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1.
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2.
In digital soil mapping (DSM), a fundamental assumption is that the spatial variability of the target variable can be explained by the predictors or environmental covariates. Strategies to adequately sample the predictors have been well documented, with the conditioned Latin hypercube sampling (cLHS) algorithm receiving the most attention in the DSM community. Despite advances in sampling design, a critical gap remains in determining the number of samples required for DSM projects. We propose a simple workflow and function coded in R language to determine the minimum sample size for the cLHS algorithm based on histograms of the predictor variables using the Freedman-Diaconis rule for determining optimal bin width. Data preprocessing was included to correct for multimodal and non-normally distributed data, as these can affect sample size determination from the histogram. Based on a user-selected quantile range (QR) for the sample plan, the densities of the histogram bins at the upper and lower bounds of the QR were used as a scaling factor to determine minimum sample size. This technique was applied to a field-scale set of environmental covariates for a well-sampled agricultural study site near Guelph, Ontario, Canada, and tested across a range of QRs. The results showed increasing minimum sample size with an increase in the QR selected. Minimum sample size increased from 44 to 83 when the QR increased from 50% to 95% and then increased exponentially to 194 for the 99% QR. This technique provides an estimate of minimum sample size that can be used as an input to the cLHS algorithm.  相似文献   

3.
Variation in soil texture has a profound effect on soil management, especially in texturally complex soils such as the polder soils of Belgium. The conventional point sampling approach requires high sampling intensity to take into account such spatial variation. In this study we investigated the use of two ancillary variables for the detailed mapping of soil texture and subsequent delineation of potential management zones for site‐specific management. In an 11.5 ha arable field in the polder area, the apparent electrical conductivity (ECa) was measured with an EM38DD electromagnetic induction instrument. The geometric mean values of the ECa measured in both vertical and horizontal orientations strongly correlated with the more heterogeneous subsoil clay content (r = 0.83), but the correlation was weaker with the homogenous topsoil clay content (r = 0.40). The gravimetric water content at wilting point (θg(?1.5 MPa)) correlated very well (r = 0.96) with the topsoil clay content. Thus maps of topsoil and subsoil clay contents were obtained from 63 clay analyses supplemented with 117θg(?1.5 MPa) and 4048ECa measurements, respectively, using standardized ordinary cokriging. Three potential management zones were identified based on the spatial variation of both top and subsoil clay contents. The influence of subsoil textural variation on crop behaviour was illustrated by an aerial image, confirming the reliability of the results from the small number of primary samples.  相似文献   

4.
Natural desalting in saline land with shallow groundwater and high evaporation is proceeding slowly. The main objective of the study was to evaluate the efficiency of straw mulching on desalinization by rainfall in saline land. Two sites of Solonchaks with different electrical conductivity (EC1:5) were selected to compare topsoil (0–40 cm) EC1:5 dynamics between bare land and straw mulching treatment. Soil samples were taken from May 2014 to April 2015 for determination of EC and pH, initial and termination samples were also used to measure Na+, Ca2+ and Mg2+ for calculating sodium adsorption ratio. The results demonstrated that supplementing salt leaching with straw mulch significantly decreased the EC1:5 of the soil profile (0–80 cm) when compared with no mulch. The both of topsoil (0–40 cm) EC1:5 and ECa/ECi decreased exponentially with the increase of cumulative rainfall and Dw/Ds under straw mulching, respectively. 178.6 and 351.9 mm of averaging rainfall were needed for removing 80% of salts in the 0–20 and 0–40 cm soil profile layers, respectively across all the cases of straw mulching and various EC1:5. These findings suggested that rainfall combined with straw mulching could be popularized as effective measures to ameliorate saline soil for agriculture and forestry utilization.  相似文献   

