Phosphorus Buffering Capacity Research Articles

The combined addition of citric and aromatic organic acids to an acid soil prolongs phosphorus availability

AbstractThe role of organic acids (both aliphatic and aromatic) in increasing soil P availability is well established. However, the effect of the combined addition of aliphatic and aromatic organic acids on soil P availability is not well studied, which is particularly important when assessing the efficacy of heterogeneous natural organic acid sources, such as compost and biochar, on soil P availability based on their total abundance of organic acid compounds. In this study, some naturally occurring aliphatic (oxalic and citric) and aromatic (benzoic, 4‐hydroxybenzoic, and protocatechuic) organic acids were incubated with an acidic soil for up to 110 days and their effect on soil P availability (Olsen extractable P) and phosphorus buffering capacity (PBC) were studied. The aliphatic and aromatic organic acids were added as individual and combined treatments. The experimental results suggested that aliphatic organic acids were more effective in increasing Olsen extractable P and decreasing soil PBC when compared to aromatic organic acids. The effect of citric acid on increasing soil P availability was prolonged when applied in combination with aromatic organic acids. The contrasting chemical nature and complementary effect between aliphatic and aromatic organic acids were suggested as the reason for this phenomenon.

Phosphorus behavior under long-term fertilization in the intensive rice cultivation system

Advocating proper phosphorus (P) fertilisation is necessary to save this limited natural resource and to save the investment in rice cultivation. This study aimed to evaluate changes in phosphorus availability, total phosphorus in soil, phosphorus buffering capacity, and phosphorus saturation in the long-term phosphorus fertilisation in the paddy rice system. Soil samples were collected in the harvest stage after seven consecutive crops over three years at Can Tho city, Vietnam. The applied phosphorus fertiliser rates were: no phosphorus fertilisation (P0), 17.4 kg P/ha (P17.4), and 26.2 kg P/ha as farmer’s practice (P26.2). The results showed that the soil phosphorus buffering capacity in P0, P17.4 and P26.2 treatments was 9.49, 9.08 and 9.04 mg/kg, respectively. The degree of phosphorus saturation of P17.4 and P26.2 treatments ranged from 17.7% to 25.5%, showing the medium to high risk of phosphorus leaching. This study indicated that the application of phosphorus rate higher than 17.4 kg P/ha might result in the reduced soil phosphorus buffering capacity in the intensive rice cropping system in the Vietnamese Mekong Delta region. Our results implied that the application of a rate lower than 17.4 kg P/ha/crop could be extended to the other rice-growing (double/triple rice) areas in the Vietnamese Mekong Delta region or other paddy rice on alluvial soils in Asia.

Evolution of watershed phosphorus buffering capacity and its response to land-use change in Poyang Lake basin, China

The watershed buffering capacity is an important pivot to regulate phosphorus (P) pressure in aquatic environment , and land use is a key factor for its regulation. However, the response mechanism of buffer capacity to land use change remains unknown. Based on the variation of “buffering capacity index” in the Poyang Lake basin from 1990 to 2019, the mechanism of their response relationship was revealed via quantifying watershed P retention threshold and P removal process in different landscapes. Results showed that the watershed P buffering capacity was significantly affected by the scale of landscape subject to certain conditions of net anthropogenic P inputs (NAPI) in the Poyang Lake basin. The decreases in agricultural land, grassland and wetland and the increase of artificial land jointly explained 66.9% of watershed P buffering capacity decrease before accumulative P retention reached the threshold. The contribution of land use to watershed P buffering capacity change decreased to 53.8% when the P retention exceeded the threshold. Decreasing in watershed P buffering capacity was closely related to the increase of P loss in cultivated land, and wetland P removal provided an optimized direction for restoring the watershed buffering capacity. The findings reinforce the understanding of P hysteresis on watershed environment, and provide a policy basis for developing sustainable P management and pollution control from the perspective of optimizing land-use. • The P buffering capacity affected by landscape scale subject to certain conditions of NAPI. • The response of watershed P buffering capacity to land-use changed when legacy P exceeded threshold. • Decreasing in watershed P buffering capacity was related to the landscapes with increased P loss. • Optimizing the distribution of wetlands may be an optimum way to improve buffering capacity.

