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1.
Agrichemicals usually contaminate groundwater via preferential flow, therefore determination of the preferential flow characteristics of soil is needed. One model that predicts solute transport due to preferential flow is the mobile–immobile (MIM) solute-transport model, which partitions total water content (θ; m3 m?3) into mobile (θm) and immobile fractions (θim). In undisturbed soils, a method is proposed for determining the MIM model parameters, i.e. immobile water fraction (θim), mass transfer coefficient (α) and hydrodynamic dispersion coefficient (D h). Breakthrough curves were obtained for five different soil textures in three replicates, by miscible displacement of Cl? in undisturbed soil columns. Cl? breakthrough curves were evaluated in terms of the MIM model. Analysis suggests that the values of D h and α increased with lighter soil textures and θim increased with heavier soil textures. The values of θim ranged from 5.31 to 14.28% in different soil textures. Furthermore, values of θim were found to be related to soil clay content. Values of α ranged from 0.0257 to 0.32 h?1 and values of D h ranged from 0.36 to 11.2 cm2 h?1 in different soil textures. A significant linear correlation was obtained between α, θim, D h and soil saturated hydraulic conductivity (K s) and pore water velocity (v). A multivariate pedotransfer function was developed to estimate α, θim and D h based on the geometric mean (d g) and the standard deviation (σg) of the diameter of soil particles and soil organic matter content. The pedotransfer functions for D h, θim and α were validated by independent data sets from other investigators.  相似文献   

2.
The concern for groundwater pollution by agrichemicals through solute movement within the soil is widespread. Zeolite is a type of soil amendment that is utilized to improve physical properties of soil and ameliorate polluted soil. The high negative charge of the zeolite and its open space structure allows adsorption and access of heavy metals and other cations and anions. The objectives of this research were (i) to determine the effects of different application rates of zeolite (0, 2, 4, and 8 g kg?1) on the immobile water content and mass exchange coefficient in a loam soil and then (ii) to determine the effects of optimum application rate of zeolite on the immobile water content and mass exchange coefficient of sandy loam and clay loam soils in saturated conditions by a mobile and immobile (MIM) model. In a disturbed soil column, a method was proposed for determination of MIM model parameters, that is, immobile water content (θim), mass exchange coefficient (α), and hydrodynamic dispersion coefficient (Dh). Breakthrough curves were obtained for different soil textures with different zeolite applications in three replicates, by miscible displacement of chloride (Cl?1) in disturbed soil column. Cl?1 breakthrough curves were evaluated in terms of the MIM model. The results showed that the pore water velocity calculated based on the total soil volumetric water content (θim+ θm) and real pore water velocity calculated based on the mobile water content (θm) increased in the loam soil with an increase in zeolite application rate, so that, between these different rates of zeolite application, the maximum value of pore water velocity and real pore water velocity occurred at zeolite application rates of 8.6 and 11.5 g kg?1, which are indicated as the optimum application rates. However, the comparison between different soils showed that the zeolite application rate of 8 g kg?1 could increase pore water velocity of sandy loam and loam soils by 31% more than that of clay loam soil. The immobile water content and mass exchange coefficient of loam soil were correlated with the zeolite application rate and reduced with an increase in the rate of applied zeolite. In a comparison between different soils at zeolite application rate of 8 g kg?1, the immobile water contents of the zeolite-treated soil decreased by 57%, 60%, and 39% on sandy loam, loam, and clay loam soils, respectively, compared with the untreated soil. Furthermore, zeolite application could reduce mass exchange coefficient by 9%, 43%, and 21% on sandy loam, loam, and clay loam soils, respectively. A positive linear relationship was found between θim and α. Zeolite application increased real pore water velocity of sandy loam soil by 39% and 46% compared with loam and clay loam soils, respectively. In other studies there was a decrease in ammonium and nitrate leaching due to the zeolite application, and therefore, an increase in real pore water velocity due to zeolite application in sandy loam soil, as compared with the loam and clay loam soils, may not show more rapid movement of solute and agrichemicals to the groundwater.  相似文献   