5.
The emergence of a new sensor technology based on the use of ion‐selective membranes provides an increasing number of opportunities for on‐the‐go field measurements of soil nutrients and soil pH. In the future, on‐the‐go sensing should provide a cost‐effective monitoring of heterogeneous soils with high sampling resolution. It is suitable for site‐specific management because it can be focused on the spatial representativity of observation. This study evaluates the on‐the‐go‐sensing sampling design by comparing it with a standard approach to soil sampling for soil pH and the base nutrients P, K, and Mg under local field conditions in Germany. Soil samples were taken in two test sites at a resolution and in a manner as if they were sampled with an on‐the‐go sensing system and were compared with soil samples taken at a coarser resolution and with standard methods. In general, a higher variability was observed among the on‐the‐go samples due to their smaller sample support. The finer sampling resolution of the on‐the‐go design improved field‐scale semivariogram‐analysis results, identifying the spatial structures for soil pH, P, and Mg clearly. In addition, kriged maps of these soil parameters had predominantly higher estimation accuracies. However, the on‐the‐go samples were strongly influenced by the small‐scale variability of K in one of the test sites. This variability increased the kriging standard deviation for K by 50% compared with standard sampling design. Despite of this problem, the on‐the‐go‐sensing sampling design revealed field‐scale spatial variability for base nutrient status more accurately. Except for K, the mean absolute error of fertilizer‐application maps was reduced when using the on‐the‐go sample design in comparison with the standard sample design (Ca: 210/268 kg ha–1, P: 2.85/6.75 kg ha–1, K: 13.7/6.0 kg ha–1, Mg 5.7/6.8 kg ha–1). This will reduce over‐ and underfertilization using variable‐rate fertilizer‐application systems. In the future, it will be of interest if real on‐the‐go soil‐sensor measurements exhibit the same variability behavior addressed here or if results will differ substantially.  相似文献   

6.
不同采样设计会对土壤呼吸空间变异特征的预测精度产生重要影响。本研究选取黄淮海平原北部潮土区1 km×1 km夏玉米样地,在7×7单元规则格网(样点间距167 m)、完全随机(样点平均间距433 m)以及3×3单元规则格网+完全随机(样点平均间距405m)3种布点方式的基础上,保持样本总量(49)不变,以占总样点2%～14%的短距离样点(样点间距4m)随机替换原方案相应样点个数的方法优化布点方式,应用普通克里金法插值,以均方根误差(RMSE)和确定系数(R2)作为验证指标,检验基于3种布点方式设置的短距离样点对土壤呼吸空间变异预测精度的影响。结果表明:研究区土壤呼吸平均速率为2.65μmol·m?2·s?1,空间分布均呈西高东低,表现出中等程度变异。采样设计对土壤呼吸空间分布的预测精度影响显著,基于3种布点方式设置短距离样点可提高预测精度7%～13%。无短距离样点替换时,规则格网+完全随机的布点方式最优,比完全随机布点和规则格网布点的空间插值预测精度分别提高10%和22%;设置短距离样点替换后,在最优布点方式(规则格网+完全随机)中,对土壤呼吸空间变异的预测精度可再提高4%～7%,其中短距离样点个数占样本总量10%对土壤呼吸空间变异预测精度的提高最为明显。研究发现,基于相同的样本数量设置短距离样点可增加区域范围内样点密度,提高土壤呼吸空间变异预测精度及试验结果的可靠性。因此,在黄淮海平原北部潮土区100 hm2尺度的夏玉米样地中,规则格网+完全随机+10%短距离样点的布点方式是预测土壤呼吸空间变异最适宜的采样布点方式。  相似文献   

7.
A field study was undertaken to compare dissolved organic carbon (DOC) concentrations in soil solutions obtained with three different sampling methods over a range of soil types. The sampling devices used were a tension‐free collector, a tension Prenart collector and a tension Rhizon collector. Samples were collected fortnightly for a year at seven sites in northern England, each collection being replicated three times. The soil solution DOC ranged from 1.3 g m?3 in an acid ranker to 34.7 g m?3 in a peat. The DOC concentrations obtained with the three methods correlated reasonably well (r2 = 0.6–0.8) but with an indication of bias, as the best fit line differed from the 1:1 line. The tension‐free collector gave generally higher DOC concentrations except at very low concentrations (in the acid ranker soil). The DOC concentrations measured with the tension‐free collectors were significantly (P < 0.05) higher than those obtained with Prenart and Rhizon collectors at four and six sites, out of seven, respectively. Subsequent laboratory tests on tension‐free collected samples showed no DOC loss on filtration through 0.1 and 0.22‐μm membranes, whereas a significant loss of DOC occurred when tension‐free collected samples were subsequently passed through Prenart and Rhizon collectors, indicating a probable sampling artefact with the tension devices. The difficulties of acquiring representative soil solution samples are discussed, together with the advantages and disadvantages of tension and tension‐free methods.  相似文献   

