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Purpose: Soil compaction resulting from mechanisation of forest operations reduces air permeability and hydraulic conductivity of soil and can result in the development of hydromorphic and/or anoxic conditions. These hydromorphic conditions can affect physico-chemical properties of the soils. However, early detection of these effects on mineralogical portion of soils is methodologically difficult. Materials and methods: To analyse the effects of soil compaction on iron minerals in loamy Luvisol, three compacted and three non-compacted soil profiles up to the depth of 50 cm were collected from an artificially deforested and compacted soils after 2 years of treatment. Soil was compacted with the help of 25 Mg wheeler's load to increase the dry bulk density of soil from 1.21 ± 0.05 to 1.45 ± 0.1 g cm. Soil samples were analysed by X-ray diffraction (XRD) and were treated by citrate bicarbonate (CB) and dithionite citrate bicarbonate (DCB) under controlled conditions. Major and minor elements (Fe, Al, Mg, Si and Mn) were analysed by ICP-AES in the CB and DCB extracts. Results and discussion: It was found that X-ray diffraction is not an enough sensitive method to detect the quick mineralogical changes due to soil compaction. Results obtained from CB-DCB extractions showed that soil compaction resulted in larger CB and smaller DCB extractable elements as compared to non-compacted soil. Labile Fe was found 30 % of total Fe oxides in compacted soil against 10-14 % in non-compacted soils. Compaction thus resulted in Fe transfer from non-labile to labile oxides (s.l.). Results showed that soil compaction leads to the reduction of Fe to Fe. The effects of hydromorphic conditions due to soil compaction were observed up to the depth of 35 cm in forest soil profile. Furthermore, a close association of Al with Fe oxides was observed in the soil samples, while Mn and Si were mainly released from other sources, Mg showing an intermediate behaviour. Conclusions: Hydromorphic conditions owing to soil compaction affect the mobility and crystallisation process of iron mineral. CB-DCB selective extraction technique, in contrast to XRD technique, can be effectively used to examine the possible effects of soil compaction on iron minerals. [ABSTRACT FROM AUTHOR]

In southern Hodna, an arid region of Algeria, the extension of irrigated agriculture and overexploitation of groundwaters have led to a rupture with traditional land use by pastoralism. Due to the arid conditions, groundwaters are the only water resources for man and irrigation. This study focuses on nitrate contamination of groundwaters and its increase since the last 40 years, on the basis of two archives and recent analyses. The chemical facies of waters is sulphate-chloride, the risk of salinity is moderate to large. The sodicity risk, as estimated by the SAR, is low due to the large salinity and the sandy soil texture. Nitrate contamination of deep groundwater is a clear evidence when recent data are compared to the historical data. From 1996 to 2008, the proportion of samples with NO concentrations larger than 50 mg/L increases from 24 to 61 %, the proportion of samples with NO concentrations larger than 100 mg/L increases from 12 to 27 %. The study points at a general contamination of aquifers from anthropic origin: phreatic water was already contaminated when pastoralism was dominant (1967); as population increased and irrigation agriculture developed with large use of N-fertilizers and organic amendments, contamination extended spatially and vertically to deep aquifer. To remediate this contamination, fertilizers should be fractionated and limited to plant requirements on the basis of soil and plant analyses. Excess of irrigation should be avoided. Soil surface should be continuously covered to prevent nitrate leaching. Secondly, more efficient irrigation techniques, such as localized irrigation, should be implemented, with adaptation of crop systems and fertilizer inputs to arid conditions. Farmers should then be trained; simultaneously, local agronomic references that are presently lacking should be acquired. [ABSTRACT FROM AUTHOR]

