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  • 1
    Language: English
    In: Geoderma, May, 2014, Vol.219-220, p.125(11)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.geoderma.2013.12.015 Byline: Emmanuel Frossard, Paolo Demaria, Sokrat Sinaj, Michael Scharer Abstract: Controlling phosphate (P) release from agricultural soils to water while maintaining optimal plant growth conditions remain a major challenge for the development of sustainable agricultural systems. To achieve this, it is important to have a proper knowledge of the amount of soil P that can be mobilized by water and of the kinetics of P release. We evaluated the ability of a flow-through reactor in which.sup.33P labeled soils can be inserted and leached continuously with deionized water, to assess P release. The experiment was conducted on five grassland soils presenting a large range in P availability. The availability of P in these soils was further modified by submitting them to 0 to 3 plant growth cycles with Italian ryegrass (Lolium multiflorum) with three levels of P added (0, 20 and 40mgPkgsoil.sup.-1). The P input-output balance, water and oxalate extractable P, the degree of P saturation of the soil and the amount of isotopically exchangeable P (E value) were assessed in all samples. A subset of these soil samples was labeled with.sup.33P, introduced in a flow-through reactor and the release of P and.sup.33P measured over 14days. The cumulated amount of P released after 14days was strongly correlated to the amount of oxalate extractable P, isotopically exchangeable P (E value), and water extractable P. The P release kinetics was modeled with a 2 pools model with each pool following first order kinetics. Plants were able to take up P from both pools. Assuming that the leached P had the same isotopic composition as the pool of soil P it came from it became possible to quantify the amount of isotopically exchangeable remaining in the soil which was called the D value. D decreased during the three first days of the flow-through experiment and then increased linearly with time reaching a maximum after 14days. This maximum remained lower than the oxalate extractable P. Processes contributing to this increase were isotopic exchange and possibly also some organic P mineralization. The D value was strongly linearly correlated to E values measured after different exchange times, but for a given exchange time, the D value was lower than the E value, whereas equality could have been expected. This difference was related to the high rate of.sup.33P export from the soil at the beginning of the flow-through experiment. The D value was also strongly correlated to the oxalate and water extractable P. In conclusion, we suggest that the use of the flow-through reactor yields relevant information on the amount of P that can be leached from a given soil, and that the D value delivers information on the amount of isotopically exchangeable P remaining in the soil and therefore which could still be leached if sufficient time would be given. Article History: Received 24 July 2013; Revised 7 December 2013; Accepted 11 December 2013
    Keywords: Oxalic Acid -- Evaluation ; Oxalic Acid -- Analysis ; Soils -- Analysis ; Phosphates -- Evaluation ; Phosphates -- Analysis ; Oxalates -- Evaluation ; Oxalates -- Analysis
    ISSN: 0016-7061
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Geoderma, 2015, Vol.257-258, p.86(8)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.geoderma.2015.01.003 Byline: Lalajaona Randriamanantsoa, Emmanuel Frossard, Astrid Oberson, Else K. Bunemann Abstract: Mineralization of organic phosphorus (P.sub.o) may be of great importance for plant nutrition in soils containing very little available inorganic phosphorus (P.sub.i). Gross organic P mineralization rates can be quantified by an isotopic dilution method using.sup.33P labeling of soil. However, its application remains a challenge in tropical soils in which the concentration of phosphate ions in the soil solution is below the detection limit of traditional colorimetric methods. This limitation can potentially be overcome by the hexanol concentration method, which uses hexanol to concentrate the blue-colored phosphomolybdate complex from large volumes. We applied the isotopic dilution method in combination with the hexanol concentration method to a Ferralsol from the highlands of Madagascar which had been preincubated in the presence or absence of plant residues for 90days before the start of the experiment. The limits of detection (DL) and quantification (QL) of the gross P.sub.o mineralization rate were 0.2 and 0.7mgPkg.sup.-1 soilday.sup.-1, respectively. Basal gross P.sub.o mineralization rates after 7days of incubation were 0.8[+ or -]0.5 and 1.7[+ or -]0.2mgPkg.sup.-1 soilday.sup.-1 in non-amended and residue-amended soils, respectively. These rates are plausible, suggesting that the isotopic dilution method is applicable in highly weathered tropical soils with P.sub.i concentrations in the soil solution below the detection limit of traditional colorimetric methods. Net P.sub.o mineralization which sustains the plant available P pool remains to be quantified. Gross and net P.sub.o mineralization rates should now be assessed in highly weathered soils under a range of land uses. Article History: Received 30 June 2014; Revised 5 January 2015; Accepted 7 January 2015
    Keywords: Phosphates – Methods
    ISSN: 0016-7061
    Source: Cengage Learning, Inc.
