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1.
Undisturbed soil cores were taken from different slope positions （upslope, backslope and footslope） and soil depths （0-15, 20-35 and 100-115 cm） in a soil catena derived from Quaternary red clay to determine the spatial changes in soil strength along the eroded slope and to ewluate an indicator to determine soil strength during compaction. Precompression stress, as an indicator of soil strength, significantly increased from topsoil layer to subsoil layer （P 〈0.05） and was affected by slope position. In the subsoil layer （20-35 cm）, the precompression stress at the footslope position was significantly greater than at the backslope and upslope positions （P 〈0.05）, while there were no significant differences at 0-15 and 100-115 cm. Precompression stress followed the spatial wriation of soil clay content with soil depth and had a significant linear relationship with soil porosity （r^2 = 0.40, P 〈 0.01）. Also, soil cohesion increased with increasing soil clay content. The precompression stress was significantly related to the applied stress corresponding to the highest change of pore water pressure （r^2 = 0.69, P 〈 0.01）. These results suggested that soil strength induced by soil erosion and soil management wried spatially along the slope and the maximum change in pore water pressure during compaction could be an easy indicator to describe soil strength.  相似文献   

2.
Abstract

An instrument for measurement of soil dielectric constant ε r , electrical conductivity EC a, and soil temperature was tested on soils under potato crop to investigate contents of soil volumetric water θ and nutrients for eventual use in a field crop model.

To approximate the dependence of θ on ε r , a logarithmic equation was chosen. Satisfactory results were obtained on stone-free areas, with the mean relative variance between θ-values determined by dielectric constant and converted from a gravimetric method remaining within the limits of measuring error. However, variances were higher for stony soils, with ε r -values at the same θ being considerably higher. To reconcile data from stony and stone-free soils, a formula was composed.

Salinity, calculated by a semi-empirical model based on Hilhorst's theory using measured values of EC a, ε r , and soil temperature, correlated well with contents of K and Mg in the soil. A lower correlation resulted for P, and was practically absent for Ca. Inequality of these regression equations at different measuring sites demonstrates the necessity of considering soil pH when assessing plant nutrients in the soil.  相似文献   

3.
Abstract

Measuring and mapping apparent soil electrical conductivity (ECa) is a potentially useful tool for delineating soil variability. The “Old Rotation,” the world's oldest continuous cotton (Gossypium hirsutum L.) experiment (ca. 1896), provides a valuable resource for evaluating soil spatial variability. The objectives of this study were to determine the relationship between soil chemical and physical properties and ECa in the Old Rotation, to determine spatial differences in these properties, and to relate differences in these properties to long‐term management effects. Soils at the site classified as fine, kaolinitic, thermic Typic Kanhapludults. Soil ECa was measured at 0–30‐ and 0–90‐cm depths (ECa‐30 and ECa‐90) using a Veris® 3100 direct contact sensor with georeferencing. Soils were grid sampled (288 points) at close intervals (1.5×3.0 m) for chemical properties and grid sampled (65 cells, 7.5×6.9 m) for soil texture. Soil organic carbon (SOC) and total nitrogen (N), extractable phosphorus (P), potassium (K), calcium (Ca), pH, buffer pH, and estimated cation exchange capacity (CECest) were measured at two depths (0–5‐ and 5–15‐cm). Soil ECa was highly spatially correlated. The ECa‐30 was more highly correlated with clay content (r=0.58, P≤0.01) and P(r=0.43, P≤0.01) than other soil properties. Total nitrogen and SOC had little or no relationship with ECa‐30. Cropping systems affected chemical properties in the Old Rotation, indicating crop rotation and cover crops are beneficial for soil productivity. The relatively poor relationship between soil chemical parameters and ECa suggest that mapping plant nutrients and SOC using ECa is problematic because of strong dependence on clay content.  相似文献   

