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In this study several simplified drainage methods were tested, for determination of soil hydraulic conductivity in the field. The methods use water content profiles values measured during the drainage process. The unsaturated hydraulic conductivity is evaluated by making assumptions regarding hydraulic head gradients and by assigning simple analytical expressions to the relationk (θ) and the law...
Soil sampling and measurement often consume a significant portion of the budget available for a project. On a national or worldwide basis these activities require large investments, which are justified if the soil information leads to better decisions on land use or environmental issues to an extend which more than counterbalances the costs. This depends on both the costs and the quality of the information...
High concentration of heavy metals caused by soil pollution processes vary in a three-dimensional space. This study focuses on a strip of land which was sampled at three different depths. Fuzzy classification by fuzzy k-means was used to analyze the spatial variability for each separate layer. The concentrations of heavy metals showed abrupt changes in geographical space and the coefficients of variation...
Field trial data are frequently collected at scales different than at which answers are needed. The effects of soil and fertilizer on crop yield is assessed by using usually small, representative and accessible sites. Yield data obtained at plot scale (kg m -2 ) need to be interpolated or extrapolated to obtain yields at field scale (kg ha -1 ), which is the relevant management...
A geostatistical descriptor of the spatial distribution of soil profile classes is discussed, the Sum of Indicator Variograms (SIV). This function may be estimated for a region from observations of the soil profile class occurring at a systematic array of sample sites, and fitted by an authorised variogram model. It is shown that the fitted variogram model can be used, given some simplifying assumptions,...
There is increasing interest in modeling soil water content over relatively large areas or scales. In general, the spatial variability of soil water content increases with scale, but it is not known how much or at which scales. High spatial variability constrains soil water models by reducing the accuracy of input parameters, calibration and verification data. It may also require representation of...
Modern site-specific agriculture uses yield estimates based on estimates of soil properties in locations other than the sampling points. Techniques are needed to assess the uncertainty of these soil property estimates. Such uncertainty assessments can be based on stochastic imaging of soil parameters: a technique that consists of generating many equiprobable maps of the parameters for the same site...
This paper introduces the extended Spatial Simulated Annealing (SSA) method to optimise spatial sampling schemes for obtaining the minimal kriging variance. Sampling schemes are optimised at the point level. Boundaries and previous observations can be taken into account. This procedure extends ordinary SSA which focuses entirely on variogram estimation and even distribution of observations over the...
The spatial variation of soil properties within landscapes is controlled by the soil forming factors relief, parent material, climate, organisms, and time. Although this relation is a paradigm in soil survey, it is rarely considered in the analysis of spatial variability of soil properties. Homogeneous soil units are mostly mapped according to the soil properties found close to the soil surface. Nevertheless,...
We measured the lateral distribution of Br in a well-structured soil (clayey, kaolinitic, thermic Typic Kanhapludults) over a period of 40 days following a leaching event with Br-tagged water (Event-1) and the subsequent vertical transport of solute that occurred following a second leaching event (Event-2). The objectives were to determine the time required for solutes to become uniformly distributed...
The variability of the transport characteristic of pesticides has rarely been investigated. In this study, 99 undisturbed soil columns representing a 1.8-ha field site in regular agricultural use were subjected to leaching tests with the two herbicides terbuthylazine and isoproturon. Emphasis was placed on the field-like flow conditions, such as water desaturation and moderate flow velocity (q=0.58...
Spatial variability of the soil hydraulic properties affects unsaturated field-scale solute transport. We obtained the hydraulic properties of a sandy loam and a loam soil through pressure outflow experiments and assessed their variability by a scaling procedure. We used the soil hydraulic properties to quantify solute transport in a fallow field over a 214-day period as a function of water table...
Continuous classification was applied to variables measuring landform, extracted from a digital elevation model (DEM) of a field. It was shown that soil physical properties (gravimetric water content at two depths and sand/clay content) and soil mineral nitrogen in the subsoil, were linearly related to membership values in these classes (the memberships having been spatially smoothed and transformed...
Predictions of soil bulk density and field capacity at 0-10, 10-20 and 20-30 cm depths in Rhodic and Xhantic Ferralsols at the Havana-Matanzas plain are validated at a number of measured sites. It was done in order to compare the prediction accuracy under the constraint of a small data set by the following three procedures: (1) soil maps, (2) kriging, considering Xhantic and Rhodic Ferralsols as different...
At all scales (delta-wide to individual fields) the acid sulphate soils of the Mekong delta show high spatial variability and closely intertwined soil types. Focusing on the field level in the Plain of Reeds, clear correlations are observed between soil physical and chemical characteristics, natural vegetation, groundwater table and microelevation. On ''high'' locations (higher than 85 cm above mean...
Soil variability within fields results from complex geological and pedological processes, therefore soil variables are expected to be correlated in a scale dependent way. An accurate soil characterization, taking into account soil and spatial variability, will allow the farmer to follow crop management practices fitted with the real soil situation. The study of the scale-dependent correlation structure...
Previous reports demonstrated that data from air- and spaceborne sensors are appropriate for delineation of soil patterns. Also, many attempts have been made to use digital elevation model (DEM) for deriving soil information. However, little is known about the potential use of low spatial resolution satellite and digital elevation data in small-scale soil mapping. A case study was conducted to assess...
Soil information is needed at the regional scale to enable planning of land utilization in accordance with its capacity. Because existing soil maps are inadequate in Australia to meet this demand, there is the need to develop models that could be used to improve soil maps at this scale for aggregation up to the national or continental scale. The most efficient and cheapest means of achieving this...
We evaluated the fine-scale (cm) variability of bulk density (ρ B ), organic matter content (%OM), volumetric water content (θ V ), and carbon mineralization rate (C min ) at specific values of water potential in an old field soil. We measured these variables in soil samples obtained using paired abutting, 5-cm diameter, 10-cm deep cores. To compare abutting core...
The accuracy of digital elevation models (DEM) and DEM-derived products depends on several factors, including the horizontal resolution and vertical precision at which the elevation data are represented, and the source of the elevation data. This accuracy becomes increasingly important as we extend the use of DEM data for spatial prediction of soil attributes. Our objective was to compare terrain...
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