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| 2. |
- Blombäck, Karin
(author)
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Evaluating the effectiveness of the phosphorus sorption index for estimating maximum phosphorus sorption capacity
- 2020
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In: Soil Science Society of America Journal. - : Wiley. - 0361-5995 .- 1435-0661. ; 84, s. 994-1005
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Journal article (peer-reviewed)abstract
- The single‐point P sorption index (PSI), which is defined as the ratio of sorbed P (S) to the log P concentration in soil solution following a single P addition, is often used to estimate maximum soil P sorption capacity (Smax). Although studies have found good correlations between PSI and Smax as determined from fitting the Langmuir model to complete sorption isotherm data, a thorough analysis of the role of added P concentration on this relationship is needed. Our first objective was to investigate the effect of added P concentration on the correlation between PSI and Smax as determined by the Langmuir equation. Our second objective was to determine if S was better than PSI for predicting Smax. Using numerical simulations, we tested the correlation between Smax and PSI for added P concentrations of 75, 100, 150, and 200 mg P L−1. Results of the simulations show that the strength of the correlation between Smax and PSI increases with increasing P concentration. Our results also show that PSI was a better predictor of Smax than S for added concentrations of 75 and 100 mg P L−1, whereas at the higher rates S was a slightly better predictor of Smax and gave a direct estimate of Smax rather than the relative estimate obtained from PSI. Results from P sorption data measured on soils from Maryland and Sweden were consistent with our results from the numerical simulations. Our findings highlight important limitations of using PSI for estimating Smax.
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| 3. |
- Getahun, Gizachew Tarekegn
(author)
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Eleven Years' Effect of Conservation Practices for Temperate Sandy Loams: I. Soil Physical Properties and Topsoil Carbon Content
- 2017
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In: Soil Science Society of America Journal. - : Wiley. - 0361-5995 .- 1435-0661. ; 81, s. 380-391
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Journal article (peer-reviewed)abstract
- Conservation agriculture (CA) has been suggested as a means of making intensification of agriculture sustainable. The purpose of this study was to understand and quantify long-term individual and combined effects of key conservation practices on soil physical properties and topsoil C content. Field experiments were conducted in 11- to 12-yr-old experiments on two Danish sandy loams at Foulum and Flakkebjerg. Three crop rotations/residue management treatments were compared and tillage was included as a split-plot factor. The tillage systems were moldboard plowing to a depth of 20 cm (MP), direct drilling (D) and harrowing to a depth of 8 to 10 cm (H). Soil sampling and in-field measurements were performed in autumn 2013 and spring 2014. In the field, soil structure was visually evaluated and penetration resistance (PR) measured. Soil C, wet stability (clay dispersion and wet aggregate stability), and soil strength were determined in the laboratory. The MP soil had a uniform soil organic carbon (SOC) content in the 0- to 20-cm depth of topsoil, whereas H and D resulted in SOC accumulation near the soil surface. Plowing resulted in the best visually assessed topsoil structure and had the lowest PR. However, H and D in combination with residue retention gave the best structural stability. Residue retention alleviated negative effects of reduced tillage on PR and improved wet stability in the MP treatment at the Foulum site. Clay and SOC correlated well with soil physical parameters, confirming their important role in soil structure formation and stabilization. Our study showed benefits of combining key CA elements, although longer-term studies are most likely needed to reveal the full potential.
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| 4. |
- Griffiths, Natalie A., et al.
