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  • 1
    Language: English
    In: Geoderma, 2015, Vol.259-260, p.224(9)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.geoderma.2015.06.011 Byline: Marcos Paradelo, Trine Norgaard, Per Moldrup, T.P.A. Ferre, K.G.I.D. Kumari, Emmanuel Arthur, Lis W. de Jonge Abstract: Sorption is considered one of the most important processes controlling pesticide mobility in agricultural soils. Accurate predictions of sorption coefficients are needed for reliable risk assessments of groundwater contamination from pesticides. In this work, we aim to estimate the glyphosate sorption coefficient, K.sub.d, from easily measurable soil properties in two loamy, agricultural fields in Denmark: Estrup and Silstrup. Forty-five soil samples in Estrup and 65 in Silstrup were collected from the surface in a rectangular grid of 15x15-m from each field, and selected soil properties and glyphosate sorption coefficients were determined. Multiple linear regression (MLR) analyses were performed using nine geo-referenced soil properties as variables to identify the parameters related with glyphosate sorption. Scenarios considered in the analyses included: (i) each field separately, (ii) both fields together, and (iii) northern and southern sections of the field in Silstrup. Considering correlations with all possible sets of the same nine geo-referenced properties, a best-four set of parameters was identified for each model scenario. The best-four set for the field in Estrup included clay, oxalate-extractable Fe, Olsen P and pH, while the best-four set for Silstrup included clay, OC, Olsen P and EC. When the field in Silstrup was separated in a northern and southern section, the northern section included EC, and oxalate-extractable Fe, Al and P, whereas the southern part included pH, clay, OC and Olsen P. The best-four set for both fields together included clay, sand, pH and EC. Thus, the most common parameters repeated in the best-four sets included clay and pH as also reported previously in the literature, but in general, the composition of the best-four set differed for each scenario, suggesting that different properties control glyphosate sorption in different locations and at different scales of analysis. Better predictions were obtained for the best-four set for the field in Estrup (R.sup.2 =0.87) and for both fields (R.sup.2 =0.70), while the field in Silstrup showed a lower predictability (R.sup.2 =0.36). Possibly, the low predictability for the field in Silstrup originated from opposing gradients in clay and oxalate-extractable Fe across the field. Also, whereas a lower clay content in Estrup may be the limiting variable for glyphosate sorption, the field in Silstrup has a higher clay content not limiting the sorption, but introducing more variability in K.sub.d due to changes in other soil properties. Article History: Received 24 September 2014; Revised 6 May 2015; Accepted 9 June 2015
    Keywords: Glyphosate – Analysis ; Oxalic Acid – Analysis ; Agricultural Land – Analysis ; Loams – Analysis ; Oxalates – Analysis
    ISSN: 0016-7061
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Geoderma, December 2015, Vol.259-260, pp.224-232
    Description: Sorption is considered one of the most important processes controlling pesticide mobility in agricultural soils. Accurate predictions of sorption coefficients are needed for reliable risk assessments of groundwater contamination from pesticides. In this work, we aim to estimate the glyphosate sorption coefficient, , from easily measurable soil properties in two loamy, agricultural fields in Denmark: Estrup and Silstrup. Forty-five soil samples in Estrup and 65 in Silstrup were collected from the surface in a rectangular grid of 15 × 15-m from each field, and selected soil properties and glyphosate sorption coefficients were determined. Multiple linear regression (MLR) analyses were performed using nine geo-referenced soil properties as variables to identify the parameters related with glyphosate sorption. Scenarios considered in the analyses included: (i) each field separately, (ii) both fields together, and (iii) northern and southern sections of the field in Silstrup. Considering correlations with all possible sets of the same nine geo-referenced properties, a best-four set of parameters was identified for each model scenario. The best-four set for the field in Estrup included clay, oxalate-extractable Fe, Olsen P and pH, while the best-four set for Silstrup included clay, OC, Olsen P and EC. When the field in Silstrup was separated in a northern and southern section, the northern section included EC, and oxalate-extractable Fe, Al and P, whereas the southern part included pH, clay, OC and Olsen P. The best-four set for both fields together included clay, sand, pH and EC. Thus, the most common parameters repeated in the best-four sets included clay and pH as also reported previously in the literature, but in general, the composition of the best-four set differed for each scenario, suggesting that different properties control glyphosate sorption in different locations and at different scales of analysis. Better predictions were obtained for the best-four set for the field in Estrup (R = 0.87) and for both fields (R = 0.70), while the field in Silstrup showed a lower predictability (R = 0.36). Possibly, the low predictability for the field in Silstrup originated from opposing gradients in clay and oxalate-extractable Fe across the field. Also, whereas a lower clay content in Estrup may be the limiting variable for glyphosate sorption, the field in Silstrup has a higher clay content not limiting the sorption, but introducing more variability in due to changes in other soil properties.
