Redox reactions and phosphorus release in re-flooded soils of an altered wetland

Phosphorus loss from land can be a major factor affecting surface water quality. We studied P‐release mechanisms in wetland soils that had been drained and cultivated for four decades and then re‐flooded. We measured redox, pH and solution composition in two sites in the field and in four peat and calcareous soils incubated in biogeochemical microcosms. The redox and pH measurements during the 120 days of incubation and the resulting soil solution composition indicated that the main process leading to P release is reductive dissolution of ferric hydroxides on which P was adsorbed and in which P was occluded. The molar Fe:P ratio increased with period of reduction from below 1 in the first week of re‐flooding to 15–60 after 120 days. This suggests an increased P‐retention capacity upon reoxidation of the soil solution, whether within the soil profile or in the drainage canals. Prolonged flooding of the calcite‐poor, gypsum‐rich peat soils increased the oversaturation of soil solutions with respect to hydroxyapatite and occasionally β‐Ca₃(PO₄)₂(c), indicating that in spite of the large Ca concentration, the rate of Ca‐P precipitation was insufficient to maintain the saturation status of the Ca‐P system. In the calcareous soils the Ca‐P system effectively controlled the P activity in soil solution throughout the incubation period. In both cases the precipitation of Ca‐P minerals could be an important P‐retention mechanism.     

Evaluation of phosphorus mobilization potential in rewetted fens by an improved sequential chemical extraction procedure

After rewetting of peatlands, phosphorus (P) pore‐water concentrations were up to three orders of magnitude greater than under pristine conditions. It was hypothesized that different mobilization processes such as ion‐exchange reactions, biotic/abiotic redox reactions, acidification and ongoing anaerobic decomposition of particulate organic matter by hydrolytic cleavage and fermentation might be responsible. To identify P pools in peat samples of varying degrees of decomposition, we modified and improved a sequential chemical extraction method that allowed conclusions on potential mobilization mechanisms in rewetted peatlands. The results indicated that the earlier drainage of rewetted fens strongly increased the P mobilization potential in the upper decomposed peat layers. Accordingly, the amount of P bound to redox‐sensitive (bicarbonate/dithionite soluble) compounds (BD‐P) was, on average, one order of magnitude greater in decomposed peat of rewetted fens (5.4–14.3 μmol P g^?1 dry matter or DM) than in underlying less‐decomposed peat layers (0.2–1.9 μmol P g^?1 DM) or slightly decomposed peat derived from pristine fens (0.4–2.0 μmol P g^?1 DM). The BD‐P fraction found in the upper very decomposed peat layers appears to be most important for P mobilization in rewetted fens and accounted for 85% of the variability of P mobilization rates. Despite uncertainties regarding P diagenetic processes in peat, as well as the development of microbial decomposition processes, in the long‐term, high pore‐water P concentrations can be expected in rewetted fens for decades to come.     

Fulvic acid composition in degraded fenlands

Fulvic acids (FAs) from topsoil and ground water solutions were investigated to discover effects of land use and peat degradation on their molecular chemical composition and thermal properties. The FAs were extracted from three Gleysols under arable land, intensive and extensive grassland, and from three Histosols under alder forest, extensive grassland, and a natural succession in a long‐term (> 200 years) cultivated fen area. Functional groups and molecular subunits of the FAs were investigated by ¹³C Nuclear Magnetic Resonance (¹³C NMR) spectroscopy. Thermal properties and structural molecular subunits were investigated by off‐line pyrolysis, and Pyrolysis‐Field Ionization Mass Spectrometry (Py‐FIMS). The ¹³C NMR spectra showed that the FAs from topsoil solutions had smaller proportions of alkyl C (mean: —8 %) and more aromatic C (mean: + 6 %) than FAs from ground water. This clear differentiation of dissolved FAs in the soil profiles is consistent with Py‐FIMS data which have shown enrichments of lipids in ground water FAs. Furthermore, Py‐FIMS revealed that the FAs from topsoils were richer in phenols + lignin monomers, carbohydrates, as well as mostly aromatic N‐containing compounds. These molecular subunits of FAs, relatively enriched in topsoil, were also the main indicators of land use and peat degradation. For topsoil solutions, the proportions of phenols + lignin monomers and carbohydrates increased stepwise with peat degradation in Gleysols and Histosols. Correspondingly, the thermal properties indicated the incorporation of these compounds into FAs by chemical bonds of larger thermal stability. Statistical evaluation by principal component analysis of Py‐FIMS clearly supported the differentiation of FAs according to the origin from topsoils and ground water, different soil types, and land use and peat degradation. Hence, it is concluded that water soluble FAs can be utilized as objective ecological indicators for soil effects on adjacent ground and surface waters.     

