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Soil Organic Matter Content (soil + organic_matter_content)
Selected AbstractsElementary processes of soil,water interaction and thresholds in soil surface dynamics: a reviewEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2004Richard S. B. Greene Abstract Elementary processes of soil,water interaction and the thresholds to these processes are important to understand as they control a range of phenomena that occur at the soil surface. In particular processes involved with wetting by rainfall that lead to particle breakdown are critical. This breakdown causes soil detachment and crust formation, which are both key elements in erosion. This paper reviews the range of approaches that have been taken in describing the processes associated with the wetting of a soil surface by rainfall. It assembles the studies that emphasize soil physics, soil chemistry, and erosion mechanics in a framework to enable a balanced consideration of important processes and management strategies to control erosion for a particular situation. In particular it discusses the factors associated with the two basic processes of soil structural breakdown, i.e. slaking and dispersion, and how these processes are critical in particle detachment, transport and surface crust formation. Besides the balance between the exchangeable cation composition and electrolyte concentration (measured as the sodium adsorption ratio (SAR) and total cation concentration (TCC) respectively) of the soil, the importance of energy input and soil organic matter content in controlling clay dispersion is emphasized. Based on the balance between these factors, the soil can be in one of three different regions, i.e. a dispersed region, a ,occulated region and one where the resilience of the soil is variable. The implications of each of these regions to soil erosion management are brie,y outlined, as are the critical roles that soil cover levels and organic matter have in controlling erosion. Finally, the relationship between various laboratory measures of aggregate stability, and corresponding ,eld erosion characteristics, is discussed. Copyright © 2004 John Wiley & Sons, Ltd. [source] Pedometric mapping of soil organic matter using a soil map with quantified uncertaintyEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2010B. Kempen This paper compares three models that use soil type information from point observations and a soil map to map the topsoil organic matter content for the province of Drenthe in the Netherlands. The models differ in how the information on soil type is obtained: model 1 uses soil type as depicted on the soil map for calibration and prediction; model 2 uses soil type as observed in the field for calibration and soil type as depicted on the map for prediction; and model 3 uses observed soil type for calibration and a pedometric soil map with quantified uncertainty for prediction. Calibration of the trend on observed soil type resulted in a much stronger predictive relationship between soil organic matter content and soil type than calibration on mapped soil type. Validation with an independent probability sample showed that model 3 out-performed models 1 and 2 in terms of the mean squared error. However, model 3 over-estimated the prediction error variance and so was too pessimistic about prediction accuracy. Model 2 performed the worst: it had the largest mean squared error and the prediction error variance was strongly under-estimated. Thus validation confirmed that calibration on observed soil type is only valid when the uncertainty about soil type at prediction sites is explicitly accounted for by the model. We conclude that whenever information about the uncertainty of the soil map is available and both soil property and soil type are observed at sampling sites, model 3 can be an improvement over the conventional model 1. [source] Calcite and gypsum solubility products in water-saturated salt-affected soil samples at 25°C and at least up to 14 dS m,1EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2010F. Visconti Calcite and gypsum are salts of major ions characterized by poor solubility compared with other salts that may precipitate in soils. Knowledge of calcite and gypsum solubility products in water-saturated soil samples substantially contributes to a better assessment of processes involved in soil salinity. The new SALSOLCHEMIS code for chemical equilibrium assessment was parameterized with published analytical data for aqueous synthetic calcite and gypsum-saturated solutions. Once parameterized, SALSOLCHEMIS was applied to calculations of the ionic activity products of calcium carbonate and calcium sulphate in 133 water-saturated soil samples from an irrigated salt-affected agricultural area in a semi-arid Mediterranean climate. During parameterization, sufficiently constant values for the ionic activity products of calcium carbonate and calcium sulphate were obtained only when the following were used in SALSOLCHEMIS: (i) the equations of Sposito & Traina for the free ion activity coefficient calculation, (ii) the assumption of the non-existence of the Ca (HCO 3)+ and CaCO3o ion pairs and (iii) a paradigm of total ion activity coefficients. The value of 4.62 can be assumed to be a reliable gypsum solubility product (pKs) in simple aqueous and soil solutions, while a value of 8.43 can only be assumed as a reliable calcite solubility product (pKs) in simple aqueous solutions. The saturated pastes and saturation extracts were found to be calcite over-saturated, with the former significantly being