    Keywords: Sorption Coefficient ; Glyphosate ; Field Scale ; Multiple Linear Regression ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
    Source: ScienceDirect Journals (Elsevier)
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  • 3
    Language: English
    In: Geoderma, January 2015, Vol.237-238, pp.9-20
    Description: Soil macropores largely control fluid and solute transport, making visualization and quantification of macropore characteristics essential for better understanding and predicting soil hydrogeochemical functions. In this study, seventeen large (19 × 20 cm) intact soil cores taken across a loamy field site (Silstrup, Denmark) were scanned at in-situ sampling conditions (~ field capacity) at a relatively coarse resolution (500 μm) by medical X-ray computed tomography (CT). In the image analyses, artifacts related to the presence of rocks were identified and removed before linking CT-derived pore parameters to measured fluid transport parameters. After CT scanning, soil cores were saturated and drained at − 20 hPa soil–water potential, leaving only pores 〉 150 μm air-filled. Air permeability (k ) and air-filled porosity (ε ) were measured to evaluate gas transport behavior in macropore networks under these conditions. Finally, tracer transport experiments at a constant, high flow rate (10 mm h ) were carried out, and the arrival time for 5% of the applied tracer (T ) was used as an index for the magnitude of water transport in macropores. Although X-ray CT scanning only identified 5–25% of the total air-filled pore network at − 20 hPa, CT-derived macroporosity (average for whole column) and macroporosity for the limiting-quarter section of each column were highly correlated to both k and T (R from 0.6 to 0.8). The CT-inferred limiting depth for soil–gas transport was typically located at 90–165 mm depth, and likely a result of soil management history. Results suggest that the functional macropore network for fluid transport was well quantified by rapid, coarse-resolution X-ray CT scanning. Linking rapid X-ray CT scanning with classical fluid transport measurements on large intact columns thus proves highly useful for characterizing soil macropore functions and in perspective may prove to be useful in predicting field-scale variations in gas, water, and chemical transport.
    Keywords: Macropores ; Limiting-Section Macroporosity ; X-Ray Computed Tomography ; Air Permeability ; 5% Tracer Arrival Time ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 4
    Language: English
    In: Geoderma, April 2014, Vol.217-218, pp.181-189
    Description: The study characterized soil structure development and evolution in six plots that were amended with varying amounts of animal manure (AM) and NPK fertilizer over a period of 106 years in a long-term fertilization experiment in Bad Lauchstädt, Germany. Two intact soil cores (10-cm diameter and 8-cm tall) and bulk soil samples were extracted from a depth between 5 and 15-cm from each plot. Soil properties including texture, organic carbon, soil–water characteristic, air permeability and diffusivity were measured and analyzed along with X-ray computed tomography (CT) data. Long-term applications of AM and NPK had a major impact on soil organic carbon content which increased from 0.015 kg kg (unfertilized plot) to 0.024 kg kg (well fertilized plot, 30 T ha 2y AM with NPK). Total porosity linearly followed the organic carbon gradient, increasing from 0.36 to 0.43 m m . The water holding capacity of the soil was considerably increased with the increase of AM and NPK applications. Gas diffusivity and air permeability measurements clearly indicated that the level of soil aeration improved with increasing AM and NPK fertilizer amount. The three-dimensional X-ray CT visualizations revealed higher macroporosity and biological (earthworm) activity in the well fertilized areas when compared to plots without or only a small amount of fertilizer applied. A combined evaluation of the soil water characteristic, gas transport and X-ray CT results suggested that pore size distributions widened, and pore connectivity was significantly improved with increasing fertilizer amount. Furthermore, the soils fertilized with both AM and NPK showed a more aggregated structure than soils amended with AM only.