8.
Soil greenhouse gas (GHG) emissions are complex, and their study requires considerable sampling of field spatial and temporal differences. Manual and simple automated gas‐collection techniques used at multiple sites during specific time intervals are labor intensive. The objective of this work was to construct a device that can independently collect GHG samples with the accuracy and precision of manually drawn samples. An automated collector of terrestrial systems (ACTS) is a 24‐h, 7‐d/week programmable sampler used in the field for real‐time gathering and containment of soil GHG emissions. The sampler opens and closes an exterior soil gas chamber, mixes gases in the chamber by turning fans on/off, and utilizes programmable circuits to purge the system and draw a sample from the chamber with a pneumatic‐driven syringe. Each sample was stored in an evacuated vial held in a 30‐vial capacity carousel. Vial content was analyzed for carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) at the U.S. Department of Agriculture (USDA)–Agricultural Research Services (ARS) Agroecosystem Management Research Unit (AMRU). A Tracor MT‐220 gas chromatograph (GC) configured with a thermal conductivity detector (TCD) was used for CO2 analysis, and an automated gas‐sampling system (AGSS) attached to a Varian 3700 GC configured with flame ionization detection (FID) and electron capture detection (ECD) was used for CH4 and N2O analysis. Field and laboratory mean values and coefficients of variation (standards and field concentrations of CO2, CH4, and N2O ranging from ambient to 71 kg ha?1 d?1 had coefficients of variation ranging from 1.2 to 4.2%) were similar between ACTS and manually drawn samples. Results showed strong correlation (R2 = 0.81 to 1.00) between sampling methods. The sampler design provides a realistic and inexpensive approach for collecting emission samples while reducing human error associated with adverse sampling conditions and fatigue. The ACTS has potential for use in monitoring and comparing management practices in terrestrial systems to determine their contribution to GHG emissions.  相似文献   

9.
Abstract. Recent developments in in situγ ray spectrometry offer a new approach to measuring the activity of radionuclides such as 137Cs and 40K in soils, and thus estimating erosion or deposition rates and field moist bulk density (ρm). Such estimates would be rapid and involve minimal site disturbance, especially important where archaeological remains are present. This paper presents the results of a pilot investigation of an eroded field in Scotland in which a portable hyper pure germanium (HPGe) detector was used to measure γ ray spectra in situ. The gamma (γ) photon flux observed at the soil surface is a function of the 137Cs inventory, its depth distribution characteristics and ρm. A coefficient, QCs, derived from the forward scattering of 137Cs γ ray photons within the soil profile relative to the 137Cs full energy peak (662 keV), was used to correct the in situ calibration for changes in the 137Cs vertical distribution in the ploughed field, a function of tillage, soil accumulation and ρm. Based on only 8 measurements, the agreement between in situγ ray spectrometry and soil sample measurements of 137Cs inventories improved from a non significant r2=0.05 to a significant r2=0.62 (P<0.05). Erosion and deposition rates calculated from the corrected in situ137Cs measurements had a similarly good agreement with those calculated from soil cores. Mean soil bulk density was also calculated using a separate coefficient, QK, derived from the forward scattering γ photons from 40K within the soil relative to the 40K full energy peak (1460 keV). Again there was good agreement with soil core measurements (r2=0.64; P<0.05). The precision of the in situ137Cs measurement was limited by the precision with which QCs can be estimated, a function of the low 137Cs deposition levels associated with the weapons testing fallout and relatively low detector efficiency (35%). In contrast, the precision of the in situ ρm determination was only limited by the spatial variability associated with soil sampling.  相似文献   

