Phosphorus activators contribute to legacy phosphorus availability in agricultural soils: A review

Rhizoplane Bacteria and Plant Species Co-determine Phosphorus-Mediated Microbial Legacy Effect

Much effort has been directed toward increasing the availability of soil residual phosphorus (P). However, little information is available for the P fertilization-induced biotic P legacy and its mediation of plant P uptake. We collected microbial inocula from a monoculture maize field site with a 10-year P-fertilization history. A greenhouse experiment was conducted to investigate whether bacterial communities, as a result of different P-fertilization history (nil P, 33 and/or 131 kg P kg ha-1 yr-1), affected the growth of a conspecific (maize) or heterospecific (clover) plant, at two levels of current P application (5 and 30 mg P kg-1 soil; P5 and P30). Deep amplicon sequencing (16S rRNA) was used to determine the maize and clover root-associated bacterial microbiome in different rhizocompartments (rhizoplane, rhizosphere, bulk soil). For both maize and clover, rhizocompartment and host identity were the dominant factors shaping bacterial assemblages, followed by P supply level and the inoculum effect was smallest. Bacterial operational taxonomic unit (OTU) numbers decreased from bulk soil to rhizoplane, whilst specific OTUs were enriched from bulk soil to rhizoplane. A clear hierarchical habitat filtering of bacterial communities was observed in the rhizoplane of the two plant species. The functional prediction of dominant bacterial taxa in the rhizoplane differed between clover and maize, and clover microbiota were more closely associated with P metabolism and maize with carbon cycling. More connected and complex interactions were observed in the clover rhizoplane compared to maize. The microbial legacy effect caused by long-term P fertilization is overridden by host identity and rhizocompartment. Our results highlight the importance of crop diversification in improving P efficiency. The fine-tuning of rhizosphere microbiome in host metabolism indicates that the functions of microbial communities should be integrated into P management to increase P use efficiency and sustainable food production.

Mitigation of Cd accumulation in rice from Cd-contaminated paddy soil by foliar dressing of S and P

Cadmium (Cd)-contaminated paddy soil has become a global agricultural safety issue. The application of foliage dressing with mineral elements to alleviate Cd toxicity in rice might offer a cost-effective and practical strategy for safe food production. In this study, a pot experiment was conducted to optimize foliar composition and dosage. Field experiments in two consecutive rice seasons were performed to investigate the effectiveness and mechanisms of foliage dressing. Foliar spray of S, P, and a mixture of both were effective to reduce the Cd concentration in rice grain. The maximum decrease by leaf-grain translocation was achieved at 84%, and the maximum decrease of bio-concentration was 69% in the stem. The reduction of Cd concentration in rice decreased the direct damage to the photosynthetic system, and then increased the rice growth. Foliage dressing relieved the oxidative stress of Cd to rice by decreasing the MDA content, and increasing antioxidant enzyme activities. Foliar spray with S likely reduced Cd accumulation in rice by minimizing the production of reactive oxygen species, improving the activities of enzymatic and non-enzymatic antioxidant defense systems, and manipulating glutathione synthesis. The detoxification of foliar spray with P was originated from the decrease of Cd translocation and maintaining photosynthetic machinery. These results indicated that foliage dressing with S and P has great potential for the remediation of vast agricultural fields.

Synergistic effects of anionic polyacrylamide and gypsum to control phosphorus losses from biogas slurry applied soils

Excessive application of phosphorus (P) fertilizer to the agriculture soil can lead to the P loss to the aquatic ecosystem. Three soils from different land use (tea, paddy, and vegetable soils) were treated with biogas slurry (BS) at rate of 79.8 kg ha^-1, anionic polyacrylamide (PAM) at rate of 12.5, 25 and 50 kg ha^-1, Gypsum (Gy) at rate of 5t ha^-1, and the control (Ck) without treatment, to control P losses in a laboratory batch experiment. The soil solution was analyzed for total P (TP), dissolved reactive P (DRP) and total dissolved P (TDP). Particulate P (PP) and dissolved unreactive P (DURP) were calculated by subtracting DRP from TP and TDP, respectively. The DRP was within a range of 68-98% of TP whereas PP varied in a range of 2-32% of TP and DURP was within a range of 0.1-19% of TP, depending on soil types and different treatments. The addition of PAM at a high rate and Gy together on the soil after BS application reduced the release of TP by 54, 46, and 51% and that of DRP by 61, 49, and 53% for tea, paddy and vegetable soils, respectively. However, the application of BS with PAM alone promoted the release of DRP by 77, 86, 70% for tea, paddy, and vegetable soils, respectively. This study suggests that the synergic application of PAM and Gy on soils after BS addition can be a good strategy to reduce P losses.

