Lateral migration of soil solid-phase material within a landscape-geochemical arena detected using the magnetic tracer method

Thorough studies of the lateral migration of the solid soil material and the large-scale mapping of the soil cover have been performed within a landscape-geochemical arena in the small catchment area of the Lokna River basin (Tula oblast). Podzolized clay-illuvial agrochernozems are the predominant soils in the catchment area. Nine soil types from four orders according to the 2004 soil classification have also been described. The morphological analysis of the soil profile structures revealed their changes related to the lateral migration of the solid-phase products of the pedogenesis. From the estimated reserves of the spherical magnetic particles as tracers of the mass transfer, the accumulation and dispersion zones of the solid-phase material in the soil cover have been separated and conclusions about the genesis of these zones and their place in the migration structure of the catchment basin have been drawn. The soil catenas within the landscape-geochemical arena have been classified in accordance with the migration intensity of the soil solid-phase material, the localization of deposits, and the degree of openness of the soil-geochemical conjugations. The effect of the lateral migration of the soil solid-phase material on the structure of the microarena soil cover and the soil genetic profiles has been revealed.     

Quantification of accelerated soil erosion using the environmental tracer caesium-137

The principal objective of this investigation was to quantify erosion rates for five agricultural fields in three separate study areas in Saskatchewan. The radionuclide tracer caesium-137 (¹³⁷Cs) was used to quantify net erosion and net deposition within the landscape over a 30-year period. Uneroded (native) sites were used to establish the mean background level of ¹³⁷Cs in each of the study areas. The assumption being that agricultural sites with ¹³⁷Cs areal activities greater than the native site were subject to deposition, and sites with ¹³⁷Cs less than the native control site were subject to erosion. A linear proportionality model was used to convert the loss or gain of ¹³⁷Cs to net soil erosion or deposition. Results have indicated that accelerated (anthropogenic) erosion has been commonplace on arable land in Saskatchewan, even on near-level fields (< 1.3 degrees). The net integrated sediment output from the five agricultural fields ranged from — 0.6 t th⁻¹ y⁻¹ to — 6.8 t ha⁻¹ y⁻¹ (where negative values represent erosion). What is more alarming is that between 40 and 75 per cent of all sites sampled within individual fields had erosion rates in excess of the generally accepted rate of soil formation (1.0 t ha⁻¹ y⁻¹). Also, in one highly eroded field (Crystal Springs medium sloping site) 65 per cent of the sites sampled exceeded the upper tolerable erosion rate of 11.0 t ha⁻¹ y⁻¹. These results indicate significant degradation of the non-renewable soil resource has occurred over the past 30 years and is still presently active. Land degradation by accelerated erosion would result in reductions in effective rooting depth, soil moisture holding capacity, essential nutrient stores, and would adversely effect the physical structure of the topsoil. The major reason for accelerated erosion on arable land in Saskatchewan is the practice of summer fallowing, where the field is left in a ‘bare’ state and repeatedly tilled every second or third year. During a fallow period, or prior to crop emergence during a cropping year, fields are subject to wind and water erosion. On near-level fields wind would be the dominant transport agent, while on sloping fields inter-rill and rill erosion would be the primary forces of erosion. It is suggested that the appropriate conservation farming response would be to increase application of surface mulches and possibly to decrease the frequency of summer fallowing. Without such efforts long-term sustainable agricultural production in the Prairies of Canada is considered to be a tenuous land use practice.     

