Gerd Wessolek

Evaluation of pedo-transfer functions for unsaturated soil hydraulic conductivity using an independent data set

Abstract The paper reviews eight well-known and accepted pedo-transfer functions used for evaluation of soil hydraulic conductivity (saturated and unsaturated) from routinely available soil data. A comprehensive data set containing detailed measurements of 63 German soil horizons, to which none of the models had been previously calibrated, were used for the evaluation of pedo-transfer functions. The paper considers only pedo-transfer functions which have shown good results in the past. The statistical analysis of the eight functions shows that the model of Wosten [J.H.M., Wosten, Pedotransfer functions to evaluate soil quality. In: E.G., Gregorich, M.R., Carter, (Eds.), Soil Quality for Crop Production and Ecosystem Health. Developments in Soils Science, vol. 25, Elsevier, (1997) 221–245.], which requires an input of measured saturated hydraulic conductivity, performs best in terms of prediction of the unsaturated hydraulic conductivity. Evaluation of the unsaturated hydraulic conductivity by the pedo-transfer functions shows, on average, better correlations if the saturated hydraulic conductivity (an input parameter) is also obtained from predictions of pedo-transfer functions rather than directly from experiments. This outcome is attributed to a dependence of the saturated hydraulic conductivity on soil structure, i.e. macropores, while the unsaturated hydraulic conductivity is generally more dependent on soil texture. The deviating results of estimated soil hydraulic conductivity, as compared to the experimental data, indicate that the use of pedo-transfer functions based only on estimated soil hydraulic parameters must be carried out with great caution.

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.

Analysing problems in describing field and laboratory measured soil hydraulic properties

Abstract Accurate in situ determination of unsaturated soil hydraulic properties is often not feasible because of natural variability of most field soils, and because of instrumental limitations. Therefore the soil hydraulic properties are often measured in the laboratory, or derived by computer models using simple standard laboratory methods. This paper analyses problems in describing field hydraulic properties of a Ap horizon of a silty loam, basing on data from different laboratory methods: (i) A standard pressure plate apparatus and (ii) a constant-head permeameter were used to measure the static retention characteristics and the saturated hydraulic conductivity independently. (iii) An instantaneous profile method was applied to measure water retention and conductivity simultanously. Relatively new technics involving “undisturbed” soil samples instrumented with mini tensiometers and Time Domain Reflectometry (TDR) mini probes characterise the experiment. The models by Mualem and van Genuchten (MvG) were used to describe the soil hydraulic functions. The different laboratory results were then compared with the hydraulic field properties measured in instantaneous profile manner. The laboratory method allows a high spatial and temporal resolution; this facilitates an investigation of some of the assumptions made, when fitting the MvG models to hydraulic data. A reasonably good description of the hydraulic data was obtained when setting the residual water content, θr, to 0 and the pore connectivity factor, l, to 0.5 because θr and l were not sensitive. However, a poor fit resulted when the saturated water content, θs, was equated to the porosity, and the saturated hydraulic conductivity, ks to its independently measured value. Values for θs and ks derived from field measurements were somewhat higher than those obtained from laboratory samples. To demonstrate the influence of the different input data on a water balance, the cumulative drainage from an initially saturated soil column was simulated with different sets of hydraulic parameters estimated from field and laboratory data. Parameters derived from the laboratory results consistently yielded lower predictions of cumulative drainage compared to hydraulic parameters derived from field measurements. The differences were relatively small when an initial water content corresponding to 60 cm suction (field capacity) was used.

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.

