Chemical migration during soil water retention curve evaluation.

Wetting and drying (W-D) cycles can induce important elemental migrations in soils. The main purpose of this work was to study the possible existence of soil chemical elemental migrations in samples submitted to repeated W-D cycles during evaluations of soil water retention curve (SWRC). The experimental measurements were carried out by Atomic Absorption Spectrometry (AAS) for Ca(2+), Mg(2+) and K(+) on samples of three different Brazilian tropical soils (Geric Ferralsol, Eutric Nitosol and Rhodic Ferralsol).

Riparian forest potential to retain sediment and carbon evaluated by the 137Cs fallout and carbon isotopic ratio techniques.

Riparian forests can provide an important service for aquatic ecosystems by sequestering hillslopederived sediments. However, the width of a riparian buffer zone required to filter sediments is not yet wellunderstood. Here are used two complementary tracers to measure sediment retention.

The 15N isotope to evaluate fertilizer nitrogen absorption efficiency by the coffee plant.

The use of the 15N label for agronomic research involving nitrogen (N) cycling and the fate of fertilizer-N is well established, however, in the case of long term experimentation with perennial crops like citrus, coffee and rubber tree, there are still shortcomings mainly due to large plant size, sampling procedures, detection levels and interferences on the system. This report tries to contribute methodologically to the design and development of 15N labeled fertilizer experiments, using as an example a coffee crop fertilized with 15N labeled ammonium sulfate, which was followed for two years. The N of the plant derived from the fertilizer was studied in the different parts of the coffee plant in order to evaluate its distribution within the plant and the agronomic efficiency of the fertilizer application practice.

Application of gamma-ray computed tomography to analysis of soil structure before density evaluations.

Several studies have shown that physical properties of a soil may vary significantly over relatively short distances. This variability is due to the nature of the soil, agricultural management practices and sampling procedures; this study is focused on the latter factor. gamma-Ray tomography was used as a tool to evaluate the quality of soil samples collected for estimating physical characteristics of the soil and to detect possible damage to the soil in the process of sampling.

Gamma-ray-computed tomography to investigate compaction on sewage-sludge-treated soil.

Soil compaction is one of the fundamental parameters to evaluate the environmental impact of agricultural machinery traffic on soils. Compaction causes modifications on soil physical properties such as changes in porosity and structure that are related to soil water movement and gas exchange The objective of this work was to evaluate soil surface sealing after sewage-sludge application, and the influence of agricultural machinery traffic, through computed tomography. A first generation tomograph was used having a 137Cs source and a 3 in x 3 in NaI(Tl) scintillation crystal detector coupled to a photomultiplier tube.

Gamma-ray computed tomography to characterize soil surface sealing.

The application of sewage sludge as a fertilizer on soils may cause compacted surface layers (surface sealing), which can promote changes on soil physical properties. The objective of this work was to study the use of gamma-ray computed tomography, as a diagnostic tool for the evaluation of this sealing process through the measurement of soil bulk density distribution of the soil surface layer of samples subjected to sewage sludge application. Tomographic images were taken with a first generation tomograph with a resolution of 1 mm.