    Keywords: Animal Manure ; Npk Fertilizers ; Soil–Water Characteristic ; Gas Diffusivity ; Air Permeability ; X-Ray Computed Tomography ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 5
    Language: English
    In: Geoderma, 15 February 2016, Vol.264, pp.150-159
    Description: Soil water repellency (SWR) of soils is a property with significant consequences for agricultural water management, water infiltration, contaminant transport, and for soil erosion. It is caused by the presence of hydrophobic agents on mineral grain surfaces. Soils were samples in different depths at three forest sites in Japan and three pasture sites in New Zealand, covering soil organic carbon (SOC) contents between 1 and 26%. The SWR was measured over a range of water contents by three common methods; the water drop penetration time (WDPT) test, the molarity of an ethanol droplet (MED) method, and the sessile drop method (SDM). The aim to (i) compare the methods, (ii) characterize the soil-water repellency characteristic curves (SWRCC) being SWR as a function of the volumetric soil-water content ( ) or matric potential ( ), and (iii) find relationships between SWRCC parameters and SOC content. The WDPT, MED, and SDM generally agreed well in predicting the range where SWR occurred, and there was close agreement between SWR results determined by average MED and SDM at similar . Generally, SWR was only found within the top 20 cm of the soil profiles. Six SWR parameters were introduced: (i) the area under the curve ( ); (ii) at the maximum SWR ( ), (iii) where SWR ceased ( ), (iv) the maximum SWR ( ), (v) at the maximum SWR ( ) and (vi) where SWR ceased ( ). The relationship between the first three parameters and SOC content were best described with Langmuir type equations (r of 0.5–0.7), while the other three parameters changed linearly with SOC contents.
    Keywords: Soil Water Repellency ; Soil Water Repellency Characteristic Curve ; Andosols ; Water Repellency Parameters ; Soil Organic Carbon ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 6
    Language: English
    In: Geoderma, 01 March 2018, Vol.313, pp.82-91
    Description: Soils deliver the regulating ecosystem services of water infiltration and distribution, which can be controlled by macropores. Parameterizing macropore hydraulic properties is challenging due to the lack of direct measurement methods. With tension-disc infiltrometry hydraulic properties near saturation can be measured. Differentiating between hydrologically active and non-active pores, at a given water potential, indirectly assesses macropore continuity. Water flow through macropores is controlled by macropore size distribution, tortuosity, and connectivity, which can be directly derived by X-ray computed tomography (CT). Our objective was to parameterize macropore hydraulic properties based on the imaged macropore network of three horizons of an Andosol and a Gleysol. Hydraulic conductivity was derived from infiltration measurements. Soil cores from the infiltration areas were scanned with X-ray CT. was significantly higher in the Andosol than in the Gleysol at all water potentials, and decreased significantly with depth in both soils. The measurements guided the definition of new macroporosity parameters from the X-ray CT reconstructions. For the Andosol, was best predicted using the imaged-limited macroporosity. A low total macroporosity, coupled with a high macropore density, indicated the abundance of smaller macropores, leading to homogeneous matrix flux. Imaged macropores were not well connected. In contrast, the Gleysol had a bi-modal macropore system with few very large, but well-connected macropores. was best predicted using the imaged macroporosity consisting only of macropores with diameters between 0.75 and 3 mm. Our research demonstrates that linking traditional soil physical measurements with soil-visualization techniques has a huge potential to improve parameterizing macropore hydraulic properties. The relevance of the relationships found in this study for larger scales and other soil types still needs to be tested, for example by a multi-scale investigation including a much wider range of different soils.
