Die Bestimmung der Aggregatstabilität - ein Methodenvergleich

The determination of aggregate stability - a comparison of methods The mechanical load bearing capacity and strength of aggregates against external forces can be described and quantified by indirect test (wet sieving method) and direct tests (e.g. crushing test, direct shear test). With the mean of the crushing test and the direct shear test in the shear box it is possible to achieve definite stresses, with which the influence of pore water pressure on soil stability can be explained by the occurence of water menisci forces. It is also possible to proof the pore water pressure dependent increase of strain by the particle reorientation during the process of aggregation. By the method of wet sieving, however, the summarized effect of hydraulic and mechanical processes can be described qualitatively only. A definite relation to single processes is therefore not possible.     

Anionenbestimmung in natürlichen wässrigen Lösungen: ein Methodenvergleich von ionenchromatographischen und Continuous-Flow-Verfahren

Analysis of anions in natural waters: a comparison of methods including ionchromatography and continuous-flow-technics Using waters from different compartments of forest ecosystems, standard solutions, moreover samples containing known internal standards, several analytical methods were tested for the comparability of nitrate, sulfate and chloride results in an inter-laboratory study. The analytical instruments were ion chromatographs with and without suppression as well as continuous-flow-analyzers. A cluster analysis showed a strong correlation between the obtained data and the analytical method used for nitrate, and a poorer relation for sulfate. Concerning nitrate-analysis, the IC-systems showed a better detection limit and a higher recovery of standards. Mean standard deviation among all tested analytical methods was calculated to be 15% for nitrate, 10% for sulfate and 14% for chloride. These results represent deviations as they may occur during laboratory routine analyses with a high amount of samples and the need for simultaneous determination of several anions. For the examined anions no significant correlation was obtained between the variation of the analytical results and the dissolved organic carbon concentrations of the samples.     

Die Beeinflussung der Bodenlösung durch Saugkerzen aus Ni-Sintermetall und Keramik

Influencing soil solution by suction cup material (Ni, ceramics) The influence of suction cup material (ceramics, Ni) on the chemical composition of the soil solution was tested in the laboratory by percolating soil solutions of different concentration (pH ～ 4.0). Ceramic cups of P 80 material can be used for the collection of soil solution and its determination for the concentrations of H, Na, K, NH₄, Ca, Mg, Mn, Al, S, Cl and NO₃. They can't be used to determine P-concentrations. The cups must be prepared and preconditioned by leaching large amounts of equilibrium soil solution which should not be oversaturated with respect to the solubility product of AlOHSO₄. The changes in the concentration of extracted soil solution when it passes through the cups depend upon the extracted volume. The lower the volume, the greater are the changes. Sintered Ni-cups show many severe disadvantages (decreasing permeability, insufficient resistence against acid solutions, large variability among single cups), and can only be used for cases where Na, Ca, K, and S are to be determined. Ceramic cups of the type ‘Czeratzki’ are comparable with those of P 80. However, they can only be used, when the concentrations don't vary too much and large amounts of water can be extracted.     

Zusammensetzung und Speziierung der Bodenlösung eines mit Schwermetallen belasteten kalkreichen Bodens

Composition and Speciation of Soil Solution collected in a Heavy Metal polluted calcareous Soil Close to a brass foundry, which had emitted heavy metal containing dusts for over 80 years, soil water was collected in the topsoil (18 cm) and in the subsoil (40 cm) of a severely polluted Calcic Fluvisol by means of polyethylen suction cups over a period of 2 years. The total metal content of the topsoil (extracted with 2M HNO₃ at 100 °C for 2 hours) was 38 nmol g^?1, 24 μmol g^?1, and 25 μmol g^?1 for Cd, Cu, and Zn, respectively. The mean heavy metal concentrations of the soil solution were 0.5 mol L^?1, 300 nmol L^?1, and 200 nmol L^?1 in the topsoil and 0.6 nmol L^?1, 90 nmol L^?1, and 30 nmol L^?1 in the subsoil for Cd, Cu, and Zn, respectively. Solubility calculations showed that the soil solutions were undersaturated with respect to heavy metal carbonates as well as to hydroxides. It seems that the heavy metal concentration is determined by sorption processes rather than by precipitation. The composition of the soil solution has been shown to be governed by the presence, of calcite, by the soil temperature and by the partial pressure of CO₂ in the soil air. The pCO₂ in the soil air (in both depths) has been estimated at 2 mbar during the winter term and at 20 mbar during the summer term. A corresponding increase of the concentration of macroelements (Ca, Mg, Na) as well as of total dissolved carbonate and of dissolved organic matter (DOC) has been measured in the summer half year. No significant seasonal variations of the heavy metal concentrations were detected and no correlations with concentrations of other components could be found.     