3.
The effect of total electrolyte concentration (TEC) and sodium adsorption ratio (SAR) of water on ESR‐SAR relationships of clay (Typic Haplustert), clay loam (Vertic Haplustept) and silt loam (Lithic Haplorthent) soils was studied in a laboratory experiment. Twenty four solutions, encompassing four TEC levels viz., 5, 10, 20, and 50 mmolc l—1 and six SAR levels viz., 2.5, 5, 10, 15, 20, and 30 mmol1/2l—1/2 were synthesized to equilibrate the soil samples using pure chloride salts of calcium, magnesium, and sodium at Mg:Ca = 1:2. SAR of equilibrium solution decreased as compared to the equilibrating solution and more so in waters of low salt concentration and high SAR. At low electrolyte concentration, high SAR values were not attained in the equilibrium solution because of addition of calcium and magnesium from the mineral dissolution and from the exchange phase. Irrespective of TEC, exchangeable sodium in all the soils increased by about 4.5 to 5‐fold and irrespective of SAR, it increased by about 1.4‐ to 1.8‐fold. A positive interaction of TEC and SAR influenced the ESP build‐up and CEC played a major role in the visual disparity in sodication of these soils. At higher TEC levels, considerable increase in ESP was observed when it was corrected for anion exclusion and more so in silt loam followed by clay loam and clay soils. The values for Gapons' constant were in the range 0.0110—0.0176, 0.0142—0.0246, and 0.0189—0.0344 mmol—1/2l1/2 in clay, clay loam, and silt loam soils, respectively. Increase in TEC from 5 to 50 mmolc l—1 resulted in 5.84, 8.33, and 9.77 % decrease in Gapons' constant of clay, clay loam, and silt loam soils, respectively. The soils exhibited differential affinity for Ca2+, Mg2+ or Na+ under different quality waters. Regression coefficients of ESR‐SAR relationship were lower for low TEC as compared with high TEC waters. The exchange equilibrium was strongly affected by TEC of the solution phase. Variation in soil pH was gradual with respect to TEC and SAR of equilibrating solution and no sharp change was observed. Soluble salt concentration was doubled upon equilibration with low salt waters at all SAR levels in all the soils. However, the salt concentration remained unchanged upon equilibration with high salt waters. Considering pH 8.5 a boundary between soil salinity and sodicity, ESP values attained at TEC 5 mmolc l—1 were 7.34, 8.02, and 14.32 for clay, clay loam, and silt loam soils, respectively.  相似文献   

4.
Mulching the soil surface with a layer of plant residue is considered an effective method of conserving water and soil because it increases water infiltration into the soil, reduces surface runoff and the soil erosion, and reduces flow velocity and the sediment carrying capacity of overland flow. However, application of plant residues increases operational costs and so optimal levels of mulch in order to prevent soil and/or water losses should be used according to the soil type and rainfall and slope conditions. In this study, the effect of wheat straw mulch rate on the total runoff and total soil losses from 60-mm simulated rainstorms was assessed for two intensive rainfalls (90 and 180 mm h−1) on three slope gradients typical conditions on the Loess Plateau of China and elsewhere. For short slopes (1 m), the optimal mulch rate to save water for a silt loam and a loam soil was 0.4 kg m−2. However, for a clay loam soil the mulch rate of 0.4 kg m−2 would be optimal only under the 90 mm h−1 rainfall; 0.8 kg m−2 was required for the 180 mm h−1. In order to save soil, a mulch rate of 0.2 kg m−2 on the silt loam slopes prevented 60%–80% of the soil losses. For the loam soil, mulch at the rate of 0.4 kg m−2 was essential in most cases in order to reduce soil losses substantially. For the clay loam, 0.4 kg m−2 may be optimal under the 90 mm h−1 rain, but 0.8 kg m−2 may be required for the 180 mm h−1 rainstorm. These optimal values would also need to be considered alongside other factors since the mulch may have value if used elsewhere. Hence doubling the optimal mulch rate for the silt loam soil from 0.2 kg m−2 or the clay loam soil under 90 mm h−1 rainfall from 0.4 kg m−2 in order to achieve a further 10% reduction in soil loss needs to be assessed in that context. Therefore, Optimal mulch rate can be an effective approach to virtually reduce costs or to maximize the area that can be treated. Meantime, soil conservationist should be aware that levels of mulch for short slopes might not be suitable for long slopes.  相似文献   

