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1.
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2.
The mineralization of nitrogen from soil organic matter is important when one tries to optimize nitrogen fertilization and assess risks of N losses to the environment, but its measurement is laborious and expensive. We have explored the possibilities for monitoring N mineralization directly using time domain reflectometry (TDR). Net N and S mineralization were monitored over a 101‐day period in two layers (0–30 and 30–60 cm) of a loamy sand soil during aerobic incubation in a laboratory experiment. At the same time electrical conductivity of the bulk soil, σa, was measured by TDR. A series of calibration measurements with different amounts of KNO3 at different soil moisture contents was made with the topsoil to calculate the electrical conductivity, σw, of the soil solution from σa and θ. The actual σw was determined from the conductivity of 1:2 soil:water extracts (σ1:2) with a mass balance approach using measured NO3– concentrations, after correction for ions present prior to the addition of KNO3. The average N mineralization rate in the topsoil was small (0.12 mg N kg?1 day?1), and, as expected, very small in the subsoil (0.023 mg N kg?1 day?1). In the top layer NO3– concentrations calculated from σa determined by TDR slightly underestimated measured concentrations in the first 4 weeks, and in the second half of the incubation there was a significant overestimation of measured NO3–. Using the sum of both measured NO3– and SO42– reduced the overestimation. In the subsoil calculated NO3– concentrations strongly and consistently overestimated measured concentrations, although both followed the same trend. As S mineralization in the subsoil was very small, and initial SO42– concentrations were largely taken into account in the calibration relations, SO42– concentrations could not explain the overestimation. The very small NO3– and SO42– concentrations in the B layer, at the lower limit of the concentrations used in the calibrations, are a possible explanation for the discrepancies. A separate calibration for the subsoil could also be required to improve estimates of NO3– concentrations.  相似文献   

3.
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   

4.
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   

5.
Measurements of water content profiles are of great interest in hydrology and soil science. Time domain reflectometry (TDR) is a well‐established method for water content measurements; however, most TDR probe designs are suitable for measurements in only a small soil volume. In this article, a 1‐m long TDR profiling probe with five measurement sections is described. Unlike most other previous profiling probes, our probe allows for both dielectric permittivity (ε) and electrical conductivity (σa) measurements. The accuracy of the ε and σa measurements was excellent; the precision of the measurements was, however, significantly poorer than with a 0.20‐m long standard three rod TDR probe. The new probe was installed in a field and successfully measured water content profiles during the growing season of 2009. During an infiltration experiment it was shown that because of its geometry, the profiling probe over‐estimated the wetting‐front velocity. At a 0.10‐m depth, the over‐estimation was almost 30%. The over‐estimate will be less significant at greater depths.  相似文献   

6.
The volumetric soil water content (θ) is fundamental to agriculture because its spatiotemporal variation in soil affects the growth of plants. Unfortunately, the universally accepted thermogravimetric method for estimating volumetric soil water content is very labour intensive and time‐consuming for use in field‐scale monitoring. Electromagnetic (EM) induction instruments have proven to be useful in mapping the spatiotemporal variation of θ. However, depth‐specific variation in θ, which is important for irrigation management, has been little explored. The objective of this study was to develop a relationship between θ and estimates of true electrical conductivity (σ) and to use this relationship to develop time‐lapse images of soil θ beneath a centre‐pivot irrigated alfalfa (Medicago sativa L.) crop in San Jacinto, California, USA. We first measured the bulk apparent electrical conductivity (ECa – mS/m) using a DUALEM‐421 over a period of 12 days after an irrigation event (i.e. days 1, 2, 3, 4, 6, 8 and 12). We used EM4Soil to generate EM conductivity images (EMCIs). We used a physical model to estimate θ from σ, accounting for soil tortuosity and pore water salinity, with a cross‐validation RMSE of 0.04 cm3/cm3. Testing the scenario where no soil information is available, we used a three‐parameter exponential model to relate θ to σ and then to map θ along the transect on different days. The results allowed us to monitor the spatiotemporal variations of θ across the surveyed area, over the 12‐day period. In this regard, we were able to map the soil close to field capacity (0.27 cm3/cm3) and approaching permanent wilting point (0.03 cm3/cm3). The time‐lapse θ monitoring approach, developed using EMCI, has implications for soil and water use and management and will potentially allow farmers and consultants to identify inefficiencies in water application rates and use. It can also be used as a research tool to potentially assist precision irrigation practices and to test the efficacy of different methods of irrigation in terms of water delivery and efficiency in water use in near real time.  相似文献   