Developing a magnetic tracer to study soil erosion

Soil erosion is commonly measured as the quantity of sediment leaving a plot or watershed. The techniques for measuring soil erosion patterns and sediment redistribution within plots or watersheds by direct monitoring are very limited. The objective of this study was to develop a direct and non-intrusive tracer method to study the sources, patterns and rates of erosion and deposition of sediments in erosion plots. The magnetic tracer developed in this study consisted of polystyrene plastic beads embedded with a magnetic powder (magnetite). The “magnetized” beads, with a mean weight diameter of 3.2 mm and particle density of about 1.2 g cm⁻³, were uniformly mixed with soil and tested in the laboratory using simulated rainfall and inflow studies to simulate the interrill and rill components of soil erosion, respectively. In the interrill and rill experiments, the tracer was transported in the same proportion it was initially mixed with the soil. Given this fact, a magnetometer, which measures the soil's magnetic susceptibility, could be used to identify areas of deposition or detachment. The magnetic susceptibility would be increased or reduced depending on whether deposition or detachment occurs. To simulate detachment and deposition, a magnetometer was tested for different tracer concentrations and different thickness of soil containing the tracer. The magnetometer promises to be a sensitive, accurate, and useful tool to study the spatial variation of soil erosion when magnetic tracers are used.     

Soil erosion under different land uses: Assessment by the magnetic tracer method

A new method of magnetic tracer was applied by the authors for a quantitative assessment of erosional processes. The rates of erosion were determined for cultivated and virgin soils (predominantly, chernozems) on slopes in different parts of the United States and Russia. Quantitative parameters of soil loss and soil deposition for the slopes of different shapes and aspects were found. Specific features of erosional processes within different parts of slopes were revealed. The relationships between the intensity of erosion and the humus state of the soils were characterized, and the effect of land use on the rates of soil erosion was estimated.     

Prediction of vertical soil organic carbon profiles using soil properties and environmental tracer data at an untilled site

Soil organic carbon (SOC) has considerable spatial and temporal variability both at the hillslope and catchment scale as well as down the soil profile. In recent years the distribution of SOC down the soil profile has become an area of interest in the understanding of the carbon sequestration potential of soils. Most studies however have concentrated on highly disturbed agricultural sites with little data available for untilled locations. In this study the vertical distribution of SOC is examined at a grassland site in the Young River area of Western Australia that has remained undisturbed by human activity for 50 years. Soil physical properties (texture, rock content) as well as the distribution of the environmental tracers ¹³⁷Cs and ²¹⁰Pb were assessed with the aim of better understanding the transport processes which produce the observed vertical distribution of SOC. While no consistent relationship was found between SOC and soil physical properties significant relationships were found between the distribution of SOC and the environmental tracers, ¹³⁷Cs and ²¹⁰Pb. Finite element simulations based on a diffusion/convection/decay model showed that the transport of ¹³⁷Cs and ²¹⁰Pb down the soil profile is likely to be driven by the same (primarily diffusive) processes. The same model used in conjunction with plant input and decay data generated from the RothC-26.3 soil carbon model revealed that transport of SOC down the soil profile, while also a diffusion process, was significantly slower indicating that different processes and/or pathways are involved in SOC transport at this site.     

Quantification of pyrophosphate in soil solution by pyrophosphatase hydrolysis

A commercial pyrophosphatase from Saccharomyces cerevisiae selectively hydrolyzed sodium pyrophosphate, but showed no significant activity towards a range of other organic and condensed inorganic phosphorus compounds. Pyrophosphate determined by pyrophosphatase hydrolysis accounted for 38 ± 12% (mean ± standard error of 19 sites) of the non-reactive phosphorus in soil solution obtained by centrifugation from a series of lowland tropical rain forest soils. Pyrophosphate concentrations were up to 89 μg P l⁻¹ and correlated positively with microbial phosphorus, soil solution pH, and native phosphomonoesterase activity in soil solution, but not with total soil pyrophosphate determined by NaOH–EDTA extraction and solution ³¹P NMR spectroscopy. In summary, we identify pyrophosphate as a major constituent of soil solution phosphorus in lowland tropical rain forests, and demonstrate that a commercial pyrophosphatase can be used as a selective tool to quantify trace concentrations of pyrophosphate in soil solution.     

