Manfred Renger

Soil physical characteristics of peat soils

Drainage and intensive use of fens lead to alterations in the physical characteristics of peat soils. This was demonstrated using parameters of water balance (available water capacity) and the evaluated unsaturated hydraulic conductivity. Deriving the distribution of the pore size from the water retention curve was flawed because of shrinkage due to drainage, especially at high soil water potentials. These errors became greater as the peat was less influenced by soil-genetic processes. The water retention curves (desorption) evaluated in the field and the laboratory satisfactorily corresponded. However, the wetting- and drainage-curves obtained in the field differed up to 30 vol.-% water content at same soil water potentials. These differences were largely due to a wetting inhibition.

Aspects of peat conservation and water management

An extended water regime model was used for calculating the evapotranspiration, groundwater recharge, and peat mineralization (CO2 and N release) for various fen locations with grassland utilization in dependence on the groundwater level. The results show that an increasing groundwater level leads to a strong decline of the actual evapotranspiration Et. For example, increasing the groundwater level from 30 to 120 cm diminishes the Et by up to 230 mm a—1. A positive groundwater recharge only takes place at groundwater levels of 90 cm and more. At smaller distances the capillary rise into the rooting zone during the summer months is greater than the water seepage during the winter months, so that a negative groundwater recharge-balance is reached in the course of a year. The CO2- and the N-release, as well as the annual decline in peat thickness, increase significantly with rising groundwater levels. The results show, that varying the groundwater level can influence the water regime and the peat mineralization significantly. The lower the groundwater level the less is the peat decomposition. The demand for a groundwater level as small as possible is, however, limited by an agricultural utilization of the fens. Choosing the optimum groundwater level should consider the aims (1) peat mineralization, (2) gas emission (CO2, CH4, N2O), and (3) crop production. If a grassland utilization is supposed to be made possible and all three aims above are given equal importance, the groundwater level should be maintained at 30 cm. At this distance, about 90 % of the optimum plant output can be reached. The peat mineralization can be reduced to 30 to 40 % of the maximum peat mineralization. The gas emission amounts to 50—60 % of the maximum value. Aspekte zum Niedermoorschutz und Wassermanagement Mit Hilfe eines erweiterten Wasserhaushaltsmodells wurden Eva-potranspiration, Grundwasserneubildung und die Torfmineralisation (CO2- und N-Freisetzung) in Abhangigkeit vom Grundwasserflurabstand fur verschiedene Niedermoorstandorte unter Grunlandnutzung ermittelt. Die Ergebnisse zeigen, dass mit zunehmendem Grundwasserflurabstand die reale Evapotranspiration Et stark ab-sinkt. So vermindert sich Et bei einem Anstieg des Grundwasserflurabstandes von 30 cm auf 120 cm bis zu 230 mm a—1. Eine positive Grundwasserneubildung findet nur bei Grundwasserflurabstanden von 90 cm und mehr statt. Bei geringeren Flurabstanden ist der kapillare Aufstieg in den Wurzelraum wahrend des Sommers groser als die Versickerung im Winterhalbjahr, so dass innerhalb eines Jahres negative Grundwasserneubildungsraten auftreten. Mit steigendem Grundwasserflurabstand nehmen die CO2- und N-Freisetzung sowie die jahrliche Abnahme der Torfmachtigkeit deutlich zu. Die Ergebnisse zeigen, dass durch Steuerung des Grundwasserflurabstandes der Wasserhaushalt und die Torfmineralisation entscheidend beeinflusst werden konnen. Je flacher der Grundwasserflurabstand ist, um so geringer ist der Torfabbau. Der Forderung nach moglichst flachen Grundwasserflurabstanden sind aber Grenzen gesetzt, wenn die Niedermoore landwirtschaftlich genutzt werden sollen. Fur die Wahl des optimalen Grundwasserflurabstandes sind die Zielgrosen (1) Torfmineralisation, (2) Gasemission (CO2, CH4, N2O) und (3) Pflanzenertrag zu be-rucksichtigen. Bei gleichrangiger Berucksichtigung dieser Grosen und unter der Voraussetzung, dass eine Grunlandnutzung moglich sein soll, ergibt sich ein einzuhaltender mittlerer Grundwasserflurabstand von 30 cm. Bei diesem Grundwasserflurabstand erreicht man etwa 90 % des optimalen Ertrags. Die Torfmineralisation kann dabei auf 30 bis 40 % der maximalen Torfmineralisation herabgesetzt werden. Die Gasemission liegt bei 50—60 % des maximalen Wertes.