Phosphorus sorption characteristics as influenced by major soil units in southern Ethiopia

AbstractBackgroundLimited soil nutrients in the soil are threat in crop production in Ethiopian soil. Low availability of phosphorus (P) is one amongst the most important crop yield‐limiting problems among the various reasons limiting P availability in tropical soils, P sorption is that the major one.AimTherefore, this study was done to identify P sorption characteristics of andosols, vertisols, and nitisols in Tachegnawgimbicho, Taba, and DelboAtwaro study sites in southern Ethiopia.MethodsAdsorption isotherms experiment was done using Langmuir and Freundlich models to spot the character of soils in their capability on P sorption and causation and to explain P sorption as influenced by the associated soil properties using SAS version 9.00.ResultsThe P sorption maxima (Xm) of andosols, vertisols, and nitisols were found to be 965, 810, and 706 μg g−1, respectively. Correlation analysis indicated that soil pH was negatively and significantly correlated with Xm (R2 = −0.88). The Langmuir affinity constant “k” was positively and significantly correlated (R2 = 0.981) with maximum phosphorus buffering capacity (MPBC) indicating bonding energy constant is a component of buffering capacity of soils. The Langmuir equation correlated significantly with P sorption maximum “b” and binding energy “k” indicating both parameters can be used for evaluating P sorption characteristics of the soils.ConclusionIn this finding, the path analysis coefficient revealed that clay and pH had direct effects on P sorption parameters. Sorption capacity is high in andosols followed by nitisols and vertisols. Andosols require more P fertilizer to maintain optimum P concentration in soil solution for crop growth as compared with nitisols and vertisols.

Influence path identification of topography, soil, hydrology and landscape on phosphorus buffering capacity in typical agricultural catchments in central subtropical China

The catchment phosphorus buffering capacity (PBF) determines the pressure-state-response relationship between anthropogenic P inputs and aquatic ecosystems at a catchment scale, and is affected by biogeochemical, hydrological, and ecological catchment characteristics. However, the complex relationship between these catchment characteristic factors and their impact pathways on PBF remains ambiguous, leading to large uncertainty in balancing agricultural productivity and water conservation via improving BF through management practices. In this study, the short-term buffering index, calculated from net anthropogenic P input and riverine P exports, was used to quantify the spatiotemporal variations in PBF in source agricultural catchments in the Dongting Lake basin. Partial least squares structural equation modeling was used to investigate the relationship between the PBF and the catchment characteristics. The results indicate that catchment PBF was directly determined by soil properties and hydrological conditions, while landscape patterns significantly mediated the effects of topography on soil and hydrology. Considering the pathway preferences of the model, landscape patterns could be the priority for characterizing and regulating PBF. According to a change-point analysis, the probability of PBF weakening increases dramatically when the proportion of farmland (Farm%) > 24.6%, degree of patch interspersion (Contagion index) < 64.5%, and Perimeter-Area Ratio Distribution (PARA) > 348.7. These findings provide new insights into catchment buffering mechanisms and can be used to promote the simultaneous achievement of agricultural production and environmental conservation goals.