Compaction of agricultural soils is a concern for many agricultural soil scientists and farmers since soil compaction, due to heavy field traffic, has resulted in yield reduction of most agronomic crops throughout the world. Soil compaction is a physical form of soil degradation that alters soil structure, limits water and air infiltration, and reduces root penetration in the soil. Consequences of soil compaction are still underestimated. A complete understanding of processes involved in soil compaction is necessary to meet the future global challenge of food security. We review here the advances in understanding, quantification, and prediction of the effects of soil compaction. We found the following major points: (1) When a soil is exposed to a vehicular traffic load, soil water contents, soil texture and structure, and soil organic matter are the three main factors which determine the degree of compactness in that soil. (2) Soil compaction has direct effects on soil physical properties such as bulk density, strength, and porosity; therefore, these parameters can be used to quantify the soil compactness. (3) Modified soil physical properties due to soil compaction can alter elements mobility and change nitrogen and carbon cycles in favour of more emissions of greenhouse gases under wet conditions. (4) Severe soil compaction induces root deformation, stunted shoot growth, late germination, low germination rate, and high mortality rate. (5) Soil compaction decreases soil biodiversity by decreasing microbial biomass, enzymatic activity, soil fauna, and ground flora. (6) Boussinesq equations and finite element method models, that predict the effects of the soil compaction, are restricted to elastic domain and do not consider existence of preferential paths of stress propagation and localization of deformation in compacted soils. (7) Recent advances in physics of granular media and soil mechanics relevant to soil compaction should be used to progress in modelling soil compaction. [ABSTRACT FROM AUTHOR]

A special experimental setup for in-field applications was developed at Mainz. It incorporates hardware for automated positioning of the Mössbauer sensor head, a Plexiglas tube, and a modified version of the space proven Miniaturized Mössbauer Spectrometer MIMOS II (Klingelhöfer et al., Science, 306:1740–1745, 2004; Klingelhöfer et al., J. Geophys. Res., 108(E12):8067, 2003; Klingelhöfer et al., Hyperfine Interact. 144/145:371–379, 2002; Génin et al., Solid State Sci., 7:545–572, 2005). MIMOS operates in backscattering geometry, thus no sample preparation is required. Also dedicated software for running measurement sequences (e.g., different depth positions at different times etc.) was developed. The setup can work autonomously up to several weeks in the field. Preliminary results confirm that fougerite mineral found in hydromorphic soils is FeII–III hydroxycarbonate green rust. [ABSTRACT FROM AUTHOR]

We have built an optical VanderLugt-type correlator that uses two Epson liquid crystal televisions (LCTV) separately generating the amplitude and phase modulation properties. The input scene is displayed in amplitudemostly regime on the first LCTV. Thereafter a phase-only filter with a different level of phase quantization is addressed in phase-mostly regime on the second LCTV. To characterize this device, the phase and amplitude modulations were experimentally measured and investigated in pattern recognition application where the grey-level input scenes and multilevel kinoforms are displayed on the LCTV. [ABSTRACT FROM AUTHOR]

Mass transfer between aquifers, vadose zone, including soils and waters may occur at equilibrium or out of equilibrium. Irrigating with low-quality waters can result in soil salinization and/or degradation of soil structure. Checking minerals/solutions equilibria from the chemical composition of solutions implies computing activities and Saturation Indexes (SI) of minerals. In semi-arid-to-arid areas, evaporation concentrates solutions and waters evolve in different geochemical pathways, mainly saline neutral path and alkaline path, separated by bifurcations. Strong non ideality of electrolyte solutions makes it difficult to compute accurately activities and SI. The objective of this paper is to compare Pitzer's model and Specific Interaction Theory (SIT), both now incorporated in Phreeqc 3.0. Samples can be assigned to the saline neutral path with dominance of sulfate which is the majority and with dominance of chloride as the minority. Data were twofold: (i) groundwaters were sampled in an irrigated plain, in Lower Chéliff valley (Algeria), and analyzed, they cover the range from low to medium ionic strength; (ii) data from a saline system (Chott El Jerid, Tunisia) were taken from the literature to cover the range from medium to very high ionic strength, including brines. Data were processed with both models to check equilibria. Results opposing classical assumptions are obtained: (i) calcite does not form at equilibrium and requires a specific oversaturation ( SI ≃ 1.4 ), then relaxes to equilibrium. This is a general result that can be extended to many situations, where calcite forms, including sedimentation; (ii) gypsum, which is more soluble, forms at equilibrium; accordingly, the assumption of equilibrium at low temperature, i.e., in Earth's surface conditions, holds for gypsum, but not for calcite; (iii) Pitzer's model gives better results than SIT for calcite and gypsum, but SIT model gives better results for halite, while it is generally admitted that Pitzer's model is better for I > 3 m . [ABSTRACT FROM AUTHOR]