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Undisturbed Soil Columns (undisturbed + soil_column)
Selected AbstractsOrganic matter quality of a forest soil subjected to repeated drying and different re-wetting intensitiesEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2010A. Schmitt Extended drought periods followed by heavy rainfall may increase in many regions of the Earth, but the consequences for the quality of soil organic matter and soil microbial communities are poorly understood. Here, we investigated the effect of repeated drying and re-wetting on microbial communities and the quality of particulate and dissolved organic matter in a Haplic Podzol from a Norway spruce stand. After air-drying, undisturbed soil columns were re-wetted at different intensities (8, 20 and 50 mm per day) and time intervals, so that all treatments received the same amount of water per cycle (100 mm). After the third cycle, SOM pools of the treatments were compared with those of non-dried control columns. Lignin phenols were not systematically affected in the O horizons by the treatments whereas fewer lignin phenols were found in the A horizon of the 20- and 50-mm treatments. Microbial biomass and the ratio of fungi to bacteria were generally not altered, suggesting that most soil microorganisms were well adapted to drying and re-wetting in this soil. However, gram-positive bacteria and actinomycetes were reduced whereas gram-negative bacteria and protozoa were stimulated by the treatments. The increase in the (cy 17: 0 + cy 19: 0)/(16:1,7c + 18:1,7c) ratio indicates physiological or nutritional stress for the bacterial communities in the O, A and B horizons with increasing re-wetting intensity. Drying and re-wetting reduced the amount of hydrolysable plant and microbial sugars in all soil horizons. However, CO2 and dissolved organic carbon fluxes could not explain these losses. We postulate that drying and re-wetting triggered chemical alterations of hydrolysable sugar molecules in organic and mineral soil horizons. [source] Effects of wetting and drying cycles on in situ soil particle mobilizationEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2008S. Majdalani Summary Understanding particle mobilization and transport in soils is a major concern for environmental protection and water resource management as they can act as vectors for sorbing pollutants. In natural soils, the existence of a finite size and renewable pool of dispersible particles has been hypothesized. Even though freeze-thaw and wetting-drying cycles have been identified as possible mechanisms of pool replenishment between rainfall events, to date the underlying phenomena ruling the renewal of particle pools are still largely unexplored. We carried out a series of infiltration-drainage experiments to study systematically the effects of periods without rain (pauses) on in situ particle mobilization in undisturbed soil columns. We found that, for a given column, pause duration between two rainfall events has a major influence on subsequent particle mobilization: the mass of leached particles increases with pause duration until it reaches a maximum (mass for a 200-hours pause is 15 time greater than for a 1-hour pause), and then it decreases for even longer pauses. This behaviour was correlated with soil water content, and can be explained by soil matrix weakening due to differential capillary stresses during drying. The consequences of this finding are important because the 15-fold increase in mass of leached particles, when pause duration is changed from 1 hour to 4 days, might overwhelm variations caused by changes in other parameters such as the ionic strength of the incoming solution or the rainfall intensity. [source] Mass fractal dimension of soil macropores using computed tomography: from the box-counting to the cube-counting algorithmEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2003J.S. Perret Summary Transport phenomena in porous media depend strongly on three-dimensional pore structures. Macropore networks enable water and solute to move preferentially through the vadose zone. A complete representation of their geometry is important for understanding soil behaviour such as preferential flow. Once we know the geometrical, topological and scaling attributes of preferential flow paths, we can begin computer simulations of water movement in the soil. The box-counting method is used in three dimensions (i.e. cube-counting algorithm) to characterize the mass fractal dimension of macropore networks using X-ray computed tomography (CT) matrices. We developed an algorithm to investigate the mass fractal dimension in three dimensions and to see how it compares with the co-dimensions obtained using the box-counting technique in two dimensions. For that purpose, macropore networks in four large undisturbed soil columns (850 mm × 77 mm diameter) were quantified and visualized, in both two and three dimensions, using X-ray CT. We observed an increasing trend between the fractal dimension and macroporosity for the four columns. Moreover, similar natural logarithm functions were obtained for the four cores by a least squares fit through plots of mass fractal dimension against macroporosity. [source] Temperature functions of the rate coefficients of net N mineralization in sandy arable soils.JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 4 2004Part II. Abstract The aim of this study was to evaluate experimentally derived temperature functions for the rate coefficients of net N mineralization in sandy arable soils from NW Germany via field measurements. In part I of this paper (Heumann and Böttcher, 2004), different temperature functions for the rate coefficients of a two-pool first-order kinetic equation were derived by long-term laboratory incubations at 3°C to 35°C. In this paper, field net N mineralization during winter of 25 plots was measured in undisturbed soil columns with a diameter of 20,cm to the depth of the Ap