5.
The response of microbial biomass carbon (Cmic), nitrogen (Nmic), basal respiration, and the metabolic quotient to 3 years of a natural succession fallow were studied in a field experiment on sandy soil in Northeast Saxony/Germany from 1996 to 1998. Soil samples were taken from Eutric Cambisol and Mollic Cambisol every six weeks during the vegetation period at soil depths of 0—10 and 10—30 cm. The Cmic content in the topsoils increased with time of succession in both soil types. This trend was more distinct in the Mollic Cambisol (70.7 μg g—1 in June 1996 to 270.9 μg g—1 in October 1998 at 0—10 cm) than in the Eutric Cambisol (69.7 μg g—1 in June 1996 to 175.0 μg g—1 in October 1998 at 0—10 cm). By contrast, the Nmic content slightly decreased in the Eutric Cambisol from 18.9 μg g—1 to 17.7 μg g—1 during the same time period. In the Mollic Cambisol, the Nmic increased from 18.8 μg g—1 in spring 1996 to 35.5 μg g—1 in fall 1998, however to a lower extent than the Cmic. Subsequently, the (C:N)mic ratio increased from 4.3 to 5.8 at soil depth of 0—10 cm and from 3.5 to 6.5 at 10—30 cm during the 3‐year‐study at the Eutric Cambisol. In the Mollic Cambisol, the enhancement of (C:N)mic ratio was more pronounced (i.e. from 4.3 to 6.7 at 0—10 cm and from 3.5 to 7.2 at 10—30 cm). Most likely this results from a shift in microbial populations towards a dominance of soil fungi. The already low basal respiration of, on average, 0.26 mg CO2 g—1 (24h)—1 (0—10 cm) in June 1996 decreased with time of succession fallow to 0.15 and 0.22 mg CO2 g—1 (24h)—1 in October 1998 in the Eutric and the Mollic Cambisol, respectively. Thus, the metabolic quotient as an indicator for the efficiency of organic matter turnover in soil was very low in both soils. During the summer months, the metabolic quotients reached minimum levels of ≤ 0.1 μg CO2 C (g Cmic)—1 h—1, probably because of low soil moisture contents. Correlation analyses revealed close relationships between Nmic and total N, Nmic and water content, and Nmic and pH values. These relationships became even more pronounced with the time period of natural succession. For the samples from fall 1998, highly significant correlations were determined between Nmic and total N (coefficients were rs = 0.91***), Nmic and water content (rs = 0.91***), and Nmic and pH value (rs = 0.76***). The values for all biological parameters studied were larger in the Mollic than in the Eutric Cambisol. This indicates higher turnover rates of different C and N fractions in the Mollic Cambisol. In general, set aside of formerly agricultural managed sandy soils resulted in greater Cmic : Nmic ratios and thus, in a change in the microbiological community structure as well as in reduced C and N turnover rates (i.e. low metabolic quotient) under the climatic conditions of the East German lowlands.  相似文献   