    Keywords: Soil Structure ; Pore Network ; Image Analysis ; Hydraulic Parameters ; Tension Disc Infiltrometry ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 7
    Language: English
    In: Geoderma, 2011, Vol.162(3), pp.319-326
    Description: Macropore density is a key parameter to predict the leaching of contaminants from the root zone. The aim of this study was to assess the influence of intrinsic soil properties and earthworm characteristics on macropore density at different depths for five typical, Danish soil types under the same agricultural management (third year of pasture). Macropores were marked on a transparent sheet (0.7 × 1.0 m) placed horizontally for the three main horizons of each soil type in eight plots along the local gradients in soil texture. Macropores were then counted on each sheet by digital image analysis. Particle size distribution was determined for the same soil horizons for each plot. The earthworm population was characterised for each plot by hand-sorting soil samples (0.5 × 0.5 × 0.3 m). Results show that the macropore density: 1) was highest for the soil types developed on glacial deposits, which were the soils with the highest clay content, 2) in the topsoil (Ap horizon) was related to the fresh biomass of anecic earthworms across all soil types and textural gradients, 3) in the B horizon was related to the clay content, 4) in the C horizon, was directly related to the soil type, and 5) that for all soil types developed on moraines, the macropore density was highest in the B horizon, indicating an accumulation of macropores with time. Our results indicate that estimates of the macropore density in agricultural soils need to consider both short-term factors (agricultural management effects on the development of earthworm communities), and long-term factors (soil intrinsic properties). Further work is needed to estimate the risk of macropore flow. ► Macropore density in the topsoil was directly related to anecic earthworm density. ► Macropore density in the B-horizons was directly related to clay content. ► The long-term macropores were related to the geology. ► The short-term macropores were related to the actual earthworm population. ► The use of graphical models eliminated the spurious relations between soil variables.
    Keywords: Macropore ; Soil Type ; Soil Texture ; Earthworms ; Graphical Model ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 8
    Language: English
    In: Geoderma, 15 September 2019, Vol.350, pp.40-45
    Description: Standard measurement methods for soil clay content, including the hydrometer and pipette methods, are laborious and difficult to repeat. This has motivated the application of proxy methods such as estimation of clay content from soil water vapor sorption isotherms. Previous studies have revealed that vapor sorption-based clay estimates are inaccurate for soils dominated by swelling or highly weathered non-swelling clays such as kaolinite. In this study, we evaluate an existing vapor sorption-based clay estimation model for soils dominated by either illite (IL), smectite (SM), or kaolinite (KA) clay minerals, and propose modifications to account for high SM and KA contents. Compared to the pipette method, the clay content obtained from the existing water sorption model at 50% relative humidity (RH) was accurate for the IL samples, but significantly overestimated (RMSE = 23.7%; ME = 19.7%) or underestimated (RMSE = 28.8%; ME = −17.0%) clay content for SM and KA rich soils, respectively. The proposed modification involves correcting the estimated clay content with a “slope factor”, for RH values ranging from 30 to 90% for both adsorption and desorption. For SM samples, averaged 0.76 and 0.72 for adsorption and desorption, respectively, and for KA samples, ranged from 2.26 to 1.19 and followed a polynomial relationship with RH. Comparison of the estimated clay content from the modified models showed markedly improved estimation of the measured clay content (for RH of 90%, RMSE = 8.0%; ME = 2.6% for SM samples and RMSE = 9.6%; ME = −5.7% for KA samples).
    Keywords: Soil Texture ; Hygroscopic Water ; Montmorillonite ; Vapor Sorption ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 9
    Language: English
    In: Geoderma, 15 March 2019, Vol.338, pp.281-290
    Description: Organic matter can render soil hydrophobic and cause soil water repellency (SWR) which has large implications for agriculture. Consequences such as fingered flow, uneven wetting patterns, and increased overland flow reduce irrigation efficiency and plant nutrient availability. The phenomenon of SWR is a transient soil property depending, , on soil water content ( ). Soil can exhibit SWR from oven-dry until the critical where it again becomes fully wettable ( ). The total SWR can be obtained from the nonlinear SWR- relationship as the integrated trapezoidal area under the SWR- curve (SWR ). We analyzed 78 soil samples, representing five dominant soil orders in the South Island of New Zealand. The soils had a large range in clay (0.000–0.520 kg kg ) and organic carbon (OC) content (0.021–0.217 kg kg ). The degree of SWR was measured on soils at air-dry conditions (SWR ) and after heat-pretreatment at 60 (SWR ) and 105°C (SWR ). Further, SWR was measured in small increments above air-dry until was reached. The SWR- curves were either unimodal or bimodal, or no SWR occurred. SWR ranged from 0.16 to 26.82 mN m  kg kg . Among the five soil orders tested, the Podzols exhibited the highest severity in SWR, whereas the Semiarid soils were the least hydrophobic soils. In conclusion, OC was the main factor for controlling the severity of SWR. Though, pH also had minor effects on SWR. Further, an upper limit critical water content was derived from the simple relationship between the and OC, which could be applied to improve irrigation practices of pastoral soils. However, there is a need for further testing on different soils and land uses.
    Keywords: Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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