The movement of anions and cations was simulated over blocks using effective transport parameters calculated from local transport parameters. The approach led to a good agreement between measured and predicted concentrations of Br^–, Na⁺, K⁺, Ca²⁺ and Mg²⁺ on four different 1 ha blocks. However, the mean concentrations of K⁺ in the soil solution in the uppermost horizons could not be described satisfactorily by the model. For the regional simulations, transport and exchange parameters were estimated by block kriging. All variograms of the exchange parameters were spatially structured with correlation lengths varying from 100 m to 300 m. Results of the regional simulations imply that Cl^– and K⁺ were transported substantially deeper in the southern part than in the northern part of the area. The transport depth of the ions strongly depended on the pore water velocities. The simulation of solute transport to the water table showed the influence of the depth of water table on the estimated travel times, superimposing the influence of the transport parameters in the region. The results of the regional simulations also emphasize the importance of careful fertilization, especially in regions with shallow water tables such as in the north of the area.  相似文献   

The use of lysimeter data for the test of two soil–water balance models: A case study     

Martin Wegehenkel  Yongqian Zhang  Thomas Zenker  Heiko Diestel 《植物养料与土壤学杂志》2008,171(5):762-776

Two soil–water balance models were tested by a comparison of simulated with measured daily rates of actual evapotranspiration, soil water storage, groundwater recharge, and capillary rise. These rates were obtained from twelve weighable lysimeters with three different soils and two different lower boundary conditions for the time period from January 1, 1996 to December 31, 1998. In that period, grass vegetation was grown on all lysimeters. These lysimeters are located in Berlin‐Dahlem, Germany. One model calculated the soil water balance using the Richards equation. The other one used a capacitance approach. Both models used the same modified Penman formula for the estimation of potential evapotranspiration and the same simple empirical vegetation model for the calculation of transpiration, interception, and evaporation. The comparisons of simulated with measured model outputs were analyzed using the modeling‐efficiency index IA and the root mean squared error RMSE. At some lysimeters, the uncalibrated application of both models led to an underestimation of cumulative and annual rates of groundwater recharge and capillary rise, despite a good simulation quality in terms of IA and RMSE. A calibration of soil‐hydraulic and vegetation parameters such as maximum rooting depth resulted in a better fit between simulated and observed cumulative and annual rates of groundwater recharge and capillary rise, but in some cases also decreased the simulation quality of both models in terms of IA and RMSE. The results of this calibration indicated that, in addition to a precise determination of the soil water‐retention functions, vegetation parameters such as rooting depth should also be observed. Without such information, the rooting depth is a calibration parameter. However, in some cases, the uncalibrated application of both models also led to an acceptable fit between measured and simulated model outputs.  相似文献   

The turnover of organic carbon in subsoils. Part 2. Modelling carbon turnover   总被引：1，自引：0，他引：1  

D. S. Jenkinson  & K. Coleman 《European Journal of Soil Science》2008,59(2):400-413

A new model, RothPC‐1, is described for the turnover of organic C in the top metre of soil. RothPC‐1 is a version of RothC‐26.3, an earlier model for the turnover of C in topsoils. In RothPC‐1 two extra parameters are used to model turnover in the top metre of soil: one, p, which moves organic C down the profile by an advective process, and the other, s, which slows decomposition with depth. RothPC‐1 is parameterized and tested using measurements (described in Part 1, this issue) of total organic C and radiocarbon on soil profiles from the Rothamsted long‐term field experiments, collected over a period of more than 100 years. RothPC‐1 gives fits to measurements of organic C and radiocarbon in the 0–23, 23–46, 46–69 and 69–92 cm layers of soil that are almost all within (or close to) measurement error in two areas of regenerating woodland (Geescroft and Broadbalk Wildernesses) and an area of cultivated land from the Broadbalk Continuous Wheat Experiment. The fits to old grassland (the Park Grass Experiment) are less close. Two other sites that provide the requisite pre‐ and post‐bomb data are also fitted; a prairie Chernozem from Russia and an annual grassland from California. Roth‐PC‐1 gives a close fit to measurements of organic C and radiocarbon down the Chernozem profile, provided that allowance is made for soil age; with the annual grassland the fit is acceptable in the upper part of the profile, but not in the clay‐rich Bt horizon below. Calculations suggest that treating the top metre of soil as a homogeneous unit will greatly overestimate the effects of global warming in accelerating the decomposition of soil C and hence on the enhanced release of CO₂ from soil organic matter; more realistic estimates will be obtained from multi‐layer models such as RothPC‐1.  相似文献   

Long‐Term Changes in Soil Carbon Stocks in the Brazilian Cerrado Under Commercial Soybean     