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  • 3
    Language: English
    In: Geoderma, June, 2013, Vol.200-201, p.120(10)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.geoderma.2013.01.019 Byline: Lalajaona Randriamanantsoa, Christian Morel, Lilia Rabeharisoa, Jean-Marie Douzet, Jan Jansa, Emmanuel Frossard Keywords: Ferralsol; Andosol; Phosphate ion sorption; Low P availability; Isotopic technique Abstract: The isotopic exchange kinetic (IEK) method allows assessing the rate of orthophosphate ions (Pi) exchange between the solid phase and the solution of the soil with time. However, two challenges have to be tackled when using this technique in soils with a very low water extractable Pi concentration (C.sub.P) and with a high sorbing capacity for Pi. The first is that current colorimetric methods do not allow quantifying Pi concentrations lower than 10[mu]gP L.sup.-1. While the second challenge is that a significant fractionation between P isotopes may occur in the soil solution system in the presence of soils with high Pi sorption capacity. We assessed here: i) whether concentrating the blue phosphomolybdate complex (BPMC) in hexanol prior to its measurement would allow to lower the detection and quantification limits of Pi, ii) whether a significant isotopic fractionation between.sup.32Pi and.sup.33Pi could occur during IEK experiments conducted in the presence of high Pi sorbing substrates (e.g., pure goethite or Malagasy soils) and iii) whether the IEK method when used in conjunction with the hexanol concentration of the BPMC to measure C.sub.P would detect changes in Pi isotopic exchangeability in a ferralsol cropped with upland rice following the input of manure or water soluble fertilizer. The detection and quantification limits of the BPMC concentrated by hexanol were 0.3 and 0.8[mu]gPL.sup.-1, respectively, using a cell of 10cm length for the colorimetric measurement. The IEK conducted on Pi amended goethite and on Malagasy soils with.sup.32Pi and.sup.33Pi did not show any systematic isotopic fractionation between both isotopes, suggesting that in these soils.sup.31Pi and.sup.32Pi or.sup.33Pi have a similar behavior during isotopic exchange. The analysis of the soils sampled in the field experiment showed a significant increase in the amount of Pi isotopically exchangeable after 1min only after the application of water soluble P. This increase was paralleled by increases in rice yield and P export by grains demonstrating an increased P availability in this treatment. In conclusion, the IEK method can be used in low P and high Pi sorbing soils as the hexanol concentration method allows measuring very low C.sub.P and as the different P isotopes have a similar behavior in the soil/solution system. The IEK experiments conducted in the presence of goethite, however, point out to the necessity of taking into account the dispersion of particles for a proper interpretation of the isotopic data. Article History: Received 20 August 2012; Revised 26 January 2013; Accepted 30 January 2013
    Keywords: Fertilizers -- Analysis ; Fertilizers -- Methods ; Iron Oxides -- Analysis ; Iron Oxides -- Methods ; Soils -- Analysis ; Soils -- Methods ; Phosphates -- Analysis ; Phosphates -- Methods
    ISSN: 0016-7061
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Geoderma, April, 2014, Vol.217-218, p.26(11)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.geoderma.2013.11.001 Byline: Aurelien Roger, Zamir Libohova, Nicolas Rossier, Stephane Joost, Alexandra Maltas, Emmanuel Frossard, Sokrat Sinaj Abstract: Phosphorus (P) is the second essential nutrient for plant growth but can become an ecological and economical concern in case of over-fertilization. Soil P dynamic is influenced by many parameters like soil physical-chemical properties and farming practices. A better understanding of the factors controlling its distribution is required to achieve best management of P in cropping systems. In Switzerland, the FRIBO network was launched in 1987 and consists of 250 sites covering a wide diversity of soils (Cambisols, Gleysols, Rendzinas, Lithosols, Luvisols, Fluvisols) and three different land uses (cropland, grassland and mountain pasture) across the Fribourg canton. A spatial investigation of the different P forms (total, organic and available) for the FRIBO network led to the following main conclusions: (i) The P status in agricultural soils was significantly different among the three land uses encountered, with the highest mean values of available P found in croplands, from 2.12 (CO.sub.2 saturated water extraction) to 81.3mg.kg.sup.