| 1. |
- Braun, Sabina, et al.
(författare)
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Assessing the ability of soil tests to estimate labile phosphorus in agricultural soils : Evidence from isotopic exchange
- 2019
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Ingår i: Geoderma. - : Elsevier. - 0016-7061 .- 1872-6259. ; 337, s. 350-358
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Tidskriftsartikel (refereegranskat)abstract
- Efficient phosphorus (P) fertilization strategies are essential for intensive crop production with minimal negative environmental impacts. A key factor in sustainable P use is assessment of the plant available soil P pool using soil P tests. This study determined isotopically exchangeable P after six days of reaction with 33PO4 (P-E (6 d)) to determine how accurately two commonly used P tests, Olsen and AL (acid ammonium acetate lactate) can quantify the amount of labile P. Soil samples were taken from both highly P-amended and unamended plots at six sites within the Swedish long-term soil fertility experiments. According to P K-edge XANES spectroscopy, the P speciation was dominated by Al-bound P and organic P, with additional contributions from Fe-bound P and Ca phosphates in most soils. The results showed that the AL test overestimated P-E (6 d) by a factor of 1.70 on average. In contrast, the Olsen test underestimated P-E (6 d), with the mean ratios of P-Olsen to P-E (6 d) being 0.52 for high-P and 0.19 for low-P soils. The 33P/31P ratio in the Olsen extract of a 33PO4 spiked soil was closer to that of a 0.005 mol L−1 CaCl2 soil extract than the corresponding ratio in the AL extract, suggesting that AL extraction solubilized more non-labile P. In conclusion, the AL and Olsen methods are not suitable for direct quantification of the isotopically exchangeable soil P pool after 6 days of equilibration. However, based on the results, Olsen may be superior to AL for classification of soil P status, due to its even performance for calcareous and non-calcareous soils and lower extraction of non-labile P.
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| 2. |
- Braun, Sabina
(författare)
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Long-term phosphorus supply in agricultural soils : size and dynamics of fast- and slow-desorbing phosphorus pools
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To improve phosphorus (P) fertiliser management, a better understanding of inorganic P exchange between the soil solution and solid phase is needed. This thesis examined the dynamics of this exchange, distinguishing between pools of P that are fast- and slowdesorbing, and compared methods for quantification of these pools. This was done using soil and data from six locations in the Swedish long-term soil fertility trials. Treatments with four levels of P addition, from zero P to replacement + 30 kg P ha−1 , were sampled. Isotopic exchange kinetics (IEK) were used to study the dynamics and size of the isotopically exchangeable P pools. The size of the isotopically exchangeable pool at t=1 min (E1 min) was affected by exchangeable Ca2+, while that of the E1 day − E1 min and E3 months − E1 day pools was affected by soil pH and Al-ox + Fe-ox. The change in P-Olsen and P-ox over time was also related to exchangeable Ca2+. Phosphorus desorption kinetics were tested with iron(hydr)oxide-coated papers as an ‘unlimited’ sink. The P desorption values were fitted to the Lookman two-compartment model, giving information about the size and desorption rate of the fast- and slow-desorbing P pools (Q1 and Q2). The desorption experiments was shown to deliver similar information as the IEK, even if they assess different mechanisms.Two extraction methods (AL and Olsen) were tested for their ability to quantify the fast-desorbing P pool, by incubation of soil with radioactive 33P before extraction. This revealed that AL extraction dissolves more stable P forms, which was further proved by the relationship between P-AL and Q1 (r2 =0.63) being weaker than for P-Olsen and Q1 (r2 =0.96).A positive P balance increased the amount of ‘P bound to Al and Fe’, and/or CaP, (according to P K-edge XANES), the desorption rate from the slow-desorbing P pool and the fraction of total P present in the fast-desorbing pool. It did not increase wheat, barley, or oat grain yield. With no P fertiliser, the extractable and exchangeable P pools decreased, but about half locations had significantly lower grain yield. This shows that the P contribution from the slow-desorbing P pool is important for plant P uptake, and that this pool can supply P for a long period. When replacement P was added, yields was not affected but P-AL and P-Olsen decreased, making ‘P in balance’ a possibly useful strategy to lower soil P levels without grain yield loss.
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| 3. |
- Braun, Sabina, et al.