10.
Soil pore size distribution(SPSD) is one of the most important soil physical properties. This research investigated the relationships of location and shape parameters of the SPSD curves with plant-available water(PAW) and least limiting water range(LLWR) of the light-textured soils at the Torogh Agricultural Research Station in north-eastern Iran. Soil moisture release curve(SMRC), PAW and LLWR in matric heads of 100 and 330 h Pa for the field capacity and location and shape parameters of the SPSD curves of 30 soils with different texture and organic carbon contents were determined, and the variable relationships were statistically analyzed. The results showed that the median equivalent pore diameter(de), mean de, standard deviation(SD*), and skewness of the SPSD curves were significantly correlated with PAW(PAW330) and LLWR(LLWR330) measured in a matric head of 330 h Pa. Decrease in deand increase in the diversity of soil pore size(SD*) increased PAW330 and LLWR330. The SD* values of all the soil samples were lower than the optimal ranges suggested in literature. Neither PAW nor LLWR values were significantly different in the soils with the optimal modal deand those with non-optimal modal de. Optimal values of median and mean equivalent pore diameters and kurtosis of SPSD curves led to a significant improvement of PAW330 and LLWR330 as soil physical quality indicators. It was recommended to revise the optimal ranges for SD* and modal defor future studies.  相似文献   

11.
设施土壤盐分的累积、迁移及离子组成变化特征   总被引：32，自引：1，他引：32  
通过对我国不同地区设施栽培现状的野外调查和取样分析,研究了设施栽培条件下土壤盐分的累积、迁移及离子组成变化特点。结果表明:1)设施栽培条件下,土壤含盐量的变化幅度大,且均明显高于露地土壤,各研究区域内已有40%8～9%的土壤含盐量超过了作物正常生长的临界浓度。2)设施栽培的可持续利用周期较短,连续种植到4年左右的设施土壤,其耕层盐分的累积量可达到作物的生长障碍临界点,之后因设施使用率的下降以及采取的措施而有所降低,但仍高于露地土壤。设施连续使用会导致土壤环境质量的不断恶化。3)设施土壤剖面(0100.cm)盐分含量均高于相邻露地,盐分含量随土层深度增加而降低,其中耕层(020.cm)的盐分含量显著高于其下各层;盐分离子在土壤剖面的运移同时存在着明显的向底层迁移和向表层聚集两种方式,但以表聚为主;此外,盐分离子的大量累积和向底层迁移,特别是NO3-的淋溶已严重影响到部分地区的地下水水质。4)设施栽培后,土壤中的NO3-、SO42-、Cl-、Ca2+、Mg2+、K+、Na+均有不同程度的累积,阴离子以NO3-和SO42-为主,阳离子以Ca2+为主。盐分的大量累积以及某些离子的相对富集在一定程度上引起了作物养分的供需失衡、土壤酸化、棚室内CO2供应不足等生产问题。  相似文献   

12.
Understanding the watershed-scale spatial distribution of soil salinity and its compositions is important for soil management. Here, we present the first study on the Manas River watershed in northwest China. In this study, we took soil samples in upper 20 cm of soil from 186 locations across the watershed and measured total salt concentration (TSC), salt ion composition and soil particle size distribution (PSD). We found that on average topsoil TSC tended to increase, from 3.55 g kg−1 in upstream regions to 19.40 g kg−1 in downstream regions. The stoichiometric analysis showed that the equivalence ratio of soil Cl- to SO42− increased from 0.53 in upstream regions to 2.12 in midstream regions, and further to 3.76 in downstream regions; thus, the soil types were classified into chloride–sulfate, sulfate–chloride and chloride soils types, respectively. Additionally, proportions of small (<2 μm in diameter) and large (>2,000 μm) soil particles increased, while that of medium sizes (2–50 μm) decreased from upstream to downstream, with an increasing coefficient of variance (CV) in PSD. Taken together, watershed-scale topsoil salinity may be horizontally characterized by increased TSC and Na+ & Cl− proportions, greater equivalence ratio of Cl− vs. SO42− and more balanced distribution of PSD along with surface water flow. Results demonstrated that soil salinity and its ions compositions showed a great variation across the watershed scale, suggesting that soil management may consider the spatial heterogeneity of saline–alkaline soil types, and our results provided scientific guidance for local soil management and restoration.  相似文献   