Threshold phosphorus level of acidic soils of eastern India

It is imperative to have a practical indicator for assessing the potential for phosphorus movement from soil to surface waters causing environmental pollution. The present study was undertaken with two groups of acidic soils from the terai and red and laterite agro-climatic zone of eastern India to estimate their phosphorus threshold values and establish a simple model with the clay content as the principal variable. The mean phosphorus adsorption maximum and phosphorus buffering capacity were higher in lateritic than terai soil. The change-point soil test values at which water soluble phosphorus enhanced abruptly ranged from 32 to 68mgkg-1 and 28 to 63mgkg-1 with Bray-1 and Mehlich-1 method, respectively, for the soils of the terai zone. Similarly, it varied from 47 to 90mgkg-1 and 44 to 89mgkg-1, respectively, for the lateritic soils. Application of phosphatic fertilizers should not be allowed beyond the threshold level, which was considered 75% of the change-point soil test value to avoid the risk of the soil becoming a source of phosphorus pollution for surface water bodies. The simplified models of phosphorus threshold level (mg kg-1) developed with either of the extractants were "4.75 × clay content (%) - 30" and "6.00 × clay content (%) - 75" for terai and lateritic soil, respectively. These models can be extended to the soils with similar mineralogy but varying in clay content for sustainable phosphorus management without limiting crop production.

Water inflow and endogenous factors drove the changes in the buffering capacity of biogenic elements in Erhai Lake, China

Buffering capacity could provide a comprehensive view to recognize the response between external loads and water quality and help address the significant challenges associated with the reduction of lake pollution. However, quantification of the dynamic change in the holistic buffering capacity of biogenic elements in lakes and its driving mechanisms has not been fully understood. Taking Erhai Lake in China as an example, this study quantified the long-term (2000–2019) dynamic changes in buffering capacity and revealed key driving forces for the changes in buffering capacity. The results showed that nitrogen buffering capacity (NBC) and organic buffering capacity (CODBC) decreased during the past 20 years, while phosphorus buffering capacity (PBC) did not change significantly. Endogenous factors are the main controlling factors of buffering capacity. Specifically, algal biomass drove the change in NBC (interpretation rate of 62.2%); the adsorption and sedimentation effects of sediments maintained the relative stability of PBC (56.30%) while algal biomass indirectly impacted the PBC (1.69% only) by affecting the redox environment of the sediments; and algae-derived organic matter and refractory organic matter accumulation dominated the change in CODBC (61.4% and 32.8%, respectively). Water inflow is another controlling factor for NBC and CODBC due to dilution of lake water. This study indicated that the accumulation of endogenous loads and a decrease in water inflow drove the decrease in the lake's buffering capacity (mainly NBC and CODBC), which could help explain why the decrease in external loads in Erhai Lake has not yet reversed the trend of water quality decline. Our study highlights the importance of comprehensive buffering capacity improvement instead of simple external load control to optimize lake environmental management. In the future, attention should be given to controlling endogenous loads, especially preventing algal blooms, and to optimizing hydrodynamic conditions to cope with the decrease in water inflow.

Effect of Hydrological Connectivity on the Phosphorus Buffering Capacity of an Urban Floodplain

Floodplains can perform nutrient buffering functions and therefore influence the riverine nutrient dynamics depending on the extent of the hydrological connectivity. This work focused on quantifying the adsorption/desorption potential of a degraded floodplain of the Danube River (Lower Lobau) based on sediment characterization (grain size distribution, organic content, and P-fractions) and sediment type-specific P-adsorption via batch experiments. We established an adsorption/desorption budget model with a high temporal and spatial resolution. With this model, we identified spatial patterns related to hydrology and calculated the phosphorus buffering capacity of permanent and temporary floodplain water bodies. Sediment characteristics were defined by the distance to the inflow area and the hydrological connectivity of the floodplain water bodies. The main factor for the concentration of total phosphorus (Ptot) in the sediments was the grain size distribution. Ptot was ten times higher in silt-dominated sediments compared to gravel-dominated sediments. Inorganic phosphorus (Pinorg) ranged between 36 and 90% depending on the organic content of the sediments. Both the adsorption and the desorption potential of SRP (soluble reactive phosphorus) were highest in large, frequently connected water bodies and were strongly controlled by hydrology. The total adsorption potential of the floodplain was up to 40 times higher in wet years (e.g., 2002) than in dry years (e.g., 2003), when floodplain water bodies were connected less frequently to the main channel of the Danube. Up to 75% of the adsorbed SRP was desorbed and released into the water column after periods of connection. Consequently, SRP adsorption directly reduced the P-load in the Danube River main channel. The adsorption/desorption mechanisms worked as a buffering system by taking up the SRP imported during floods and releasing it over a longer period after the floods. This stimulated high primary production in the floodplain water bodies and impacted the overall P-retention of the floodplain.