(author)
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Temporal and Spatial Variation in Peatland Carbon Cycling and Implications for Interpreting Responses of an Ecosystem-Scale Warming Experiment
- 2017
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In: Soil Science Society of America Journal. - : ACSESS. - 0361-5995 .- 1435-0661. ; 81:6, s. 1668-1688
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Journal article (peer-reviewed)abstract
- We are conducting a large-scale, long-term climate change response experiment in an ombrotrophic peat bog in Minnesota to evaluate the effects of warming and elevated CO2 on ecosystem processes using empirical and modeling approaches. To better frame future assessments of peatland responses to climate change, we characterized and compared spatial vs. temporal variation in measured C cycle processes and their environmental drivers. We also conducted a sensitivity analysis of a peatland C model to identify how variation in ecosystem parameters contributes to model prediction uncertainty. High spatial variability in C cycle processes resulted in the inability to determine if the bog was a C source or sink, as the 95% confidence interval ranged from a source of 50 g C m(-2) yr(-1) to a sink of 67 g C m(-2) yr(-1). Model sensitivity analysis also identified that spatial variation in tree and shrub photosynthesis, allocation characteristics, and maintenance respiration all contributed to large variations in the pretreatment estimates of net C balance. Variation in ecosystem processes can be more thoroughly characterized if more measurements are collected for parameters that are highly variable over space and time, and especially if those measurements encompass environmental gradients that may be driving the spatial and temporal variation (e.g., hummock vs. hollow microtopographies, and wet vs. dry years). Together, the coupled modeling and empirical approaches indicate that variability in C cycle processes and their drivers must be taken into account when interpreting the significance of experimental warming and elevated CO2 treatments.
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| 5. |
- Hansson, Linnea, et al.
(author)
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Soil Compaction Effects on Root-Zone Hydrology and Vegetation in Boreal Forest Clearcuts
- 2019
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In: Soil Science Society of America Journal. - : Wiley. - 0361-5995 .- 1435-0661. ; 83
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Journal article (peer-reviewed)abstract
- Soil compaction is a common consequence of forestry traffic traversing unprotected, moist soils; it decreases porosity and affects hydraulic conductivity even in coarse-textured soils. The aim here was to study root-zone hydrology and vegetation in three microsites (in, between, and beside wheel tracks) 4 to 5 yr after forwarder traffic, on stony and sandy till soils in two clearcuts in northern Sweden. Measurements of soil volumetric water content (VWC), vegetation indicators and one-dimensional hydrological modeling (Hydrus-1D) of wheel tracks and undisturbed soil were conducted. Soil VWC was monitored hourly during 2017 and 2018 in three or four plots along a slope on each site. Soil VWC was also measured once with a portable sensor in 117 plots along two slopes at each site, where the vegetation was recorded and analyzed using Ellenberg indicator indexes. Soil VWC was highest in wheel tracks and lowest between tracks; this was corroborated by the species composition in the wheel tracks (Ellenberg indicator for soil moisture). Bare soil was more frequent in wheel tracks and between tracks than in undisturbed soil. The model simulations indicated that the changed soil hydraulic properties influenced the VWC results in the wheel tracks. However, the differences in average pressure heads in the root zone were small between the microsites and only apparent during dry periods. In the wheel tracks, air-filled porosity was <0.10 m(3) m(-3), indicating insufficient soil aeration during 82% (Site T) and 23% (Site R) of the 2017 growing season. Insufficient aeration could be one explanation for the presence of some still unvegetated areas.