13.
Deriving an accurate three-dimensional (3D) spatial distribution of heterogeneous soil pollutants at contaminated sites using traditional spatial interpolation methods, such as inverse distance weighting (IDW), is challenging; especially when only limited borehole data are available. This study presents a novel IDW-COV method, where weighting is determined by optimizing relative importance between feature distances of covariates and spatial distances to soil sample locations. The method was tested by mapping the 3D distributions of Cr (VI) and total Cr at a Cr salt production workshop (Site A) and a legacy Cr slag stacking site (Site B). The results were compared with those of IDW, the soil land inference model (SoLIM), and the SoLIM combined with IDW method (SoLIM-IDW). The proposed IDW-COV method returned the highest accuracy, with R2 values of 0.83 for Cr (VI) in Site A and 0.75 for total Cr in Site B, compared with 0.65 and 0.57 for IDW, 0.16 and 0.58 for SoLIM, and 0.73 and 0.61 for SoLIM-IDW. This study highlights the importance of considering differences in explanatory power between multidimensional covariate and geographical spatial distance when incorporating multisource auxiliary data into weighted average estimators and provides guidance for mapping 3D distributions of heterogeneous pollutants from sparse soil borehole data .  相似文献   

14.
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   

15.
Spatial distribution of soil mineral‐N content (Nmin) is a scale‐variant process. Precision farming assumes knowledge about the spatial distribution of Nmin. Moreover, sampling in management zones is based on the assumption of spatial dependence between sampling points. In the present study, variability structure of Nmin and the sources of variability were investigated. Within an agricultural landscape, Nmin was investigated across a field in a nested design over four consecutive years. Temporally unstable structure of individual nests require a sampling with several nests in the field. In the investigated field, 35%–49% of the total variability derived from small‐scale variability observed at spatial distances of <5 m and from sampling and analytical errors. Differences between 10 and 26 kg N ha–1 for the soil depth increment 0–60 cm can be expected. Uncertainty due to analytical errors were in the order of 5–10 kg N ha–1 for a 0–60 cm layer.  相似文献   

16.
In Germany, field‐average soil NO3‐ measurements are used to identify agricultural risks of groundwater pollution and to evaluate the compliance of land users with environmental regulations. In the present study, it was tested at three typical agricultural sites if common practices of soil NO3‐ sampling were appropriate to obtain reliable estimates of the mean field NO3‐ content in fall. Three sites of 1 ha area were extensively sampled for NO3‐. Ordinary statisticial analyses were conducted on the NO3‐ data in order to calculate how many samples per ha were required to predict the mean field NO3‐ with a given accuracy. Variograms were derived to assess applicability and relevance of ordinary statistical methods for heterogeneous fields. Results from statistical analysis suggest that at two sites common practices of soil NO3‐ sampling would have been adequate to obtain estimates of the actual mean field NO3‐ content with a sampling error less than 10 kg NO3‐‐N ha—1 at a 95% probability level. At the other site, common practices obviously would have failed because NO3‐ contents varied much more spatially. It remains a problem of soil sampling for NO3‐ analysis that information on field heterogeneity is frequently not available a priori.  相似文献   

17.
Soil physicochemical properties and microbial communities are highly heterogeneous and vary widely over spatial scales, necessitating careful consideration of sampling strategies to provide representative and reproducible soil samples across field sites. To achieve this, the study aimed to establish appropriate sampling methodology and to determine links between the variability of parameters, utilising two sampling strategies. The first (design 1) involved extracting 25 cores from random locations throughout the field and pooling them into five sets of five cores. The second (design 2) involved a further 25 cores within five 1 m2 sub-plots. Sub-samples from each sub-plot were pooled in order to determine between and within sub-plot variability. All samples were analysed independently and as pooled sub-samples. Results indicate that pooling spatially separated samples significantly reduced the variability in pH, compared to individual samples. Pooling samples from a small area resulted in lower within sub-plot variability than between sub-plots for pH and bacterial community composition assessed by terminal-restriction fragment length polymorphism analysis. Following multivariate statistical analysis, a large amount of variation in community composition was explained by soil pH, which is remarkable given the relatively small size of the sampling area and minor differences in pH. Moisture content was also important in determining bacterial communities in the random design (design 1). In the 1 m2 sub-plot design (design 2), the spatial location of the plots explained a large degree of the variation in bacterial community composition between plots, which was due to spatial autocorrelation of pH and possible additional environmental parameters. This study emphasises the importance of sampling design for obtaining representative samples from soil.  相似文献   