Isolation and characterization of phosphate solubilizing bacteria from rhizosphere soils of the Yeyahu Wetland in Beijing, China

Phosphate solubilizing bacteria (PSB) can convert insoluble forms of phosphorus (P) to accessible forms. 11 strains of PSB, including five inorganic phosphate solubilizing bacteria (IPSBs) and six organic phosphate solubilizing bacteria (OPSBs), were isolated from rhizosphere soils of three plants Scirpus planiculmis, Zizania latifolia, and Phrnagmites australis in the Yeyahu Wetland of Beijing, China to investigate P-solubilizing activities. In addition, the distributions of P fractions in soil samples were also observed. All strains evaluated above 1.0 by the ratio of transparent circle diameter to colony diameter (D/d) on Ca₃(PO₄)₂ or lecithin plates were identified by 16S rRNA sequencing. Results showed that Ca-bound P (Ca-P) was the main species of inorganic P (IP), and highly resistant organic P (HR-OP) accounted for the most part of organic P (OP). These strains were identified as bacterial species of Enterobacter asburiae, Acinetobacter sp., Bacillus cereus strain, and so on. The most efficient IPSB strain could convert over 430 mg L^-1 orthophosphate, while the equivalent OPSB strain only liberated less than 4 mg L^-1 in liquid culture, which indicated that IPSBs have a better P-solubilizing ability than OPSBs in rhizosphere soils of the Yeyahu Wetland and IPSBs are likely to regulate the P transformation process in this wetland. Graphical abstract ᅟ.

Influence of rainfall intensity and slope on suspended solids and phosphorus losses in runoff

Suspended solids (SS) and phosphorus (P) losses in rainfall generated runoff can lead to the deterioration of surface water quality. Simulated rainfall experiments were conducted to investigate the effects of rainfall intensity (30, 50, 65, and 100 mm h^-1) and land slope (0°, 5°, and 10°) on SS and P losses in runoff from experimental rigs containing bare land soil and soil planted with grass (tall fescue). In addition, total phosphorus (TP), particulate phosphorus (PP), and dissolved phosphorus (DP) losses in runoff were also measured. Results showed that tall fescue could reduce loads of SS by 86-99.5%, PP by 92-98.5%, and TP by 55-89.8% in runoff compared with losses from bare soil; this is due to a combination reduced raindrop kinetic energy at the soil surface, reduced soil erodibility in the presence of plant roots and shoots, and an increase in roughness and consequently reduced overland flow velocity resulting in the trapping of particles. Linear relationships between losses of SS and TP and between TP and PP in runoff were significant (R² > 0.93) in both bare soil and grass. In addition, SS and TP losses increased greatly significantly with rainfall intensity and slope. The influence of rainfall intensity on SS and P losses was greater than the influence of slope. Simple linear regressions were constructed between losses of SS and P, the rainfall intensity (30 to 100 mm h^-1), and land slope (0° to 10°). The multiple regression equations of SS and P losses in runoff established in this study can provide a simple predicting approach for estimating the non-point source pollution load of SS and P arising from rainfall.