-1 (acetate ammonium+EDTA extraction); whereas total P was more abundant in permanent grasslands (1186mg.kg.sup.-1), followed by mountain pastures (1039mg.kg.sup.-1) and croplands (935mg.kg.sup.-1). This full characterization of the soil P status provides important data on P distribution related to soil properties and land use. (ii) Environmental variables such as altitude, slope, wetness index or plan curvature, derived from the digital elevation model (DEM) only explained a small part of the spatial variation of the different P forms (20 to 25%). Thus, the geostatistical analyses revealed that land use plays a significant role in soil P distribution. Improved predictions of the spatial distribution of P-related forms at landscape scales are needed and would require additional data points and variables such as parent material, soil types and terrain attributes. Article History: Received 2 July 2013; Revised 31 October 2013; Accepted 8 November 2013
    Keywords: Soil Phosphorus -- Chemical Properties ; Soil Phosphorus -- Analysis
    ISSN: 0016-7061
    Source: Cengage Learning, Inc.
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  • 5
    Language: English
    In: Geoderma, May 2014, Vol.219-220, pp.125-135
    Description: Controlling phosphate (P) release from agricultural soils to water while maintaining optimal plant growth conditions remain a major challenge for the development of sustainable agricultural systems. To achieve this, it is important to have a proper knowledge of the amount of soil P that can be mobilized by water and of the kinetics of P release. We evaluated the ability of a flow-through reactor in which P labeled soils can be inserted and leached continuously with deionized water, to assess P release. The experiment was conducted on five grassland soils presenting a large range in P availability. The availability of P in these soils was further modified by submitting them to 0 to 3 plant growth cycles with Italian ryegrass ( ) with three levels of P added (0, 20 and 40 mg P kg soil ). The P input–output balance, water and oxalate extractable P, the degree of P saturation of the soil and the amount of isotopically exchangeable P ( value) were assessed in all samples. A subset of these soil samples was labeled with P, introduced in a flow-through reactor and the release of P and P measured over 14 days. The cumulated amount of P released after 14 days was strongly correlated to the amount of oxalate extractable P, isotopically exchangeable P ( value), and water extractable P. The P release kinetics was modeled with a 2 pools model with each pool following first order kinetics. Plants were able to take up P from both pools. Assuming that the leached P had the same isotopic composition as the pool of soil P it came from it became possible to quantify the amount of isotopically exchangeable remaining in the soil which was called the value. decreased during the three first days of the flow-through experiment and then increased linearly with time reaching a maximum after 14 days. This maximum remained lower than the oxalate extractable P. Processes contributing to this increase were isotopic exchange and possibly also some organic P mineralization. The value was strongly linearly correlated to values measured after different exchange times, but for a given exchange time, the value was lower than the value, whereas equality could have been expected. This difference was related to the high rate of P export from the soil at the beginning of the flow-through experiment. The value was also strongly correlated to the oxalate and water extractable P. In conclusion, we suggest that the use of the flow-through reactor yields relevant information on the amount of P that can be leached from a given soil, and that the value delivers information on the amount of isotopically exchangeable P remaining in the soil and therefore which could still be leached if sufficient time would be given.