Soil physical characteristics of peat soils

Drainage and intensive use of fens lead to alterations in the physical characteristics of peat soils. This was demonstrated using parameters of water balance (available water capacity) and the evaluated unsaturated hydraulic conductivity. Deriving the distribution of the pore size from the water retention curve was flawed because of shrinkage due to drainage, especially at high soil water potentials. These errors became greater as the peat was less influenced by soil‐genetic processes. The water retention curves (desorption) evaluated in the field and the laboratory satisfactorily corresponded. However, the wetting‐ and drainage‐curves obtained in the field differed up to 30 vol.‐% water content at same soil water potentials. These differences were largely due to a wetting inhibition.     

氧化势影响下的滇池沉积物孔隙水磷浓度变化

The sediment redox potential was raised in the laboratory to estimate reduction of internal available phosphorus loads, such as soluble reactive phosphorus （SRP） and total phosphorus （TP）, as well as the main elements of sediment extracts in Dianchi Lake. Several strongly reducing substances in sediments, which mainly originated from anaerobic decomposition of primary producer residues, were responsible for the lower redox potential. In a range of -400 to 200 mV raising the redox potential of sediments decreased TP and SRP in interstitial water. Redox potentials exceeding 320 mV caused increases in TP, whereas SRP maintained a relatively constant minimum level. The concentrations of Al, Fe, Ca^2＋, Mg^2＋, K^＋, Na^＋ and S in interstitial water were also related to the redox potential of sediments, suggesting that the mechanism for redox potential to regulate the concentration of phosphorus in interstitial water was complex.     

Change of soil hydrological properties of fens as a result of soil development

This study deals with the change and evaluation of hydrological properties of peat soils (Histosols) in the course of soil development. Ash content, volumetric water content, and dry bulk density, unsaturated hydraulic conductivity, water retention function, and wetting properties were measured for 84 fen sites in 19 fen regions of North‐Eastern Germany. Soil development resulted in porosity decrease. On the contrary, the macropore space and the capillary rise increased. With the start of consolidation processes and the development of segregation structure, a'noticeable reduction of the macropores and unsaturated hydraulic conductivity were observed. In course of soil development and decreasing of aggregate size, these processes reversed. Both parameters increased from segregation structure horizon to earthyfied fen and weak moorshyfied fen horizon, until they partly exceeded the starting values of pedogenetic almost unchanged fen in strongly moorshyfied stadium. Differences in wetting properties of peat could not be explained by the changes of peat properties in the course of soil development.     

Water-table management in lowland UK peat soils and its potential impact on CO2 emission

The rate of oxidation of peat soils is highly seasonal and varies with temperature and soil moisture content. Large variations in soil moisture content result in wet–dry cycles that can enhance peat degradation. Water‐table management plays a crucial role in controlling and damping the effect of these environmental factors. However, maintaining high ditch water levels in fields bounded by ditches does not guarantee a high field groundwater level. The effect of installing subsurface irrigation at different spacings on water table elevation was studied in a low‐lying peat grassland. The water table elevation data were compared against values predicted with a water balance model. In addition, greenhouse experiments were carried out on undisturbed soil core samples collected from the peat grassland as well as a low‐lying peatland under intensive arable faming to measure CO₂ evolution under different water regimes. The field data from the peat grassland suggest that sub‐irrigation spacing as low as 10 m is necessary during summer periods to maintain groundwater levels similar to those in the ditches. Over the same period of observation, the difference in water level between the ditches and the non‐irrigated fields is as high as 0.7 m. Modelled outputs are in good correlation with the field observations, and demonstrate that simple water balance models can provide an effective tool to study the effect of water management practices and potential changes in subsurface conditions, climate and land use on water‐table levels. The measurement of CO₂ emission from undisturbed peat soil columns shows that the rate of oxidation of soil organic matter from peat soils is highly seasonal and that drainage exacerbates the rate of peat mineralization.     

