Microalgae-derived hydrogels/membranes for phosphorus removal and recovery from aquaculture tailwater: Waste utilization and phosphorus recycling.

Efficient removal and recovery of phosphorus from aquaculture tailwater is challenging due to increasing strict water environment restrictions. This study presents a sustainable approach by using microalgae-waste-derived hydrogels/membranes for phosphorus adsorption and microalgae cultivation. Waste from Euglena gracilis (or Haematococcus pluvialis), modified with magnesium, was converted into biochars (abbreviated as MEBC or MHBC). This biochars were then combined with sodium alginate to fabricate hydrogels and with polyvinyl chloride to create membranes. Due to the almost 100 % phosphorus removal of MEBC (or MHBC) biochar, the as-obtained hydrogels/membranes demonstrated excellent phosphate adsorption, reducing total phosphorus in real aquaculture tailwater from 11 mg/L to 0. Additionally, the phosphorus-saturated hydrogel served as a phosphorus source for microalgae cultivation, while the membranes facilitated microalgae harvesting with a water flux over 40 L/m2/h. This study provides an eco-friendly solution for using microalgae-waste-derived materials to effectively address phosphorus removal and recovery challenges in aquaculture tailwater.

Fish stocks as phosphorus sources or sinks: Influenced by nutritional and metabolic variations, not solely by dietary content and stoichiometry.

The study provides a descriptive understanding of when fish (Cyprinus carpio model) are the source or sink of phosphorus. Dissolved reactive phosphorus (DRP; PO4-P) losses (51.1 ± 5.9 % of intake-P) increase at excess of bioavailable P (>0.83 g 100 g-1 dry matter, DM fed) or when food (digestible) N:P mass ratio (≤4.4:1) approaches organismal storage threshold (~4:1). This is known, however, even at a sub-threshold food P content (0.57 g 100 g-1 DM) and food N:P mass ratio (7.3:1), DRP losses (57.8 ± 4.5 % of intake-P) may be extraordinary if two indispensable amino acids are biologically insufficient (lysine ≤1.43 g, methionine ≤0.39 g 100 g-1 DM fed). Given that methionine and lysine are sufficient, DRP losses cease (≈0 %) and even some P from water is absorbed, given there is support from non-protein energy (NPE). Insufficient NPE (<180 kcal 100 g-1 DM fed) may drive DRP losses (81.6 ± 4.3 % of intake-P) beyond expected levels (46-59 % of intake-P) at a given food P content (0.91 g 100 g-1 DM). Natural food seldom fulfills low P, high lysine + methionine, and high NPE contents simultaneously, thus keeping fish in a perpetual P recycling for algae (scaleless carp > scaly carp). Such P recycling ceases only during basal metabolism. During feeding state, the richness of lysine + methionine bound N and lipid + carbohydrate bound C in the food base may enhance the fishes' threshold of P storage. P storage can be diminished when they are insufficient. We show that for fish, the decision of P recycling or not recycling (for algae) may change based on the supply of specific fractions of N or C from the food web or metabolic variations (basal metabolism, presence of scales). NOVELTY STATEMENT: The ecological stoichiometry theory is better connected to fish nutritional bioenergetics for better understanding and biomanipulation of eutrophication processes.

Multi-omics analysis reveals the roles of purple acid phosphatases in organic phosphorus utilization by the tropical legume Stylosanthes guianensis.