6.
Water-repellent(WR) soil greatly influences infiltration behavior. This research determined the impacts of WR levels of silt loam soil layer during infiltration. Three column scenarios were utilized, including homogeneous wettable silt loam or sand, silt loam over sand(silt loam/sand), and sand over silt loam(sand/silt loam). A 5-cm thick silt loam soil layer was placed either at the soil surface or 5 cm below the soil surface. The silt loam soil used had been treated to produce different WR levels, wettable, slightly WR, strongly WR, and severely WR. As the WR level increased from wettable to severely WR, the cumulative infiltration decreased. Traditional wetting front-related equations did not adequately describe the infiltration rate and time relationships for layered WR soils. The Kostiakov equation provided a good fit for the first infiltration stage. Average infiltration rates for wettable, slightly WR, strongly WR, and severely WR during the 2 nd infiltration stage were 0.126, 0.021, 0.002, and 0.001 mm min~(-1) for the silt loam/sand scenario,respectively, and 0.112, 0.003, 0.002, and 0.000 5 mm min~(-1) for the sand/silt loam scenario, respectively. Pseudo-saturation phenomena occurred when visually examining the wetting fronts and from the apparent changes in water content(?θ_(AP)) at the slightly WR,strongly WR, and severely WR levels for the silt loam/sand scenario. Much larger ?θAPvalues indicated the possible existence of finger flow. Delayed water penetration into the surface soil for the strongly WR level in the silt loam/sand scenario suggested negative water heads with infiltration times longer than 10 min. The silt loam/sand soil layers produced sharp transition zones of water content. The WR level of the silt loam soil layer had greater effects on infiltration than the layer position in the column.  相似文献   

7.
In the quest for better understanding of cation movement through undisturbed soils, leaching experiments on 300-mm long undisturbed soil columns of two contrasting soils were carried out. One soil was a weakly-structured alluvial fine sandy loam, the other a well-structured aeolian silt loam. About 2000 mm of solutions of MgCl2 and Ca(NO3)2 of 0·025 M were applied at unsaturated water flow rates of between 3 and 13 mm h?1. Solute movement was monitored over several weeks by collecting effluent under suction at the base. In the sandy loam anion transport was influenced by exclusion from the double layer, whereas in the Ramiha soil anion adsorption occurred. Cation transport was described by coupling the convection-dispersion equation with cation exchange equations. Good simulations of the Mg2+ and Ca2+ concentrations in the effluent and on the exchange sites were obtained if 80% of the exchangeable cations, as measured using the 1 M ammonium acetate method, were assumed to be active. Local physical or chemical disequilibrium did not need to be explicitly taken into account. About 400 kg ha?1 of native potassium was leached from the alluvial soil, but only about 10 kg ha?1 was leached from the aeolian soil. The convection-dispersion equation coupled with exchange theory was found to describe cation transport under unsaturated flow through undisturbed soil satisfactorily.  相似文献   

8.
The effects of soil texture (silt loam or sandy loam) and cultivation practice (green manure) on the size and spatial distribution of the microbial biomass and its metabolic quotient were investigated in soils planted with a permanent row crop of hops (Humulus lupulus). The soil both between and in the plant rows was sampled at three different depths (0–10, 10–20, and 20–30 cm). The silt loam had a higher overall microbial biomass C concentration (260 g g-1) than the sandy loam (185 g g-1), whereas the sandy loam had a higher (3.1 g CO2-C mg-1 microbial Ch-1) metabolic quotient than the silt loam (2.6 g CO2-C mg-1 microbial C h-1), on average over depth (0–30 cm) and over all treatments. There was a sharp decrease in the microbial biomass with increasing depth for all plots. However, this was more pronounced in the silt loam than in the sandy loam. There was no distinct influence of sampling depth on the metabolic quotient. The microbial biomass was considerably higher in the rows than between the rows, especially in the silt loam plots. There was no significant difference between plots without green manure and plots with green manure for either the microbial biomass or the metabolic quotient.  相似文献   

9.
Biuret is a known contaminant of urea fertilisers that might be useful as a slow release N fertiliser for forestry. We studied carbon (C), net nitrogen (N) mineralisation and soil microbial biomass C and N dynamics in two forest soils (a sandy loam and a silt loam) during a 16-week long incubation following application of biuret (C 23.3%, N 40.8%, O 30.0% and H 4.9%) at concentrations of 0, 2, 10, 100 and 1000 mg kg−1 (oven-dried) soil to assess the potential of biuret as a slow-release N fertiliser. Lower concentrations of biuret specifically increased C mineralisation and soil microbial biomass C in the sandy loam soil, but not in the silt loam soil. A significant decrease of microbial biomass C was found in both soils at week 16 after biuret was applied at higher concentrations. C mineralisation declined with duration of incubation in both soils due to decreased C availability. Biuret at concentrations from 10 to 100 mg kg−1 soil had a significantly positive priming effect on soil organic N mineralisation in both soils. The causes for the priming effects were related to the stimulation of microbial growth and activity at an early stage of the incubation and/or the death of microbes at a later stage, which was biuret-concentration-dependent. The patterns in NH4+-N accumulation differed markedly between the two soils. Net N mineralisation and nitrification were much greater in the sandy loam soil than in the silt loam soil. However, the onset of net nitrification was earlier in the silt loam soil. Biuret might be a potential slow-release N source in the silt loam soil.  相似文献   

10.