Ein Verfahren zur Gewinnung der Gleichgewichts-Bodenporenlösung

A procedure for obtaining the equilibrium soil pore solution A percolation system for 100 cm³ soil cores is presented. Only filter materials with negligeable interferring properties are used, and during percolation an air filled porosity is maintained. Results from soil cores of a spruce site show, that conventional homogenization of soil samples may lead to a great loss of information about the variability of acidity parameters and to an underestimation of the real soil acidification in the rhizosphere.     

Einfluß von Bodenreaktion,Redoxbedingungen und organischer Substanz auf die Phosphatgehalte der Bodenlösung

Influence of soil reaction, redox conditions and organic matter on the phosphate content of soil solutions Samples of seven agriculturally used soils of different composition (A_p-horizons), one marine underwater soil and two garbage composts were adjusted in suspensions (soil-water-ratio 1:3) to different pH values between 3 and 8 by additions of NaOH or HCl. By a different degree of aeration the redox potential was kept constant at selected values between +600 and ?300 mV. After an incubation period of 22–24 days under controlled E_h-pH-conditions the content of total phosphate and orthophosphate was measured in the equilibrium solutions. At oxidizing conditions all soil and compost samples show the lowest phosphate content in solution at pH S6. At higher and lower pH values the phosphate content increases. The results indicate that the phosphate concentration is determined by adsorption/desorption processes – mainly connected with iron oxides – and not by dissolution or precipitation of definite phosphorus compounds. Under reducing conditions the phosphate content increases in the equilibrium solutions of all samples. Especially in samples with high content of sulphides a considerable increase of the phosphate concentration could be measured at Eh values below +300 mV at pH 5, +200 mV at pH 6, and ± 0 mV at pH7 and 8. Below these values phosphate containing iron(II1) oxides were reduced and – with further decreasing redox potentials – transformed to iron sulphides. In samples without sulphide formation the phosphate mobilization is much lower. With increasing amount of soluble organic matter the phosphate content of the solutions also increases because of phosphate desorption by organic anions or complexation of aluminium and iron from phosphate adsorbing compounds. But also the content of soluble organically bound phosphate increases and may amount to 70 % of the total phosphate content in solution.     

Kurzmitteilung Einfluß der Qualität der organischen Substanz auf die Konsistenz landwirtschaftlicher Böden

Influence of organic matter quality on consistency of agricultural soils The soil organic matter of two samples similar in the texture and approximately in the organic C contents, but very differently in the consistency properties, were investigated by pyrolysis-field ionization mass spectrometry (Py-FIMS). The shifts of the values of the liquid and plastic limits towards higher moisture contents are explained by a different quality of soil organic matter, in particular by higher amounts of longchained lipids (C_8-32 alkanes, alkenes, fatty acids), N-compounds and lignin dimers.     

Reaktion der Zuckerrübe (Beta vulgaris var. altissima) auf die Kaliumdüngung – ein 20‐jähriger Feldversuch

Response of sugar beet ( Beta vulgaris var. altissima ) to potassium fertilization—a 20‐year field experiment A long‐term fertilizer experiment was performed to develop a K fertilization strategy to achieve highest extractable sugar yields (BZE). Sugar beet was grown in a crop rotation with wheat and barley on an alluvial soil (clayic silt) in Lower Saxony with annual recycling of straw and beet tops, respectively. Since 1983, the treatments were as follows: 1) K fertilization with 0, 29, 58, 87,174, and 524 kg K ha^–1 a^–1 corresponding to 0, 0.5, 1, 1.5, 3, and 9 times the average annual K removal by the marketable products of the crop rotation—since 1995, the two highest treatments (3 and 9 times the removal) received only 174 kg ha^–1 every third year; 2) K fertilization according to the average K removal, given each year (58 kg K ha^–1) or every third year (174 kg ha^–1) to sugar beet; 3) annual K fertilization of 87 kg K ha^–1 (1.5 times the removal) applied in autumn or spring, respectively; 4) annual K fertilization, applied as mineral fertilizer or as organic material (recycling of grain and straw or root and leaves); 5) application of 29 kg NaCl ha^–1 to sugar beet supplemental to a yearly application of 58 kg K ha^–1. Both root yield and soil concentration of lactate‐soluble K increased with K fertilization up to the highest K treatment. The extractable sugar content reached a maximum at a yearly application of 174 kg K ha^–1. Averaged over years, the extractable sugar yield (BZE) increased up to the highest K application. The time of K application (autumn or spring) and the source of K (mineral fertilizer or organic material) had no effect on BZE. An additional fertilization with NaCl increased BZE only slightly in single years. Low‐grade muriate of potash containing 33% K and 3% Na can thus be used. The economically optimal K‐fertilization rate was 174 kg K ha^–1 given once in the crop rotation to sugar beet. A soil K concentration of about 110 mg (kg soil)^–1 (lactate‐extractable K) is sufficient in this soil to achieve a high BZE.     