Effects of bok choy on the dissipation of dibutyl phthalate (DBP) in mollisol and its possible mechanisms of biochemistry and microorganisms

Phytoremediation is an ecologically sustainable method for remediating contaminated soils, however, research on phytoremediation and its mechanisms are still rarely reported. The highest dibutyl phthalate (DBP) dissipation rate was 91% in 0-3mm bok choy rhizosphere via a 45-day rhizo-box experiment, and bok choy could regulate soil nutrients by increasing soil ammonia nitrogen (AN) and available phosphorus (AP). The biochemistry mechanism of interaction between dissolved organic matter (DOM) and DBP was also elucidated by various spectroscopy techniques. It was found that the alkyl ester in DBP produced the fastest response during the binding process, and the aromatic, hydroxyl and phenolic groups of the DOM humic-like substances preceded amide in DOM protein-like substance. It was found that DBP pollution reduced the Chao1 richness and Shannon index of bacteria in black soil via a pot experiment and high-throughput sequencing, which disturbed the metabolic activities and functional diversity of microorganisms in Mollisol. The microbial abundance increased in bok choy amendments, which has a specific microbial community structure and a high abundance of Actinobacteria and Acidobacteria. We concluded that some enriched genera were responsible for DBP dissipation, Alsobacter, Lacibacter, Myceligenerans, Schrenkiella parvula and Undibacterium. The findings of this study revealed that the possible biochemistry and microbial mechanisms of phytoremediation promoting the DBP dissipation in rhizosphere Mollisol and provided more useful information for phytoremediation of organic pollutants.

Phosphate-solubilizing bacteria will not significantly remobilize soil cadmium remediated by weathered coal

Cadmium (Cd) re-mobilize by phosphate-solubilizing bacteria (PSB) from immobilization contaminated soil has drawn great attention due to its serious threat to human health through food chain. However, Cd binding with weathered coal (WC), an effective Cd immobilization material, will be re-mobilized by PSB or not is still unclear. In this study, the soil and sand pots with Cd were respectively mixed with the weight fractions of 0‰, 2‰, and 3‰ WC, inoculated with or without PSB, and planted with Amaranthus mangostanus L. The experimental results indicated that: (i) Cd in soil was transformed into organic fraction with WC, which has been led to the Cd accumulation concentrations in roots and shoots reduced by 38.8% and 20.5%, respectively; (ii) PSB could promote the concentration of exchangeable-Cd fraction and soil Cd uptake by amaranth in all treatments; and (iii) WC application in sand pot respectively reduced the Cd accumulation by 47.5% in roots and 24.1% in shoots, but PSB inoculation showed no significant effect on Cd accumulation in plants under WC application. SEM, zeta potential, and FT-IR results showed that PSB inoculation after Cd immobilized by WC had no influence on the microstructure, amount of negative charge, type, and content of functional groups in WC, indicating that organic fraction Cd in WC was not re-mobilized by PSB. Therefore, the application of WC in contaminated soil was conducive to transforming Cd in organic-bound forms and intensifying Cd immobilization effects.

Biochar amendment effects on the activities of soil carbon, nitrogen, and phosphorus hydrolytic enzymes: a meta-analysis

The aim of this meta-analysis was to synthesize the effects of biochar amendment on soil enzyme activities (SEAs) related to carbon (C), nitrogen (N), and phosphorus (P) cycling. Based on 401 paired comparisons from 43 published studies, the SEAs and main influential factors were analyzed in response to biochar characteristics, soil properties, and experiment conditions. Results showed that biochar additions to soils overall increased the N- and P-cycling SEAs by 14 and 11%, respectively. The enhancement of the N- and P-cycling SEAs was mainly attributable to the microbial stimulation by biochar properties (i.e., nutrient content and porosity) and soil nutrients (e.g., soil organic C and total N). The enhancement was the most significant under the conditions with biochars produced at low temperatures and using feedstock materials with high nutrient content, and biochar applications in acidic or neutral soils, coarse or fine soils, and farmland soils. Biochar additions to soils overall reduced the C-cycling SEAs by 6.3%. The C-cycling SEAs were greatly suppressed under the conditions with low and very high biochar loads, biochars produced at high temperatures and with feedstock materials of herb and lignocellulose, and biochar applications in alkaline, fine, and forest soils. The results were mainly related to the adsorption and inhibition effects of biochars and soil properties (e.g., liming effect, high biochar porosity and aromatic C content) on fungi and the enzymes. Biochar feedstock, C/N and load, and soil total N were the main influential factors on the SEAs. The results from this study demonstrate that biochar amendment is beneficial to improving soil N and P cycling and C sequestration.