Purpose

The nitrification inhibitor dicyandiamide (DCD) has been shown to be highly effective in reducing nitrate (NO3 ?) leaching and nitrous oxide (N2O) emissions when used to treat grazed pasture soils. However, there have been few studies on the possible effects of long-term DCD use on other soil enzyme activities or the abundance of the general soil microbial communities. The objective of this study was to determine possible effects of long-term DCD use on key soil enzyme activities involved in the nitrogen (N) cycle and the abundance of bacteria and archaea in grazed pasture soils.

Materials and methods

Three field sites used for this study had been treated with DCD for 7 years in field plot experiments. The three pasture soils from three different regions across New Zealand were Pukemutu silt loam in Southland in the southern South Island, Horotiu silt loam in the Waikato in the central North Island and Templeton silt loam in Canterbury in the central South Island. Control and DCD-treated plots were sampled to analyse soil pH, microbial biomass C and N, protease and deaminase activity, and the abundance of bacteria and archaea.

Results and discussion

The three soils varied significantly in the microbial biomass C (858 to 542 μg C g?1 soil) and biomass N (63 to 28 μg N g?1), protease (361 to 694 μg tyrosine g?1 soil h?1) and deaminase (4.3 to 5.6 μg NH4 + g?1 soil h?1) activity, and bacteria (bacterial 16S rRNA gene copy number: 1.64?×?109 to 2.77?×?109 g?1 soil) and archaea (archaeal 16S rRNA gene copy number: 2.67?×?107 to 3.01?×?108 g?1 soil) abundance. However, 7 years of DCD use did not significantly affect these microbial population abundance and enzymatic activities. Soil pH values were also not significantly affected by the long-term DCD use.

Conclusions

These results support the hypothesis that DCD is a specific enzyme inhibitor for ammonia oxidation and does not affect other non-target microbial and enzyme activities. The DCD nitrification inhibitor technology, therefore, appears to be an effective mitigation technology for nitrate leaching and nitrous oxide emissions in grazed pasture soils with no adverse impacts on the abundance of bacteria and archaea and key enzyme activities.  相似文献   

11.
Landfills are regarded as important sources of the atmospheric methane (CH4), one of the major greenhouse gases. In this study we investigated the CH4 dynamics of landfill cover soils in a long‐term field experiment. The CH4 emission rates were low, mostly ranging from —100 to 100 μmol m—2 h—1, with prevailing negative values. Higher values of up to 130,000 μmol m—2 h—1, obtained concurrently, were due to mice burrows, connecting the reduced soil sections with the aerated ones. Thus, the appearance of spatial dissimilarity was the most important factor influencing temporal variability. Reducing the soil cover from 120 cm to at least 60 cm caused a tendency of increased CH4 emission. The oxidation rates were also low and differed with low temporal variability from 1.0—11.9 nmol g—1 h—1 in 0—10 cm soil depth and 0—5.3 nmol g—1 h—1 in 40—50 cm, respectively. Highest rates were obtained at 25—30 % soil water content. A mapping of CH4 concentrations over the whole landfill showed a large spatial variation with values of 3.1—343 nmol g—1. Subsequent CH4 emission rates were between —0.2 and 120,000 mmol m—2 d—1 and showed a positive correlation to the CH4 concentrations (r = 0.993, P < 0.05). Thus, by a large scale mapping of CH4 concentrations a low‐cost procedure is proposed to identify the hot spots of CH4 release which should be treated with additional thick and well aerated cover soil materials.  相似文献   

