Ein neues Verfahren zur Extraktion von organischen Stoffen aus Böden mit überkritischen Gasen

A new procedure for the extraction of organic matter from soils by supercritical gases Organic solvents beyond critical temperature and pressure have excellent properties for solving polymere organic substances. For soil samples yields of organic material with low ash content are much higher than those obtained by the common NaOH/HCl-extraction. Fractionation of the samples is easily achieved by a simple change of solvent bottles. In comparison to the original material oxygen contents are lower, due to a thermal or solvolytical split off of methanol or water. Extraction with supercritical gases – in addition to oxidative degradation –may be regarded as a useful method to enlighten the structure of humic acids. The effective extraction of firmly bound pesticides in soil is another point of interest.     

Extraktion von Schwermetallen aus Böden mit Ionenaustauscherharz

Extraction of Heavy Metals from Soils by Ion Exchangers The aim of this investigation was to optimize an extraction method for the analysis of available heavy metals (Cd, Cu, Pb, Zn) in soils. LEWATIT was used as an ion exchanger (IEX) which absorbs heavy metals specificly. A special extraction vessel with two chambers was developed to recover the IEX from the soil solution. Nitric acid was used for the desorption of heavy metals from the ion exchanger. The described method measures water soluble and exchangeable ions as well as acid soluble heavy metals. The amount of acid soluble heavy metals can be regulated by conditioning the IEX with K⁺. Using an IEX conditioned with 30% K⁺, the maximum change of pH in the soil solution was 2 units. This is the same range of acidity changes occuring in the rhizosphere of plants by nutrient uptake. The extract contains no organic compounds. Thus the co-determination of stabil organic complexes is excluded. Accordingly, this method is also feasible for the investigation of forest soils with humic layers.     

DELPHI - Ein Modell zur Langzeitprognose der Verlagerung von Stoffen in Böden

DELPHI - a leaching model for long term simulation

• ? the integration of a cascade model for the simulation of water movement

• ? the determination of typical monthly rates of decomposition due to soil temperature

• ? an iterative solution of convective-dispersive solute transport equation and

• ? the possibility to consider the spatial variability of pore water velocity

the model is proper for long term simulations A new model for the behaviour of chemicals in soil is described. Because of     

Stickstoffdynamik von Böden mit Abwasserverrieselung

Nitrogen dynamic of soils with wastewater irrigation The nitrogen status of a Sandy Cambisol and a Loamy Luvisol of Berlin, which were flooded with wastewater over a period of 100 years were studied. The two-year examination of the water, redox and nitrogen dynamics showed great differences in nitrogen leaching and the intensity of nitrification and denitrification processes.     

Methodenvergleich zur pH-Bestimmung von Böden

Comparison of methods for determining of soil-pH Comparative studies are being described of pH-determinations in suspensions with m-KCl, 0.1 m-KCl, 0.01 m-CaCl₂ and water of soils derived from loess and sand. For a standard the pH-values in 0.01 m-CaCl₂-suspensions were chosen, considering, that such CaCl₂-solution reflects best conditions in natural soil solution. Mean differences of pH(H₂O)-, m-KCl- and 0.1 m-KCl-values as compared to pH(CaCl₂)-values were + 0.56, — 0.27 and — 0.02 for the soils derived from loess, and + 0.63, — 0.11 and + 0.18 for those from sand. Taking into account the pH-dependence of the difference pH(CaCl₂)-values were + 0.56 – 0.11, — 0.27 – 0.26 and — 0.02 – 0.21, for the soils derived from loess, and + 0.63 – 0.21, — 0.11 – 0.14 and + 0.18 – 0.10 for those from sand. Taking into account the pH-dependence of the difference of pH(H₂O)-values of sandy soils, and its dependence on the present electrolyte content with all soils, further the unequal differences of the pH(KCl)-values with soils from loess as compared to sand, and their particular large variability with soils from loess, it is being argued that the CaCl₂-method may only insufficiently be substitued by any one of these methods. pH-values obtained at a soil-to-liquid-ratio of 1:2.5 were only slightly different from those with a ratio of 1:1. A suspension effect could not be observed with the application of a glasselectrode.     