Interpretation of soil phosphorus availability by Mehlich-3 in soils with contrasting phosphorus buffering capacity

ABSTRACT Increasingly rational use of phosphate fertilizers by agriculture is important, especially in Brazil, due to its importance for global food security and its high dependence on phosphate fertilizers for crop production. Thus, correlation and calibration researches with soil available phosphorus (P) extractants to improve the recommendation and the use of P are extremely important. Our objectives were (i) to determine soil P recovery rates and critical levels by the extractants Mehlich-1 (M1), Mehlich-3 (M3), and Ion Exchange Resin (RTI); [...]

Phosphate sorption indices as affected by the calcareousness of soils

An experiment was carried out to study the effects of calcareousness on phosphate sorption indices of soils using three representative calcareous soils, namely Sara (Aquic Eutrochrept), Gopalpur (Aquic Eutrochrept), and Ishurdi (Aeric Haplaquept) series of Bangladesh. Three non-calcareous soils, namely Belabo (Typic dystrudepts), Sonatala (Aeric Endoaquepts) and Ghatail (Aeric Haplaquept) series were also selected for comparison purposes. Phosphate sorption indices of soils were calculated using Langmuir and Freundlich isotherms. Isotherms were constructed taking one gram of air-dried sieved (&lt; 2 mm) soil into a 50 ml centrifuge tube, and subsequently adding seven initial P concentrations, namely 0, 1, 10, 25, 50, 100 and 150 μg/ml to each centrifuge tube employing a soil/solution ratio of 1 : 20 (w/v). According to the Langmuir equation, the amount of phosphate sorbed followed the order: Sonatala &gt; Ghatail &gt; Sara = Gopalpur &gt; Ishurdi &gt; Belabo. The abundance of amorphous iron rather than the calcareousness was putatively responsible for the high phosphate sorption capacity of soils. Maximum phosphorus buffering capacity (MPBC) of the calcareous soils ranged from 33.4 - 62.8 l/kg. Langmuir and Freundlich equations produced different values for soil P requirements (SPR) at 0.2 and 1.0 mg P/l. Calcareous soils would require 27 - 44 mg P/kg soil to attain 0.2 mg P/l soil solution, which is deemed sufficient for crop growth. The soils would require 32 - 58 mg P/kg soil to reach 1.0 mg P/l soil solution, which is regarded to be safe for soils in terms of susceptibility to P losses. The calculated Langmuir constant b values were higher than the threshold value of 0.07 l/mg for two of the calcareous soils. Therefore, even though the non-calcareous soils sorbed more phosphate, higher bonding energy of P sorption for calcareous soils makes them less vulnerable to loss via surface runoff.&#x0D; Dhaka Univ. J. Biol. Sci. 28(1): 93-110, 2019 (January)

Evaluation study for phosphorus mobilisation-release behaviour on different marine sediments: focus on phosphate sorption characteristics