12.
Phosphorus (P) forms were sequentially extracted from peat derived soils (Eutric Histosols and Gleysols) at eight sites in Saxony‐Anhalt (Germany) to disclose general differences in P pools between mineral and organic soils and to investigate effects of peat humification and oxidation in conjunction with land use and soil management on the P status of soils. Overall 29 samples providing a wide variety of basic chemical properties were subjected to the Hedley fractionation. The Histosol topsoils contained more total P (Pt) (1345 ± 666 mg kg—1) than the Gleysol topsoils (648 ± 237 mg kg—1). The predominant extractable fractions were H2SO4‐P (36—63 % of Pt) in calcareous and NaOH‐Po (0—46 % of Pt) in non‐calcareous Histosols. These soils had large pools of residual P (13—93 % of Pt). Larger contents and proportions of Po and of labile P fractions generally distinguished organic from mineral soils. Regression analyses indicated that poorly crystalline pedogenic oxides and organic matter were binding partners for extractable and non‐extractable P. Intensive management that promotes peat humification and oxidation results in disproportional enrichments of labile P fractions (resin‐P, NaHCO3‐Pi, and NaHCO3‐Po). These changes in P chemistry must be considered for a sustainable management of landscapes with Histosols and associated peat derived soils.  相似文献   

13.
Soil cover and rainfall intensity (RI) are recognized to have severe impacts on soil erosion and an interaction exists between them. This study investigates the effect of rainfall intensity (RI) and soil surface cover on losses of sediment and the selective enrichment of soil organic carbon (SOC) in the sediment by surface runoff. A field rainfall simulator was used in the laboratory to produce 90 min rainfall events of three rainfall intensities (65, 85 and 105 mm h− 1) and four cover percentages (0%, 25%, 50% and 75%) on soil material at 9% slope. A strong negative exponential relation was observed between cover percentage and RI on sediment loss under 85 and 105 mm h− 1 of rain, while under RI of 65 mm h− 1, the highest sediment loss was observed under 25% cover. Overall, higher RI and lower cover produced higher sediment and consequently higher nutrient loss, but resulted in a lower SOC enrichment ratio (ERSOC) in the sediment. The amount of runoff sediment rather than the ERSOC in the sediment was the determinant factor for the amount of nutrients lost. The values of ERSOC were high and positively correlated with the ER values of particles smaller than 20 µm (p < 0.01). Although the sediment contained substantially more fine fractions (fine silt and clay, < 20 µm), the original soil and runoff sediment were still of the same texture class, i.e. silt clay loam.  相似文献   

14.
The herbicide glyphosate, supplied as Roundup (Monsanto Canada Inc.), was tested for effects on nitrification in four soils from Atlantic Canada. These included a sandy loam (pH 6.8), two silt loam (pH 6.4 and 5.8) agricultural soils and a clay loam forest soil (pH 3.5). Glyphosate was tested at normal field exposure rates (FR) and levels up to 200 times higher. FR values ranged from 19.83 to 29.26 ppm (jig glyphosate g?1 soil). Glyphosate had no deleterious effects on nitrification in any soil when tested at FR concentrations. In the sandy loam soil nitrification was significantly stimulated at a glyphosate level 50 times higher than FR. With this soil and one of the silt loam soils (pH 6.4) glyphosate levels of 100 times FR and higher were required for a significant inhibition of nitrification. With the other silt loam soil (pH 5.8) glyphosate significantly inhibited nitrification at concentrations 10 times FR and higher. Nitrification in the acidic forest soil was very low and accurate toxicity data could not be obtained. The EC50 of glyphosate towards nitrification in soil ranged from 1435 to 2920 ppm, which corresponds to exposure levels from 67 to 150 times higher than recommended field application rates. The use of glyphosate in agriculture and forestry should have no toxic effects on nitrification in soil.  相似文献   