Identification of environmental factors controlling phosphorus fractions and mobility in restored wetlands by multivariate statistics

Phosphorus is a dominant environmental factor in fostering eutrophication, and its biogeochemical behavior has attracted much attention. This study investigated the distribution of phosphorus fractions and the adsorption-desorption characteristic in the soils of wetlands converted from paddy fields with a restoration duration of 1, 2, 3, 5, 13, or 19 years. The results demonstrated the content of total phosphorus (TP) first increased, which was then reversed until the process stabilized after 5 restoration years. Labile inorganic phosphorus (L-Pi), labile organic phosphorus (L-Po), iron-aluminum-bound phosphorus (Fe.Al-P), and humic phosphorus (Hu-P) peaked at 1-3 restoration years, respectively, while moderately labile organic phosphorus (Ml-Po), calcium-magnesium-bound phosphorus (Ca.Mg-P), and residual phosphorus (Re-P) decreased within 0-5 restoration years. During the 5th to 19th restoration years, the contents of all phosphorus fractions stabilized within a minor fluctuating range. Redundancy analysis (RDA) results indicated that total nitrogen (TN) and soil organic matter (SOM) are the important environmental factors controlling redistribution of phosphorus fractions. The capability of restored wetlands to retain phosphorus increased first and then decreased with the extension of the restoration duration. Path analysis (PA) results demonstrated that pH, TN, and Fe are the primary factors for the capacity of soil to retain phosphorus, followed by SOM, Mn, and electrical conductivity(EC). Fe.Al-P and Hu-P had a higher release risk with approximate amounts of 197.25-337.25 and 113.28-185.72 mg/kg during the first stage of restoration, which needs to be focused.

Can Phosphorus from Recycled Fertilisers Replace Conventional Sources? An Agronomic Evaluation in Field-Scale Experiments on Temperate Luvisols

Facing phosphate rock scarcity, growing food requirements and pollution problems with phosphorus (P)-containing waste, re-using P as fertiliser is becoming a real need. Innovative fertilisers from sewage sludge ash, animal bones and blood, activated by phosphorus solubilising microorganisms (PSM), were tested in field experiments with winter or spring wheat and compared with commercial fertilisers (superphosphate, phosphorite). Three levels of P doses were established (17.6, 26.4 and 35.2 kg/ha). This paper discusses the fertilisers’ impact on total soil P content and on the P content and P accumulation in wheat grain and straw, weeds and post-harvest residues. Recycled fertilisers maintained soil P stocks and supplied plants with P in the same way as traditional fertilisers, and ensured a comparable P pool in the post-harvest residues to traditional fertilisers. They also did not favour weeds during competitive crop-weed interactions. The PSM included in waste-fertilisers did not exert an evident effect on the soil P content or on the P content and P accumulation in plant biomass. The findings show the potential of recycled fertilisers to act as a substitute to fertilisers from primary sources. Further field research is needed to settle the question of the reasonability of PSM inclusion into fertilisers.

Novel phosphate-solubilising bacteria isolated from sewage sludge and the mechanism of phosphate solubilisation

A great amount of insoluble phosphate in agricultural soils is not available for crops. Three strains of bacteria (Bacillus megaterium YLYP1, Pseudomonas prosekii YLYP6 and Pseudomonas sp. YLYP29) isolated from activated sludge and soil could efficiently solubilise tricalcium phosphate. In particular, the novel strain P. prosekii YLYP6 produced 716 mg L^-1 of available phosphate within 6 days under the optimal culture conditions [20 °C, pH 7.9, inoculum size of 0.5% (v:v)] determined by response surface methodology. P. prosekii YLYP6 demonstrated efficient phosphate solubilisation in response to broad variations in pH (5-9) and temperature (15-35 °C). The phosphate solubilisation curves of the strains fit well with a first-order kinetic model (R² > 0.939), with a half-life of 1.51-5.94 d for 5.0 g L^-1 calcium phosphate. Continuous culture experiments combined with scanning electron microscopic observations and gas chromatography-mass spectrometry analysis revealed that 2,3-dimethylfumaric acid, gluconic and N-butyl-tert-butylamine that were produced by P. prosekii YLYP6 were responsible for phosphate solubilisation by supplying H⁺ ions and organic anions. Efficient phosphate solubilisation in actual soil by P. prosekii YLYP6 demonstrated the strong application potential to reduce the use of chemical P fertilisers and the resulting agricultural nonpoint pollution.