Environmental contextPhosphorus is a key nutrient element associated with eutrophication in aquatic ecosystems. We studied phosphate sorption processes, which play a key role in phosphorus cycling, in sediments collected from 23 sites including estuary, coastal sea and aquaculture areas in China. The results show the influence of sediment type on phosphorus buffering capacity and allow better interpretation of phosphorus migration in aquatic ecosystems. AbstractPhosphorus is well known as an important nutrient element associated with eutrophication in the marine ecosystem, and its sorption on sediments plays a key role in its immobilisation in the bio-geochemical cycle. In this paper, the sorption behaviour of phosphorus onto sediments collected from 23 different sites in estuary, coastal sea and aquaculture areas of China was studied. The main aim is to determine the phosphorus sorption characteristics of these sediments thereby assessing their phosphorus buffering capacities. Both kinetic and equilibrium isotherms of the sorption and desorption of phosphorus were assessed. The resultant sorption and desorption kinetic curves fit well to a two-compartment first-order equation. The equilibration time was considered as 48h. The isotherms agreed well with the Freundlich and Langmuir equations. The hysteresis coefficient values showed an obvious sorption-desorption hysteresis. Decreasing salinity was favourable for the sorption ability in the range from 30 to 3. The mean values of the phosphorus sorption-desorption equilibrium concentration and the maximum phosphorus sorption capacity were 0.098mgL−1 and 0.086mgg−1 for sediments in the Changjiang Estuary and East China Sea shelf, and 0.138mgL−1 and 0.067mgg−1 for the sediments in the aquaculture area. The fractions of clay, calcite and organic matter influenced the sorption and retention abilities and the effects were different for sediments obtained from different origins.

Varying redox potential affects P release from stream bank sediments.

Sediments in streams that drain agricultural watersheds may be sinks that can adsorb P from the stream or sources that can release P to the stream. Sediment characteristics and environmental factors, including the oxidation-reduction (redox) potential of the water associated with the sediment, determine whether P will be adsorbed or released by the sediment. We investigated P adsorption and release by four sediments [three Holocene-age sediments (Camp Creek, Roberts Creek and Gunder) as well as Pre-Illinoian-age Till] that occur in Walnut Creek, a second-order stream in Jasper County, Iowa, that is representative of many small streams in the glaciated upper Midwest of the US. The effects of two redox potentials on phosphorus buffering capacity (PBC) and equilibrium phosphorus concentration (EPC) were evaluated in batch adsorption experiments. We also simulated aerobic and anerobic conditions over a 24-day period and measured solution-phase P concentrations in stirred systems where the sediments were isolated from the water by dialysis tubing. The batch experiment indicated that the EPCs of the three Holocene-age sediments were similar to one another and increased with decreasing redox potential. In the stirred flow reactors, more dissolved P was released from the Camp Creek and Roberts Creek sediments under anaerobic conditions than from the other sediments. This observation suggests that these two sediments, which are younger and higher in the stratigraphic sequence, are more likely to be P sources in suboxic settings. The P buffering capacity was greatest in the till. Where it is in contact with the stream water, the till is likely to serve as an adsorbing sink for P in the water column.

Low buffering capacity and slow recovery of anthropogenic phosphorus pollution in watersheds

Excess anthropogenic phosphorus in watersheds, transported with runoff, can result in aquatic eutrophication, a serious global water quality concern. Watersheds can retain phosphorus, especially in their soils, which can serve as a buffer against the effect of excessive use of phosphorus. However, whether there is a quantifiable threshold at which a watershed exceeds its optimal phosphorus buffering capacity (beyond which riverine loads would dramatically increase) remains unknown. Here we quantified a watershed phosphorus buffering capacity threshold based on accumulation data over 110 years in 23 watersheds of a large North American river basin with globally representative agricultural soils. We found a surprisingly low threshold of just 2.1 t P km−2 (0.03–8.7 t P km−2). Beyond this, further P inputs to watersheds cause a significant acceleration of P loss in runoff. Using a simple exponential decay model, the time estimated to eliminate legacy P via runoff in our watersheds ranges from ~ 100 to over 2,000 years. The rapidity with which the watershed buffering threshold can be surpassed during accumulation, particularly given current anthropogenic phosphorus input rates, versus the long return to baseline suggests that new strategies to reconcile watershed activities and water quality are urgently needed. Watersheds have a low buffering capacity for phosphorus inputs, and their recovery from phosphorus pollution can take over 2,000 years, according to an analysis of phosphorus data from a large North American river.