4.
Abstract

Pedotransfer functions (PTFs) to estimate plant available water were developed from a database of arable soils in Sweden. The PTFs were developed to fulfil the minimum requirements of any agro-hydrological application, i.e., soil water content at wilting point (θ wp ) and field capacity (θ fc ), from information that frequently is available from soil surveys such as texture and soil organic carbon content (SOC). From the same variables we also estimated bulk density (ρ) and porosity (ε), which seldom are included in surveys, but are needed for calculating element mass balances. The seven particle-size classes given in the data set were aggregated in different ways to match information commonly gained from surveys. Analysis of covariance and stepwise multiple linear regression were used for quantifying the influence of depth, particle size class, textural class and soil organic carbon on the characteristic variables. PTFs developed from other data sets were also tested and their goodness-of-fit and bias was evaluated. These functions and those developed for the Swedish database were also tested on an independent data set and finally ranked according to their goodness of fit. Among single independent variables, clay was the best predictor for θ wp , sand (or the sum of clay and silt) for θ fc and SOC for ρ and ε. A large fraction of the variation in θ wp and θ fc is explained by soil texture and SOC (up to 90%) and root mean square errors (RMSEs) were as small as 0.03 m3 water m?3 soil in the best models. For the prediction of ρ and ε in the test data set, the best PTF could only explain 40–43% of the total variance with corresponding RMSEs of 0.14 g cm?3 and 5.3% by volume, respectively. Recently presented PTFs derived from a North American database performed very well for estimating θ wp (low error and bias) and could be recommended for Swedish soils if measurements of clay, sand and SOC were available. Although somewhat less accurately, also θ fc could be estimated satisfactorily. This indicates that the determination of plant available water by texture and SOC is rather independent of soil genesis and that certain PTFs are transferable between continents.  相似文献   

5.
Electrical conductivity(EC) of soil-water extracts is commonly used to assess soil salinity. However, its conversion to the EC of saturated soil paste extracts(ECe), the standard measure of soil salinity, is currently required for practical applications. Although many regression models can be used to obtain ECe from the EC of soil-water extracts, the application of a site-specific model to different sites is not straightforward due to confounding soil factors such as soil texture. This study was...  相似文献   

6.
WANG Jing-Hua 《土壤圈》1995,5(3):193-202
The sensitivity of a large number of variable charge soils to acid rain was evaluated through examining pH-H2SO4 input curves. Two derivative parameters, the consumption of hydrogen ions by the soil and the acidtolerant limit as defined as the quantity of sulfuric acid required to bring the soil to pH 3.5 in a 0.001mol L-1 Ca(NO3)2 solution, were used. The sensitivity of variable charge soils was higher than that of constant charge soils, due to the predominance of kaolinite in clay mineralogical composition. Among these soils the sensitivity was generally of the order lateritic red soil > red soil > latosol. For a given type of soil within the same region the sensitivity was affected by parent material, due to differences in clay minerals and texture. The sensitivity of surface soil may be lower or higher than that of subsoil, depending on whether organic matter or texture plays the dominant role in determining the buffering capacity. Paddy soils consumed more acid within lower range of acid input when compared with upland soils, due to the presence of more exchangeable bases, but consumed less acid within higher acid input range, caused by the decrease in clay content.  相似文献   

7.
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   

8.
In coastal China, there is an urgent need to increase land for agriculture. One solution is land reclamation from coastal tidelands, but soil salinization poses a problem. Thus, there is need to map saline areas and identify appropriate management strategies. One approach is the use of digital soil mapping. At the first stage, auxiliary data such as remotely sensed multispectral imagery can be used to identify areas of low agricultural productivity due to salinity. Similarly, proximal sensing instruments can provide data on the distribution of soil salinity. In this study, we first used multispectral QuickBird imagery (Bands 1–4) to provide information about crop growth and then EM38 data to indicate relative salt content using measurements of apparent soil electrical conductivity (ECa) in the horizontal (ECh) and vertical (ECv) modes of operation. Second, we used a fuzzy k‐means (FKM) algorithm to identify three salinity management zones using the normalized difference vegetation index (NDVI), ECh and ECv/ECh. The three identified classes were statistically different in terms of auxiliary and topsoil properties (e.g. soil organic matter) and more importantly in terms of the distribution of soil salinity (ECe) with depth. The resultant three classes were mapped to demonstrate that remote and proximally sensed auxiliary data can be used as surrogates for identifying soil salinity management zones.  相似文献   