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| 6. |
- Inselsbacher, Erich
(author)
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Alternative Methods for Measuring Inorganic, Organic, and Total Dissolved Nitrogen in Soil
- 2010
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In: Soil Science Society of America Journal. - : Wiley. - 0361-5995 .- 1435-0661. ; 74, s. 1018-1027
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Journal article (peer-reviewed)abstract
- There are numerous methods for measuring inorganic, dissolved organic, and microbial N in soils, although many of these are complex or require expensive equipment. We have modified methods for the measurement of NH(4)(+), NO(3)(-), total dissolved N (TDN), and soil microbial biomass N (SMBN) in soils. The methods are based on a microtiter plate format and are rapid and simple to perform. Ammonium is quantified by a colorimetric method based on the Berthelot reaction. Total dissolved N and SMBN (by CH(3)Cl fumigation-extraction) are quantified as NO(3)(-) after alkaline persulfate oxidation. Nitrate is estimated directly or after persulfate oxidation by reduction of NO(3)(-) to NO(2)(-) by VCl(3) and subsequent colorimetric determination of NO(2)(-) by acidic Griess reaction. The new suite of methods was compared with conventional methods such as high-performance anion-exchange chromatography for NO(3)(-) and high-temperature catalytic oxidation for TDN. Our methods produced comparable detection limits, linearities, and precisions compared with the conventional methods. Limits of quantification were 7 mu g NH(4)(+)-N L(-1), 55 mu g NO(3)(+)-N L(-1), and 0.275 mg TDN L(-1). The accuracy of the proposed methods was excellent, with recoveries of added NH(4)(+), NO(3)(-), and glycine ranging between 96 and 99%. Linearities of the respective calibrations were high (R(2) > 0.99), and precisions for NH(4)(+) (CV = 2.1%), NO(3)(-) (CV = 3.5%), and TDN (CV = 3.9%) were comparable to the reference methods. The simplicity, rapidity, and low cost of the proposed methods therefore allow an expansion of the scope and range of N cycle studies where sophisticated instrumentation is not available.
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| 7. |
- Kardol, Paul
(author)
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Multiple Climate Change Factors Interact to Alter Soil Microbial Community Structure in an Old-Field Ecosystem
- 2011
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In: Soil Science Society of America Journal. - : Wiley. - 0361-5995 .- 1435-0661. ; 75, s. 2217-2226
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Journal article (peer-reviewed)abstract
- Climate change has the potential to alter both the composition and function of a soil's microbial community, and interactions among climate change factors may alter soil communities in ways that are not possible to predict from experiments based on a single factor. This study evaluated the direct and interactive effects of three climate change factors-elevated CO2, altered amounts of precipitation, and elevated air temperature-on soil microbial communities from an old-field climate change experiment being conducted at Oak Ridge, TN. Soil microbial community composition and biomass were determined by phospholipid fatty acid (PLFA) and neutral lipid fatty acid composition. We found that the interactive effects of precipitation and temperature treatments, as well as the interactive effects of precipitation and CO2 treatments, had significant impacts on microbial community composition. We found that total soil PLFA concentration, a measure of microbial biomass, was greater in the low-precipitation treatments, especially when low precipitation was combined with ambient CO2 concentrations or ambient temperature. Ordination analysis indicated that temperature was the most significant predictor of shifts in the soil microbial community composition, explaining approximately 12% of the variance in relative abundance of PLFA biomarkers. The elevated-temperature treatment increased the abundance of Firmicutes (low-guanine-cytosine Gram positive) and decreased the abundance of Gram-negative bacteria. Elevated temperature also reduced the abundance of the arbuscular mycorrhizal fungi PLFA biomarker 16:1 omega 5c and saprophytic fungal PLFA biomarker 18: 2 omega 6,9. Overall, our data indicate that the interactions among climate change factors alter the composition of soil microbial communities in old-field ecosystems, suggesting potential for changes in microbial community function under predicted future climate conditions.
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| 8. |
- Karlsson, Torbjörn, et al.
(author)
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Modeling Copper(II) Complexation in a Peat Soil Based on Spectroscopic Structural Information
- 2008
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In: Soil Science Society of America Journal. - : American Society of Agronomy. - 0361-5995 .- 1435-0661. ; 72:5, s. 1286-1291
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Journal article (peer-reviewed)abstract
- The speciation of Cu in soils and surface waters is largely influenced by complexation reactions with natural organic matter (NOM). In this study, ion selective electrode data for the binding of Cu2+ to a forest peat soil were collected as a function of equilibration time, pH (2.4–6.6), and total Cu(II) concentration (1–54g Cu kg–1 dry soil). As a first step, a one-site Langmuir isotherm was successfully fitted to the Cu adsorption data for the complete concentration range at pH 4.6. In a second step, structural information extracted from extended x-ray absorption fine structure (EXAFS) spectroscopy, showing that Cu(II) forms five-membered rings with possible combinations of amine, carboxyl, and carbonyl functional groups in NOM, were used as input for chemical speciation calculations (using the chemical equilibrium model MINTEQA2). In agreement with the EXAFS results, a model consisting of one RNH2, forming monodentate complexes (Cu2+ + RNH2 RH2NCu2+; log stability constant KRH2NCu2+ = 9.2; –log acid dissociation constant [pKa] = 9.0 for RNH3+), and two adjacent RCOO– groups, forming bidentate complexes (Cu2+ + 2RCOO– Cu(OOCR)2; log stability constant β(RCOO)2Cu = 4.7; pKa = 4.5 for RCOOH), gave the best fit to the experimental data. Determined stability constants for Cu(II)–amine and Cu(II)–carboxyl complexes were in good agreement with well-defined Cu complexes with amino acids and carboxyls, respectively.