Enhanced Phosphorus Release from Phosphate Rock Activated with Lignite by Mechanical Microcrystallization: Effects of Several Typical Grinding Parameters

Recently, microcrystallization technology has gained much interest because of the enhanced dissolution of the target sample and promotion of the sustainable development of agriculture. Phosphorus (P) is one of the most important nutrients for increasing crop yield; the increase in effective P ratio directly from raw phosphate rock (PR) powder by mechanical grinding to increase its microcrystallinity is believed to be the best choice for this purpose. This study reports the improvement in the activation property of PR powder with different lignite ratios (1%, 2%, 3%, and 5%), particularly the relationship between particle-size distribution, specific surface area, granule morphology, and the citric acid-soluble P. It was found that a 3% lignite addition was the optimal treatment for increasing the release of citric acid-soluble P. The maximum total amount of dry matter from rapeseed cultivation and the available P after the test increased by 56.1% and 89.6%, respectively, with direct use of PR and microcrystallized PR powder (PR2), compared with the control test without any addition of phosphate minerals.

Characterization of phosphate solubilizing bacteria isolated from heavy metal contaminated soils and their potential for lead immobilization

Phosphate solubilizing bacteria (PSB) were isolated from heavy metal contaminated soils and their potentials for lead (Pb) immobilization in soil were studied in this paper. 53 PSB strains were isolated and their minimum inhibitory concentrations (MICs) for lead were determined. The results showed that strains B3, B4, B10, F2-1 and L1-5 had relatively high lead resistant capabilities with MICs ranged from 0.5 to 8 mM, and were identified as species of Leclercia adecarboxylata and Pseudomonas putida by 16S rRNA. The most efficient PSB strains could solubilize 200 mg L^-1 of P, and phosphate solubilizing capacity of those PSBs was related to the concentrations of organic acids, acid phosphatase activity and pH. Furthermore, the growth pattern of L1-5 strain with the presence of Pb(NO₃)₂ was observed and a mechanism of biomineralization of lead ions in bacteria biomass was determined by FT-IR and XRD analyses. Results showed that high concentration of lead can inhibit the growth of PSBs, and L1-5 isolate can transform lead ions into lead hydroxyapatite and pyromorphite. The PSBs, which possessing the properties of immobilizing lead through phosphate solubilization and biomineralization could be exploited for bioremediation of Pb polluted soils in future.

Struvite—An Innovative Fertilizer from Anaerobic Digestate Produced in a Bio-Refinery

This paper presents the results of a pot experiment aimed at the assessment of the fertilizer value of struvite, a precipitation product obtained from a liquid fraction of the digestate. The effects of struvite (STR), struvite + ammonium sulphate (STR + N) and ammonium phosphate (AP) treatments were examined on maize and grass cultivation on silty loam and loamy sand soil. The crop yields were found to depend on both the soil type and experimental treatment. Crop yields produced under STR and STR + N exceeded those under the control treatments by respectively 66% and 108% for maize, and 94% and 110% for grass. Crop yields under STR + N were similar or greater than those under the AP treatment. The nitrogen recovery by maize and grass reached respectively 68% and 62% from the struvite and 78% and 52% from AP. The phosphorus recovery by maize and grass reached 7.3% and 4.8%, respectively, from struvite (i.e., STR and STR + N), which was lower than that from the AP (18.4% by maize and 8.1% by grass).