7.
Warland and Thurtell (2000) proposed an analytical dispersion Lagrangian analysis (hereafter WT analysis) to relate the mean scalar concentration field to source profiles inside the canopy. The first objective of this study was to evaluate the performance of the WT analysis with existing turbulence statistics parameterizations in a corn canopy, by comparing its inferred net ecosystem CO2 exchange (NEE) and latent heat flux (λE) with eddy covariance measurements. The second objective was to assess the performance of the WT analysis to infer the soil CO2 flux. Four parameterizations of turbulence statistics were used to estimate Lagrangian time scale (TL) and standard deviation of vertical wind velocity (σw) profiles. The estimated TL and σw profiles were then corrected for atmospheric stability conditions. The field experiment was carried out in a corn field from August to October 2007 and 2008. Profiles of water vapour and CO2 mixing ratios were measured using a multiport sampling system connected to an infrared gas analyzer. Wind velocity within and above the canopy and eddy covariance measurements over the canopy were taken. The soil respiration, estimated using the WT analysis, was compared to estimates obtained by an empirical model. WT analysis fluxes showed good correlation (R2 = 0.77-0.88) with NEE and λE obtained by the eddy covariance technique, but overestimated net fluxes, especially when corrections for atmospheric stability were applied. The optimization of TL and σw profiles using in-canopy turbulence measurements improved the agreement between measured and modeled NEE and λE. Inferred soil CO2 fluxes were underestimated and were poorly correlated (R2 = 0.02-0.01) with estimates obtained using an empirical model based on soil temperature. This poor performance in estimating the soil respiration is likely caused by the decoupling between inside and above canopy flows.  相似文献   

8.
In the range of volumetric water content, θ, from about 0.12 cm3 cm–3 to saturation the relation between bulk electrical conductivity, Cb, and bulk electrical permittivity, ε, of mineral soils was observed to be linear. The partial derivative ?Cb/?ε appeared independent of the moisture content and directly proportional to soil salinity. We found that the variable Xs = ?Cb/?ε determined from in situ measurements of Cb(θ > 0.2) and ε(θ > 0.2) can be considered as an index of soil salinity, and we call it the ‘salinity index’. Knowing the index and sand content for a given soil we could calculate the electrical conductivity of the soil water, Cw, which is a widely accepted measure of soil salinity. The two variables from which the salinity index can be calculated, i.e. Cb and ε, can be read simultaneously from the same sensor by time-domain reflectometry. Quantities and symbols a constant /dS m–1 b constant c constant /dS m–1 C b electrical conductivity of bulk soil /dS m–1 C b′ constant equal to 0.08 dS m–1 C s electrical conductivity of a solution used to moisten soil samples /dS m–1 C w electrical conductivity of soil water defined as the soil salinity /dS m–1 C wref reference salinity (that truly existing) resulting from the procedure of moistening samples, expressed as Cs + Cr/dS m–1 C r baseline value of Cs due to residual soluble salts present in the soil /dS m–1 d constant D dry soil bulk density /g cm–3 l slope r ratio S sand content /% by weight t time /s X s salinity index /dS m–1 X si initial salinity index when distilled water is used to moisten soil samples /dS m–1 Y a moisture-independent salinity-dependent variable /dS m–1 z coordinate along direction of flow of the soil solution ε′ constant equal to 6.2 ε relative bulk electrical permittivity (dielectric constant) of the soil θ volumetric water content determined thermogravimetrically using oven-drying /cm3 cm–3  相似文献   