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| 9. |
- Keller, Thomas
(author)
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Determining Soil Stress beneath a Tire: Measurements and Simulations
- 2016
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In: Soil Science Society of America Journal. - : Wiley. - 0361-5995 .- 1435-0661. ; 80, s. 541-553
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Journal article (peer-reviewed)abstract
- This study measured soil stress underneath a rolling wheel by using two different types of sensors: a load cell type probe referred to as an Arvidsson probe to read vertical soil stress and a fluid inclusion type sensor referred to as a Bolling probe to read soil mean normal stress. Measurements were compared with simulations using a semi-empirical as well as a finite element model. The latter allowed us to consider a layered soil profile as well as an elastoplastic constitutive relationship in the simulations. In addition, the finite element model was used to quantify the ratio between the Bolling probe pressure and the soil mean normal stress. The Bolling probe pressure was found to be primarily a function of the soil's Poisson ratio, which supports findings from earlier studies. Our results showed better agreement between measurements and simulations for vertical stress ( obtained from the Arvidsson probe readings) than for mean normal stress ( calculated from the Bolling probe measurements). The finite element simulations revealed that soil properties had little influence on vertical stress, and the distribution with depth of the vertical stress could be well described by the classical Boussinesq solution. However, soil properties had a significant impact on the mean normal stress. The widely used semi-empirical Frohlich model performed poorly, which may have been because of an inconsistency in the model assumptions.
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| 10. |
- Keller, Thomas, et al.
(author)
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Soil structure recovery following compaction: Short-term evolution of soil physical properties in a loamy soil
- 2021
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In: Soil Science Society of America Journal. - : Wiley. - 0361-5995 .- 1435-0661. ; 85, s. 1002-1020
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Journal article (peer-reviewed)abstract
- Soil compaction by farm machinery may persist for decades, hampering soil productivity and functioning. Assessing compaction costs and guiding recovery strategies are hindered by paucity of data on soil structure recovery rates. A long-term Soil Structure Observatory was established on a loamy soil in Switzerland to monitor soil structure recovery after prescribed compaction, and to better assess the roles of natural processes (vegetation, macrofauna, and shrink-swell cycles) on recovery patterns. The aim of this study was to quantify short-term soil structure recovery under natural conditions in the presence and absence of plant cover (ley and bare soil). We measured soil porosity and gas and water transport capabilities at 0.1 and 0.3 m depth. Two years after the compaction event, soil physical properties have not recovered to precompaction levels, even within the topsoil. Surprisingly, no differences were observed in the recovery patterns of ley and bare soil treatments. Measurements show that recovery rates differ among soil properties with the most severely affected properties by compaction (permeability) exhibiting highest recovery rates. Total soil porosity shows no recovery trend, suggesting lack of soil decompaction. Improved soil functions and decompaction are distinct aspects of soil structure recovery, with the latter requiring net upward transport of soil mass. We suggest that soil structure recovery proceeds at two fronts: from the soil surface downward, and expanding around local biologically-active pockets (marked by biopores) into the compacted soil volumes. This concept could be tested with additional data of longer time series at our site as well as in other soils and climates.
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