有机物料在潮土中的腐解残留率测定方法改进与变化规律

在河南省潮土上进行有机物料的腐解残留率两种测定方法的比较研究。结果表明，在潮土区用锦纶袋——重铬酸钾容量法测定有机物料腐解残留率更符合田间实际情况，建议用该法替代砂滤管——重铬酸钾容量法进行相关研究。用锦纶袋法测定小麦秸秆在潮土中的腐殖化系数为12．25％。     

土壤侵蚀磁性示踪剂对大白菜生理特性及产量和品质的影响

通过大田试验研究了不同浓度的土壤侵蚀磁性示踪剂对大白菜生理特性及产量、品质的影响。结果表明,在4个浓度(1%、3%、5%、10%)的示踪剂处理下,大白菜叶长、叶宽及产量均明显增大;低浓度(3%～5%)的示踪剂提高了大白菜的株高,促进了根的伸长,显著提高了叶绿素含量(p<0.05),同时对大白菜净光合速率、蒸腾速率也有促进作用。示踪剂处理使叶片中超氧化物歧化酶(SOD)活性显著降低(p<0.05),而根系中SOD活性则显著升高(p<0.05);示踪剂对过氧化物酶(POD)活性的影响与对SOD活性的影响恰好相反,对过氧化氢酶(CAT)活性影响较小,在低浓度条件下,叶片与根系中POD和CAT保持有较高活性;示踪剂还导致叶片中丙二醛(MDA)含量显著提高(p<0.05)。同时,示踪剂降低了大白菜可溶性糖含量,但不显著。示踪剂浓度大于5%时显著降低维生素C含量(p<0.05)。低浓度(1%～3%)处理时有效改善了大白菜品质。总之,低浓度的示踪剂用量对大白菜生长有促进作用,高浓度的示踪剂对大白菜生长有抑制作用。     

Quantification of soil shrinkage in 2D by digital image processing of soil surface

Knowledge of soil shrinkage behavior is needed to improve the understanding and prediction of changes of unsaturated hydraulic properties in non-rigid soils. The heterogeneity and interaction of horizontal and vertical soil shrinkages that produce soil cracks and associated soil subsidence require additional quantification. Vertical shrinkage can be calculated easily by soil height with vernier caliper. However, a quantitative and feasible measurement of horizontal shrinkage has not been developed yet because of the complicated and irregular geometry of soil cracks. This paper introduces a new method to measure soil cracks non-destructively and continuously by digital image analysis. Using Adobe Photoshop and Windows Scion 4.02 image processing, the proposed procedure accurately identifies changes as small as 1.0 mm² and shows differences even when areas of soil cracks were increased by as little as 1%. Various geometry factor values indicated soil shrinkage in the two dimensions was anisotropic during the whole drying. During initial dehydration from saturation, only subsidence shrinkage could be identified. With the further dehydration, the soil cracks developed and increased in size. These results suggest that the heterogeneity of soil shrinkage in 2D should be taken into account when modeling the total soil shrinkage behavior and associated unsaturated hydraulic properties.     

Quantitative determination of red-soil erosion by an Eu tracer method

Soil erosion is a serious problem and it is affected by land use and tillage (positive or negative). Even though there are a lot of studies to quantify soil erosion through erosion plots, the models used so far for determination the soil erosion are not well accepted. The purposes of this study were to set up a new erosion quantitative method in determination short-term erosion and sedimentation and to develop spatial erosion distribution models. We chose Eu (europium) as tracer atom. Based on the field experiment, positioning soil core Eu (europium) tracer (PSCET) was established. There were 80 cores set to 8 different slope sections. The samples were taken with soil sampler in 1.5 months interval. We further analyzed the data using multiple linear regressions and multiple linear stepwise regressions to model relationships between soil erosion and its factors. PSCET was applied to bamboo field (Deqing county, southeastern of China). The field was 54 m in length and 15 m in width. The experimental results indicated that erosion modulus increased with gradient increasing and ranged from 83.6 to −53.4 t ha yr⁻¹ in different slope sections. Temporal erosion distribution pattern was consistent with rainfall within a year. The 57.0% of annual rainfall (1068 mm) were accumulated in 3 months (June–August) and 80.1% of the annual soil losses were recorded on bamboo field in 1996–1997 (June–August). The statistical data showed that correlations between erosion modulus with rainfall agent of erosion, slope length, and slope degree index were positive; and with plant cover, organic matter contents, and clay particle contents were negative. Our field experiment results strongly suggest that PSCET makes it possible to study spatial erosion and deposition distributions.     