Organic matter quality of a forest soil subjected to repeated drying and different re‐wetting intensities

Extended drought periods followed by heavy rainfall may increase in many regions of the Earth, but the consequences for the quality of soil organic matter and soil microbial communities are poorly understood. Here, we investigated the effect of repeated drying and re‐wetting on microbial communities and the quality of particulate and dissolved organic matter in a Haplic Podzol from a Norway spruce stand. After air‐drying, undisturbed soil columns were re‐wetted at different intensities (8, 20 and 50 mm per day) and time intervals, so that all treatments received the same amount of water per cycle (100 mm). After the third cycle, SOM pools of the treatments were compared with those of non‐dried control columns. Lignin phenols were not systematically affected in the O horizons by the treatments whereas fewer lignin phenols were found in the A horizon of the 20‐ and 50‐mm treatments. Microbial biomass and the ratio of fungi to bacteria were generally not altered, suggesting that most soil microorganisms were well adapted to drying and re‐wetting in this soil. However, gram‐positive bacteria and actinomycetes were reduced whereas gram‐negative bacteria and protozoa were stimulated by the treatments. The increase in the (cy 17: 0 + cy 19: 0)/(16:1ω7c + 18:1ω7c) ratio indicates physiological or nutritional stress for the bacterial communities in the O, A and B horizons with increasing re‐wetting intensity. Drying and re‐wetting reduced the amount of hydrolysable plant and microbial sugars in all soil horizons. However, CO₂ and dissolved organic carbon fluxes could not explain these losses. We postulate that drying and re‐wetting triggered chemical alterations of hydrolysable sugar molecules in organic and mineral soil horizons.     

Leaching of Solutes from an Intensively Managed Peat Soil to Surface Water

In many peat land areas in The Netherlands target concentrations for nitrogen (N) and phosphorus (P) in surface water are exceeded. A considerable, but poorly quantified, fraction, of the N and P loading of surface water in these areas originate from the subsoil. Waterboards, responsible for the water management, are currently exploring options to improve surface water quality, whilst sustaining agricultural production. Therefore, insight into dynamics of nutrient pools in peat soils is required. The aim of this study was to measure concentration profiles (0–12 m) of the soil solution in an intensively managed grassland on peat soil and to explore the effects of a rise in surface water level on N and P loading of surface water, using budgeting approaches and two dimensional simulation modeling. The concentration profiles of N, P and Cl reflect by the presence of nutrient-rich anaerobic peat and a nearly impermeable marine clay in the subsoil. Concentrations of N, P and Cl tended to increase with depth till about 6 m and then decreased. In the top soil, inputs of N and P via fertilizers and animal manure were only partly retrieved in the soil solution, suggestion that biogeochemical processes, uptake and lateral transport processes had a dominant influence on dissolved N and P. Exploring scenario simulations showed that major drainage fluxes passed through the peat layer that transported nutrients to adjacent surface water. Raising surface water levels with 20 cm suppresses this kind of nutrient loading of surface water by more than 30%, but nutrient rich peat layers will remain persistent as a potential source of nutrients in surface water in many peat polders in the western part of The Netherlands.     

Variations of Phosphorus Release from Sediments in Stratified Lakes

The aim of this investigation was to study the temporal variation in phosphorus release from the sediments and its influence on water quality of stratified lakes. The concentrations of soluble reactive phosphorus (SRP), calcium and sulfate in the interstitial water and the pH in the wet sediments of dimictic lakes were investigated during the spring circulation and at the end of summer stratification. Multiple regression analysis using the calculated diffusive fluxes of SRP out of the sediments and the morphometric characteristics of the lakes (reduced water depth), explained 73 % of the variance of the SRP-accumulation in the hypolimnia during summer stagnation. At the end of surnmer stratification diffusive fluxes of SRP out of the sediments increased and pH-values and sulfate-concentrations decreased at the sediment surface (0–2 em) and in the hypolimnia. The maximum diffusive flux of SRP was calculated to be 5.8 mg/m²/d at the end of summer stagnation. Prob able reasons for these higher diffusive fluxes of SRP at the end of summer stagnation are higher supply of labile organic matter and thereby higher mineralization rates. lower redox potential and thus higher dissolution of redox sensitive P-binding forms and/or dissolution of phosphorus being bound to Ca-phases at lower pH.     