less so (p IAP = 8.29) than the latter (p IAP = 8.22). The calcite over-saturation of saturated pastes increased with the soil organic matter content. Nevertheless, the inhibition of calcite precipitation is caused by the soluble organic matter from a dissolved organic carbon threshold value that lies between 7 and 12 mm. The hypothesis of thermodynamic equilibrium is more adequate for the saturated pastes than for the saturation extracts. [source] Neural network models to predict cation exchange capacity in arid regions of IranEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2005M. Amini Summary Design and analysis of land-use management scenarios requires detailed soil data. When such data are needed on a large scale, pedotransfer functions (PTFs) could be used to estimate different soil properties. Because existing regression-based PTFs for estimating cation exchange capacity (CEC) do not, in general, apply well to arid areas, this study was conducted (i) to evaluate the existing models and (ii) to develop neural network-based PTFs for predicting CEC in Aridisols of Isfahan in central Iran. As most researches have found a significant correlation between CEC and soil organic matter content (OM) and clay content, we also used these two variables for modelling of CEC. We tested several published PTFs and developed two neural network algorithms using multilayer perceptron and general regression neural networks based on a set of 170 soil samples. The data set was divided into two subsets for calibration and testing of the models. In general, the neural network-based models provided more reliable predictions than the regression-based PTFs. [source] Soil Phosphorus Fractionation during Forest Development on Landslide Scars in the Luquillo Mountains, Puerto Rico,BIOTROPICA, Issue 1 2002Jacqueline Frizano ABSTRACT Mineral soils from a chronosequence of landslide scars ranging in age from 1 to more than 55 years in a subtropical montane rain forest of eastern Puerto Rico were used to determine the rate at which labile P capital recovers during primary succession. Nine organic and inorganic soil P fractions were measured using the Hedley sequential extraction procedure. Deep soil cores (9 m) from a nearby site were also analyzed to determine the distribution of P fractions below the solum. Litterfall P was measured for two years in the landslide scars to estimate allochthonous litter P inputs, and published precipitation data were used to estimate annual atmospheric inputs of P to the recovering forests. In the upper solum (0,10 cm), organic matter increased with landslide age, as did resin-Pi, labile P (defined here as resin-Pi + HCO3 -Pi + HCO3 -Po) and total organic P. Occluded P decreased with increasing landslide age. No significant changes in P concentrations or pools were observed in 10 to 35 or in 35 to 60 cm depth intervals across the chronosequence. Labile soil P increased to approximately two-thirds of the pre-disturbance levels in the oldest landslide scar (>55 yr). Thus, plants, their associated microflora/fauna, and P inputs from off-site substantially altered the distribution of soil P fractions during forest recovery. Across the chronosequence, the increase in labile P accumulated in soil and biomass appeared to be greater than the estimated allochthonous inputs from litter and precipitation, indicating that as the forest developed, some occluded P may have been released for use by soil biota. Resin-Pi and labile P were correlated with soil organic matter content, suggesting, as in other highly weathered soils, organic matter accumulation and turnover are important in maintaining labile P pools. Primary mineral P (apatite) was scarce, even in deep soil cores. [source] Changes in organic matter, nitrogen, phosphorus and cations in soil as a result of fire and water erosion in a Mediterranean landscapeEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2000E. Gimeno-García Summary Fire affects large parts of the dry Mediterranean shrubland, resulting in erosion and losses of plant nutrients. We have attempted to measure these effects experimentally on a calcareous hillside representative of such shrubland. Experimental fires were made on plots (4 m × 20 m) in which the fuel was controlled to obtain two different fire intensities giving means of soil surface temperature of 439°C and 232°C with temperatures exceeding 100°C lasting for 36 min and 17 min. The immediate and subsequent changes induced by fire on the soil's organic matter content and other soil chemical properties were evaluated, together with the impact of water erosion. Seven erosive rain events, which occurred after the experimental fires (from August 1995 to December 1996), were selected, and on them runoff and sediment produced from each plot were measured. The sediments collected were weighed and analysed. Taking into account the variations induced by fire on the soil properties and their losses by water erosion, estimates of the net inputs and outputs of the soil system were made. Results show that the greatest losses of both soil and nutrients took place in the 4 months immediately after the fire. Plots affected by the most intense fire showed greater losses of soil (4077 kg ha,1) than those with moderate fire intensity (3280 kg ha,1). The unburned plots produced the least sediment (72.8 kg ha,1). Organic matter and nutrient losses by water erosion were related to the degree of fire intensity. However, the largest losses of N-NH4+ and N-NO3, by water erosion corresponded to the moderate fire (8.1 and 7.5 mg N m,2, respectively). [source] | ||||||||||