Schätzrahmen für die effektive Durchwurzelungstiefe mehrschichtiger Böden

Estimating the effective rooting depth of layered soils The values of the effective rooting depth given by the Soil Mapping Instruction are valid only for homogenous soils. In addition to these values a calculation is presented estimating the effective rooting depth of layered soils. This method is proposed as a reference method in databases of soil information systems.     

Die Bedeutung der Aggregierung für die Nährstoffsorption in Böden

The role of structure for nutrient sorptivity of soils The influence of the aggregation in 2 differently textured and structured soils (Haplumbrept and Chromudert) on the cation exchange capacity CEC was investigated. The results clearly demonstrated, that from the total soil (< 2 mm), natural and disturbed aggregates (Ø 5–8 mm) and the separated outer and inner part of those aggregates, the undisturbed aggregates had the lowest CEC. Furthermore, the aggregate skin was more chargeable than the inner part, due to a higher amount of silt and clay in that part. Because of higher bulk densities of the aggregates and theoretically increased tortuosity, the solution of elements in percolating water, especially in clay soils, is limited to the interaggregate pores. Thus, measured differences between the element distribution in different compartments can be explained.     

Untersuchungen zum Bodenlufthaushalt in einem Bodenbearbeitungsversuch. 2. Gasdiffusionskoeffizienten als Strukturmaße für Böden

Investigation of the soil gas regime in a tillage experiment: 2. Apparent diffusion coefficients as a measure of soil structure In a soil tillage experiment with nursery stock on three different soils the apparent diffusion coefficients for CO₂ were measured using soil cores of different depths at different times. Not-tilled, herbicide treated plots were compared with rototilled plots. The relationship between the relative apparent diffusion coefficient and the air content may be described by an exponential regression function D_s/D_a = 0.0085 · e^6.8E_L, if all measurements are taken into the calculation. By dividing into different soil textures different regressions are obtained for the three studied soils: a sand, a silt and a clay loam. In many cases it is possible to show by the changing D_s(E_L) regression changes of the soil structure with depth or as a result of tillage. In all these cases the soil of the not tilled plots turns out to be better structurized than that of the tilled ones, demonstrated by higher D_s-values at equal E_L. The interpretation of the differences is being tried with the aid of soil pore tortuousity and continuity. Finally the measured D_s(E_L) relationships are applied to characterize the soil gas regime for two seasons, using CO₂ concentration profiles of the soil air on a day in summer and fall, respectively. It is shown, that CO₂ production reaches farther down in summer than in fall.     

Bodengefüge gegen Verdichtungen schützen – Lösungsansätze für den Schutz landwirtschaftlich genutzter Böden

Protecting soil structure against compaction—proposed solutions to safeguard agricultural soils To safeguard the ecological soil functions and the functions linked to human activities, measures against harmful changes to the soil are required, in line with the precautionary principle. The German Federal Soil Protection Act sets obligations for precaution in agricultural land use and, if harmful changes to the soil are foreseeable, measures for averting a danger. The results of a research project of the Federal Environmental Agency show that it is possible to describe an impairment of the soil structure, using methods of soil analysis. But this as a sole information would not qualify for the identification of harmful changes to the soil in the context of the Soil Protection Act, which requires an assessment of the severity of disruption of soil functions and the respective subject of protection. This would make additional soil investigations on site mandatory. Approaches in agricultural engineering and soil physics have introduced procedures to preserve the soil structure, in accordance with the precautionary principle. But these procedures have different goals and different ranges of application and hence offer partial solutions to safeguard against soil compaction. The assessment model of “trafficability by measuring the rut depth” provides information about the compaction status of the soil under applied conditions for farming gear, without providing detailed information about affected soil layers. The soil‐physical model of classifying soils into “risk classes for harmful soil compaction” focuses on the relationship between topsoil compaction and crop yields. The soil‐physical models “precompression stress” and “loading ratio” provide information for the assessment of subsoil compaction and a prognosis of a possible impairment of the soil structure at the water content of field capacity. It is necessary to validate the individual models with additional regional data about soil structure before a final assessment of the prognoses is made.     

Untersuchungen über den Einfluß des Bodengefüges für den Eindringwiderstand in Böden

The influence of soil structure on penetration resistance Penetration resistance depends strongly on the soil structure. However, because roots may either penetrate aggregates or grow around them, the value determined for the bulk soil can only be used as a first approximation. If e.g. unconfined aggregates are penetrated, the penetration resistance increases with increasing size. If however, the aggregates are confined by being embedded in gypsum then the penetration resistance is higher but is independent of aggregate size. Thus, the outer skin is stronger than the inner part of the aggregates. When single prisms are penetrated horizontally, then the penetration resistance is smaller than the resistance to vertical penetration. On the other hand, for polyhedral structure the penetration resistance is of the same order of magnitude in both directions.     