    Keywords: Desorption ; Flow-through Reactor ; Isotopic Exchange ; Kinetics ; Phosphate ; Soil ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 6
    Language: English
    In: Geoderma, November 2015, Vol.257-258, pp.86-93
    Description: Mineralization of organic phosphorus (P ) may be of great importance for plant nutrition in soils containing very little available inorganic phosphorus (P ). Gross organic P mineralization rates can be quantified by an isotopic dilution method using P labeling of soil. However, its application remains a challenge in tropical soils in which the concentration of phosphate ions in the soil solution is below the detection limit of traditional colorimetric methods. This limitation can potentially be overcome by the hexanol concentration method, which uses hexanol to concentrate the blue-colored phosphomolybdate complex from large volumes. We applied the isotopic dilution method in combination with the hexanol concentration method to a Ferralsol from the highlands of Madagascar which had been preincubated in the presence or absence of plant residues for 90 days before the start of the experiment. The limits of detection (DL) and quantification (QL) of the gross P mineralization rate were 0.2 and 0.7 mg P kg soil day , respectively. Basal gross P mineralization rates after 7 days of incubation were 0.8 ± 0.5 and 1.7 ± 0.2 mg P kg soil day in non-amended and residue-amended soils, respectively. These rates are plausible, suggesting that the isotopic dilution method is applicable in highly weathered tropical soils with P concentrations in the soil solution below the detection limit of traditional colorimetric methods. Net P mineralization which sustains the plant available P pool remains to be quantified. Gross and net P mineralization rates should now be assessed in highly weathered soils under a range of land uses.
    Keywords: Isotopic Dilution ; Soil Organic Phosphorus ; Gross Basal Mineralization ; Low P Availability ; Phosphate Sorption ; Ferralsol ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
    Source: ScienceDirect Journals (Elsevier)
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  • 7
    Language: English
    In: Geoderma, April 2014, Vol.217-218, pp.26-36
    Description: Phosphorus (P) is the second essential nutrient for plant growth but can become an ecological and economical concern in case of over-fertilization. Soil P dynamic is influenced by many parameters like soil physical–chemical properties and farming practices. A better understanding of the factors controlling its distribution is required to achieve best management of P in cropping systems. In Switzerland, the FRIBO network was launched in 1987 and consists of 250 sites covering a wide diversity of soils (Cambisols, Gleysols, Rendzinas, Lithosols, Luvisols, Fluvisols) and three different land uses (cropland, grassland and mountain pasture) across the Fribourg canton. A spatial investigation of the different P forms (total, organic and available) for the FRIBO network led to the following main conclusions:
    Keywords: Soil Phosphorus ; Soil Properties ; Land Use ; Spatial Variability ; Geostatistics ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 8
    Language: English
    In: Geoderma, June 2013, Vol.200-201, pp.120-129
    Description: The isotopic exchange kinetic (IEK) method allows assessing the rate of orthophosphate ions (Pi) exchange between the solid phase and the solution of the soil with time. However, two challenges have to be tackled when using this technique in soils with a very low water extractable Pi concentration ( ) and with a high sorbing capacity for Pi. The first is that current colorimetric methods do not allow quantifying Pi concentrations lower than 10 μg P L . While the second challenge is that a significant fractionation between P isotopes may occur in the soil solution system in the presence of soils with high Pi sorption capacity. We assessed here: i) whether concentrating the blue phosphomolybdate complex (BPMC) in hexanol prior to its measurement would allow to lower the detection and quantification limits of Pi, ii) whether a significant isotopic fractionation between Pi and Pi could occur during IEK experiments conducted in the presence of high Pi sorbing substrates (e.g., pure goethite or Malagasy soils) and iii) whether the IEK method when used in conjunction with the hexanol concentration of the BPMC to measure would detect changes in Pi isotopic exchangeability in a ferralsol cropped with upland rice following the input of manure or water soluble fertilizer. The detection and quantification limits of the BPMC concentrated by hexanol were 0.3 and 0.8 μg P L , respectively, using a cell of 10 cm length for the colorimetric measurement. The IEK conducted on Pi amended goethite and on Malagasy soils with Pi and Pi did not show any systematic isotopic fractionation between both isotopes, suggesting that in these soils Pi and Pi or Pi have a similar behavior during isotopic exchange. The analysis of the soils sampled in the field experiment showed a significant increase in the amount of Pi isotopically exchangeable after 1 min only after the application of water soluble P. This increase was paralleled by increases in rice yield and P export by grains demonstrating an increased P availability in this treatment. In conclusion, the IEK method can be used in low P and high Pi sorbing soils as the hexanol concentration method allows measuring very low and as the different P isotopes have a similar behavior in the soil/solution system. The IEK experiments conducted in the presence of goethite, however, point out to the necessity of taking into account the dispersion of particles for a proper interpretation of the isotopic data. ► Soil water extractable orthophosphate ions can be measured in a nanomolar range. ► There is no significant fractionation between P isotopes during isotopic exchange. ► Isotopic exchange kinetic experiments provide relevant results in tropical soils.