9.
Salt-affected soils are widespread, particularly in arid climates, but information on nutrient dynamics and carbon dioxide (CO2) efflux from salt-affected soils is scarce. Four laboratory incubation experiments were conducted with three soils. To determine the influence of calcium carbonate (CaCO3) on respiration in saline and non-saline soils, a loamy sand (6.3% clay) was left unamended or amended with NaCl to obtain an electrical conductivity (EC) of 1.0 dS?m?1 in a 1:5 soil/water extract. Powdered CaCO3 at rates of 0%, 0.5%, 1.0%, 2.5%, 5.0% and 10.0% (w/w) and 0.25-2 mm mature wheat residue at 0% and 2% (w/w) were then added. Cumulative CO2-C emission from the salt amended and unamended soils was not affected by CaCO3 addition. To investigate the effect of EC on microbial activity, soil respiration was measured after amending a sandy loam (18.8% clay) and a silt loam (22.5% clay) with varying amount of NaCl to obtain an EC1:5 of 1.0–8.0 dS?m?1 and 2.5 g glucose C?kg?1 soil. Soil respiration was reduced by more than 50% at EC1:5?≥?5.0 dS?m?1. In a further experiment, salinity up to an EC1:5 of 5.0 dS?m?1 was developed in the silt loam with NaCl or CaCl2. No differences in respiration at a given EC were obtained between the two salts, indicating that Na and Ca did not differ in toxicity to microbial activity. The effect of different addition rates (0.25–2.0%) of mature wheat residue on the response of respiration to salinity was investigated by adding NaCl to the silt loam to obtain an EC1:5 of 2.0 and 4.0 dS?m?1. The clearest difference between salinity levels was with 2% residue rate. At a given salinity level, the modelled decomposition constant ‘k’ increased with increasing residue addition rate up to 1% and then remained constant. Particulate organic carbon left after decomposition from the added wheat residues was negatively correlated with cumulative respiration but positively correlated with EC. Inorganic N (NH 4 + -N and NO 3 ? -N) and resin P significantly decreased with increasing salinity. Resin P was significantly decreased by addition of CaCl2 and CaCO3.  相似文献   

10.
The purpose of this study was (1) to find a matching factor (u) between infiltration rate and hydraulic conductivity during steady-state infiltration, and (2) to propose equations based on infiltration and soil moisture-retention functions for prediction of the hydraulic conductivity K(θ) within the rapidly (non-capillary) drainable pores (RDP) and capillary-matrix pores of soils. The K(θ) of capillary pores was divided into K(θ)SDP, K(θ)WHP and K(θ)FCP within slowly drainable pores (SDP), water-holding pores (WHP) and fine capillary pores (FCP), respectively. Five soil profiles of calcareous sandy loam, alluvial saline and non-saline clay, located at the Nile Delta, were used to apply the proposed equations. The highest and the lowest values of K(θ)RDP were observed in calcareous and saline clay soil profiles, respectively. Values of K(θ)RDP remained higher than those for capillary pores in the studied soils. The predicted values of K(θ) in capillary and non-capillary pores classes were in the expected range for unsaturated hydraulic conductivity. Water sorptivity (S) was determined at initial unsaturated soil water conditions and calculated at steady-state infiltration (S w) using a derived equation. There was a decrease in S with an increase in soil water content; i.e. at steady-state infiltration, S decreased by 35–40% in calcareous soils and by 45–60% in alluvial clay soils. The parameter values of u and S w tended to be uniform in calcareous soils, but nonuniform in saline and non-saline clay soils.  相似文献   

11.
Abstract

The possibility of measuring both the volumetric water content (ν θ) and bulk electrical conductivity (ECb) of media using a single instrument makes time domain reflectometry (TDR) invaluable for greenhouse potting media ν and ECb determination. Laboratory experiments in three different potting media instrumented with triple‐wire TDR probes were performed to calibrate the TDR system for the determination of potting media water electrical conductivity (ECw). The performance of the TDR for in situ determination of ECw, using the experimentally‐determined conductivity model, was investigated using packed columns of potting media. Linear relationships between the ECb‐ECw data were found for all the tested media at the three water contents (0.30, 0.36, 0.45 cm3cm‐3) for four solute concentrations ranging from 1.481 to 3.797 dS m‐1. Linear regression coefficient of determination, r2, of between 0.97 and 0.99 were achieved. Calibration accuracies ranged from 94% to 98% for ECwpredictions. Results indicate that TDR is a useful technique for the accurate determination of potting media Ecb. TDR allows determination of ECw, from the measured ECb and θν, to be made quickly and simultaneously using a single and relatively inexpensive probe combined with the TDR cable tester.  相似文献   