Einfluß der Kalkung und Düngung auf den Ionenaustausch und die chemische Zusammensetzung der Bodenlösung am Beispiel von vier Waldstandorten im Hessischen Bergland

Impact of liming and fertilization on ionic exchange and chemical composition of soil solutions from four forest sites in the colline region of Hesse Between February 1985 and July 1987 soil seepage experiments were carried out on fertilizer trial plots in mature beech stands of four forest districts of Hesse. Encompassed by this study are in addition the most important results from soil-chemical analyses of the subsequent years 1988 to 1991. Aim of the investigations was to study the influence of liming and K/Mg-fertilization on the chemical composition of soil and soil solution under different site conditions. In the percolated soil solution liming did not led to a significant pH increase in subsequent years. In contrast, in some cases the pH level dropped by 0.1 to 0.2 units on average and Al-concentration increased correspondingly. In most cases, fertilization led to a significant increase in soil solution concentrations of the metal cations potassium, calcium and magnesium, especially at a depth of 50 cm. On those trial plots where a pH decrease was observed, the concentrations of K, Ca and Mg exhibited either a slight or no increase at all. Furthermore on some trial sites with freely drained soils, liming led to a faster mineralisation of the humus layer and thus to an increase of nitrate contents in the percolated soil solution from about 1–2 mg/l to 10–20 mg/l on average. Increased concentrations of sulfate and in most cases also of heavy metals (Mn, Zn, Cu. Cd) were observed in the soil solution which was attributed to the mobilizing effect of Ca-fertlization. In general, the mobility of most chemical parameters showed a slight increase following liming and soil tillage. Even after 5 to 8 years considerably higher pH-values and base saturation were evident in limed and fertilized soils, especially in the top 15 cm of soil profiles.     

Entwicklung,Eigenschaften und Klassifikation von Dünenböden der Ostfriesischen Inseln – am Beispiel Spiekeroogs

Pedogenesis, properties, and classification of dune soils of the East Frisian Islands (southern North Sea coast of Germany)—exemplified by the island Spiekeroog The aim of this study was a detailed pedological investigation and exact classification of dune soils of the East Frisian Islands. The following soil‐forming processes were identified on a laboratory‐data basis: humus accumulation and dislocation, carbonate loss, acidification, modification of exchangeable cations, and base‐saturation decrease. A slight iron oxide accumulation was visible in the field, but not confirmed by laboratory data. Applying the qualitatively and quantitatively defined horizons from the German classification, these soils cannot be classified as Regosols, Braunerden, and Podsols but they fit perfectly in the Arenosols as defined in the WRB.     

Vergleich zwischen Perkolation und Extraktion mit 1 M NH4Cl‐Lösung zur Bestimmung der effektiven Kationenaustauschkapazität (KAKeff) von Böden

Comparison between percolation and extraction with 1 M NH₄Cl solution to determine the effective cation exchange capacity (CEC_eff) of soils A simple method is proposed for the determination of the effective cation exchange capacity (CEC_eff). The soil is extracted with 1 M NH₄Cl‐solution, manually shaken for three times, and the exchangeable cations are determined by ICP‐OES and pH‐measurement. Comparison with corresponding results of the percolation method (n = 110 samples) shows good agreement in reproducibility, exchangeable cations (except Fe and Na), base saturation and CEC_eff.     