15.
This study evaluates soil properties in organically managed olive groves and natural zones in a mountainous area of Andalusia, Spain. Two soil types (Eutric Regosol and Eutric Cambisol) and the most common soil management methods (tillage and two intensities of grazing) were studied. Both soil types in the groves had values not much lower than those in the natural areas. Average (±SE) values in the groves were 1.58 ± 0.71% for organic carbon, 323 ± 98 g kg?1 for macroaggregate stability, 1.11 ± 0.16 g cm?3 for bulk density, 3.5 ± 1.6 mm h?1 for saturated hydraulic conductivity and 1209 ± 716 mg CO2 kg?1 for soil respiration. Overall, these values tended to be lower in the tilled compared with that in the grazed groves. The average phosphorus soil content (5.83 ± 5.22 mg kg?1) was low for olive production and within adequate ranges for N (0.12 ± 0.05%) and K (142 ± 81 mg kg?1). Soil erosion was high in the tilled groves (35.5 ± 18.2 t ha?1 year?1) with soil loss correlating with indicators of soil degradation such as organic carbon content and water stable macroaggregates. In the grazed groves, soil loss was moderate with no clear indications of soil degradation. Overall, there was significant farm‐to‐farm variability within the same soil and land management systems. Olive production had a moderate effect on soil degradation compared with natural areas and olive cultivation could be sustained in future if cover crop soil management replaced tillage, especially in the most sloping areas.  相似文献   

16.
Extensive use of chemical fertilizers in agriculture can induce high concentration of ammonium nitrogen(NH4+-N) in soil. Desorption and leaching of NH4+-N has led to pollution of natural waters. The adsorption of NH4+-N in soil plays an important role in the fate of the NH4+-N. Understanding the adsorption characteristics of NH4+-N is necessary to ascertain and predict its fate in the soil-water environment, and pedotransfer functions(PTFs) could be a convenient method for quantification of the adsorption parameters. Ammonium nitrogen adsorption capacity, isotherms, and their influencing factors were investigated for various soils in an irrigation district of the North China Plain. Fourteen agricultural soils with three types of texture(silt, silty loam, and sandy loam) were collected from topsoil to perform batch experiments. Silt and silty loam soils had higher NH4+-N adsorption capacity than sandy loam soils.Clay and silt contents significantly affected the adsorption capacity of NH4+-N in the different soils. The adsorption isotherms of NH4+-N in the 14 soils fit well using the Freundlich, Langmuir, and Temkin models. The models’ adsorption parameters were significantly related to soil properties including clay,silt, and organic carbon contents and Fe2+ and Fe3+ ion concentrations in the groundwater. The PTFs that relate soil and groundwater properties to soil NH4+-N adsorption isotherms were derived using multiple regressions where the coefficients were predicted using the Bayesian method. The PTFs of the three adsorption isotherm models were successfully verified and could be useful tools to help predict NH4+-N adsorption at a regional scale in irrigation districts.  相似文献   

17.
Intact soil cores were collected to a depth of 15 cm from a Lexington silt loam. Simulated precipitation with adjusted pH values of 3.7, 4.7 and 5.7 (control), was applied to the cores in increments of 500 mL day?1 until totals which approximated 10, 20, 40, and 80 yr of effective rainfall in Louisiana were reached. The exchangeable acidity and Al and H2O and KC1 pH were measured from 2.5 cm sections of the cores after treatment. Only the 3.7 treatment at the 80 yr volume significantly affected the soil pH and exchangeable acidity and Al.  相似文献   

18.
Heat-pulse technique (HPT) has shown promise for predicting soil water flux (Jw). This study evaluated the accuracy of HPT in predicting Jw in packed saturated columns of quartz, sand, silt loam, and sandy clay loam. Jw was predicted using the maximum dimensionless temperature differences (MDTD), ratio of downstream to upstream temperature increases (Td/Tu), and an improved Td/Tu method. Results indicated that Jw predictions had a good linear relationship with measurements (R2 > 0.93). The HPT underestimated Jw to varying degrees, and the underestimations increased as Jw increased and soil texture became fine. The Td/Tu method outperformed the MDTD and the improved Td /Tu because of its higher accuracy, fewer parameters, and simpler calculations. The MDTD exhibited the poorest performance. In coarse-textured soil materials (e.g. quartz and sand), Jw predictions by the Td/Tu method were most accurate, and even with high Jw (up to 72.4 μm s?1), relative errors still remained within 9.8%. However, in fine-textured soil materials, Jw was underestimated significantly by 16.9% in silt loam and by 23.3% in sandy clay loam. The lower Jw limits were 1.0, 2.3, 2.4, and 4.0 μm s?1 for quartz, sand, silt loam, and sandy clay loam, respectively (P > 0.05).  相似文献   