泥沙含量对盐液示踪法经验系数影响的研究

示踪法经验系数可能受坡度、水流速度、流量等多种因素的影响，该文经过流量法和盐液示踪法的实验结果比较发现：泥沙含量较低时，随流速增加而增大，泥沙含量较高，其值基本不变，但经验系数与速度的相关性都较差，而各种坡度下测量经验系数的平均值与泥沙含量具有较好的正相关性，泥沙含量是影响经验系数的主要因素。     

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

Purpose

Vertical transfer of solid matter in soils (bioturbation and translocation) is responsible for changes in soil properties over time through the redistribution of most of the soil constituents with depth. Such transfers are, however, still poorly quantified.

Materials and methods

In this study, we examine matter transfer in four eutric Luvisols through an isotopic approach based on ¹³⁷Cs, ²¹⁰Pb_(xs), and meteoric ¹⁰Be. These isotopes differ with respect to chemical behavior, input histories, and half-lives, which allows us to explore a large time range. Their vertical distributions were modeled by a diffusion-advection equation with depth-dependent parameters. We estimated a set of advection and diffusion coefficients able to simulate all isotope depth distributions and validated the resulting model by comparing the depth distribution of organic carbon (including ^12/13C and ¹⁴C isotopes) and of the 0–2-μm particles with the data.

Results and discussion

We showed that (i) the model satisfactorily reproduces the organic carbon, ¹³C, and ¹⁴C depth distributions, indicating that organic carbon content and age can be explained by transport without invoking depth-dependent decay rates; (ii) translocation partly explains the 0–2-μm particle accumulation in the Bt horizon; and (iii) estimates of diffusion coefficients that quantify the soil mixing rate by bioturbation are significantly higher for the studied plots than those obtained by ecological studies.

Conclusions

This study presents a model capable of satisfactorily reproducing the isotopic profiles of several tracers and simulating the distribution of organic carbon and the translocation of 0–2-μm particles.

     

Measurement and modelling of the effects of initial soil conditions and slope gradient on soil translocation by tillage

Tillage erosion studies have mainly focused on the effect of topography and cultivation practices on soil translocation during tillage. However, the possible effect of initial soil conditions on soil displacement and soil erosion during tillage have not been considered. This study aims at investigating the effect of the initial soil conditions on net soil displacement and the associated erosion rates by a given tillage operation of a stony loam soil. Tillage erosion experiments were carried out with a mouldboard plough on a freshly ploughed (pre-tilled) soil and a soil under grass fallow in the Alentejo region (Southern Portugal).

The experimental results show that both the downslope displacement of soil material and the rate of increase of the downslope displacement with slope gradient are greater when the soil is initially in a loose condition. This was attributed to: (i) a greater tillage depth on the pre-tilled soil and (ii) a reduced internal cohesion of the pre-tilled soil, allowing clods to roll and/or slide down the plough furrow after being overturned by the mouldboard plough.

An analysis of additional available data on soil translocation by mouldboard tillage showed that downslope displacement distances were only significantly related to the slope gradient when tillage is carried out in the downslope direction. When tillage is carried out in the upslope direction, the effect of slope gradient on upslope displacement distances was not significant. This has important implications for the estimation of the tillage transport coefficient, which is a measure for the intensity of tillage erosion, from experimental data. For our experiments, estimated values of the tillage transport coefficient were 70 and 254 kg m⁻¹ per tillage operation for grass fallow and pre-tilled conditions, respectively, corresponding to local maximum erosion rates of ca. 8 and 35 Mg ha⁻¹ per tillage operation and local maximum deposition rates of ca. 33 and 109 Mg ha⁻¹ per tillage operation.     