Zur Bedeutung des Aggregierungsgrades für die Spannungsverteilung in strukturierten Böden

The effect of soil aggregation on stress distribution in structured soils The mechanical compressibility of arable soils can be described by preconsolidation load value and by the shear resistance parameters of the bulk soil and single aggregates. In order to quantify the effective stress equation must be also known the hydraulic properties of the soil in dependence of the intensity, kind, and number of loading events. The soil reacts as a rigid body at very fast wheeling speed inclusive a very pronounced stress attenuation in the top soil while stresses will be distributed in the soil threedimensionally to deeper depths at slower speed. These variations can be explained by the mechanical as well as by the hydraulic parameters of the bulk soil and single aggregates. Thus, the pore water pressure value of the bulk soil as a parameter of the effective stress equation further depends on the hydraulic properties of the inter- and intraaggregate pore system and continuity. As can be derived from the results the pore water pressure values are identical irrespective of the predessication for clayey polyhedres at high load while in coarse textured prisms the pore water pressure value depends on load and predryness. The consequences for soil strength under dynamic loading are shortly discussed.     

Die Interpretation des Eindringwiderstands zur flächenhaften Darstellung physikalischer Unterschiede in Böden

The interpretation of penetration resistance in use of spatial discrimination of physical differences in soils Penetration resistance (PR) was measured for two natural Loess-Parabraunerden (Udalfs) and a reclaimed Loess-Parabraunerde. Concerning these measurements two methods of interpretation of PR are compared: 1. sums and means of PR for each point for all depths. 2. typified PR-depth-functions for each point. They are deduced from the differences of PR for each depth increment. Means and PR-depth-functions are rarely comparable in their spatial distribution: The same means are correlated with different PR-depth-functions and vice versa. The correlation is higher on the reclaimed area. The different contents and the lag of spatial correlation are interpreted as the need for doing both: calculating means as well as PR-depth-functions. Both methods complement each other. To discriminate spatially between top soil compactions, plowpans, high densities in the underground, flat sola above rocks PR-depth-functions are suggested as a method of interpretation.     

Regenwürmer als Bioindikatoren für Schwermetallbelastungen von Böden unter Freilandbedingungen

The use of earthworms in monitoring soil pollution by heavy metals Total heavy metal contents (HNO₃-soluble) and exchangeable fractions (Ca(NO₃)₂-soluble) of Pb, Zn and Cd were measured in soils, litter layers and earthworms (dry masses) from forest, arable and pasture sites in a transect of the main wind direction and varying distances (1.5, 5.4, 11.4, 15.6 km) to a lead smelter near Bad Ems, Germany. Additionally, cast materials of Lumbricus terrestris-individuals were collected from the surface of the pasture sites. In the observed area total soil contents of Pb and Cd exceeded the C-level and total contents of Zn the B-level of the “Netherland-list”. Heavy metal contents in soils and earthworms decreased with increasing distance to the smelter. Pb showed the best correlation. Correlation between total contents of Pb and Cd in soils and earthworms were significant (rs = 0.66; p < 0.05 and rs = 0.67; p < 0.01, respectively). The uptake of heavy metals by Lumbricus rubellus, L. terrestris and Aporrectodea caliginosa was metal specific rather than species specific with factors of accumulation being <1 (Pb), 2.7–7.6 (Zn) and 19.5–85.5 (Cd). The heavy metal contents of the observed cast materials signified the different transfer of elements from soil material via earthworm individuals to the faeces. In the cast materials the amounts of Pb were high and the amounts of Zn and Cd were low. This indicates a high accumulation rate for Zn and especially for Cd in the tissues of the observed earthworm individuals. The present data support the necessity of ecotoxicological threshold levels.     

Die Bedeutung amorpher AI-Verbindungen für Al-Freisetzungsraten in carbonatfreien,sandigen Böden

The importance of amorphous Al-compounds regarding Al-release rates in carbonate-free, sandy soils In a preceding investigation the kinetics of proton consumption and the release of elements in carbonate-free, sandy forest soil horizons was analyzed by pH-stat-titrations. The soil matrix should reveal losses of Al and DOC equivalent to the amounts mobilized, and several extraction procedures (wet combustion: C_org; Pyrophosphateextraction: Al_p, C_org-p; Oxalate-extraction: Al_o) were applied in order to distinguish between different pools. In eight of the ten horizons investigated the dissolution of Al resulted in equivalent decreases of organically bound Al (Al_p), four of them also exhibited reductions of C_org-p?levels equal to the release of DOC. For the other two horizons, Al mobilization could be attributed to the dissolution of organic and inorganic amorphous Al-compounds, each fraction contributing about half of the total. Like the release of Al and DOC, the losses of Al_p, Al_o and inorganically bound Al (Al_o?Al_p) could be well described as 1st order reactions, the constants of dissolution [h^?1] of Al_p (0.027), Al_o (0.023) and C_org-p (0.026) being in accordance with those of Al-(0.027) and DOC- (0.024) release, respectively. For the dissolution of inorganic Al-compounds the reaction constants (0.066 and 0.052) were calculated to be nearly double.     