(författare)
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Modelling heterogeneous phosphate sorption kinetics on iron oxyhydroxides and soil with a continuous distribution approach
- 2018
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Ingår i: European Journal of Soil Science. - : Wiley. - 1351-0754 .- 1365-2389. ; 69, s. 475-487
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of orthophosphate (PO4) sorption in soil has far reaching consequences on its long-term fate. Traditionally, a distinction is made between fast, reversible adsorption and slow fixation. The kinetics are commonly described by compartmental models (CMs) assuming kinetically distinct homogeneous pools (e.g. a rapid- and slow-sorbing pool), with phenomenological equations or with complex diffusion-based models. Alternatively, this process can be described by assuming frequency distributions of both adsorption and desorption rate constants and, thereby, enabling better description of experimental data with fewer adjustable parameters. Here, we developed such a rate constant distribution (RCD) model and compared it with CMs and other commonly used rate equations. Batch (PO4)-P-33 sorption was measured in agitated suspensions between 2minutes and 20days after spiking in 13 contrasting types of soil and two iron oxyhydroxides. Overall, the RCD model, with three adjustable parameters, describes the data better than the other models tested. The so-called slow reactions, denoted as the factor change in soluble (PO4)-P-33 between 1 and 20days after spiking, were described better by the RCD model and ranged from 1.0 (i.e. no change) to 6.9. The extent of slow reactions increased with the increase in the fraction of poorly crystalline iron in the soil (r=0.69; P=0.0088). Equilibrium was elusive up to 20days for PO4 sorption on ferrihydrite and on soil samples with a large fraction of poorly crystalline iron oxyhydroxides. The RCD model code is available as freeware from the first author.
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| 4. |
- Braun, Sabina, et al.
(författare)
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Phosphorus desorption and isotope exchange kinetics in agricultural soils
- 2020
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Ingår i: Soil use and management. - : Wiley. - 0266-0032 .- 1475-2743.
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Tidskriftsartikel (refereegranskat)abstract
- To improve phosphorus (P) fertilization and environmental assessments, a better understanding of release kinetics of solid-phase P to soil solution is needed. In this study, Fe (hydr)oxide-coated filter papers (Fh papers), isotopic exchange kinetics (IEK) and chemical extractions were used to assess the sizes of fast and slowly desorbing P pools in the soils of six long-term Swedish field experiments. The P desorption data from the Fh-paper extraction of soil (20 days of continual P removal) were fitted with the Lookman two-compartment desorption model, which estimates the pools of fast (Q1) and slowly (Q2) desorbing P, and their desorption rates k1 and k2. The amounts of isotope-exchangeable P (E) were calculated (E1min to E>3 months) and compared with Q1 and Q2. The strongest relationship was found between E1 min and Q1 (r2 =.87, p <.01). There was also an inverse relationship between the IEK parameter n (the rate of exchange) and k1 (r2 =.52, p <.01) and k2 (r2 =.52, p <.01), suggesting that a soil with a high value of n desorbs less P per time unit. The relationships between these results show that they deliver similar information, but both methods are hard to implement in routine analysis. However, Olsen-extractable P was similar in magnitude to Q1 (P-Olsen = 1.1 × Q1 + 2.3, r2 =.96), n and k1 were related to P-Olsen/P-CaCl2, while k2 was related to P-oxalate/P-Olsen. Therefore, these extractions can be used to estimate the sizes and desorption rates of the different P pools, which could be important for assessments of plant availability and leaching.
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| 5. |
- Gustafsson, Jon Petter, 1964-, et al.
(författare)
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A Probabilistic Approach to Phosphorus Speciation of Soils Using P K-edge XANES Spectroscopy with Linear Combination Fitting
- 2020
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Ingår i: Soil systems. - : MDPI. - 2571-8789. ; 4:2
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Tidskriftsartikel (refereegranskat)abstract
- A common technique to quantitatively estimate P speciation in soil samples is to apply linear combination fitting (LCF) to normalized P K-edge X-ray absorption near-edge structure (XANES) spectra. Despite the rapid growth of such applications, the uncertainties of the fitted weights are still poorly known. Further, there are few reports to what extent the LCF standards represent unique end-members. Here, the co-variance between 34 standards was determined and their significance for LCF was discussed. We present a probabilistic approach for refining the calculation of LCF weights based on Latin hypercube sampling of normalized XANES spectra, where the contributions of energy calibration and normalization to fit uncertainty were considered. Many of the LCF standards, particularly within the same standard groups, were strongly correlated. This supports an approach in which the LCF standards are grouped. Moreover, adsorbed phytates and monetite were well described by other standards, which puts into question their use as end-members in LCF. Use of the probabilistic method resulted in uncertainties ranging from 2 to 11 percentage units. Uncertainties in the calibrated energy were important for the LCF weights, particularly for organic P, which changed with up to 2.7 percentage units per 0.01 eV error in energy. These results highlight the necessity of careful energy calibration and the use of frequent calibration checks. The probabilistic approach, in which at least 100 spectral variants are analyzed, improves our ability to identify the most likely P compounds present in a soil sample, and a procedure for this is suggested in the paper.