Surface analysis of soil material by X-ray photoelectron spectroscopy

The surface composition of particles present in the fine earth (< 2 mm) of 50 soil horizons differing in composition and pedogenetic origin (13 soil profiles) was analysed by X‐ray photoelectron spectroscopy (XPS) to assess the capability and limitations of this technique and to gain better knowledge of the soil samples. The surfaces were systematically enriched in carbon, sometimes up to 1000 times, indicating that the soil particle surfaces are coated with organic substances, even in horizons where the bulk organic content is less than 0.1 g kg^?1. The distribution of carbon in the various oxidation states was 0.569 ± 0.008 C^[0], 0.275 ± 0.004 C^[+1], 0.089 ± 0.003 C^[+2] and 0.066 ± 0.002 C^[+3] for most horizons (mean ± standard error, 69 data). Only Andosol surface horizons systematically had surface organic matter in a more oxidized state. After correcting the results for the presence of organic coatings, we found that Si was generally depleted and Al enriched at the surface of soil particles, while Fe was either depleted or enriched depending on the sample considered. However, the coating of the coarser soil particles by the finer ones and their differential composition explained this observation and limits the interest of XPS for characterizing the surface enrichment of inorganic elements in crude soil samples. These limitations should be considered when interpreting XPS results in future work. Nevertheless, XPS can analyse the adsorbed organic matter and its functional composition of carbon without the need for any chemical or physical extraction that might alter the structure and composition of the organic molecules.     

An automated colorimetric method for the determination of urease activity in soil and plant material

Abstract

An automated colorimetric method Cor determining urease activity in soils and plant material is described. The method, using ammonium determination by the nitroprusside‐catalysed indophenol reaction, is Caster and more precise than a colorimetric measurement of urea.     

Quantification of the predominant monomeric catechins in baking chocolate standard reference material by LC/APCI-MS

Catechins are polyphenolic plant compounds (flavonoids) that may offer significant health benefits to humans. These benefits stem largely from their anticarcinogenic, antioxidant, and antimutagenic properties. Recent epidemiological studies suggest that the consumption of flavonoid-containing foods is associated with reduced risk of cardiovascular disease. Chocolate is a natural cocoa bean-based product that reportedly contains high levels of monomeric, oligomeric, and polymeric catechins. We have applied solid-liquid extraction and liquid chromatography coupled with atmospheric pressure chemical ionization-mass spectrometry to the identification and determination of the predominant monomeric catechins, (+)-catechin and (-)-epicatechin, in a baking chocolate Standard Reference Material (NIST Standard Reference Material 2384). (+)-Catechin and (-)-epicatechin are detected and quantified in chocolate extracts on the basis of selected-ion monitoring of their protonated [M + H](+) molecular ions. Tryptophan methyl ester is used as an internal standard. The developed method has the capacity to accurately quantify as little as 0.1 microg/mL (0.01 mg of catechin/g of chocolate) of either catechin in chocolate extracts, and the method has additionally been used to certify (+)-catechin and (-)-epicatechin levels in the baking chocolate Standard Reference Material. This is the first reported use of liquid chromatography/mass spectrometry for the quantitative determination of monomeric catechins in chocolate and the only report certifying monomeric catechin levels in a food-based Standard Reference Material.     

Automatic spectrophotometric determination of copper in plant material,soil, and fertilizer mixtures by a kinetic method

Abstract

Knowledge of metal concentration in soils, plant material, and fertilizers is important both for plant nutrition as for environment contamination studies. In this paper, an automated spectrophotometric method using Flow Injection Analysis (FIA) for copper (Cu) determination was studied. That method was based on the catalytic effect of Cu²⁺ ions in the color fading of the red‐purplish complex formed when iron (Fe³⁺) and thiosulfate (S₂O₃ ^2‐) ions react. The principal feature of the studied method is its high selectivity, which allowed the Cu determination in a complex matrix as nitrogen (N):phosphorus (P):potassium (K) fertilizer mixtures without effect of interference. Soil and plant tissue samples were also analyzed with good precision and accuracy when compared with atomic absorption spectrophotometry.     