9.
The site‐specific cultivation as part of the precision‐agriculture concept is more and more introduced into practical farming. However, soil information is often not available in a spatial resolution intrinsically needed for precision farming or other site‐specific soil use and management purposes. One approach to obtain spatially high‐resolution soil data is the non‐invasive measurement of the apparent electrical conductivity (ECa). In this study, we recorded the ECa on three fields with an EM38 (Geonics, Canada). The ECa data were compared with (1) ground truth data obtained by conventional drilling, (2) traditional soil maps (large scale, ≤1:5,000), (3) the growth and yield of corn. The temporal variability of the ECa due to varying soil moisture and temperature was taken into account by repeated measurements of the same fields and subsequent averaging of the ECa values. Significant correlations (r² = 0.76) were found between the mean weighted clay content (0–1.5 m) and the ECa. Furthermore, in soils with differently textured layers, ECa was used to estimate the thickness of the uppermost loess layer. A comparison of ECa and large‐scale soil maps reveals some pros and cons of ECa measurements. The main advantages of ECa recordings are the high spatial resolution in combination with low efforts. Yet, the ECa signal is no direct measure for a soil type or unit. Depending on the variability of substrates and layering, the ECa pattern can be a precise indicator for the spatial distribution of different soils. A strong conformity of the spatial variability of plant growth (derived from orthophotos and yield maps) and ECa patterns within a field indicates that the ECa signal per se—without conversion to traditional soil parameters—integrates the effects of various soil variables that govern soil fertility. Altogether, ECa surveys can be a powerful tool to facilitate and improve conventional soil mapping.  相似文献   

10.
Soil is a limited natural resource that needs to be efficiently salvaged during landscape construction operations for its further use as topsoil. To avoid inclusion of undesirable subsoil material (e.g. excess clay from Bt horizon), the majority of current guidelines define borrowed topsoil material as the surface layer of native soil, or the soil A horizon. Using information from over 7000 soil pedons from the 48 contiguous United States, we characterized selected topsoil properties and simulated the mixing of A and E horizons. The selected soil properties were compared among four different operationally defined topsoils: A surface layer, ASL; AP surface layer, APL; A horizon, A; and a mix of A and E horizons, AE. Average topsoil depth decreases in the order: AE > A > APL > ASL; sand content decreases in the order: ASL > AE > A > APL; clay decreases in the order: APL > A > ASL > AE; and organic carbon decreases in the order: ASL > A > APL > AE. On average, mixing of A and E horizons increases excavation depth by over 2.5 fold while having minor effects on soil texture; with AE/A ratio of 1.03, 1.00 and 1.07 for sand, silt and clay content, respectively. Yet, average soil organic matter content decreases by 38% upon mixing A and E horizons. Given the marked increase in soil volume and minor effect on soil texture, it is our suggestion that, for landscaping purposes, protocols for salvaging excavated soil material, for reuse as topsoil material include the E horizon (where it exists). Supplementing the recovered soil material with organic matter, such as compost, to overcome its dilution due to the incorporation of E horizon is recommended.  相似文献   

11.
Texture and salt type influence the relationships between saturated paste electrical conductivity (ECe) and EC of other soil/water ratios. The objectives of this study were to develop and validate relationships between ECe and EC1:5 suspension for soils in Yazd Province and evaluate the effects of soil texture and gypsum on those relationships. Three hundred twenty-two soil samples were collected, of which 272 (all data) were used to develop the models and 50 were used to validate them. The soils were divided into two general textural categories of coarse and fine and two categories of with (G) and without gypsum (NG). Gypsum content had a stronger impact on the accuracy of the suspension method in predicting ECe than texture. The ECe = 5.60 EC1:5 ? 4.37 and ECe = 5.37 EC1:5 + 0.57 models are recommended for soils with and without gypsum, respectively. The methodology can be implemented in other regions, particularly if gypsum is present.  相似文献   