Change in the Distribution of Phosphorus Fractions in Aggregates under Different Land Uses: A Case in Sanjiang Plain, Northeast China

Phosphorus in agro-ecosystems has attracted much attention due to its impact on the nutrient supply of plants and the risk of loss of non-point source pollution. This study investigated the fraction distribution and release of phosphorus from soil aggregates structure under different land uses (rice, maize and soybean). The soil aggregates were characterized as large macro-aggregates (L-mac, >1 mm), small macro-aggregates (S-mac, 0.25⁻1 mm), micro-aggregates (MIC, 0.053⁻0.25 mm) and silt clay (SC, <0.053 mm) with the wet-sieving method. A sequential chemical extraction scheme was used to separate phosphorus into labile inorganic phosphorus (L-Pi), labile organic phosphorus (L-Po), moderately labile organic phosphorus (Ml-Po), iron-aluminum bound phosphorus (Fe.Al-P), calcium-magnesium bound phosphorus (Ca.Mg-P), humic phosphorus (Hu-P) and residual phosphorus (Re-P). Experimental results indicated that soil aggregates were mainly S-mac and MIC, followed by L-mac and SC, and they accounted for 52.16%, 25.20%, 14.23% and 8.49% in rice fields, 44.21%, 34.61%, 12.88% and 8.30% in maize fields, and 28.87%, 47.63%, 3.52% and 19.99% in soybean fields, respectively. Total nitrogen (TN), soil organic matter (SOM), Fe and Mn in soil aggregate fractions decreased with the reduction in soil aggregate grain-sizes. For phosphorus fractions (P-fractions), Fe.Al-P and Re-P tended to condense in L-mac and S-mac. MIC and SC were the primary carriers of Ca.Mg-P. Adsorption isotherm simulation results demonstrated that L-mac and S-mac have a strong capacity to retain phosphorus. In rice fields, phosphorus bioavailability and utilization rate were high. However, the P-fractions there were easily changed under aerobic-anaerobic conditions. Therefore, the risk of phosphorus loss during drainage should be given considerable attention.

Influence of phosphate amendment and zinc foliar application on heavy metal accumulation in wheat and on soil extractability impacted by a lead smelter near Jiyuan, China

Higher concentrations of Pb and Cd in wheat grains harvested in several lead-smelting-polluted areas in northern China have been reported. This field experiment was conducted to investigate the effect of phosphate amendment and Zn foliar application on the accumulation of Pb and Cd in wheat grains grown in a lead-smelting impacted area in Jiyuan in northern China. The soil (total Pb and Cd are 261 and 2.65 mg kg^-1, respectively) was amended with superphosphate at P:Pb ratios (mol:mol) of 1.90 or 2.57 either during wheat (Triticum aestivum L.) planting or a split of 60% of the phosphate applied at planting, with remaining 40% applied at the jointing stage. Zn was sprayed on the canopy of the wheat plants at the jointing stage. The phosphate amendment resulted in lower DTPA (diethylene triamine pentaacetic acid)-extractable Pb (1.39-10.7% lower than the control) and Cd (0.040-7.12%) in the soil. No significant effect of split application of phosphate was found on Pb and Cd availability in soil; however, higher rates of P resulted in lower Pb and Cd availabilities in the soil. Grain Pb (5.41-21.5% lower than the control), Cd (3.62-6.76%), and Zn (4.29-9.02%) concentrations were negatively affected by the phosphate application, with higher rates of phosphate resulting in lower grain heavy metal concentrations. Foliar application had no statistically significant influence on Pb and Cd concentrations in the grain (p > 0.05). Although Pb and Cd concentrations in wheat grains were reduced by the phosphate application, their concentrations were still much higher than the maximum permissible concentrations for wheat in the national standards of China. The results suggest that it is feasible to reduce wheat grain concentrations of Pb and Cd in Pb-smelting-polluted areas in northern China by soil application of superphosphate; however, the split application of the phosphate and the foliar application of Zn compounds do not have substantial impact on reducing accumulation of Pb and Cd in the wheat grains.