Phosphorus dynamics in peat‐based substrates

The mobility of nutrients in soils is well characterized, whereas little information is available for common horticultural substrates based on peat. Aim of the current study was to investigate the mobility and dynamics of phosphorus (P) as well as the parameters involved in P transport to plant roots in peat‐based substrates. A series of experiments was run to determine the impedance factor (f) and the buffer power (b). The impedance factor was determined for black peat and black peat mixed with 20% and 40% (v/v) of mineral component at volumetric water content (θ) of 40%, 50%, 60%, and 70% and at different diffusion time. Buffer power was calculated for black peat and black peat mixed with 20% (v/v) of seven different mineral components. Phosphorus was applied at rates of 0, 35, and 100 mg (L substrate^–1), respectively. The impedance factor was not affected by addition of the mineral component to peat. However, f increased from 0.03 to 0.2, by increasing θ from 40% to 60%, indicating that water content has a significant effect on this parameter. Substrate‐solution P ranged from 0.3 to 27 and from 1 to 95 mg P (L solution)^–1 for the P‐application rate of 35 and 100 mg P (L substrate)^–1, respectively. Buffer power of the substrates ranged from 1 to 17.25 depending on the mineral component, and it was positively correlated with oxalate‐soluble Fe and Al in the substrate. The calculated effective diffusion coefficient for P in the substrate was in the range of 10^–7 to 10^–8 cm² s^–1. This high value could be attributed mostly to the low buffer power rather than to the high impedance factor.     

The role of soil chemical properties,land use and plant diversity for microbial phosphorus in forest and grassland soils

Management intensity modifies soil properties, e.g., organic carbon (C_org) concentrations and soil pH with potential feedbacks on plant diversity. These changes might influence microbial P concentrations (P_mic) in soil representing an important component of the P cycle. Our objectives were to elucidate whether abiotic and biotic variables controlling P_mic concentrations in soil are the same for forests and grasslands, and to assess the effect of region and management on P_mic concentrations in forest and grassland soils as mediated by the controlling variables. In three regions of Germany, Schwäbische Alb, Hanich‐Dün, and Schorfheide‐Chorin, we studied forest and grassland plots (each n = 150) differing in plant diversity and land‐use intensity. In contrast to controls of microbial biomass carbon (C_mic), P_mic was strongly influenced by soil pH, which in turn affected phosphorus (P) availability and thus microbial P uptake in forest and grassland soils. Furthermore, P_mic concentrations in forest and grassland soils increased with increasing plant diversity. Using structural equation models, we could show that soil C_org is the profound driver of plant diversity effects on P_mic in grasslands. For both forest and grassland, we found regional differences in P_mic attributable to differing environmental conditions (pH, soil moisture). Forest management and tree species showed no effect on P_mic due to a lack of effects on controlling variables (e.g., C_org). We also did not find management effects in grassland soils which might be caused by either compensation of differently directed effects across sites or by legacy effects of former fertilization constraining the relevance of actual practices. We conclude that variables controlling P_mic or C_mic in soil differ in part and that regional differences in controlling variables are more important for P_mic in soil than those induced by management.     

Sequentially extracted phosphorus fractions in peat‐derived soils

Phosphorus (P) forms were sequentially extracted from peat derived soils (Eutric Histosols and Gleysols) at eight sites in Saxony‐Anhalt (Germany) to disclose general differences in P pools between mineral and organic soils and to investigate effects of peat humification and oxidation in conjunction with land use and soil management on the P status of soils. Overall 29 samples providing a wide variety of basic chemical properties were subjected to the Hedley fractionation. The Histosol topsoils contained more total P (P_t) (1345 ± 666 mg kg^—1) than the Gleysol topsoils (648 ± 237 mg kg^—1). The predominant extractable fractions were H₂SO₄‐P (36—63 % of P_t) in calcareous and NaOH‐P_o (0—46 % of P_t) in non‐calcareous Histosols. These soils had large pools of residual P (13—93 % of P_t). Larger contents and proportions of P_o and of labile P fractions generally distinguished organic from mineral soils. Regression analyses indicated that poorly crystalline pedogenic oxides and organic matter were binding partners for extractable and non‐extractable P. Intensive management that promotes peat humification and oxidation results in disproportional enrichments of labile P fractions (resin‐P, NaHCO₃‐P_i, and NaHCO₃‐P_o). These changes in P chemistry must be considered for a sustainable management of landscapes with Histosols and associated peat derived soils.     