12.
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13.
《Soil Use and Management》2018,34(2):219-235
Spatial variation in soils is required to supply ameliorants and fertilisers in the Australian sugarcane industry. However, traditional approaches are cost‐prohibitive. We investigated how a digital soil mapping (DSM) approach could be used to identify management zones. First, ancillary data including electromagnetic induction and gamma‐ray spectrometry data were collected. Using fuzzy k‐means (FKM) clustering, two to six management zones were identified. A similar approach was used to cluster percentage yield variations (2014, 2015 and 2016). Using restricted maximum likelihood analysis of topsoil (0–0.3 m) and subsoil (0.6–0.9 m) physical (e.g. clay) and chemical (e.g. exchangeable sodium percentage [ESP], and exchangeable calcium and magnesium) properties, three zones were found to minimise the mean squared prediction error (). By comparison, the three zones obtained using the percentage yield variation only minimised for subsoil ESP, which suggested it had some influence on sugarcane yield and productivity. Different rates of gypsum were required to manage the moderately sodic topsoil ESP for each zone. This was similarly the case with lime to overcome deficiencies in exchangeable calcium and magnesium. The results were consistent with yield variance, suggesting the smaller yield in some zones was due to topsoil sodicity and strongly sodic subsoil with a greater clay content. We concluded that the DSM approach was successful in identifying soil management zones and can be used to improve soil structural stability and fertility. The zones also had ramifications for strip trials to determine yield increases by comparing variable rate applications of gypsum and lime.  相似文献   

14.
为探究松嫩平原西部典型盐生景观土壤颗粒粒度组成及分形特征与土壤盐碱化之间的关系,采用体积分形维数模型计算了6种典型盐生景观土壤表层0—30 cm颗粒组成及分形维数,结合相关分析法分析了土壤分形维数与质地、盐碱特征之间的相关性。结果表明:(1)6种典型盐生景观中农田土壤分形维数值最小(2.35),碱蓬群落土壤最大(2.61),分形维数均值为2.48,分形维数随盐生景观土壤碱化程度增加而增大。(2)土壤质地越粗,砂粒含量越高,分形维数值越小;土壤质地越细,黏粒和粉粒含量越高,分形维数越大。(3)分形维数与盐分含量呈显著正相关(r=0.87,P0.05),尤其与盐分组成中HCO_3~-含量呈极显著正相关(r=0.89,P0.01),与养分中总磷含量呈极显著正相关(r=0.90,P0.01)。(4)土壤颗粒组成中砂粒、粉粒和黏粒与盐分、HCO_3~-及总磷含量也存在极显著相关性。不同盐生景观土壤分形维数与土壤颗粒组成和土壤盐分之间存在显著的相关性,因此可以用分形维数来反映土壤质地和指示土壤盐碱化特征。  相似文献   

15.
崩岗不同土层土壤水力学特性差异性分析   总被引：1，自引：0，他引：1  
为研究崩岗不同土层土壤水力学特性的差异性,采用离心法测定不同土层土壤水分特征曲线,筛选出适合的土壤水分特征曲线拟合模型,结合统计模型,推求土壤的当量孔径分布、比水容量、非饱和导水率和扩散率,分析崩岗不同土层土壤水力学参数的变化规律。结果表明,崩岗土层从红土层到砂土层的变化过程中,土壤质地由黏土向砂土变化;Fredlund&Xing模型对崩岗土壤土水特征曲线拟合效果最好;参数θs、α、n随着质地变黏重逐渐减小;随着土层深度的增加,土壤的持水性能降低;土壤比水容量、非饱和导水率和扩散率受土壤质地和基质吸力的共同影响。在低吸力阶段,3个指标随基质吸力变化比较平缓,砂土层土壤比水容量和非饱和导水率最大,扩散率最小;而在高吸力阶段,砂土层土壤的这些指标降低较快,且低于其他土层,各层土壤间导水率和扩散率差异随着基质吸力的增加而增大。  相似文献   