    Keywords: Ferralsol ; Andosol ; Phosphate Ion Sorption ; Low P Availability ; Isotopic Technique ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 9
    Language: English
    In: Geoderma, November 2015, Vol.257-258, pp.123-133
    Description: Degradation of tropical pastures on highly weathered soils is linked to soil structural decline and associated losses of organic matter, which could both also affect soil phosphorus (P) dynamics and availability. Our aim was to elucidate these linkages by examining the effect of pasture degradation on the contents and forms of P contained within aggregate size classes and macroaggregate fractions (collectively referred to as soil structural components). We conducted a study on nine farms in a deforested part of the Colombian Amazonia, each farm with degraded and productive spp. pastures. Topsoil (0–10 cm) samples were separated by wet-sieving into aggregate size classes, and macroaggregates were further separated into occluded fractions. Soils and structural components were analyzed for concentrations of total P, available P (extracted using anion exchange resins), NaOH–EDTA extractable organic and inorganic P, and enzyme-hydrolyzable organic P (simple monoester-like, DNA-like, -inositol hexakisphosphate-like) in the NaOH–EDTA extracts. Degraded pasture soils had significantly fewer large macroaggregates and more microaggregates, both with significantly lower organic P concentrations (in mg P kg of structural component) than those in productive pasture soils. At the same time, total and extractable inorganic P concentrations in bulk soil and structural components did not differ between pasture types, suggesting a shift from organic to non-extractable P upon degradation. Soils under productive pastures contained 37% more organic P than degraded pasture soils (in mg P kg soil), mainly in large macroaggregates. The organic P concentrations were strongly correlated with C concentrations across all soil structural components, suggesting similar stabilization mechanisms for organic P and C. In bulk soil and most structural components, around 60% of organic P was enzyme-hydrolyzable. The lower contents of all enzyme-hydrolyzable as well as enzyme-stable organic P in degraded vs. productive pasture soils indicate a reduction of all organic P classes during pasture degradation. The large macroaggregates and, in particular, microaggregates occluded within this fraction were identified as an important site for organic P storage. Our results highlight a linkage between soil structure and organic P, both of which can play an important role in maintaining the productivity of pastures established on highly weathered soils.
    Keywords: Amazon Basin ; Colombia ; Tropical Pastures ; Pasture Degradation ; Soil Aggregation ; Phosphorus ; Phosphorus Forms ; Enzyme Additions ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 10
    Language: English
    In: Geoderma, 01 July 2019, Vol.345, pp.31-37
    Description: In terrestrial ecosystems, a large proportion of the phosphorus (P) in soil is often found within soil organic matter. However, the majority of organic P in soil remains ‘unresolved’ and is largely observed as a ‘broad’ signal within the phosphomonoester region of a solution P nuclear magnetic resonance (NMR) spectrum on soil extracts. Our aim was to gain insight into the composition of four soils using the transverse relaxation (T ) time of the magnetisation in solution P NMR spectroscopy as a probe of their structure. We found the broad signal within the phosphomonoester region rapidly decayed compared to the sharp signals (i.e. - and -inositol hexakisphosphate) across all soils, which corresponded to the former having a shorter T time than the latter, and supports the existence of a broad signal due to supra-/macro-molecular structures. Furthermore, measures of the broad signal's line-width at half peak intensity based on T times were found to be less than that obtained from spectral deconvolution fitting. Therefore, our results strongly suggest that the broad signal is itself comprised of more than one component. The significance of this is that the chemical nature of a large proportion of soil organic P appears to be structurally complex.
    Keywords: Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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