Assessment of co‐blending water treatment residual with dairy manure to reduce phosphorus concentrations in run‐off in Northern Ireland

Losses of phosphorus (P) to water that follow manure applications can be high while water treatment residuals (WTR) have an appreciable capacity to sorb soluble P which is an important risk factor in determining the susceptibility of manure P to run‐off losses. The objective of this study was to assess whether co‐blending WTR with dairy cow manure prior to surface application would reduce P concentrations in run‐off from grassland. An alum‐derived WTR was collected from a water treatment works (WTW), dried and characterized for its phosphorus sorption capacity (PSC) based on oxalate‐extractable Al and Fe. Multipoint P sorption isotherms were used to calculate the Langmuir P sorption maximum (P_max) and equilibrium P concentration (EPC₀). The WTR contained 170 g Al_ox/kg and 2.2 g Fe_ox/kg with a nominal long‐term PSC of 118 g/kg. Following a 6 day incubation of WTR, the Langmuir P_max was 82.6 g/kg and the EPC₀ of 0.13 mg P/L. Laboratory incubations of manure co‐blended with WTR indicated that 144 g WTR/kg dry matter (DM) manure significantly lowered (P < 0.001) manure WSP by 71.5 ± 16.6% after 108 h, but lower WTR mixing rates of 72 and 36 g WTR/kg had no statistical effect on manure WSP. Results from a field experiment using simulated rain on 0.5‐m² grassland plots showed no significant effect on run‐off P 2 days after applying 50 m³/ha of 6% DM manure co‐blended WTR at rates of 150 and 250 g WTR/kg.     

Phosphorus speciation in cultivated organic soils revealed by P K‐edge XANES spectroscopy

Cultivated organic soils make a significant contribution to phosphorus (P) leaching losses from agricultural land, despite occupying a small proportion of cultivated area. However, less is known about P mobilisation processes and the P forms present in peat soils compared with mineral soils. In this study, P forms and their distribution with depth were investigated in two cultivated Histosol profiles, using a combination of wet chemical extraction and P K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy. Both profiles had elevated P content in the topsoil, amounting to around 40 mmol kg^?1, and P speciation in both profiles was strongly dominated by organic P. Topsoils were particularly rich in organic P (P‐org), with relative proportions of up to 80%. Inorganic P in the profiles was almost exclusively adsorbed to surface reactive aluminium (Al) and iron (Fe) minerals. In one of the pro‐files, small contributions of Ca‐phosphates were detected. A commonly used P saturation index (PSI) based on ammonium‐oxalate extraction indicated a low to moderate risk of P leaching from both profiles. However, the capacity of soil Al and Fe to retain P in organic soils could be reduced by high competition from organic compounds for sorption sites. This is not directly accounted for in PSI and similar indices. Accumulation of P‐org in the topsoil may be attributable by microbial peat decomposition and transformation of mineral fertiliser P by both microbiota and crops. Moreover, high carbon–phosphorus ratio in the surface peat material in both profiles suggests reduced net mineralisation of P‐org in the two soils. However, advancing microbial peat decomposition will eventually lead to complete loss of peat horizons and to mineralisation of P‐org. Hence, P‐org in both profiles represents a huge potentially mobilised P pool.     

Wettability of humic acid and its salts

Homoionic humates are well wetted by hydrocarbons (apolar liquid) and water (polar liquid). By wetting with hydrocarbons low heats of immersion (or wetting) are registered, whereas by wetting with water high heats of immersion are registered and colloidal solutions are formed. Humic acid is well wetted by hydrocarbons, producing low heats. It floats on the water surface, but once wetted by water it produces the heat of immersion. Studies of the properties of humic acid and humate permit to conclude that their surfaces are covered by hydrophilic and hydrophobic sites. By adsorption of butanol molecules it is established that humic acid and humate contain nearly two hydrophobic sites per 100 Ų.     

Mechanical properties of metastable glacial till before and after water‐induced compaction

The mechanical properties of metastable soils have been approached from different backgrounds by civil engineers and soil scientists, with the main focus being on water‐induced self‐compaction rates. This study was conducted to determine the rebound‐recompression properties of metastable soil before and after wetting and to study the effect of water‐induced compaction on the mechanical stability depending on the overburden pressure. Rebound and recompression properties were measured with oedometer tests using sieved sandy loam, taken from a nonweathered Saalian glacial till layer, as the metastable test soil. The mechanical stability (preconsolidation load) of the dry and wetted soil was derived mathematically from recompression data after the test soil was unloaded. Void‐ratio changes during unloading and reloading were on a low level (Δe = 0.03). Rebound and recompression rates of the dry samples increased with load, whereas the void‐ratio change was twofold higher during recompression. Rebound rates of the wetted samples tended to decrease with load, while the recompression rates remained constant. Preconsolidation load calculated for the dry samples overestimated the simulated overburden pressure, whereas the wetted samples showed a high congruence. In both cases, the point of greatest curvature estimated in the earlier step of deviation gave values that were more realistic to the loads from which the unloading started. Our results indicate that both dry compaction and water‐induced compaction induce primarily plastic deformation. Furthermore, we found that in both the dry and wetted state the mechanical stability of the soil reflecting the overburden pressure remained constant.     