12.
In previous studies, Al extracted by acid ammonium acetate (Ala) or Na-pyrophosphate (Alp), rather than silt or clay content and climate conditions, was the most important factor that controls organic matter (OM) levels in volcanic soils. Here, the hypothesis was tested that Ala is a comparable method (as much as CuCl2) to quantify the proportion of Al bound to OM in allophanic soils. As far as we know, there are no previous antecedents in which selective dissolution method has been compared with this extractant. Secondly, we examine the effects of (a) Al, (b) silt plus clay content (particles size 0-53 µm) and (c) clay mineralogy on the control of organic carbon (OC) level in Chilean volcanic soils. This was achieved by sampling 16 soils series (11 Andisols, one Alfisol and four Ultisols, USDA classification) including 48 soil pedons up to 0.4 m depth. Soils were analyzed for Ala, Alp, oxalate (Alo, Sio and Feo), cold NaOH (Aln) and un-buffered salts, CuCl2 (AlCu), LaCl3 (AlLa) and KCl (Alk). We also measured the Al-humus as soluble C fraction after pyrophosphate extraction and the C associated to the silt plus clay fraction after sonication and gravity decantation. The statistical package (S)MATR was used to examine bivariate linear regressions among soil properties by computing the standardized major axis (SMA). Our results indicate that Ala had a good correspondence with Alp (R2 = 0.76) in the top soil with Ala/Alp ratio of 0.19 and both extractans presented significant and positively relationship with soil OC (R2 > 0.62). Acid ammonium acetate was as effective as AlCu to determine the Al-OM in allophanic soils. It is cheaper than AlCu and Alp and 0.5 h shaking is required compared to 2 h of AlCu and 16 h of Alp. The efficiency of the extraction was: Aln ≥ Alo > Alp > AlCu ≥ Ala > AlLa > Alk. We also found that allophane content (estimated by Al/Si ratio) was strongly correlated (R2 = 0.82) with the OC in the fine silt plus clay and that Al-humus together with C in the finest particles explained (R2 > 0.60) the largest proportion of variation of soil OC across studied soils.  相似文献   

13.
The ability of three soil Na indices to predict soil conduciveness or suppressiveness to disease caused by the soil fungus Fusarium oxysporum f. sp. cubense was evaluated in seven banana plantations from the Canary Islands (Spain). These indices were exchangeable sodium percentage (ESP), soluble Na (SS0) and sodium adsorption ratio (SAR0) in 1:2.5 soil-water extracts (SARw and total cationic concentration (TCCw)=0. Sodium selectivity coefficients (KG0,K0) and TCC0 were calculated from soil exchange and solution data. The effects of ESP, SAR0, SS0, TCC0, KG0 and K0 on soil available iron (Fe extracted from soil by DTPA) and aggregate stability in water (water-stable aggregates (WSA), 200-2000 μm) were also studied. Our results showed that SAR0 calculated using cationic concentrations in 1:2.5 extracts might be a good indication of a relationship between SS0 and soluble divalent cations in conducive and suppressive volcanic soils to Fusarium. Both TCC0 and dispersion-flocculation concentrations seem to be not linked to soil suppressiveness or conduciveness to Fusarium wilt. These results suggested that soil physical properties seem to be not controlled by Na behaviour in these type of soils and, therefore, sodicity and salinity should not be a problem from a physical point of view. Moreover, SS0 and SAR0 were always greater in suppressive areas than in conducive areas. SAR0 was significantly correlated with SS0 but correlations between ESP against SS0 and SAR0 were weak. For SAR0 values above 2.5 (mmolc l−1)1/2 and ESP values below 15%, the exchangeable Na did not seem to be related to the capacity of suppressive areas to release more Na to soil solution. Larger values of SS0 were observed in suppressive areas for these values of SAR0 and ESP. It implies a lower quantity of soluble Na salts in conducive samples. A high Na salt content in soil can produce an increase of soil pH, which exerts a negative influence on available Fe release to soil solution. A clear separation between conducive and suppressive samples from relations between SS0 and SAR0 against WSA and Fe-DTPA showed that SS0 and SAR0 can be satisfactory indices to study the influence of Na concentrations on the incidence of Fusarium wilt. The mass of WSA increase in conducive areas might be favoured by the smaller amounts of soil solution Na found in these samples. In conclusion, our data provide evidence that release of Na to soil solution could favour soil suppressiveness to Fusarium wilt limiting soil aggregation and the availability of Fe, at least in soils of volcanic nature that are not affected by salinity or sodicity processes.  相似文献   