Schätzung der mikrobiellen Biomasse von Böden aus anthropogenen und natürlichen Substraten — ein Beitrag zur Standortbewertung

Field estimation of the microbial biomass of soils derived from natural and anthropogenic parent materials Whereas the estimation and evaluation of physical and chemical soil properties is possible with the use of widely accepted methods, there is still no procedure with respect to microbiological parameters. Therefore, our objective was to develop a field procedure for estimating the integral parameter ”︁microbial biomass”. For this purpose, microbial biomass data (C_mic in dry matter) of soils developed in natural parent materials from 116 sites in Germany and abroad were analyzed. Additionally, C_mic in 33 German soils developed in anthropogenic parent materials was determined. In the soils under consideration, C_mic varied between 100 and 4000 kg ha^—1 in the upper 30 cm. For soils of natural substrates statistical relations between C_mic and the humus and clay content as well as pH were derived. From these parameters which are combined as the diagnostic characteristics of humus a simple procedure for estimating C_mic of arable soils was developed. For soils developed in anthropogenic parent materials, however, an estimation procedure was developed that uses the nature of the parent material and the degree of soil development. To evaluate the estimated amount of C_mic, a frame consisting of 6 classes is proposed: < 200 kg ha^—1 (= very low), 200—400 kg ha^—1 (= low), 400—800 kg ha^—1 (= moderate), 800—1600 kg ha^—1 (= medium), 1600—3200 kg ha^—1 (= high), and > 3200 kg ha^—1 (= very high).     

Der Einfluß der natürlichen organischen Substanzen auf die Metallverteilung zwischen Boden und Bodenlösung in einem sauren Waldboden

The influence of organic matter in the translocation of metals between soil and soil solution of an acid forest soil Water extracts were prepared from soil samples which were collected from a soil profile showing very little variation in the texture down to a depth of 120 cm and thus only little translocation of clay in the soil profile. The aim of the study was to describe the distribution between soil and soil solution of several metals like Cu, Pb, Cd, Zn, Al and Mn as a function of humic substances, electrolyte concentration and pH. From the experimental results the following hypothesis on the reaction mechanisms involving metals and humus derived substances has been deduced. The metals Cu, Fe, Al and Pb are mobilized through complexation by soluble humus substances in addition to the usual pH dependent desorption and dissolution of hydroxides. This mobilization determines the solution concentration of Cu and Fe at pH > 3.7 and Al and Pb at pH > 4.2. Al, Fe and Pb are complexed selectively by high molecular weight humus derived substances which undergo adsorption on soil mineral surfaces. Cu interacts with low molecular weight humus derived substances which are not easily adsorbed by the mineral surfaces. Zn, Cd and Mn primarily undergo sorption and are thus controlled by pH and electrolyte concentration of solutions because their complexation with humus derived substances seems to be weak or nonexistant. It is further postulated that the humus derived substances mobilize Al³⁺ and Fe³⁺ ions. By this, other metals like Cd, Zn, Mn, Ca and Mg can occupy the free exchange sites.     

Abbau von Isoproturon in Regenwurm‐Makroporen und in der Unterbodenmatrix – Eine Feldstudie

Degradation of isoproturon in earthworm macropores and subsoil matrix—a field study The objective is to compare the time scale of microbial degradation of the herbicide Isoproturon at the end of earthworm burrows with the time scale of microbial degradation in the surrounding soil matrix. To this end, we developed a method which allows the observation of microbial degradation on Isoproturon in macropores under field conditions. Study area was the well‐investigated Weiherbach catchment (Kraichgau, SW Germany). The topsoil of a 12 m² large plot parcel was removed, the parcel was covered with a tent and instrumented with TDR and temperature sensors at two depths. After preliminary investigations to optimize application and sampling techniques, the bottom of 55 earthworm burrows, located at a depth of 80–100 cm, was inoculated with Isoproturon. Within an interval of 8 d, soil material from the bottom of 5–6 earthworm burrows was taken into the laboratory and analyzed for the Isoproturon concentration for investigation of the degradation kinetics. Furthermore, the degradation of Isoproturon in the soil matrix, that surrounded the macropores at the field plot, was observed in the laboratory. Microbial degradation of Isoproturon at the bottom of the earthworm burrows was with a DT‐50‐value of 15.6 d almost as fast as in the topsoil. In the soil matrix that closely surrounded the center of the earthworm burrows, no measurable degradation was observed within 30 d. The clearly slower degradation in the soil matrix may be likely explained by a lower microbial activity that was observed in the surrounding soil matrix. The results give evidence that deterministic modeling of the fate of pesticides once transported into heterogeneous subsoils by preferential flow requires an accuracy of a few centimeters in terms of predicting spatial locations: time scales of microbial degradation in the subsoil drop almost one order of magnitude, in case the herbicides dislocates from the bottom of an earthworm burrow a few centimeter into the surrounding soil matrix. If at all, predictions of such an accuracy can only be achieved at locations at sites where the soil hydraulic properties and the macropore system are known at a very high spatial resolution.