Phosphate sorption and desorption by two contrasting volcanic soils of equatorial Africa

Volcanic soils cover 1% of the Earth's surface but support 10% of the world's population. They are among the most fertile soils in the world, due to their excellent physical properties and richness in available nutrients. The major limiting factor for plant growth in volcanic soils is phosphate fixation, which is mainly attributable to active species of aluminium and iron. The sorption and desorption of phosphate is studied on the surface horizons of two African agricultural soils, a silandic Andosol (Rwanda) and a vitric Andosol (São Tomé and Principe). Both soils are slightly acid. The silandic Andosol is rich in active aluminium forms, while the vitric Andosol has high amounts of crystalline iron and aluminium oxides. Sorption isotherms were determined by equilibrating at 293K soil samples with phosphate solutions of concentrations between 0 and 100 mg P L^-1 in NaNO₃; phosphate was determined by visible spectrophotometry in the equilibrium solution. To study desorption, the soil samples from the sorption experiment were equilibrated with 0.02 M NaNO₃. The isotherms were adjusted to mathematical models. In almost all the concentration range, the adsorption of phosphate by the silandic Andosol was greater than 90% of the amount added, being lower in the vitric Andosol but always higher than 65%. The high sorption by the silandic Andosol is attributed to its richness in non-crystalline Fe and Al, while in the vitric Andosol crystalline iron species seem to play a relevant role in the adsorption. The sorption isotherms of both soils fitted to the Temkin model, the adjustment to the Langmuir or Freundlich models being unsatisfactory; throughout the range studied, the sorption increases with increasing phosphorus concentration, a maximum sorption is not predictable (as occurs when the sorption is adjusted to the Langmuir model). For an added P concentration of 100 mg L^-1 (3.2 mmol L^-1), the sorption is 47.7 µmol P g^-1 in the silandic Andosol and 41.6 µmol P g^-1 in the vitric Andosol. The desorption is low and the comparison of the sorption and desorption isotherms reveals a pronounced hysteresis, that is, the irreversibility of the sorption. The high phosphate sorption and its irreversibility are comparable to those published for other volcanic soils with high contents of allophane, active aluminium and free iron. The strong phosphate adsorption is a serious limiting factor for plant growth, which requires a careful management of phosphorus fertilization.

Effect of residential development on stream phosphorus dynamics in headwater suburbanizing watersheds of southern Ontario, Canada

Suburban landscapes are known to have degraded water quality relative to natural settings, including increased total phosphorus (TP) levels; however, the effect of subdivision construction activities on stream TP dynamics are less understood. This study measured TP and its constituents particulate, dissolved organic, and dissolved inorganic phosphorus (PP, DOP, and DIP, respectively) in two headwater streams of contrasting urbanization activity to examine whether the land-use conversion process itself contributed to TP concentrations and export. The nested watershed undergoing significant active residential community construction contained large areas of cleared former agricultural field and associated sediment mounds with elevated soil TP (~1000 mg kg^-1), and twice as many stormwater management (SWM) ponds than the watershed with completed suburban communities. Daily stream sampling for six months revealed limited differences in TP between urbanized and urbanizing watersheds regardless of season or stream flow condition; however, the forms of TP varied significantly. The proportion of TP as DOP was consistently higher in the urbanizing stream relative to the urban stream, which was in line with significant decreases in DOP concentration as proportion of cleared former agricultural land decreased and density of SWM ponds increased. The DOP, and to a lesser extent DIP and PP, dynamics resulted in a 2.5× greater areal export of TP from a small watershed actively being suburbanized during the study period compared to the larger watershed with greater land urbanized 3-5 years ago. The results of this study suggest stream TP concentrations are relatively unresponsive to active versus established suburban cover, but the forms of TP can be quite different, and the period of home construction can increase phosphorus (P) delivery to and export through nearby streams. This information can aid land managers and urban planners update best management practices to mitigate the transfer of terrestrial P to the aquatic environment.

How do root exudates of bok choy promote dibutyl phthalate adsorption on mollisol?