Ein Bestimmungsschlüssel für natürliche und technogene Substrate in Böden städtisch-industrieller Verdichtungsräume

A key to recognize natural and technological materials in soils of urban and industrial environment In the most cases soils of urban and industrial environment are influenced by man. They often consist of mixtures of changed natural or technological materials. The identification of these materials means a problem to the soil scientist missing exact characteristics, especially of the technological materials. Improving the field examinations a key was developed to recognize the materials of the urban environment.     

Modelluntersuchungen zum Mechanismus der bakteriellen Eisenreduktion in Hydromorphen Böden

Model experiments on the mechanism of bacterial iron-reduction in water-logged soils In model experiments, iron-reduction with Bacillus polymyxa (nit⁺) and Clostridium butyricum (nit^?) was followed in relation to the development of pH, Eh and glucose fermentation. In parallel tubes, the influence of NO, (KNO,) and/or Mn02-Powder (Merck) on Fe(I1) formation and rH (calculated from pH and Eh) was measured. All tubes were incubated anaerobically (N2/C02 = 9/1) at 30°C. Both with Bacilluspolymyxa (nit⁺) as well as with Clostridium butyricum (nit^?), the reduction-intensity rH decreased rapidly reaching entirely reducing conditions (rH = 0) within 2–3 days. In both cases iron-reduction and glucose utilization developed sigmoidal and miror symmetrically (Fig. 1) In the case of B. polymyxa (nit⁺) the addition of NO, and/or Mn02 suppressed iron-reduction nearly entirely. With C. butyricum, only Mn02 (but not nitrate) affected iron-reduction significantly. Nitrate remained unchanged throughout the incubation period, although completely reducing conditions (rH = 0) were obtained (Fig. 2). Apparently, nitrate, Mn02 or Fe203 are reduced directly and specifically rather than indirectly as a consequence of reducing metabolites and/or by a lowered redox potential in the environment. If nitrate, Mn02 and Fe203 are reduced chemically by reducing condition, the reduction sequence nitrate → Mn(1V)-oxides → Fe(II1)-oxides should occur in relation to pH and Eh (rH) and independently of the type of organism (nit⁺ or nit^?) in question. This view is rejected by the results presented. With nit⁺ bacteria such as B. polymyxa, the enzyme nitrate reductase seems to act as one mechanism of iron- and manganese-reduction. However, with C. butyricum (nit^?), another, so far unknown enzym system (ferrireductase?), should be made responsible for iron- and manganese-reduction.     

Ein Vergleich und eine Bewertung von Dränformeln für die Drändistanz von geschichteten Grund- und Stauwasserböden

A comparison and an evaluation of drain spacing equations for layered soils Drain spacings, calculated with different steady-state tile drainage formulas for layered soils, were compared. The formulas under consideration were those of Ernst, van Beers and of Toksöz and Kirkham. It was found that, for certain ranges of the drainage parameters, the drain spacings compare well. For other conditions, differences of over 100 percent did occur. Especially, results obtained with the Ernst equation may deviate considerably from those of the other authors. However, also drain spacings calculated with the van Beers equation do occasionally differ from those of Toksöz and Kirkham. For practical use the equation of Toksöz and Kirkham is recommended.     

Die Bedeutung der K-Ca-Austauschisotherme für eine Beurteilung der K-Versorgung der Pflanzen bei Lößböden

K-Ca-exchange isothermes of soils from loess and the potassium supply of plants From 80 Ap-horizons of Luvisols and Phaeozems on loess from south of Hannover K-Ca-exchange isotherms and cation concentrations in saturation extracts were investigated. Though not K deficient these soils show a very wide range of available K. From the very high K-concentrations in the saturation extracts (up to 3 meq/1) of part of the soils it was concluded, that mass flow should be sufficient for plant needs of K. The only soil property varying the exchange isotherms seems to be the clay content (Fig. 4). In order to calculate available K from the exchange isotherms in the same way as available water from pF characteristics the isotherms were extended down to activity ratios, according to literature, marginal for plant uptake of K (Fig. 6). The estimated soil K content, sufficient for plant in loess soils, amounts to about half that considered marginal by the regional extension service. With the assumption that so called non exchangeable, but plant available K is essentially very slowly exchangeable, an experiment was performed at 80°C to accelerate the exchange and to establish a true equilibrium. The comparison between the new exchange curve and the 25°C curve (Fig. 8) seems to reveal additional 180–450 kg/ha · 30 cm bound with equal free energy of exchange as easily exchangeable K.     

Die Anwendung der CP(Critical Point)-Trocknung bei der Präparation von Böden für licht- und elektronenmikroskopische Untersuchungen

The use of critical point (CP) drying for light and electron microscopy of soils The preparation of soils for light and electron microscopy usually requires the removal of water. Different dehydration techniques result in varying degrees of damage to the soil structure. The advantages and disadvantages of three dehydration techniques (CP drying, air drying and freeze drying) for soil clays are discussed in this paper. Observations with the scanning electron microscope (SEM) and shrinkage tests suggest that CP drying is particularly appropriate in soil samples > 5-6 mm.