18.
The plant minimal exchangeable K (EPl,min) defines the lower accessible limit of the most available pool of soil K to plants. It is also an index of long‐term K reserve in soils. However, its estimation by the classical method of exhaustion cropping is laborious. This study aimed at comparing EPl,min values obtained by the exhaustion cropping method with EPl,min values estimated by an alternative approach based on the cationic exchange capacity (CEC) of the infinitely high selective sites for K (i.e., always saturated with K) in the K‐Ca exchange (EK‐Ca,min). A set of 45 soil samples, corresponding to the various fertilization K treatments of 15 long‐term K fertilization trials, was used in this study. The selected soil samples presented a wide range of texture, CEC, and exchangeable K. The plant minimal exchangeable K was found more or less independent of the K treatment, whereas EK‐Ca,min increased when the soil exchangeable K content increased. The plant minimal exchangeable K was systematically lower than EK‐Ca,min, showing that EK‐Ca,min is at least partially available to the plant. Hence, EK‐Ca,min is not a surrogate of EPl,min. Conversely, the plant minimal exchangeable K was strongly, positively correlated to soil CEC (measured at soil pH; r2 = 0.90***). This soil property can consequently be used as a proxy of EPl,min.  相似文献   

19.
Effects of charcoal production on soil physical properties in Ghana   总被引：15，自引：0，他引：15  
Charcoal production, widespread in Ghana like in other W African countries, is a major driver of land‐cover change. Effects of charcoal production on soil physical, including hydrological, properties, were studied in the forest–savannah transition zone of Ghana. Core and composite samples from 12 randomly selected sites across the width of Kotokosu watershed were taken from 0–10 cm layer at charcoal‐site soils and adjacent field soils (control). These were used to determine saturated hydraulic conductivity (Ksat), bulk density, total porosity, soil texture, and color. Infiltration rates, surface albedo, and soil‐surface temperature were also measured on both sites. The results showed that the saturated hydraulic conductivity of soils under charcoal kilns increased significantly (p < 0.01) from 6.1 ± 2.0 cm h–1 to 11.4 ± 5.0 cm h–1, resulting to a relative increase of 88%. Soil color became darkened under charcoal kilns with hue, value, and chroma decreasing by 8%, 20%, and 20%, respectively. Bulk density on charcoal‐site soils reduced by 9% compared to adjacent field soils. Total porosity increased from 45.7% on adjacent field soils to 50.6% on earth kilns. Surface albedo reduced by 37% on charcoal‐site soils while soil‐surface temperature increased up to 4°C on average. Higher infiltration rates were measured on charcoal‐site soils, which suggest a possible decrease in overland flow and less erosion on those kiln sites.  相似文献   

20.
The aim of this study was to investigate how electromagnetic induction can be used to improve the characterization of N dynamics in a 1.2 ha pasture. The soil apparent electrical conductivity (ECa) was measured by electromagnetic induction using an EM38DD. At 116 locations, soil samples were taken according to a clustered sampling design, three times during one winter, and analyzed for the NO3––N content in the topsoil (0–60 cm). Management zones were delineated using a fuzzy k-means classification of the interpolated ECa measurements. Two ECa zones were found, reflecting mainly differences in soil texture. Since the mean NO3––N content was different for the two ECa zones (24 and 65 kg/ha in November 2002), the residuals were interpolated using stratified simple kriging. This allowed evaluating the NO3– dynamics during the winter in both zones; one ECa zone showed a higher risk for NO3– losses than the other calling for a site-specific N management. As a validation, NO3––N was interpolated using ordinary kriging without stratification. This resulted in similar zones confirming the usefulness of the ECa measurements to assess N-specific management zones, even within small fields.  相似文献   

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