Simulation of the dry matter production and seed yield of common beans under varying soil water and salinity conditions

Abstract We present a model that simulates the effects of water and salinity stress on the growth of beans. The model derives a combined soil water/salinity stress factor from the total water potential (combination of the matric and the osmotic potentials) and uses this stress factor as a growth limiter in a growth model. The model was tested on data obtained from two greenhouse trials of beans ( Phaseolus vulgaris ) grown under a range of soil water and salinity conditions. The simulated dry weight of the bean generally followed those observed. In the first trial, the comparison between simulated and observed total dry weight and seed yield gave R 2 values of 0.97 and 0.92, respectively. Comparison of the simulated to the observed dry weight for the second trial gave R 2 values of 0.85 and 0.89, respectively. These indicate a good performance of the model in general. The principle of deriving a combined water/salinity stress from the matric and osmotic potentials is simple and can be included as a simple routine in many existing crop models without much difficulty.

Potential hazards of lime application in a damaged pine forest ecosystem in Berlin, Germany

Ninety percent of the pines (P. Sylvestris) in the forests of Berlin (West) are classified as damaged. Needle and leaf analyses do not indicate nutrient deficiencies. In site of high S-inputs (55 kg ha−1 yr−1 with throughfall) total acid inputs are moderate (2.4 kmol ha−1 yr−1) due to their neutralization by carbonatic dusts. Heavy metal depositions have led to accumulations in the forest floor (e.g. Pb 150 mg kg−1, Cd 0.5 mg kg−1). The dominating soil type, a cambic arenosol (Ustipsamment) is strongly acidified (pH 3.2 – 4.0) and poor in available nutrients. On an experimental plot, the application of dolomitic lime (6.1 tons ha−1) and fertilizer (145 kg ha−1 K2SO4) led to a significant increase m pH and base saturation in the top 10 cm of the mineral soil after 2 yr. The data on element fluxes give evidence for increased mineralization rates, enhanced heavy metal accumulation in the forest floor and increased soil solution concentrations of potentially hazardous substances (Al, Cd, NO3). The lime application is discussed in terms of site specific effects on ecosystem stability and groundwater quality.

