| 1. |
- Bahri, Akissa, et al.
(författare)
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Nitrogen source impact on the spatial variability of organic carbon and nitrogen in soil
- 1996
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Ingår i: Soil Science. - : Ovid Technologies (Wolters Kluwer Health). - 0038-075X. ; 161:5, s. 288-297
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Tidskriftsartikel (refereegranskat)abstract
- Sewage sludge amendment of soils leads to an increase in soil fertility, but may induce heterogeneities not initially present in the soil. Spatial variation of soil organic carbon (C) and nitrogen (N) was studied in a heavy clay soil after a sewage sludge application and NPK-treatment (nitrogen, phosphorus, and potassium) using geostatistical approaches. In total, 314 soil samples were taken on two adjacent 40 m × 40 m plots (one sludge-amended and one NPK-treated) at three different scales (scale 40 m: 40 m × 40 m, scale 10 m: 10 m × 10 m, and scale 2.5 m: 2.5 m × 2.5 m). The coefficient of variation almost doubled for both C and N after sludge treatment. Because of this, more samples were needed to estimate mean values for the sludge-amended plot compared with the NPK-treated plot. To estimate the population mean at the 95% confidence level with 10% uncertainty (for all scales and all treatments), 5 to 13 samples were required for C and 4 to 7 for N. The C was spatially more structured compared to N. Semivariances of the sludge-amended plot displayed higher values compared with the NPK-treated plot, except for N at the smallest scale. This was probably due mainly to the sludge characteristics and the application technique of the sewage sludge. Constant semivariance (sill) was reached at ranges up to 15 m for C, but it was often unbounded (>40 m) for N.
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| 2. |
- Olsson, Jonas, et al.
(författare)
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Nonlinear and scaling spatial properties of soil geochemical element contents
- 2001
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Ingår i: Water Resources Research. - 0043-1397. ; 37:4, s. 1031-1042
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Tidskriftsartikel (refereegranskat)abstract
- The present study aimed at investigating whether a nonlinear and scaling approach is suitable for statistically characterizing the spatial variability of soil geochemical element contents at field conditions. Spatial distributions of 20 soil geochemical elements' contents in an agricultural field soil were investigated. Two indicators of nonlinear scaling were employed, empirical probability distribution functions (pdfs) and structure functions. For the pdfs, a trend was discovered with major elements naturally occurring in the soil being hyperbolic and minor trace elements being close to Gaussian. Further, fertilizer management was found to modify the behavior of related elements. The structure functions were generally nonscaling for major elements and scaling for minor elements, however, without any noticeable effect of fertilizer application. The scaling was of both monoaffine and multiaffine type. This suggests that the random cascade models recently used within geophysics may be useful also for geochemical element variability in soil.
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| 3. |
- Yasuda, Hiroshi, et al.
(författare)
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Lateral bromide distribution in a vertic clay soil
- 1998
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Ingår i: Soil Science. - : Ovid Technologies (Wolters Kluwer Health). - 0038-075X. ; 163:7, s. 544-555
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Tidskriftsartikel (refereegranskat)abstract
- In order to control the transport of toxic elements, dissolved salts, and nutrients in agricultural areas, information on the spatial variability of field-scale transport properties is needed. To evaluate this for an unsaturated layered clayey soil, tracer tests were conducted at the Cherfech experimental field research station in Tunisia. Bromide-tagged water was infiltrated under ponding conditions on a 21.7-m2 horizontal field plot equipped with 60 solute samplers, 15 neutron probe access tubes, and 15 piezometers. Volumetric soil water content was measured by means of a neutron probe at five depths, and soil moisture samples were withdrawn through ceramic soil water samplers at four depths, each with 15 suction samplers. The results showed typical evidence of preferential flow, with a wide variety of travel times with depth. This was noted especially for deeper soil layers, which displayed a large horizontal variation. In two tracer experiments, the groundwater tracer concentration increased up to twice the concentration of the water in the unsaturated zone withdrawn from different depths. This shows that bypass directly to the groundwater, initially at 1.5 m depth, occurred under ponding with chemigation.
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