Stylo (Stylosanthes guianensis) is a tropical legume known for its exceptional tolerance to low phosphate (Pi), a trait believed to be linked to its high acid phosphatase (APase) activity. Previous studies have observed genotypic variations in APase activity in stylo; however, the gene encoding the crucial APase responsible for this variation remains unidentified. In this study, transcriptomic and proteomic analyses were employed to identify eight Pi starvation-inducible (PSI) APases belonging to the purple APase (PAP) family in the roots of stylo and seven in the leaves. Among these PSI-PAPs, SgPAP7 exhibited a significantly positive correlation in its expression levels with the activities of both internal APase and root-associated APase across 20 stylo genotypes under low-Pi conditions. Furthermore, the recombinant SgPAP7 displayed high catalytic activity toward adenosine 5'-diphosphate (ADP) and phosphoenolpyruvate (PEP) in vitro. Overexpression (OE) of SgPAP7 in Arabidopsis facilitated exogenous organic phosphorus utilization. Moreover, SgPAP7 OE lines showed lower shoot ADP and PEP levels than the wild type, implying that SgPAP7 is involved in the catabolism and recycling of endogenous ADP and PEP, which could be beneficial for plant growth in low-Pi soils. In conclusion, SgPAP7 is a key gene with a major role in stylo adaptation to low-Pi conditions by facilitating the utilization of both exogenous and endogenous organic phosphorus sources. It may also function as a PEP phosphatase involved in a glycolytic bypass pathway that minimizes the need for adenylates and Pi. Thus, SgPAP7 could be a promising target for improving tolerance of crops to low-Pi availability.

Hotspots and future trends of phosphorus recycling from livestock manure: A bibliometric review.

In recent decades, the importance of managing the earth's dwindling phosphorus (P) has grown exponentially, as have efforts to develop a circular economy. Livestock manure represents a P-rich waste product, so recycling P from livestock manure has garnered the attention of scholars worldwide. Based on a global database from 1978 to 2021, this study presents the current status of recycling P from livestock manure and proposes strategies for efficient P utilization. Unlike traditional review articles, this work establishes a visual collaborative network on P recycling from livestock manure of research areas, countries, institutions, and authors through a bibliometric analysis using Citespace and VOSviewer software. The co-citation analysis of literature revealed the development of the main research content in this field, and further clustering analysis illustrated the current key research directions. Keyword co-occurrence analysis identified the hotspots and new frontiers of research in this field. According to the results, the United States was the most influential and actively contributing nation, and China was the country with the tightest international ties. The most popular research area was environmental science, and the Bioresource Technology published the largest number of papers in this area. The research priority was the technologies development of P recycling from livestock manure, of which the most used method was struvite precipitation and biochar adsorption. Subsequently, evaluation is also essential, including the economic benefits and environmental impacts of the recycling process by life cycle assessment and substance flow analysis, as well as the agronomic efficiency of the recycled products. New directions for technological innovation in recycling P from livestock manure and potential risks in the recycling process are explored. The results of this study may provide a framework for understanding the mechanisms of P utilization in livestock manure, and support the overall popularization of P recycling technology from livestock manure.

PULSE process: recovery of phosphorus from dried sewage sludge and removal of metals by solvent extraction.

Phosphorus (P) is an indispensable nutrient for agriculture. Recovery and recycling of phosphorus from waste streams is necessary to ensure a circular P economy and reduce dependence on disproportionately distributed mineral P resources. In this study, a new process called 'PULSE' is presented for the recovery of P from sewage sludge, which can handle high metal contents. The process involves drying of sludge prior to acidic leaching to overcome the challenge of solid-liquid separation at low pH and to reduce the overall material flows. Another key point of the process is the removal of metals using reactive extraction to obtain a high-quality product with good plant availability. Laboratory experiments were conducted to evaluate and select the best process options. A chemical equilibrium tool was developed to simulate the unit operations of the process for optimization. Dissolution of P from sludge depends on leaching pH and the fraction of inorganic P in the sludge. The maximum P leaching efficiency for the sludge used in the study was between 65 and 70%. Under the tested conditions, Fe, Cd, Cu, Hg, Pb, and Zn were successfully removed from the sludge leach liquor by reactive extraction. The recovered product has a nutrient mass fraction of about 51% that includes Ca, PO43-, Mg, and K. Pot trials confirmed that the agronomical efficiency of the product is comparable to that of triple superphosphate.

Acidification and alkalinization pretreatments of biowastes and their effect on P solubility and dynamics when placed in soil.