Eduardo Miranda  Janaina Carmo  Eduardo Couto  Plínio Camargo 《Land Degradation \u0026amp; Development》2016,27(6):1586-1594

The net effect of agriculture on soil carbon is not yet fully understood. While a number of studies on shallow profiles have been published, evidence suggests that carbon stock changes occur in deeper layers. In this study we analyzed the effect of agriculture in the Cerrado soil C looking at changes in seven different profile depths from 0 to 100 cm in a commercial grain farm. We also used isotopic techniques to distinguish between the original Cerrado C₃ carbon and the C₄ carbon derived from the grasses used in agriculture. At 0–5 cm depth C stocks significantly decreased with cultivation time. The C stock did not change significantly when it was calculated using the 0–10, 0–20, 0–30, 0–50 or 0–75 cm profile (p > 0·05) but increased with cultivation time when the profile considered was 0–100 cm (p < 0·05). A two‐source isotope model revealed that there was a significant increase in carbon derived from C₄ grasses for all depths with cultivation time. Annual carbon sequestration rates for the upper 100 cm of soil were 1·1 Mg C ha⁻¹ year⁻¹ for total carbon and 0·8 Mg C₄ C ha⁻¹ year⁻¹ for C₄ carbon. The oldest area, with 23 years of cultivation, had a soil C stock increase compared to the native Cerrado soil of 17·6%. These findings suggest that commercial grain farms practices may increase soil C stock compared to native Cerrado soil, if a more complete soil profile down to 100 cm is used to assess C stocks. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Spatial variability of water retention parameters and saturated hydraulic conductivity in a calcareous Inceptisols (Khuzestan province of Iran) under sugarcane cropping     

Farzad Moradi  Bijan Khalili Moghaddam 《Archives of Agronomy and Soil Science》2016,62(12):1686-1699

The objective of this study was to quantify inherent spatial variability and spatial cross-correlation of the van Genuchten retention parameters and saturated hydraulic conductivity (K_s) of surface and subsurface layers in a calcareous Inceptisols (Khuzestan province, Iran) under sugarcane cropping. Measurements were performed on 100-cm³ undisturbed soil cores collected at 94 locations along a 30-m-long transect with horizontal sampling distance intervals of 0.3 and 1 m at soil depths of 0–40 and 40–80 cm, respectively. Spatial variability was investigated using conventional statistics and geostatistical techniques. Coefficient of variation (CV) varied from 8.2% (for shape parameter, n at 40–80 cm depth) to 256.7% (for K_s at 0–40 cm depth). The n parameter and saturated water content, θ_s, showed a small-scale spatial heterogeneity with a maximum CV of 11.3% for the first depth and 9.2% for the second depth. Most of the hydraulic parameters at both depths showed a spatial structure and convex experimental semivariograms with dominant spherical models with the influence range of 3.2–41 m. In most cases, the extent of spatial correlation scales of cross-semivariograms for pairs of cross-correlated hydraulic variables was found to be different with reference to those relating to the direct semivariograms of correlated variables.  相似文献   

Temperature variations in unfrozen soils with variable hydrothermal properties          下载免费PDF全文

S. Nikoosokhan  H. Nowamooz  C. Chazallon 《European Journal of Soil Science》2015,66(2):378-388

A comprehensive understanding of the hydrothermal properties of soil is required to model heat distribution in unsaturated soils. In this study, we aim to model heat distribution throughout the profile of unfrozen soil while its thermal diffusivity varies with time and depth. The proposed model is based on the fundamental solution of the one‐dimensional transient heat conduction equation using the decomposition method. We calibrate our model using experimental data from soils of different textures in the literature. The new model can estimate soil thermal diffusivity at different depths and times and uses easily accessible characteristics such as the degree of saturation and the texture of the soil. In this study, the performance of the new model is compared to the performance of the simplified model in which constant thermal diffusivity is considered throughout the profile. Moreover, the model is validated by comparing it with in‐situ temperature measurements within depth of soil profiles with different textures. The results show a very good agreement between the predicted and the measured temperature throughout the soil profiles. Such a validation shows that with increasing degree of soil saturation, depletions in temperature for fine‐textured soils are more significant than those for coarse‐textured soils. Finally, the new model is applied to a double‐layer soil in the Alsace region to define temperature variation in the profile of soil with different characteristics in each layer. For a double‐layer profile, the continuity of the temperature as well as the heat flux is verified at the interface between the two layers.  相似文献   

Quantification of vertical solid matter transfers in soils during pedogenesis by a multi-tracer approach     

Marianna Jagercikova  Sophie Cornu  Didier Bourlès  Olivier Evrard  Christine Hatté  Jérôme Balesdent 《Journal of Soils and Sediments》2017,17(2):408-422

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Effect of organic matter on the charge and phosphate adsorption characteristics of kikuyu red clay from kenya     