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| 6. |
- Gustafsson, Jon-Petter, et al.
(författare)
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Where does all the phosphorus go? Mass balance modelling of phosphorus in the Swedish long-term soil fertility experiments
- 2023
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Ingår i: Geoderma. - 0016-7061 .- 1872-6259. ; 440
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Tidskriftsartikel (refereegranskat)abstract
- To gain insights into phosphorus (P) dynamics in soils and the ability to predict soil responses to varying fertilizer inputs, mass balance models prove to be valuable tools. In this study, a new dynamic mass balance model, PBalD8, was used to describe the change in extracted P in the A horizon of soils subjected to diverse fertilizer treatments over a period of 50 to 60 years in five soil fertility experiments. The model employed a Freundlich equation to describe soil-solution partitioning of P and assumed that acid-lactate-extractable P represented a labile pool of P in instant equilibrium with soil solution P. Additionally, oxalate-extractable inorganic P was presumed to comprise the sum of the labile and stable pools of P, with mass flux to and from the latter described by Fick's first law. The model was evaluated using results from extractions and P K-edge XANES spectroscopy. Notably, organic P, as revealed by P K-edge XANES, did not substantially contribute to long-term changes in soil P content and was therefore excluded from consideration. In general, the model offered reasonable fits to the extracted P concentrations. However, for the P-depleted treatments, a prerequisite was that the P removal through harvest was lower compared to measurements. Conversely, in three of the soils, the modelled fertilizer inputs needed to be reduced to 70 % to 85 % of the known additions. These discrepancies may be attributed to the involvement of deeper soil horizons, including deep crop uptake and mixing with lower soil layers, although other factors such as lateral dispersion and inaccuracies in estimating applied fertilizers cannot be discounted. These results underscore the necessity of gaining a more comprehensive understanding of how deeper soil horizons influence P mass balances in agricultural soils. In one of the soils, Fja center dot rdingslo center dot v, P K-edge XANES results demonstrated the formation of calcium phosphate over time in the highest fertilization treatment, consistent with the model. Additionally, in two soils, Kungsa center dot ngen and the P-depleted Vreta Kloster soil, the model predicted a significant contribution from mineral weathering. However, the PBalD8 model also projected higher P leaching rates than those observed, suggesting that the model may not fully capture this P output term.
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| 7. |
- Spohn, Marie, et al.
(författare)
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Continuous decrease in soil organic matter despite increased plant productivity in an 80-years-old phosphorus-addition experiment
- 2023
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Ingår i: Communications earth & environment. - 2662-4435. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to understand how eight decades of tillage affected soil element dynamics. We measured soil chemical properties and the C-14:C-12 ratio (& UDelta;C-14) of organic carbon in one of the oldest cropland experiments in Europe with different levels of phosphorus addition. Soil total and organic phosphorus stocks in the uppermost 20 cm did not differ significantly between the control and the phosphorus addition treatments after 80 years, indicating plant phosphorus uptake from the subsoil. Crop yields increased from 220 g dry weight m(-2) in 1936 to more than 500 g dry weight m(-2) in the 2010s. The soil total organic carbon and total organic phosphorus stocks decreased by 13.7% and 11.6%, respectively, in the uppermost 20 cm of the soils during the experiment, irrespective of phosphorus addition. Based on modeling of & UDelta;C-14, we show that the mean transit time of carbon in the soil was below 10 years, indicating that a large share of the carbon inputs to soil is quickly respired. Our results suggest that the current agricultural practice at this long-term experiment is not sustainable because it led to a continuous decrease in soil organic matter over the last decades, despite increases in plant productivity.Several decades of tillage drives continual decreases in soil organic carbon, nitrogen and organic phosphorus with mean carbon transit times in soils estimated at less than 10 years despite increased plant productivity, suggest chemical analyses of European cropland soils.
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