Higher yield of cherry tomato grown in culture medium with microbially inoculated feather compost without fertilizer application

Arthrobacter ureafaciens K10, with multiple functions, such as feather degradation, phosphate solubilization, and IAA formation, and Streptomyces sp. CP3, with pitaya cladode‐degrading ability, were co‐inoculated in compost composed of pitaya‐pruning waste (PPW), spent mushroom waste (SMW), and duck feathers (DF) in order to produce a compost called Sapf‐M. Another compost, called Sapf, was manufactured via the same composting procedure but without inoculation. The two compost products were slightly acidic and had a bulk density less than 0.25 g cm^?3, a water‐holding capacity (WHC) greater than 85%, a C : N ratio of nearly 10, and a germination index higher than 85%. Higher IAA concentration, EC, phosphate‐solubilizing bacterial numbers, actinobacterial numbers, and water‐soluble nutrients, such as ammonium, magnesium, copper, manganese, and iron, were found in Sapf‐M compared to Sapf. Five different culture media were prepared: peat mixed with Sapf at a 2 : 1 volume ratio (P‐Sapf), peat mixed with Sapf‐M at a 2 : 1 volume ratio (P‐Sapf‐M), Sapf, Sapf‐M, and peat. Each of these was analyzed for its ability to produce cherry tomatoes without fertilization. Higher WHC and water‐soluble ammonium were found in P‐Sapf‐M than in P‐Sapf. Cherry tomato cultured in P‐Sapf‐M showed the highest fruit number and yielded 1.04 kg per plant. Fruit firmness, splitting rate, BER incidence, TSS/acidity, and nutrition were all analyzed. After eradication, the mineral concentrations of roots and culture media were also determined. The results of this study show that the bio‐inoculated Sapf‐M had longer‐lasting fertility and greater plant growth‐promoting abilities than the Sapf when used as the growing medium for cherry tomato production without further fertilization.     

地表滴灌土壤湿润体特征值的经验解

粘壤土地表点源入渗试验研究表明 ,其土壤湿润体形状近似为半椭球体 ,水平和竖直方向的最大入渗距离与入渗时间存在极显著的幂函数关系。湿润体体积和灌水量之间存在显著的线性关系 ,在2～ 4Lh-1的滴头流量范围内 ,灌水量相同时不同流量滴头对应的湿润体体积的最大差异保持在 5 %以内。地表点源入渗过程中 ,土壤湿润体内平均体积含水率的增量和入渗时间、滴头流量无关保持为一定值 ,在本研究条件下为 0 32 6。综合以上结果 ,提出了预测地表滴灌入渗土壤湿润体特征值的经验解模型     

Phosphorus in sequentially extracted fen peat soils: A K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy study

The speciation of phosphorus (P) in native and degraded peat soils is an analytical challenge, and synchrotron‐based P K‐edge X‐ray absorption near‐edge structure (XANES) is a suitable method to gain information on P species in soils and organic materials. The objective of the present study was to test if P K‐edge XANES reflected differences in P fractions in fen peat due to sequential extraction and peat degradation. We investigated each one top‐ and subsoil sample of a Fibric Histosol, which differed in the degree of humification (H8 vs. H5) and concentration of total P (P_t) (1944 mg kg^–1 vs. 436 mg kg^–1). In the topsoil, residual P, H₂SO₄‐P, and NaOH‐P accounted for roughly the same proportions of P_t (≈30%). In the subsoil, residual P (64% of P_t) was more abundant than NaOH‐P (21% of P_t) and H₂SO₄‐P (10% of P_t). Among many different P reference standards, the P XANES spectra reflected differences in mineral P more distinctive than in organic P compounds. Phosphorus XANES spectra of the residues after each sequential extraction step all showed a prominent white‐line peak at around 2152 eV. Stepwise removal of resin‐P, NaHCO₃‐P, and NaOH‐P were reflected mainly by the peak intensity but scarcely by distinct spectral features. Extraction with H₂SO₄ led to the disappearance of spectral features of Ca and Mg phosphates which is a first direct hint to these compounds in the peat. In conclusion, a combined sequential fractionation and spectroscopic (³¹P NMR, P K‐ and L‐edge XANES with linear‐combination fits) approach is proposed to overcome limitations of the present study and gain more insight into the P species in peat soils.