19.
This research aims to improve erosion control practice in the Loess Plateau, by studying the surface erosion processes, including splash, sheet/interrill and rill erosion in four contrasting soils under high rainfall intensity (120 mm h−1) with three-scale indoor artificial experiments. Four contrasting soils as sandy loam, sandy clay loam, clay loam and loamy clay were collected from different parts of the Loess Plateau. The results showed that sediment load was significantly impacted by soil properties in all three sub-processes. Splash rate (4.0–21.6 g m−2∙min−1) was highest in sandy loam from the north part of the Loess Plateau and showed a negative power relation with the mean weight diameter of aggregates after 20 min of rainfall duration. The average sediment load by sheet/interrill erosion (6.94–42.86 g m−2∙min−1) was highest in clay loam from middle part of the Loess Plateau, and the stable sediment load after 20 min showed a positive power relation with the silt content in soil. The average sediment load increased dramatically by rill and interrill erosion (21.03–432.16 g m−2∙min−1), which was highest in loamy clay from south part of the Loess Plateau. The average sediment load after the occurrence of rill showed a positive power relation with clay content and a negative power relation with soil organic matter content. The impacts of slope gradient on the runoff rate and sediment load also changed with soil properties. The critical factors varied for different processes, which were the aggregate size for splash erosion, the content of silt particles and slope gradient for sheet/interrill erosion, and the content of clay particles, soil organic matter and slope gradient for rill erosion. Based on the results of the experiments, specific erosion control practices were proposed by targeting certain erosion processes in areas with different soil texture and different distribution of slope gradient. The findings from this study should support the improvement of erosion prediction and cropland management in different regions of the Loess Plateau.  相似文献   

20.
A method is proposed which follows Darrah's experimental procedure and takes advantage of a mathematical solution provided by Carslaw & Jaeger to estimate the diffusion coefficients of adsorbed and non-adsorbed solutes in soil. The method requires only the values of the concentration of the solute at the input face of a uniform column of soil, Cs, and of the total amount, Qt, that has entered the soil after a specified time during which the surface of the block is in contact with a thin porous pad containing a known initial amount of solute, Q0, at concentration C0, expressed in the same units as Cs. In the Cs/C0 vs. Qt/Q0 space there is a unique relationship between the effective diffusion coefficient, De, of the solute in the soil and the contact conductance for this solute, h, between the pad and the soil surface. The proposed procedure is firstly to determine De, and h for a non-adsorbed solute in the experimental soil using the experimental values of Cs/C0 and Q/Q for that solute. This value of De, gives the diffusion impedance factor for the solute in the soil, f, which is assumed also to apply to adsorbed solutes. A first estimate of the effective diffusion coefficient of an adsorbed solute, 1Dea, is then made using f and the diffusion coefficient of the free solute in water, DL, obtained from the literature (i.e. 1Dea= DLf). Only if the solute is weakly adsorbed will the values of Cs/C0, and Qt/Q0 lie in Cs/C0, vs. Qt/Q0, space as defined by 1Dea and the contact conductance, h. Instead a second space relating Cs/C0 and Qt/Q0, is now constructed from nominated values of h and De, where De, is defined in terms of 1Dea, the adsorption coefficient, F , and the volumetric moisture content of the soil, θ. The position of the experimental values of Cs/C0, and Qt/Q0 within this new space defines h and the actual De, and F of the solute as it diffuses and is adsorbed in the soil. The advantages and limitations of the method are discussed. In particular, the method assumes that the adsorption process is linear and reversible.  相似文献   

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