Decoupled water-sediment interactions restrict the phosphorus buffer mechanism in agricultural streams

Our study aimed to explore the effects of agriculture on the phosphorus buffer capacity of 11 headwater streams in Austria. We used phosphorus adsorption curves and re-suspension experiments to determine both, the potential of the sediments to act as phosphorus source or sink and the actual phosphorus exchange between water and sediments. Additionally, we determined the alkaline phosphatase activity (APA) in epilithic and epipsammic biofilms as indicator for the phosphorus demand of the benthic and hyporheic community. We hypothesized that highly polluted streams will show decreased phosphorus buffer capacities, which were either due to saturation or restricted water-sediment interactions.Our results support the second hypothesis. Fine sediment accumulations, organic matter content, and phosphorus concentrations in water and sediments increased with percent cropland in the catchment. Below SRP concentrations of 120μgL−1 in the stream water, sediments showed a high potential for phosphorus release, with zero equilibrium phosphorus concentrations (EPC0) being more than twice as high as SRP concentrations. Above 150μgL−1, EPC0 reached only 20–50% of SRP concentrations, indicating a high potential of the sediments to act as phosphorus sinks. These findings were confirmed by phosphorus uptake of these sediments during re-suspension. While APA in epilithic biofilms decreased with increasing SRP concentrations, APA in epipsammic biofilms showed the reverse pattern, indicating a restricted phosphorus supply of the hyporheic community despite phosphorus surplus in the water column.Our study shows that inputs of fine sediments from agricultural sources may reduce the phosphorus buffering mechanism of stream sediments through restrictions of water-sediment interactions. Consequently, water column and sediment processes are increasingly decoupled and phosphorus-rich stream water will not effectively reach the reactive sites in the sediments responsible for uptake. Therefore, phosphorus mitigation measures in stream ecosystems must comprise sediment management in the catchment as well as in-stream measures for the rehabilitation of the hyporheic zone.

Relation between various soil phosphorus extraction methods and sorption parameters in calcareous soils with different texture

The aim of this study was to investigate the influence of soil texture on phosphorus (P) extractability and sorption from a wide range of calcareous soils across Hamedan, western Iran. Fifty seven soil samples were selected and partitioned into five types on the basis of soil texture (clay, sandy, sandy clay loam, sandy loam and mixed loam) and the P extracted with calcium chloride (PCaCl2), citrate (Pcitrate), HCl (PHCl), Olsen (POls), and Mehlich-3 (PM3) solutions. On the average, the P extracted was in the order PHCl>PM3>Pcitrate>POls>PCaCl2. The P extracted by Pcitrate, PHCl, POls, and PM3 methods were significantly higher in sandy, sandy clay loam and sandy loam textures than clay and mixed loam textures, while soil phosphorus buffer capacity (PBC) was significantly higher in clay and mixed loam soil textures. The correlation analysis revealed a significant positive relationship between silt content Freundlich sorption coefficient (KF), maximum P sorption (Qmax), linear distribution coefficient (Kd), and PBC. All extractions were highly correlated with each other and among soil components with silt content. The principal component analysis (PCA) performed on data identified five principal components describing 74.5% of total variation. The results point to soil texture as an important factor and that silt was the crucial soil property associated with P sorption and its extractability in these calcareous soils. DPSM3-2 (PM3PM3+Qmax×100) and DPScitrate (PcitratePcitrate+Qmax×100) proved to be good indicators of soil's potential P release in these calcareous soils. Among the DPS, 21% of soils reported DPSM3-2, values higher than the environmental threshold, indicating build-up of P and P release. Most of the studied sandy clay loam soils had exceeded the environmentally unacceptable P concentration. Various management practices should be taken into account to reduce P losses from these soils. Further inorganic and organic P fertilizer inputs should be reduced in some parts of studied area.

