Ole Wendroth

University of Kentucky

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D. R. Nielsen

University of California, Davis

Kurt Christian Kersebaum

Leibniz Centre for Agricultural Landscape Research

H.I. Reuter

Eurostat

Yang Yang

Institute of Soil and Water Conservation

Christopher J. Matocha

University of Kentucky

José Dörner

Austral University of Chile

Rainer Horn

Kiel University

Riley J. Walton

University of Kentucky

J. W. Hopmans

University of California, Davis

Antje Giebel

Leibniz Institute for Agricultural Engineering and Bioeconomy

Cooperative Institutions

University of Kentucky

Leibniz Centre for Agricultural Landscape Research

University of California, Davis

Northwest A&F University

Austral University of Chile

Chinese Academy of Sciences

Agricultural Research Service

Institute of Soil and Water Conservation

Iowa State University

Beijing Normal University

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Parameter Estimation Analysis of the Evaporation Method for Determining Soil Hydraulic Properties

Soil Science Society of America Journal (1998)

Jiřı́ Šimůnek Martinus Th. van Genuchten Ole Wendroth

Abstract Soil hydraulic properties are important parameters affecting water flow in variably saturated soils. We estimated the hydraulic properties from a laboratory evaporation experiment using both a parameter estimation method and the modified Wind method. The parameter estimation method combined a one‐dimensional numerical solution of the Richards equation with the Marquardt‐Levenberg optimization scheme. In our study we used both numerically generated data and data measured in the laboratory. Two experiments were carried out on 10‐cm‐high soil cores containing two different soils. Pressure heads inside the cores were measured with five tensiometers, while evaporative water loss from the top was determined by weighing the soil samples. The objective function for the parameter estimation analysis was defined in terms of the final total water volume in the core and pressure head readings by one or several tensiometers. An analysis of numerically generated data showed that the optimization method was most sensitive to the shape factor ( n ) and the saturated water content (θ s ) and least to the residual water content (θ r ). Pressure heads measured close to the soil surface were found to be more valuable for the parameter estimation technique than those measured at lower locations. The optimized hydraulic parameters corresponded closely with those obtained using Wind's analysis. All optimizations gave similar results for the soil hydraulic properties within the range of measured pressure heads (0 to −700cm). Extrapolation beyond this range involved a high level of uncertainty because of high correlation between parameters θ r and n .

Pressure head

Richards equation

Hydraulic head

Water potential

10.2136/sssaj1998.03615995006200040007x

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Lignin-based Hydrogel for Water Retention in Silt Loam Soil

2021 ASABE Annual International Virtual Meeting, July 12-16, 2021 (2021)

Toby A. Adjuik Sue E. Nokes Michael D. Montross Ole Wendroth

Abstract. Superabsorbent polymers (hydrogels) have been proposed as soil amendments to increase plant available water in soil. Synthetic hydrogels have been widely investigated for use in agriculture. Due to increasing environmental concerns related to synthetic hydrogels, hydrogels from natural sources which are more degradable and biocompatible compared to synthetic hydrogels are being developed. Here, a lignin-based hydrogel was synthesized. The swelling properties of the hydrogel were determined in different aqueous solutions and in soil. Fourier Transform Infrared (FTIR) spectroscopy was used to characterize the hydrogel. Using the hanging water column and the pressure plate method, the soil water retention curve was measured from a soil water pressure head range of -3 cm to the permanent wilting point i.e -15,000 cm for a silt loam soil. For this purpose, the soil was amended with the lignin-based hydrogel at rates of 0, 0.1 and 0.3% (w/w) concentration. Results of the swelling properties of the lignin-based hydrogel show a maximum swelling ratio of 2030% of the hydrogel‘s original mass in deionized water, 1092% in tap water, and 825% in the 0.9% NaCl solution. FTIR spectra of the hydrogel show the presence of O-H bonds which come from the lignin structure and render the hydrogel reactive to water molecules causing swelling as a result. Lignin hydrogel treatment significantly increased water retention near saturation compared to a control treatment of soil with no added lignin hydrogel.

10.13031/aim.202100216

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Citations (3)

Field scale heterogeneity of soil structural properties in a moraine landscape of north-eastern Germany

International Agrophysics (1995)

Sylvia Koszinski Ole Wendroth J. Lehfeldt

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Know Your Community: How Suitable Are Models for Reflecting Spatially Variable Field Conditions?

CSA News (2018)

Ole Wendroth Kurt Christian Kersebaum

10.2134/csa2018.63.0221

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Prediction of winter wheat yield with the SWAP model using pedotransfer functions: An evaluation of sensitivity, parameterization and prediction accuracy

Agricultural Water Management (2015)

Quirijn de Jong van Lier Ole Wendroth J.C. van Dam

Pedotransfer function

10.1016/j.agwat.2015.02.011

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Citations (36)

Soil and Water Quality at Different Scales

Journal of Environmental Quality (2000)

Ole Wendroth

10.2134/jeq2000.00472425002900010044x

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Reexamination of the Field Capacity Concept in a Brazilian Oxisol

Soil Science Society of America Journal (2016)