A.O. Moshi  A. Wild  D.J. Greenland 《Geoderma》1974,11(4):275-285

Two profiles from Muguga, Kenya, one cultivated and one under forest, contained similar contents of clay of apparently uniform composition. The profiles differed in their organic matter contents, surface (0–15 cm) samples containing 6.8% C and 3.8% C in forest and cultivated profiles, respectively. In both profiles the amounts of organic matter decreased with depth.The positive charge, measured at pH 4 in 0.2M NH₄ Cl, increased down the cultivated profile to 3.6 me/100 g at 90–120 cm. The charge was lower in the forest profile at equivalent depths, and at 90–120 cm the value was 1.2 me/100 g. Phosphate adsorption measured at pH 5 was also higher in the cultivated profile. The amount of phosphate required to raise the solution concentration to 0.2 p.p.m., ΔP, was 45 and 11 mg/kg in the surface horizon (0–15 cm) of the cultivated and forest profiles, respectively, and increased in both profiles with depth of sample.The differences between, and within, the two profiles are largely attributed to the blocking of positively charged sites and phosphate adsorption sites by organic matter.  相似文献   

Modeling vertical movement of organic matter in a soil incubated for 41 years with C labeled straw     

Sander Bruun  Bent T. Christensen  Erik S. Jensen 《Soil biology & biochemistry》2007,39(1):368-371

The distribution of organic matter (OM) in the soil profile reflects the balance between inputs and decomposition at different depths as well as transport of OM within the profile. In this study we modeled movement of OM in the soil profile as a result of mechanisms resulting in dispersive and advective movement. The model was used to interpret the distribution of ¹⁴C in the soil profile 41 years after the labeling event. The model fitted the observed distribution of ¹⁴C well (R²=0.988, AIC_c=−82.6), with a dispersion constant of D=0.71 cm² yr⁻¹ and an advection constant of v=0.0081 cm yr⁻¹. However, the model consistently underestimated the amount of OM in the soil layers from 27 to 37 cm depth. A possible explanation for this is that different fractions of OM are transported by different mechanisms. For example, particulate OM, organomineral colloids and dissolved OM are not likely to be transported by the same mechanisms. A model with two OM fractions, one moving exclusively by dispersive processes (D=0.26 cm² yr⁻¹) and another moving by both dispersive (D=0.99 cm² yr⁻¹) and advective (v=0.23 cm yr⁻¹) processes provided a slightly better fit to the data (R²=0.995, AIC_c=−83.6). More importantly, however, this model did not show the consistent underestimation from 27 to 37 cm soil depth. This corroborates the assumption that differing movement mechanisms for different OM fractions are responsible for the observed distribution of ¹⁴C in the profile. However, varying dispersion, advection, and decay of OM with depth are also possible explanations.  相似文献   

Root development of winter wheat in erosion‐affected soils depending on the position in a hummocky ground moraine soil landscape          下载免费PDF全文

Marcus Herbrich  Horst H. Gerke  Michael Sommer 《植物养料与土壤学杂志》2018,181(2):147-157

Agricultural soil landscapes of hummocky ground moraines are characterized by 3D spatial patterns of soil types that result from profile modifications due to the combined effect of water and tillage erosion. We hypothesize that crops reflect such soil landscape patterns by increased or reduced plant and root growth. Root development may depend on the thickness and vertical sequence of soil horizons as well as on the structural development state of these horizons at different landscape positions. The hypotheses were tested using field data of the root density (RD) and the root lengths (RL) of winter wheat using the minirhizotron technique. We compared data from plots at the CarboZALF‐D site (NE Germany) that are representing a non‐eroded reference soil profile (Albic Luvisol) at a plateau position, a strongly eroded profile at steep slope (Calcaric Regosol), and a depositional profile at the footslope (Anocolluvic Regosol). At each of these plots, three Plexiglas access tubes were installed down to approx. 1.5 m soil depth. Root measurements were carried out during the growing season of winter wheat (September 2014–August 2015) on six dates. The root length density (RLD) and the root biomass density were derived from RD values assuming a mean specific root length of 100 m g^?1. Values of RD and RLD were highest for the Anocolluvic Regosol and lowest for the Calcaric Regosol. The maximum root penetration depth was lower in the Anocolluvic Regosol because of a relatively high and fluctuating water table at this landscape position. Results revealed positive relations between below‐ground (root) and above‐ground crop parameters (i.e., leaf area index, plant height, biomass, and yield) for the three soil types. Observed root densities and root lengths in soils at the three landscape positions corroborated the hypothesis that the root system was reflecting erosion‐induced soil profile modifications. Soil landscape position dependent root growth should be considered when attempting to quantify landscape scale water and element balances as well as agricultural productivity.  相似文献