Ein Mischzellenmodell zur Abschätzung der Nitratauswaschung aus landwirtschaftlich genutzten Böden im Winterhalbjahr

A mixing-cell model for estimating nitrate seepage losses from agricultural soils in winter A mixing-cell model is developed with which the leaching of nitrate from agricultural soils in temperate regions during winter can be estimated. The model assumes steady-state flow conditions and takes nitrogen mineralization in the upper soil as well as nitrate deposition from the atmosphere into consideration. Model results are compared with results from a convective-dispersive solute flow model. They show that for common field soil dispersivities mixing-cell model results compare well with those obtained from convective-dispersive theory. With the mixingcell model nitrate leaching calculations were carried out for a variety of soil and climatic conditions. They show that the combined effect of N-mineralization and N-deposition may influence the amount of leached nitrate in winter considerably, especially in regions with light soils and high seepage rates. It is shown that the model can be used to derive late fall site-specific upper limits for soil mineral nitrogen for groundwater protection purposes. Such upper limits should reflect the crop-specific rate of N-mineralization that can be expected during winter.     

Prüfung von 3 Verfahren zur Vorhersage der hydraulischen Leitfähigkeit ungesättigter Böden aus Wasserretentionsdaten oder aus der Bodenart

Testing of three methods to predict unsaturated soil hydraulic conductivity from water retention data or from texture class Using 60 soils taken from UNSODA (Leij et al., 1996) the method proposed by Renger et al. (1999) and the prediction according to Mualem (1976)/van Genuchten (1980) were tested. The parameters of the Mualem/vanGenuchten model were estimated either from water retention data or from a table of reference values. Using the reference values requires only the knowledge of texture class (German classification system). An advantage of the method proposed by Renger et al. (1999) is its capability to predict saturated conductivity too. The model of Mualem/vanGenuchten using reference values of parameters yields the best results. The standard deviation between observed and predicted values of unsaturated hydraulic conductivity was 0.93 lg (K) for the Mualem/vanGenuchten model and 1.3 lg (K) for the Renger et al. (1999) predictions.     

Die Verwendung von Antimon-Elektroden zur pH-Messung in Böden

The application of antimony electrodes for soil pH measurements Glass electrodes are unsuitable for long-term, micro-volume pH measurements in soils because of their form, size and drying of the glass membrane. Sb-electrodes are suited for pH measurements in soils whose oxygen saturation does not vary excessively. pH values determined with Sb electrodes decrease with increasing water tension or decreasing moisture. Colour changes of pH indicators confirm this trend.     

Kurzmitteilung Ein methodischer Beitrag zur Porengrößen-Messung bei Böden

A methodic contribution for the measuring of volume of pores in soils An apparatus for determination of the soil pores in the pF-range 0–2,5, partially produced in home-work, is described. Thereby are used ceramic plates 50 × 35 cm with a thickness of 5–8 mm. The ceramic plates are sticked on 63 × 50 cm gum plates with Teroson-Cement-BE and packed in correspondingly great wooden boxes. The soil samples are dehydrated in an over-pressure chamber.     