Quirijn de Jong van Lier Ole Wendroth

Core Ideas Field capacity depends on considered profile depth for irrigation. Hydraulic conductivity at bottom of soil profile can be used to assess field capacity. Time to reach field capacity should not correspond to considerable transpiration. “Field capacity” is the most frequently cited soil physical quantity and also the most ambiguous one. Its true assessment involves an internal drainage experiment in the absence of evaporation and transpiration, together with the establishment of a negligible drainage rate. For practical reasons however, estimating field capacity using an arbitrary value of pressure head is common practice. The objective of this study was to assess field capacity based on a fixed bottom flux or on a fixed time. This goal should be achieved through numerical simulations of internal drainage experiments using experimentally determined soil hydraulic properties on 46 locations on a 50-m transect in a layered soil. Flux-based estimates of field capacity exhibited high correlation to unsaturated hydraulic conductivity at the lower profile boundary, hydraulic gradients ranging from 0.25 to almost 1. Considering the 46 locations, bottom flux at a fixed time varied over one order of magnitude, whereas the time to reach a predetermined bottom flux associated to field capacity also showed a variation of about an order of magnitude. By setting hydraulic conductivity equal (or slightly higher to compensate for a smaller hydraulic gradient) to a pre-established bottom flux, the pressure head or water content of field capacity was then assessed. Based on the flux criterion of 1 mm d-1, field capacity corresponded to a pressure head of about -0.55 m in the evaluated soil; the corresponding time of drainage to establish this bottom flux was 4 d when considering only the top 0.15 m to almost 2 wk for a 0.75-m profile depth.

Pressure head

Hydraulic head

10.2136/sssaj2015.01.0035

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Citations (41)

Estimating saturated hydraulic conductivity and air permeability from soil physical properties using state-space analysis

Soil Science Society of America Journal (2003)

Tjalfe G. Poulsen Per Møldrup Ole Wendroth D. R. Nielsen

Estimates of soil hydraulic conductivity (K) and air permeability (k a ) at given soil-water potentials are often used as reference points in constitutive models for K and k a as functions of moisture content and are, therefore, a prerequisite for predicting migration of water, air, and dissolved and gaseous chemicals in the vadose zone. In this study, three modeling approaches were used to identify the dependence of saturated hydraulic conductivity (K S ) and air permeability at -100 cm H 2 O soil-water potential (k a100 ) on soil physical properties in undisturbed soil: (i) Multiple regression, (ii) ARIMA (autoregressive integrated moving average) modeling, and (iii) State-space modeling. In addition to actual soil property values, ARIMA and state-space models account for effects of spatial correlation in soil properties. Measured data along two 70-m-long transects at a 20-year old constructed field were used. Multiple regression and ARIMA models yielded similar prediction accuracy, whereas state-space models generally gave significantly higher accuracy. State-space modeling suggested K S at a given location could be predicted using nearby values of K S , k a100 and air-filled porosity at -100 cm H 2 O soil-water potential (∈ 100 ). Similarly, k a100 could be predicted from nearby values of k a100 and ∈ 100 . Including soil total porosity in the state-space modeling did not improve prediction accuracy. Thus, macro-porosity (∈ 100 ) was the key porosity parameter for predicting both Ks and k a100 in undisturbed soil.

Pedotransfer function

Infiltration (HVAC)

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Modeling Crop Growth and Nitrogen Dynamics for Advisory Purposes Regarding Spatial Variability

CRC Press eBooks (2002)

Kurt Christian Kersebaum Karsten Lorenz H.I. Reuter Ole Wendroth

Advisory committee

10.1201/9781420032413.ch11

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Assessment of Pasture Biomass with the Normalized Difference Vegetation Index from Active Ground-Based Sensors

Agronomy Journal (2008)

E. Scott Flynn Charles T. Dougherty Ole Wendroth

Calculating forage availability is challenging for managers of grazing systems due to the spatial heterogeneity of swards. Remote sensing applications may help to overcome this problem through estimates of biomass made with reflectance data. The objectives of this study were to (i) estimate herbage mass using an active, on-the-go, ground-based, narrow band sensor to calculate the normalized difference vegetation index (NDVI), (ii) determine if NDVI may be used to assess spatial variability of herbage mass of grasslands, and (iii) determine if NDVI may be used to evaluate management of grazing systems. The NDVI was measured using an active ground-based sensor, the GreenSeeker (Ntech Industries, Ukiah, CA). In tall fescue [Schedonorus arundinaceus (Schreb.) Dumort], NDVI was correlated with biomass determined by destructive harvesting (r2 = 0.68) and also with a calibrated rising plate meter (RPM) (r2 = 0.54). Semivariograms revealed that NDVI sampling intervals of 0.76 m adequately described the spatial variability structure of grazed swards. The frequency distributions of sward biomass derived from NDVI may reflect the foraging strategies of cattle. Negative skewness and high kurtosis are consistent with selective grazing, while positive skewness and low kurtosis are consistent with less diet selectivity. Frequency distributions also improved definition of available forage within each field. We concluded that spatial properties of grassland biomass may be derived from high resolution NDVI and RPM data and could be used to evaluate conditions of grassland landscapes and to aid decision-making of managed grazing systems.

Enhanced vegetation index

Kurtosis

10.2134/agrojnl2006.0363

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Citations (25)