Soil hydrology and CO2 release of peat soils

A simple model to predict soil water components and the CO2 release for peat soils is presented. It can be used to determine plant water uptake and the CO2 release as a result of peat mineralization for different types of peat soils, various climate conditions, and groundwater levels. The model considers the thickness of the root zone, its hydraulic characteristics (pF, Ku), the groundwater depth and a soil-specific function to predict the CO2 release as a result of peat mineralization. The latter is a mathematical function considering soil temperature and soil matric potential. It is based on measurements from soil cores at varying temperatures and soil water contents using a respiricond equipment. Data was analyzed using nonlinear multiple regression analysis. As a result, CO2 release equations were gained and incorporated into a soil water simulation model.  Groundwater lysimeter measurements were used for model calibration of soil water components, CO2 release was adapted according long-term lysimeter data of Mundel (1976).  Peat soils have a negative water balance for groundwater depth conditions up to 80—100 cm below surface. Results demonstrate the necessity of a high soil water content i.e. shallow groundwater to avoid peat mineralization and soil degradation. CO2 losses increase with the thickness of the rooted soil zone and decreases with the degree of soil degradation. Especially the combination of deep groundwater level and high water balance deficits during the vegetation period leads to tremendous CO2 losses. Wasserhaushalt und CO2-Freisetzung von Niedermooren Es wird ein kombiniertes Wasserhaushalts-CO2-Freisetzungs-Modell vorgestellt, das eine Berechnung der Wasserhaushaltskomponenten und der CO2-Freisetzung fur unterschiedlich degradierte Niedermoore als Funktion des Grundwasserflurabstands und des Klimageschehens auf taglicher Basis ermoglicht. Die Boden werden im Modell durch ihre Moormachtigkeit und hydraulischen Eigenschaften (pF, Ku) berucksichtigt. Die Steuerungsfunktion zur Berechnung der CO2-Freisetzung fust auf Respiricondmessungen an ungestorten Bodenproben, wobei die CO2-Freisetzung bei variablen Temperatur- und Bodenfeuchtebedingungen gemessen wurde. Aus diesen Messdaten wurde mittels multipler Regressions-analysen bodenspezifische CO2-Freisetzungsfunktionen abgeleitet, die in das Wasserhaushalts-Simulationsmodell integriert wurden. Die Wasserhaushaltsberechnungen wurden anhand von Grundwasser-Lysimetermessungen kalibriert, die CO2-Freisetzung mit Hilfe langjahriger Lysimetermessungen von Mundel (1976). Niedermoore weisen bis zu einem Grundwasserstand von 80—100 cm u. GOF eine negative Wasserbilanz auf und wirken im Landschaftswasserhaushalt als Wasserzehrgebiete. Die CO2-Freisetzung nimmt mit der Durchwurzelungstiefe zu und ist zusatzlich vom Substrattyp und der Zersetzungsstufe abhangig. Bei gleichen Klima- und Grundwasserstandsbedingungen steigt die CO2-Freisetzung in der Reihenfolge Erd-Niedermoor > Mulm-Niedermoor > Anmoor. Besonders die Kombination von niedrigen Grundwasserflurabstanden und hohen Wasserbilanzdefiziten wahrend der Vegetationsperiode kann zu immensen Torfabbauraten bzw. Emissionen fuhren.

Large effect of leaching of DOC on water adsorption properties of a sandy soil

Abstract In this study, changes of adsorption properties of a sandy soil from a former sewage farm due to the leaching of dissolved organic carbon (DOC) were examined. The leaching of DOC at various pH levels was simulated in laboratory experiment using sodium hydroxide as the leaching agent. An increase of pH resulted in an increase of the amount of DOC in the studied soil. The removal of DOC altered the surface properties of the remaining solid. In particular, the surface area was reduced and the water vapour adsorption energy distribution function was shifted to lower energy ranges, thus showing the increase of the hydrophobic character of the soil. The intensity of these changes was more pronounced when the soil had been previously acidified.

Influence of DOM-quality, DOM-quantity and water regime on the transport of selected heavy metals

Abstract The spatial and temporal variability of heavy metal concentrations in the soil solution were investigated at a field station on a former sewage farm in Berlin (Germany). In these sandy soils, heavy metal content in the soil solid phase is highly correlated to the organic matter content, which shows distinct distribution patterns related to the former sewage water inputs. In addition, spatial variability within short distances is very high, due to the uneven restribution of the organic topsoil when the fields were remodelled. In the soil solution, Cu- and Zn-concentrations increase with depth, although solid phase contents are up to 100-fold higher in the topsoil. In 50 cm depth, these heavy metal concentrations correlate with the seasonal variations in DOC-concentrations. In 100 and 180 cm depth, a closer relationship was found to pH, which also shows a distinct seasonality, attributed to mineralization processes. Source and sink aspects of heavy metal mobility in the soil profile are discussed with respect to DOC, pH and precipitation/dissolution of mineral phases.