Substitution of Clay Content for P-Remaining as an Index of the Phosphorus Buffering Capacity for Soils of Rio Grande do Sul

Mehlich-1 soil extract is currently used in Rio Grande do Sul (RS) and Santa Catarina (SC) States, in Brazil, to evaluate soil phosphorus available to plants and Mehlich-1 is sensitive to soil buffering capacity. This limitation is overcome partly by soil separation into buffering classes based on soil clay content. However, soil clay content has some technical and operational limitations, such as the underestimation of soil clay levels in soils under no-till. The aim of this study was to evaluate the remaining phosphorus (P-rem) compared to soil clay content as an index of the buffering capacity in soils of RS. The relationship between P-rem and soil clay content was assessed using 200 soil samples from a wide range of locations across the state. In 20 representative soil types, P-rem, soil clay content, P maximum adsorption capacity, total and pedogenic Fe contents, amount of P2O5 needed to increase soil P in 1 mg kg-1 extracted by Mehlich-1 and -3 methods and P capacity factor were determined. Furthermore, a pot experiment was carried out with plants to determine soil P content extracted by Mehlich-1 and -3 at the maximum technical efficiency (MET) and the maximum absorption efficiency (MEA). Correlation analyses were performed between P-rem and soil clay content and, with the attributes of soils involving the P buffering capacity. The relationship between P-rem and soil clay content was described as a decreasing exponential function; however, the adjustment was not adequate to propose critical levels for P-rem. The P-rem index was superior to soil clay index in practically all relationships with the attributes related to the soil buffering capacity of the soils. In some cases, the indexes were similar; however, P-rem was not lower than the soil clay content in any case. The P-rem is a more reliable index to represent soil buffering capacity than the soil clay content in soils from RS, and P-rem might be used to implement soil classes for Mehlich-1 and Mehlich-3 determinations of soil P.

Phosphorus retention of forested and emergent marsh depressional wetlands in differing land uses in Florida, USA

The translocation of phosphorus (P) from terrestrial landscapes to aquatic bodies is of concern due to the impact of elevated P on aquatic system functioning and integrity. Due to their common location in depressions within landscapes, wetlands, including so-called geographically isolated wetlands (GIWs), receive and process entrained P. The ability of depressional wetlands, or GIWs, to sequester P may vary by wetland type or by land use modality. In this study we quantified three measures of P sorption capacities for two common GIW types (i.e., emergent marsh and forested wetlands) in two different land use modalities (i.e., agricultural and least impacted land uses) across 55 sites in Florida, USA. The equilibrium P concentration (EPC0) averaged 6.42 ± 5.18 mg P L−1 (standard deviation reported throughout); and ranged from 0.01–27.18 mg P L−1; there were no differences between GIW type or land use modality, nor interaction effects. Significant differences in phosphorus buffering capacity (PBC) were found between GIW types and land use, but no interaction effects. Forested GIWs [average 306.64 ± 229.63 (mg P kg−1) (µg P L−1)−1], and GIWs in agricultural settings [average 269.95 ± 236.87 (mg P kg−1) (µg P L−1)−1] had the highest PBC values. The maximum sorption capacity (Smax) was found to only differ by type, with forested wetlands (1274.5 ± 1315.7 mg P kg−1) having over three times the capacity of emergent GIWs (417.5 ± 534.6 mg P kg−1). Classification trees suggested GIW soil parameters of bulk density, organic content, and concentrations of total P, H2O-extractable P, and HCl-extractable P were important to classifying GIW P-sorption metrics. We conclude that GIWs have high potential to retain P, but that the entrained P may be remobilized to the wetland water column depending on storm and groundwater input P concentrations. The relative hydrologic dis-connectivity of GIWs from other aquatic systems may provide sufficient retention time to retain elevated P within these systems, thereby providing an ecosystem service to downstream waters.