14.
土壤电导率对时域反射仪测定土壤水分的影响   总被引：10，自引：1，他引：10       下载免费PDF全文
曹巧红  龚元石 《土壤学报》2001,38(4):483-490
试验通过往土壤中加入电介质溶液 ,以及在不同粘粒含量土壤上用时域反射仪 (TDR)测定土壤含水量 ,研究结果表明 :在较低含水量情况下 (砂土 <0 1 5cm3cm- 3,砂质壤土 <0 .1 8cm3cm- 3) ,电导率的增加不易引起TDR测定值的明显偏差 ;但在较高含水量下 ,当溶液电导率增加到 8dSm- 1 (砂质壤土 )和 1 1dSm- 1 (砂土 )时 ,TDR测得的含水量值明显高于实际值。在较高电导率 ( <1 6dSm- 1 )下 ,K0 .5a 与实际含水量仍呈较好的线性关系 ,但电导率引起的介电损失影响了K0 .5a ～θ线性关系的斜率和截距。本文给出了考虑电导率影响的K0 .5a ～θ线性关系的校正方程。土壤粘粒含量的增加也会引起TDR测定偏差 ,在低含水量时测定值偏低 ,在高含水量时测定值偏高。粘粒含量 <5 0 %时 ,测定偏差 <0 .0 2cm3cm- 3。  相似文献   

15.
Time domain reflectometry (TDR), while widely used to measure volumetric water content (θ) and bulk electrical conductivity (BEC) in unsaturated granular soils, remains less studied in peat than mineral soils. Empirical models commonly used in mineral soils are not applicable to peat for accurate determination of θ from measured apparent dielectric permittivity (?). Past studies for peat report highly variable calibrations, and suggest differences in origin of organic matter, degree of decomposition and bound water to explain such variability. This study shows that bound water appears to have minimal impact on calibration because of its negligible volumetric fraction at the low bulk densities of peat. Increased volumetric air fraction at the same θ values attributed to high porosity of peat makes the ?‐θ relationships of mineral soils inapplicable. Temperature effects on ? resulted in a correction factor for θ. The temperature correction factor decreased with decreasing θ and was determined experimentally to lie between ?0.0021 m3 m?3 per °C for θ≥ 0.79 m3 m?3 and ?0.0005 m3 m?3 per °C for θ = 0.35 m3 m?3. The decreasing value of the correction factor with θ can be explained by dependence of the ?‐θ relationship on properties of free water alone. Temperature dependence of BEC was close to that of soil solution. Maxwell‐De Loor's four‐phase mixing model (MDL) based on physical properties of the multiphase soil system can efficiently simulate the effect of increased air volume and varying soil temperature on the ?‐θ relationship in peat. In addition, linear ?‐θ calibration in peat can be improved when BEC is included in the calibration equation.  相似文献   

16.
Previous studies have shown that carbon (C) mineralization in saline or sodic soils is affected by various factors including organic C content, salt concentration and water content in saline soils and soil structure in sodic soils, but there is little information about which soil properties control carbon dioxide (CO2) emission from saline-sodic soils. In this study, eight field-collected saline–sodic soils, varying in electrical conductivity (ECe, a measure of salinity, ranging from 3 to 262 dS m−1) and sodium adsorption ratio (SARe, a measure of sodicity, ranging from 11 to 62), were left unamended or amended with mature wheat or vetch residues (2% w/w). Carbon dioxide release was measured over 42 days at constant temperature and soil water content. Cumulative respiration expressed per gram SOC increased in the following order: unamended soil<soil amended with wheat residues (C/N ratio 122)<soil with vetch residue (C/N ratio 18). Cumulative respiration was significantly (p < 0.05) negatively correlated with ECe but not with SARe. Our results show that the response to ECe and SARe of the microbial community activated by addition of organic C does not differ from that of the less active microbial community in unamended soils and that salinity is the main influential factor for C mineralization in saline–sodic soils.  相似文献   

17.
Measurement of volumetric water content by TDR in saline soils   总被引：4，自引：0，他引：4  
Time-domain reflectometry (TDR) evaluates the bulk dielectric constant, K, of the soil by measuring the travel time of an electromagnetic pulse through a sensor, and through it estimates the volumetric water content. We show that for saline soils the effects of conductivity and frequency on the travel time cannot be neglected and that, as a result, TDR systematically overestimates the water content in saline soils. Simultaneously the bulk electrical conductivity of soils can be estimated by TDR. The equivalent impedance after multiple reflections is related to the bulk electrical conductivity, σ This relation differs from sensor to sensor and requires calibration for each individual sensor. A method is proposed for correcting the volumetric water content in saline soils. First, the bulk electrical conductivity, o, is estimated from the equivalent impedance at a specific equivalent distance of cable, several times the actual length of the sensor. The zero-salinity dielectric constant, KO, of this soil is obtained by correcting the apparent K as a function of the measured bulk electrical conductivity. The volumetric water content is estimated from Ko. The correction of K is a function of the equivalent frequency of the electromagnetic pulse. The imaginary part of the dielectric constant is primarily due to ohmic losses. The model, which calculates the velocity of propagation of the electromagnetic pulse and which takes into consideration the imaginary part, performs reasonably well. An empirical approach based on calibration gave slightly better results.  相似文献   