Comparison of fractal dimensions of soils estimated from adsorption isotherms, mercury intrusion, and particle size distribution

The values of the surface fractal dimensions were determined for several samples of Cambisols and Luvisols from analysis of nitrogen and water vapor adsorption isotherms and from mercury intrusion data. Moreover, the values of fractal dimension characterizing the particle size distributions of soil samples were calculated by using a number-based method. For almost all investigated soils the values of the surface fractal dimension, obtained from water vapor isotherms were lower than those obtained from nitrogen isotherms. Largest were the surface fractal dimensions evaluated form mercury intrusion data. No significant correlations between different kinds of surface fractal dimensions were found, and the reasons of this finding are discussed. However, the values of the surface fractal dimensions calculated from mercury intrusion data correlate with those characterizing the texture of soils. The paper also reports on correlations between of the values of surface area, fractal dimensions and some selected physico-chemical characteristics of soils. Vergleich der fraktalen Dimensionen von Boden auf Basis von Adsorptionsisothermen, Quecksilberporosimetrie und der Korngrosenverteilung An verschiedenen Proben von Braunerden aus Geschiebelehm und Sand wurden die fraktalen Oberflacheneigenschaften mittels Stickstoff- und Wasserdampfadsorption sowie Quecksilberporosimetrie bestimmt. Auserdem wurden charakteristische Werte fur die fraktalen Eigenschaften mit numerischen Methoden aus Texturanalysen abgeleitet. Es wurde nachgewiesen, dass fur fast alle untersuchten Boden die aus Wasserdampf-Adsorptionsisothermen abgeleiteten fraktalen Oberflachendimensionen niedriger sind als die Werte, die aus Stickstoff-Adsorptionsisothermen abgeleitet wurden. Die fraktalen Dimensionen, die auf Grund der porosimetrischen Daten berechnet wurden, waren am hochsten. Es wurde keine Korrelation zwischen verschiedenen Arten der fraktalen Oberflachendimensionen gefunden, und die Grunde dafur werden diskutiert. In der vorliegenden Arbeit werden auserdem Untersuchungsergebnisse uber die vorkommende Korrelation zwischen den Werten der Oberflache und der fraktalen Dimension und ausgewahlten physiko-chemischen Bodencharakteristiken besprochen.

Surface fractal dimension of thermally treated peat soils from adsorption isotherms of nitrogen.

Adsorption isotherms of nitrogen at 80 K were measured on thermally modified peat soils. The isotherms were used to evaluate the surface fractal dimension from the Frenkel-Halsey-Hill equation. We also tested if surface characteristics were correlated to the water holding capacity index, which characterizes the degree of the secondary transformation of peat soils. In most cases the thermal treatment lowered the value of the surface fractal dimension, i.e. diminished the roughness of the part of the surface that adsorbs nitrogen molecules. Bestimmung fraktaler Oberflacheneigenschaften von thermisch behandelten Torfboden durch Stickstoffadsorptionsisothermen Die Adsorptionsisothermen von Stickstoff wurden bei 80 K an unterschiedlichen, thermisch bei 50, 100 und 150°C vorbehandelten Torfboden untersucht. Die experimentell ermittelten Adsorptionsisothermen wurden benutzt, um die fraktalen Dimensionen von Oberflachen gemas der Frenkel-Halsey-Hill-Gleichung zu berechnen. Die ermittelten Daten wurden auf Korrelationen zwischen Oberflacheneigenschaften und dem Wasserhaltekapazitatsindex (Mas fur den Grad der Humifizierung) untersucht. Die thermische Behandlung fuhrte in den meisten Fallen zu einer Verringerung des Wertes der fraktalen Dimension. Das bedeutet, dass die Rauhigkeit der Oberflachenanteile geringer wurde, an der die Stickstoffmolekule adsorbiert wurden.

Reactions of sewage farm soils to different irrigation solutions in a column experiment. 1. Solid phase physicochemical properties

Physicochemical properties of two sandy soils taken from a present and from a former sewage farm were studied during a 2.5 years column experiment, m which lime and irrigation water of various compositions were applied The amount of exchangeable bases and base saturation percentage in both soils changed markedly during the experiment. These changes were governed by changes in soil pH The specific surface area as well as the cation exchange capacity were closely related to the organic carbon content in the soil profile The surface charge density of both soils was roughly equal and independent of the soil depth