Ermittlung des Spannungszustandes von Böden aus Werten des Eindringwiderstandes von Sonden

Evaluation of the soil consolidation state by using data from penetration resistance probes Penetration resistance data (EW) from handdriven equipment are easily obtainable because the equipment is simple, cheap, and easily carriable. Measurements are performed quickly without extensive destruction of the site. It is the only method to measure soil strength directly and in situ. Therefore, it is worthwhile to propose an interpretation of the results in order to obtain more conclusive statements on the structural soil state. The procedure applied in our study consists in assigning EW values to the principal stress σ_x and in using an auxiliary construction for the vertical component (σ_z ) as a function of penetration depth. The EW value obtained at the final soil depth is assumed to represent stresses at rest, i.e., K₀ = σ_x/σ_z = 1. Drawing a straight line from this point towards the origin of the coordinates EW and soil depth supplies values of the hydrostatic condition for each depth; e.g., values for σ_z are available for each depth. The coefficient for the equivalent stress at rest (K_0E) per depth can now be calculated simply by comparing the measured EW values with the assumed (hydrostatic) vertical depth function of EW. From a total volume of 29 sets of EW versus depth relations, means and standard deviation of K_0E are presented for arable and forest soils from central Europe. K_0E of forest soils tends to be close to 1 showing approximately normal compaction. In arable sites, K_0E > 2 prevail, indicating precompation. These results confirm the general feasibility of the approach to evaluate the compaction state of soil from EW data. Examples are given to show the K_0E characteristics for special cases of mechanical stress situations.     

Verhalten von Schwermetallen in Böden. 2. Extraktion mobiler Schwermetalle mittels CaCl2 und NH4NO3

Behaviour of heavy metals in soils. 2. Extraction of mobile heavy metals with CaCl₂ and NH₄NO₃ 156 soil samples from arable fields, grassland and forest stands were analysed for the CaCl₂^? and NH₄NO₃^? extractable contents of Cd, Zn, Mn, Cu and Pb. The average amounts of Cd, Zn, Cu and Pb extracted with CaCl₂ are higher compared with NH₄NO₃ whereas the relation for Mn is vice versa. The proportion of the NH₄NO₃^? extractable contents in percent of the CaCl₂^? extractable contents of Cd, Zn and Pb decrease with increasing pH, whereas the contents of Mn and Cu increase. Inspite of a differing extraction behaviour of the two salt solutions the CaCl₂^? and NH₄NO₃^? extractable amounts of Cd, Mn, Zn und Pb are highly correlated and can be converted one into another. The mobile (CaCl₂, NH₄NO₃) proportion of the corresponding total, EDTA and DTPA heavy metal contents is in close relation to the pH of the soils. Using CaCl₂ solution the threshold pH values for an increasing mobility decrease in the order Cd > Mn > Zn > Cu > Pb, using NH₄NO₃ as extractant the order is Mn > Cd > Zn > Cu > Pb. In the case of CaCl₂ as extractant soluble chloro-Cd-complexes will be formed so that the Cd mobility in soils will be overestimated in most cases.     

Bestimmung von nichtaustauschbarem Ammonium in Böden mit einer Halbmikromethode

Determination of non exchangeable Ammonia in Soils by a semicro method A semi-micro version (sample weight 0,1 g) for the determination of nonexchangeable NH₄⁺ of soils, based on the method of Silva and Bremner (1966) is described. The results of the semi-micro version are compared with the original method. The regression-coefficient is r = 0,9906. Analysis time is reduced by a factor of 2, reagent needs approximately by a factor of 20. Exactness and reproducibility are satisfactory for routine measurements. Pampean soils from Argentina, analyzed with the semi-micro method contain between 50 and 90 ppm nonexchangeable NH₄⁺.     

Mineralselektive K-Freisetzung aus Böden mit Oktodecylammonium-Ionen (nc = 18)