The effect of soil moisture on the vertical movement of rock fragments by tillage

Chiselling in air-dry soils can rapidly create inverse grading of the plough layer as field experiments showed, i.e., the largest particles (rock fragments) are brought to the surface and the smallest particles concentrate at the bottom of the plough layer. Since no information about the effect of soil moisture and fine earth characteristics on this process is available laboratory experiments were conducted to examine the effect of soil moisture and fine earth characteristics on the vertical movement (segregation) of rock fragments due to tillage. An experimental trough, 120×60×40 cm³, was filled with three layers (each 4 cm thick) of fine earth (sand or silt loam), and rock fragments (1.2–2.2 and 2.7–4.0 cm). Tillage was simulated by moving a hand-held cultivator through the mixture. The results for the sandy soil matrix showed that inter-particle percolation was slowed down by soil moisture, however, at the same rate for different moisture levels. This was attributed to water-films that surround the sand particles. In the silt-loam soil matrix inter-particle percolation was stronger than that occurring in the sandy matrix at similar volumetric moisture contents but vertical movement was impossible at higher moisture contents (0.17 m³ m⁻³) because of a strong increase in stickiness. The results imply that at low moisture contents farmers in areas threatened by desertification can use moderate tillage as a means to create a surface rich in rock fragments which helps to increase water infiltration and decrease erosion.     

Quantification of uncertainty in trace gas fluxes measured by the static chamber method

Fluxes of methane (CH₄) and nitrous oxide (N₂O) are commonly measured with closed static chambers. Here, we analyse several of the uncertainties inherent in these measurements, including the accuracy of calibration gases, repeatability of the concentration measurements, choice of model used to calculate the flux and lack of fit to the model, as well as inaccuracies in measurements of sampling time, temperature, pressure and chamber volume. In an analysis of almost 1000 flux measurements from six sites in the UK, the choice of model for calculating the flux and model lack‐of‐fit were the largest sources of uncertainty. The analysis provides confidence intervals based on the measurement errors, which are typically 20%. Our best estimate, using the best‐fitting model, but substituting the linear model in the case of concave fits, gave a mean flux that is 25% greater than that calculated with the linear model. The best‐fit non‐linear model provided a better (convex) fit to the data than linear regression in 36% of the measurements. We demonstrate a method to balance the number of gas samples per chamber (n_samples) and the number of chambers, so as to minimize the total uncertainty in the estimate of the mean flux for a site with a fixed number of gas samples. The standard error generally decreased over the available range in n_samples, suggesting that more samples per chamber (at the expense of proportionally fewer chambers) would improve estimates of the mean flux at these sites.     

Measurements and modeling of tracer transport in a sandy soil

A physically-based dual-porosity model of water and solute transport under transient field conditions was used to simulate³H transport in seven undisturbed monoliths of a coarse-textured sand under bare soil conditions over a period of 15 months. A double-tracer application of³H and³⁶Cl was performed to test whether sidewall flow occurred in this experimental set-up. The objectives of this study were: to identify any impacts of preferential flow in this type of soil, to quantify³H losses from the soil due to evaporation, and to assess the suitability and relative behavior of³H and³⁶Cl as tracers of water. The model input parameter values were obtained by a combination of direct measurements and model calibration. One domain flow simulations of water flow and tracer concentrations in seepage agreed fairly well with those observed, indicating convective-dispersive behavior in this sandy soil. From the observed tracer and water balance for the entire observation period, the recovery of³H and³⁶Cl in seepage was 33 and 91% respectively, with 67% of the applied H lost by evaporation. Both³H and³⁶Cl broke through in seepage simultaneously, showing that³⁶Cl is equally suitable as a tracer of water as³H. The double-tracer test showed that sidewall flow did not occur.