This study investigates the interaction between the bok choy root exudates and dibutyl phthalate (DBP) onto mollisol during the adsorption. The result elucidated that the adsorption reached equilibrium within 12 h, the adsorption capacity of rhizosphere mollisol containing root exudates and ordinary mollisol were 243.46 mg kg^-1 and 281.95 mg kg^-1, separately. The adsorption kinetics and isotherm model followed the pseudo-second order and the Frendlish model, respectively, which hinted that the adsorption process was multi-layer heterogeneous chemisorption. We characterized the root exudates and analyzed its effects on soil physical and chemical properties and structure. The result revealed that the root exudates contained hydrocarbons, sulfur compounds and acids. Root exudates made the dissolved organic matter (DOM) dissolution from soil and the increase of organic matter, which might be one of the reasons that root exudates promote DBP adsorption on mollisol. We selected three-dimensional excitation-emission matrix (3D-EEM), synchronous fluorescence and Fourier transform infrared spectroscopy (FTIR) to analyze the interactions between root exudates and DBP, DOM and DBP, respectively. Fluorescence spectrum revealed that the main component of root exudates was protein, for DOM was humic acid, the fluorescence of root exudates and DOM gradually disappeared with the increase of DBP concentration. FTIR revealed that -COO in root exudates and -CH₂ in DOM respectively reacted with DBP. The results of this study are of great importance to reveal that the root exudates are significant in the environmental behavior of DBP adsorption on mollisol, and also provide more useful information for phytoremediation of organic pollutants in the mollisol.

Microbial community composition and activity controls phosphorus transformation in rhizosphere soils of the Yeyahu Wetland in Beijing, China

Microorganisms in the rhizosphere of wetland plants can have a significant impact on phosphorus (P) interception. We investigated the seasonal pattern of microbial community structure and its relationship with different P forms in the rhizosphere of three plants Scirpus planiculmis, Zizania latifolia, and Phragmites australis from the Yeyahu Wetland, China. Chloroform fumigation-extraction was used to determine the soil microbial biomass P (SMBP) and phospholipid fatty acids (PLFA) were used to characterize microbial community composition. P fractions in rhizosphere soil samples were also observed using sequential chemical fractionation. Results showed that the average total PLFA (TPLFA) contents of rhizosphere soils ranged from 34.9 to 40.7nmol·g^-1 and were highest in summer. Bacteria were predominant in the rhizospheres of all three plants, accounting for >63% of TPLFA. Aerobic bacteria, represented by 16:0 PLFA, were most abundant. Both organic P (OP) and inorganic P (IP) accumulated in the rhizosphere during the winter die-back phase. Furthermore, both TPLFA and bacterial PLFA decreased with increases in highly resistant OP (HR-OP), occluded P (Oc-P) and Calcium-bound P (Ca-P). This suggests that bacteria play an important role in P transformation and can make use of various P forms. We also found that SMBP was significantly negatively correlated with labile OP (L-OP), moderately labile OP (ML-OP) and HR-OP, reflecting a high degree of cross correlation between SMBP and the PLFA indices.

Controlled release of phosphorous fertilizer bound to carboxymethyl starch-g-polyacrylamide and maintaining a hydration level for the plant

A controlled release fertilizer system based on phosphate bound-carboxymethyl starch-graft-polyacrylamide (P-CMS-g-PAM) has been prepared in order to deliver the phosphate fertilizer to the plant at a constant rate thereby. This system aims to increase fertilizer phosphorus use efficiency (FPUE) and maintain a hydration level for the plant at the same time. Two types of starch phosphate monoesters were prepared using mono-ammonium (MAP) and di-ammonium phosphate (DAP). First, starch was converted to carboxymethyl starch and then was phosphorylated with mono-ammonium dihydrogen phosphate and di-ammonium dihydrogen phosphate. After phosphorylation, the samples were grafted with acrylamide in the presence of methylene bisacrylamide as a crosslinking agent. The prepared systems of P-CMS-g-PAM were differently characterized by Fourier transformer infrared (FT-IR), thermogravimetric analysis (TGA), scanning electron microscope (SEM) and phosphorous analysis. The swelling behavior was investigated. The kinetics of grafting reaction were also studied. The release behavior of phosphate bound was studied at pH 7 and 25 °C. The mechanism of the phosphate release from P-CMS-g-PAM was examined using the Korsmeyer-Peppas model.