Mineral-selective K release from soils by octodecylammonium- ions (n_c = 18) n_c18-releasable potassium was determined on soils of five different areas. n_c18-releasable K is the potassium which is displaced by octodecylammonium ions (ODA). Because the main sources of this potassium are trioctahedral micas, it is called briefly biotite-K. The investigated soils are from different areas in Bavaria (loess and clay stone derived soils, alluvial soils); partly the locations are K fertilizer trials. Soils of known age are locations from the Niederrhein terraces (Holocene soils). In the 0.2–2 μm (coarse clay) and 2–6 μm (fine silt) fractions the biotite-K content lies between 12 and 40% of total K. At given fractionation the highest amounts of K were released from the coarse clay of the soils. In the loess soils rich in silt the biotite-K pool in the medium and coarse silt fractions was also considerable. Clay soils showing poor K supplying power (K fertilizer trials) in the field are characterized by very low biotite-K quantities in all silt fractions. In the Holocene soils the age of which varies between 4 000 and 8 000 years the ODA releaseable values are greater than in the loess soils. In all fractions of the young Holocene soils the released K is greater than in the same fractions of the old Holocene soils. Calculated to a soil depth of 60 cm the K release in kg/ha reaches from 25 000 (young soil form) to 17 000 (old soil form).     

Verhalten von Schwermetallen in Böden 1. Untersuchungen zur Schwermetallmobilität

Behaviour of heavy metals in soils. 1. Heavy metal mobility 158 soil samples with widely varying composition were analysed for their total, EDTA, DTPA and CaCl₂ extractable contents of Cd, Zn, Mn, Cu and Pb. By means of single and multiple regressions the relations between the different heavy metal fractions and the pH, organic carbon and clay content were considered. The correlations between the total, EDTA and DTPA extractable contents are very close, whereas the CaCl₂ extractable contents are not or only weakly correlated with these fractions. According to these statistical results the former fractions are considered to be the total quantity (total content) and the reactive quantity (EDTA and DTPA extractable contents) of the heavy metals, whereas the CaCl₂ extractable fraction represents the mobile fraction of the heavy metals in soils. The multiple regressions show that the mobile content of heavy metals is closely correlated with each of the quantity fractions and with soil pH. In the same way the proportion of the mobile fraction (in %) of the total, EDTA and DTPA extractable heavy metal content of the soil samples is closely related to the soil pH. Hereby the proportion of the mobile content of the various elements increases in the pH range 6,5 - 3 below element-specific threshold pH values (in brackets) in the order Cd (6,5) > Mn (5,7) > Zn (5,3) > Cu (4,5) > Pb (3,5). In the pH range 6,5 - 7,5 mainly Cu and to a lesser degree also Pb show an increasing mobility due to the influence of soluble organic substances.     

Modelluntersuchungen zur K-Freisetzung aus Böden mit höherer elektrischer Leitfähigkeit durch die Elektro-Ultrafiltration (EUF)

Model experiments on the potassium release of soils with higher electric conductivities by electro-ultrafiltration (EUF) For investigations on the effects of higher ion concentrations in soils on results of EUF (electro-ultrafiltration), performed at constant current, a light soil (12% clay) was analyzed by adding increasing amounts of a NaCl solution to the soil slurry in the EUF middle cell. Recording the course of voltage and current through the EUF cell, it was found, that,

• 1) a continuous decrease of electrode voltage occurs over extended time periods, when the electric conductivity of the soil was increased.
• 2) As a function of this voltage decline, the potassium concentration in the EUF-20°C fraction was reduced, whereas in the EUF-80°C fraction higher amounts of potassium could be found.
• 3) Unlike at very high levels of electric conductivity, the total K extraction by EUF was nearly unaffected, because losses in K content in the fraction EUF-20°C could be compensated by the fraction EUF-80°C.
• 4) According to Németh and Ziegler (1988) the ratio of EUF-K-80°C to EUF-K-20°C should be between 0.1 and 0.2 for light, but about 0.6 for heavy soils. Under the influence of higher electric conductivities this figure for light soils, however, approached values for heavy soils.
• 5) Also, the contents of magnesium and calcium showed marked decreases at higher electric conductivities in the EUF-fractions a and b (= EUF-20°C). Contrary to the total amount of extractable potassium, the total contents of magnesium and calcium, extract-able by EUF, were markedly decreased by higher electric conductivities in the light soil.

It is recommended, that the parameters voltage and current should be considered in interpretations of EUF-fractions from soils with higher levels of electric conductivity.