16.
Installation of pipeline utilities (oil, natural gas, water) in central Canada prior to the 1970s often resulted in extensive mixing of topsoil with subsoil materials within the easements due to largely unregulated construction practices. The main objectives of this study were (1) to develop a simple field protocol for the rapid delineation of the zone of topsoil disturbance (or topsoil–subsoil mixing) around buried utilities on agricultural land in southern Ontario, and (2) to characterize the zone of topsoil disturbance in the vicinity of an existing pre-1970s pipeline in terms of agronomically important soil properties. The study was carried out at six farm sites chosen along a pipeline easement (30+ years old) in southern Ontario. Soil organic carbon content, CaCO3 content and pH were found to be useful in delineating the zone of topsoil disturbance around the buried utility. Standardized laboratory techniques for determination of these three soil attributes were used to analyse surface soil samples (Ap horizons) taken at 1·5 m intervals along 45·7 m long transects oriented perpendicular to the easement. In addition, rapid field tests for these same three variables were adopted/developed and tested, and two portable instruments were evaluated for their usefulness for in situ soil property measurements. In particular, a Minolta™ CR-310 Chroma Meter was successfully used to relate moist soil colour to the organic carbon content of the surface soil. The chromaticity coordinate a* (CIE L*a*b* colour space notation) was shown to provide good estimates of organic carbon content for soils of medium to fine texture in this region of Ontario. The zone of topsoil disturbance was most often characterized by an appreciable increase in per cent CaCO3 equivalent and pH, and a decrease in organic carbon content (dilution), over the pipeline trench when compared to off-easement areas. The zone of topsoil disturbance was usually a minimum of 15 m wide (i.e. the approximate width of the original trench and workspace areas during construction), and frequently much wider due most likely to wet soil conditions at the time of construction, agricultural tillage translocation of topsoil over time, and other factors. It is recommended that rapid on-site determinations of the zone of topsoil disturbance should be based primarily on field estimates of CaCO3 content (10 per cent HCl) and organic carbon content (a* chromaticity coordinate using a portable colorimeter). Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

17.
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   

18.
Chickpea (Cicer arietinum L.) roots exude carboxylates. While chickpea commonly grows where the topsoil dries out during crop growth, the importance of carboxylate exudation by the roots and mobilization of soil P from below the dry topsoil has not been examined. The study investigates the response of carboxylate exudation and soil P mobilization by this crop to subsoil P fertilizer rate. In constructed soil columns in the glasshouse, the P levels (high, low, and nil P) were varied in the well‐watered subsoil (10–30 cm), while a low level of P in the dry topsoil (0–10 cm) was maintained. At flowering, rhizosphere carboxylates and rhizosphere soil from topsoil and subsoil roots were collected separately and analyzed. The concentration of total carboxylates per unit rhizosphere mass in the subsoil was nearly double that of the topsoil. Plants depleted sparingly soluble inorganic P (Pi), NaOH‐Pi, and HCl‐Pi, along with the labile Pi (water soluble and NaHCO3‐Pi). The P depletion by plants was greater from the subsoil than the topsoil. The study concluded that depletion of sparingly soluble P from the chickpea rhizosphere in the subsoil was linked with the greater levels of carboxylates in the rhizosphere. These findings indicate that chickpea, with its deep rooting pattern, can increase its access to subsoil P when the topsoil dries out during crop growth by subsoil rhizosphere modification.  相似文献   

19.
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   

20.
In the Far West Texas region in the USA, long‐term irrigation of fine‐textured valley soils with saline Rio Grande River water has led to soil salinity and sodicity problems. Soil salinity [measured by saturated paste electrical conductivity (ECe)] and sodicity [measured by sodium adsorption ratio (SAR)] in the irrigated areas have resulted in poor growing conditions, reduced crop yields, and declining farm profitability. Understanding the spatial distribution of ECe and SAR within the affected areas is necessary for developing management practices. Conventional methods of assessing ECe and SAR distribution at a high spatial resolution are expensive and time consuming. This study evaluated the accuracy of electromagnetic induction (EMI), which measures apparent electrical conductivity (ECa), to delineate ECe and SAR distribution in two cotton fields located in the Hudspeth and El Paso Counties of Texas, USA. Calibration equations for converting ECa into ECe and SAR were derived using the multiple linear regression (MLR) model included in the ECe Sampling Assessment and Prediction program package developed by the US Salinity Laboratory. Correlations between ECa and soil variables (clay content, ECe, SAR) were highly significant (p ≤ 0·05). This was further confirmed by significant (p ≤ 0·05) MLRs used for estimating ECe and SAR. The ECe and SAR determined by ECa closely matched the measured ECe and SAR values of the study site soils, which ranged from 0·47 to 9·87 dS m−1 and 2·27 to 27·4 mmol1/2 L−1/2, respectively. High R2 values between estimated and measured soil ECe and SAR values validated the MLR model results. Results of this study indicated that the EMI method can be used for rapid and accurate delineation of salinity and sodicity distribution within the affected area. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

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