horizon. Mean simulated net N mineralization with the most adequate multiple functions corresponded also best with the mean of the measured values despite of an overestimation of about 10%. Distinctly larger deviations under use of other temperature functions (Arrhenius, Q10) were directly related to their deviations from mean, experimentally derived rate coefficients. Simulated net N mineralization in the soil columns was significantly correlated with measured values, regardless of the temperature functions. Yet the goodness of fit was generally relatively low due to the spatial variability of measured net N mineralization within replicate soil columns, although the mean CV (38%) was by far not extraordinary. The pool of slowly mineralizable N contributed considerably to net N mineralization during four to five winter months, on an average 10.0 kg N ha,1, about one third of total simulated N mineralization. Sometimes, it contributed even 21.3 kg N ha,1, which is almost sufficient to reach the EU drinking-water limit for nitrate in these soils. Simulations with widely used functions that were once derived from loess soils overestimated mineralization from pool Nslow in the studied sandy arable soils by a factor of two. Die Temperaturfunktionen der Reaktionskoeffizienten der N-Nettomineralisation in sandigen Ackerböde nII. Überprüfung anhand von Mineralisationsmessungen im Freiland Ziel dieser Untersuchung war die Überprüfung experimentell ermittelter Temperaturfunktionen für die Reaktionskoeffizienten der N-Nettomineralisation in sandigen Ackerböden NW-Deutschlands anhand von Freilandmessungen. In Teil I der Arbeit (Heumann and Böttcher, 2004) wurden verschiedene Temperaturfunktionen für die Reaktionskoeffizienten zweier N-Pools mit Reaktionskinetik erster Ordnung mittels Langzeit-Laborinkubationen bei 3 bis 35°C bestimmt. In diesem Artikel wurde von 25 Plots die winterliche N-Nettomineralisation im Freiland in ungestörten Bodensäulen mit einem Durchmesser von 20,cm bis zur Tiefe des Ap-Horizontes gemessen. Im Mittel gaben die Simulationen mit den am besten passenden, multiplen Funktionen die Messergebnisse auch am besten wieder, trotz einer Überschätzung um etwa 10%. Deutlich größere Abweichungen bei Benutzung anderer Temperaturfunktionen (Arrhenius, Q10) standen in direkter Beziehung zu deren Abweichungen von den mittleren, experimentell ermittelten Reaktionskoeffizienten. Die simulierte N-Nettomineralisation war unabhängig von den Temperaturfunktionen signifikant mit den Messergebnissen korreliert. Jedoch war die Güte der Anpassung im Allgemeinen relativ niedrig aufgrund der räumlichen Variabilität der gemessenen N-Nettomineralisation innerhalb der einzelnen Säulen eines Plots, obwohl der mittlere CV (38%) bei weitem nicht außergewöhnlich war. Der langsam mineralisierbare N-Pool trug beträchtlich zur N-Nettomineralisation innerhalb von vier bis fünf Wintermonaten bei, durchschnittlich 10,0 kg N ha,1, etwa ein Drittel der gesamten simulierten N-Mineralisation. In manchen Böden waren es sogar 21,3 kg N ha,1, was fast ausreicht, um den EU-Trinkwassergrenzwert für Nitrat in diesen Böden zu erreichen. Simulationen mit häufig benutzten Funktionen, die ursprünglich an Lössböden ermittelt wurden, überschätzten die Mineralisation aus dem Pool Nslow in den untersuchten Sandböden um den Faktor zwei. [source] Modelling approaches to compare sorption and degradation of metsulfuron-methyl in laboratory micro-lysimeter and batch experimentsPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 12 2003Maik Heistermann Abstract Results of laboratory batch studies often differ from those of outdoor lysimeter or field plot experiments,with respect to degradation as well as sorption. Laboratory micro-lysimeters are a useful device for closing the gap between laboratory and field by both including relevant transport processes in undisturbed soil columns and allowing controlled boundary conditions. In this study, sorption and degradation of the herbicide metsulfuron-methyl in a loamy silt soil were investigated by applying inverse modelling techniques to data sets from different experimental approaches under laboratory conditions at a temperature of 10 °C: first, batch-degradation studies and, second, column experiments with undisturbed soil cores (28 cm length × 21 cm diameter). The column experiments included leachate and soil profile analysis at two different run times. A sequential extraction method was applied in both study parts in order to determine different binding states of the test item within the soil. Data were modelled using ModelMaker and Hydrus-1D/2D. Metsulfuron-methyl half-life in the batch-experiments (t1/2 = 66 days) was shown to be about four times higher than in the micro-lysimeter studies (t1/2 about 17 days). Kinetic sorption was found to be a significant process both in batch and column experiments. Applying the one-rate-two-site kinetic sorption model to the sequential extraction data, it was possible to associate the stronger bonded fraction of metsulfuron-methyl with its kinetically sorbed fraction in the model. Although the columns exhibited strong significance of multi-domain flow (soil heterogeneity), the comparison between bromide and metsulfuron-methyl leaching and profile data showed clear evidence for kinetic sorption effects. The use of soil profile data had significant impact on parameter estimates concerning sorption and degradation. The simulated leaching of metsulfuron-methyl as it resulted from parameter estimation was shown to decrease when soil profile data were considered in the parameter estimation procedure. Moreover, it was shown that the significance of kinetic sorption can only be demonstrated by the additional use of soil profile data in parameter estimation. Thus, the exclusive use of efflux data from leaching experiments at any scale can lead to fundamental misunderstandings of the underlying processes. Copyright © 2003 Society of Chemical Industry [source] | ||||||||||