18.
Net carbon dioxide (CO2) emission from soils is controlled by the input rate of organic material and the rate of decomposition which in turn are affected by temperature, moisture and soil factors. While the relationships between CO2 emission and soil factors are well-studied in non-salt-affected soils, little is known about soil properties controlling CO2 emission from salt-affected soils. To close this knowledge gap, non-salt-affected and salt-affected soils (0-0.30 m) were collected from two agricultural regions: in India (irrigation induced salinity) and in Australia (salinity associated with ground water or non-ground water associated salinity). A subset (50 Indian and 70 Australian soils) covering the range of electrical conductivity (EC) and sodium adsorption ratio (SAR) in each region was used in a laboratory incubation experiment. The soils were left unamended or amended with mature wheat residues (2% w/w) and CO2 release was measured over 120 days at constant temperature and soil water content. Residues were added to overcome carbon limitation for soil respiration. For the unamended soils, separation in multidimensional scaling plots was a function of differences in soil texture (clay, sand), SOC pools (particulate organic carbon (POC) and humus-C) and also EC. Cumulative CO2-C emission from unamended and amended soils was related to soil properties by stepwise regression models. Cumulative CO2-C emission was negatively correlated with EC in saline soils (R2 = 0.50, p < 0.05) from both regions. In the unamended non-salt-affected soils, cumulative CO2-C emission was significantly positively related to the content of POC for the Indian soils and negatively related to clay content for the Australian soils. In the wheat residue amended soils, cumulative CO2-C emission had positive relationship with POC and humus-C but a negative correlation with EC for both Indian and Australian soils. SAR was negatively related (β = −0.66, p < 0.05) with cumulative CO2-C emission only for the unamended saline-sodic soils of Australia. Cumulative CO2-C emission was significantly negatively correlated with bulk density in amended soils from both regions. The study showed that in salt-affected soils, EC was the main factor influencing for soil respiration but the content of POC, humus-C and clay were also influential with the magnitude of influence depending on whether the soils were salt affected or not.  相似文献   

19.
Agrichemical spills and discharges to soil can cause point-source contamination of surface and ground waters. When high contaminant concentrations inhibit natural attenuation in soils, chemical treatments can be used to promote degradation and allow application of treated soils to agricultural lands. This approach was used to remediate soil containing >650 mg atrazine, >170 mg metolachlor and >18,000 mg nitrate kg?1. Results indicated a decrease in metolachlor concentration to <1 mg kg?1 within 95 days of chemical treatment with zerovalent iron (Fe0, 5% w/w) and aluminum sulfate (Al2(SO4)3, 2% w/w) but after one year >150 mg atrazine and >7000 mg nitrate kg?1 remained. Laboratory experiments confirmed that subsequent additions of sucrose (table sugar) to the chemically pretreated soil promoted further reductions in atrazine and nitrate concentrations. Field-scale results showed that adding 5% (w/w) sucrose to windrowed and pretreated soil significantly reduced atrazine (<38 mg kg?1) and nitrate (<2,100 mg kg?1) concentrations and allowed for land application of the treated soil. These results provide evidence that zerovalent iron in combination with Al2(SO4)3 and sucrose can be used for on-site, field-scale treatment of pesticide- and nitrate-contaminated soil.  相似文献   

20.
In order to develop a method for extensive pomiculture on marginal soils in semiarid Brazil, a field experiment was conducted to study the impacts of the soil conditioners biochar, clay substrate and goat manure on soil physical parameters of a sandy soil and on seedling performance of Spondias tuberosa Arruda. Manure significantly increased total porosity, soil water content and reduced bulk density of the sandy soil. Water content at field capacity (θfc) and at permanent wilting point (θpwp) were increased due to manure application. Neither biochar nor clay substrate had a significant impact on the soil physical parameters. Biochar combined with clay substrate led to lower soil water content and significantly reduced the period of retaining atmospheric water. Due to a strong correlation (R2 = 0.75) between θfc and θpwp, the available water capacity within all treatments remained unchanged. Amelioration and initial nutrient supplies had no effect on seedling survival and stem growth of S. tuberosa during the 23-month experiment. This underlines the nondomesticated character of the available plant material of S. tuberosa. The independence of the seedling performance of soil management makes S. tuberosa an interesting species for low-input orchards and for reforestation within the Caatinga.  相似文献   

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