Phosphorus Sorption Capacity of Six Iowa Soils before and after Five Years of Use as Vegetative Treatment Areas

Abstract. Accumulation of phosphorus in soil is a major factor limiting the operational life (period of time where the soil can serve as an effective phosphorus sink) of land application waste disposal systems. Better evaluation of phosphorus operational life requires improved understanding of how manure application to soil can affect its phosphorus sorption characteristics. In this study, laboratory experiments were conducted to investigate the impact of feedlot runoff effluent application on phosphorus sorption capacities, equilibrium phosphorus concentrations, and phosphorus buffering capacities of six Iowa soils. Soil samples were collected from vegetative treatment areas that had received feedlot runoff application for the previous five years and from a paired grassed area that did not. Subsamples of each soil were incubated with a series of 12 phosphorus solutions ranging in concentration from 0 to 200 mg P/L to determine the sorption characteristics and results fitted to the Langmuir model to determine the phosphorus equilibrium concentration, phosphorus buffering capacity, and maximum phosphorus sorption capacity. Results indicated that vegetative treatment areas generally had elevated phosphorus equilibrium concentrations, indicating an elevated risk of loss of dissolved phosphorus. In most cases, the ability of the soil to sorb phosphorus was significantly increased, as was the remaining phosphorus sorption capacity of the soil. These results indicate that vegetative treatment area life could be greatly extended due to soil property modifications that occur as a result of system operation.

Phosphorus sorption characteristics of some representative soils of south India

Studies were conducted to investigate P sorption characteristics of representative soils from ten locations of alfisol and ultisol of India using Langmuir and Freundlich equations. The P sorption maxima (b) of soils derived from Langmuir equation in alfisol varied from 520.6 to 574.7 ?g g-1 and ultisol varied from 561.6 to 678.1 ?g g-1. The maximum phosphorus buffering capacity (MPBC) in alfisol ranged from 80.7 to 180.2 ml ?g-1 and ultisol ranged from 162.1 to 284.4 ml ?g-1. Phosphorus sorption maxima was significantly correlated with clay (r2=0.70), Al (r2= 0.73) and Fe (r2=0.81) forms, MPBC (r2=0.67) and Freundlich constants (r2=0.82). The standard P requirement (SPR) to maintain 0.2 mg l-1 P in soil solution for alfisol ranged from 15.62 to 27.62 mg kg-1 and ultisol from 41.98 to 46.35 mg kg-1. The SPR (0.2 mg l-1) was significantly correlated with binding strength coefficient (r2= 0.97) and binding strength coefficient supporting the fact that energy coefficient of a soil is an important index for planning P management strategies. Among the two soil orders in order to maintain optimum P concentration in soil solution for crop growth, ultisol will be required to supply with more P fertilizer as compared to alfisol.SAARC J. Agri., 13(1): 14-26 (2015)

Phosphorus buffering capacity of substrate clays and its significance for plant cultivation

AbstractPeat is commonly used as the main component of horticultural substrates, but it has a very low buffering capacity for the anionic macronutrient phosphorus (P), which can be increased by the addition of clays. The aim of this study was to characterize the P adsorption capacity of different substrate clays and to evaluate its significance for plant P uptake. Substrate clays were characterized with a single‐point batch experiment and adsorption and desorption isotherms. The data were fitted to the Langmuir equation for a calculation of the maximum adsorption capacity. Additionally, the contents of oxalate extractable Fe and Al (ΣFeox + Alox) were determined. The influence of a varying P adsorption capacity of the clays on the P availability to plants in the respective peat–clay substrates and pure peat was investigated in a growth experiment with Impatiens walleriana fertigated with 0, 17, and 35 mg P L−1 solution, respectively.The observed and calculated (Langmuir) P adsorption capacity of the clays could be well‐characterized by both the batch experiment and the adsorption isotherms and was highly correlated with the ΣFeox+Alox. A higher P adsorption capacity of the clay amendment in mixed substrates resulted in a lower P concentration in the substrate solution, while the CAT extractable P concentration (PCAT) was the same. Plant growth and shoot P concentrations were enhanced in the substrates, showing a higher P adsorption capacity, since plants were able to take up the whole amount of PCAT, and also part of the non‐CAT extractable P. However, the release rate was too low to ensure optimal plant growth, which was in accordance with the result of the desorption experiment. The absolute extent of P release was increased with the increasing P adsorption capacity of the clays and higher degree of P saturation (DPS).