Suitability of models for the estimation of soil hydraulic parameters

Abstract This paper deals with the applicability and validation of three predictive models for the estimation of soil hydraulic parameters (soil water characteristic and unsaturated hydraulic conductivity) by using routinely available soil data. Comparisons were made of the models of Campbell [Campbell, G.S., 1974. A simple model for determining unsaturated conductivity from moisture retention data. Soil Sci. 117, 311–314; Campbell, G.S., 1985. Soil Physics with BASIC. Elsevier, New York]; regression equations of Vereecken et al. [Vereecken, H., Feyen, J., Maes, J., Darius, P., 1989. Estimating the soil moisture retention characteristic from texture, bulk density, and carbon content. Soil Sci. 148, 389–403; Vereecken, H., Maes, J., Feyen, J., 1990. Estimating unsaturated hydraulic conductivity from easily measured soil properties. Soil Sci. 149, 1–12] and the model of G regson, H ector, M cGowan (GHM model) [Gregson, K., Hector, D.J., McGowan, M., 1987. A one-parameter model for the soil water characteristic. J. Soil Sci. 38, 483–486.]. The predictions of the above models were evaluated based on measured and calculated data from six German soils. Regression analysis showed that the GHM model, based on a single paired measurement of water content vs. matric head, produced noticeably better results than the other two models, which require input of textural properties of the soils. It is recommended that hydraulic parameters be estimated from paired measurements of water content vs. matric head rather than from textural properties of soils.

Immobilization of heavy metals in a polluted soil of a sewage farm by application of a modified aluminosilicate: a laboratory and numerical displacement study

Abstract The efficiency of the modified alumino-silicate “Berengite” to fix heavy metals in contaminated soils was studied using a soil from a former sewage disposal site with high loads of Zn and Cd. The immobilization effects for different additions of Berengite were described on the laboratory scale with the cation exchange capacity and a two component Freundlich sorption isotherm. Long term displacement of Cd and Zn were calculated with a numerical simulation model. The simulation studies show a rather high immobilization of Zn and Cd in the solid phase for the next 80 years. Far more Berengite is required for the fixation of Cd than for Zn.

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.

Effect of biochar on reclaimed tidal land soil properties and maize (Zea mays L.) response

Reclaimed tidal land soil (RTLS) often contains high levels of soluble salts and exchangeable Na that can adversely affect plant growth. The current study examined the effect of biochar on the physicochemical properties of RTLS and subsequently the influence on plant growth performance. Rice hull derived biochar (BC) was applied to RTLS at three different rates (1%, 2%, and 5% (w/w)) and maize (Zea mays L.) subsequently cultivated for 6weeks. While maize was cultivated, 0.1% NaCl solution was supplied from the bottom of the pots to simulate the natural RTLS conditions. Biochar induced changes in soil properties were evaluated by the water stable aggregate (WSA) percentage, exchangeable sodium percentage (ESP), soil organic carbon contents, cation exchange capacity, and exchangeable cations. Plant response was measured by growth rate, nutrient contents, and antioxidant enzyme activity of ascorbate peroxidase (APX) and glutathione reductase (GR). Application of rice hull derived biochar increased the soil organic carbon content and the percentage of WSA by 36-69%, while decreasing the ESP. The highest dry weight maize yield was observed from soil which received 5% BC (w/w), which was attributed to increased stability of water-stable aggregates and elevated levels of phosphate in BC incorporated soils. Moreover, increased potassium, sourced from the BC, induced mitigation of Na uptake by maize and consequently, reduced the impact of salt stress as evidenced by overall declines in the antioxidant activities of APX and GR.

Metal leaching in a highway embankment on field and laboratory scale

Increasing worldwide motor vehicle traffic leads to the question of the possible environmental consequences. This paper aims to analyse metal leaching in a highway embankment using both field and laboratory experiments. Soil, soil solution and road runoff were collected along one of the oldest highways in the world to characterize leaching of the metals Cd, Cr, Cu, Ni, Pb and Zn. Batch, column and adsorption experiments were carried out to study the reliability and transferability of laboratory approaches. Depending on the element, the ratio of particle-bound metals in road runoff varied between 15-90%. Metal levels in embankment soils were significantly higher compared to a reference site in a forest at 800 m distance (up a factor of 30). High metal concentrations in soil solution at 50 cm soil depth were not a direct result of road runoff but rather of elevated concentrations in the soil matrix. The use of batch S4 elution was found to be the best overall laboratory method to predict soil solution concentrations in field. Adsorption experiments showed a relative increase in retention capacity in roadside soil of up to a factor of 20 after nearly 100 years of operation. The input of alkaline dust and organic carbon into roadside soils increases its retention capacity in the long term.