BACKGROUND: Sustainability concerns as well as recent increases in fertilizer prices exacerbates the need to optimise the use of biowastes as fertilizers. For this reason, we investigated how different pretreatments affect the P dynamics when biofertilizers are placed in the soil. METHODS: Sewage sludge (SS), sewage sludge ash (SS-ash), meat and bone meal (MBM), and the solid fraction of biogas digestate (BGF) were pretreated with H2SO4, NaOH, and Ca(OH)2 and incubated for 2 and 12 days, respectively, in a one-dimensional reaction system for detailed studies of the interactions in the biomaterial-soil interface and the soil adjacent to the placement zone. RESULTS: Our results showed that acidification and treatment with NaOH increased the P solubility of the biomaterials. The P loss from the biomaterial layer to the soil was correlated with water-extractable P in the biomaterials (0.659) and water-extractable P in the soil (0.809). Acidification significantly increased the total amount of P depleted from the biomaterial to the soil whereas NaOH pre-treatment did not. However, for NaOH-treated SS and SS-ash, the apparent recoveries were significantly higher compared to the acidification due to a decrease in soil P sorption capacity as the soil pH increased due to residual alkalinity in the biomaterials. CONCLUSIONS: Acidification showed promising results by increasing the P solubility of all the biomaterials, and the alkalinization of SS and SS-ash with NaOH by increasing the apparent recovery in the soil. However, further studies are needed to assess the effects of these treatments on plant growth and P uptake.

Formation of vivianite in digested sludge and its controlling factors in municipal wastewater treatment.

Engineering solutions to recover phosphorus from municipal wastewater are required to close the anthropogenic phosphorus cycle. After chemical phosphorus elimination by iron, the ferrous iron­phosphorus mineral vivianite forms in digested sludge, and its separation is being researched at the pilot scale. In this study, sludge samples from 16 wastewater treatment plants (WWTPs) demonstrated that phosphorus bound to biomass and redox-sensitive iron in activated sludge was transformed into other phosphorus binding forms, including vivianite, during digestion. Vivianite quantity was approximated using X-ray diffraction and two sequential extractions. These three independent methods of approximating vivianite quantity were closely related confirming their relationship to the vivianite content in the samples. The digested sludge from three WWTPs exhibited comparatively high levels of vivianite-bound phosphorus approximated between 31 % and 51 % of total phosphorus. The controlling factors of vivianite formation were investigated in order to enhance its formation in digested sludge and increase the amount of phosphorus recoverable as vivianite. They were identified using single and multivariate correlation (MLR), considering the sludge properties, sludge composition, and process parameters within the operating range of the 16 WWTPs. Increasing iron content was verified as the primary predictor of significantly increased vivianite formation (MLR: p < 0.001). In addition, increasing sulphur content was found to be an additional significant factor that decreased vivianite formation (MLR: p < 0.05). Furthermore, a comparison of plants using sulphur-free (FeCl2 and FeCl3) and sulphur-containing (FeSO4 and FeClSO4) precipitants indicated that the latter could increase the sulphur content in digested sludge (one-tailed Welch two-sample t-test: t(14.6) = 2.3, p = 0.02). Thus, by increasing the sulphur content, the use of sulphur-comprising precipitants may counteract vivianite formation, whereas sulphur-free precipitants may facilitate it and, hence, promote vivianite recovery.

Selectivity in Enzymatic Phosphorus Recycling from Biopolymers: Isotope Effect, Reactivity Kinetics, and Molecular Docking with Fungal and Plant Phosphatases.

Among ubiquitous phosphorus (P) reserves in environmental matrices are ribonucleic acid (RNA) and polyphosphate (polyP), which are, respectively, organic and inorganic P-containing biopolymers. Relevant to P recycling from these biopolymers, much remains unknown about the kinetics and mechanisms of different acid phosphatases (APs) secreted by plants and soil microorganisms. Here we investigated RNA and polyP dephosphorylation by two common APs, a plant purple AP (PAP) from sweet potato and a fungal phytase from Aspergillus niger. Trends of δ18O values in released orthophosphate during each enzyme-catalyzed reaction in 18O-water implied a different extent of reactivity. Subsequent enzyme kinetics experiments revealed that A. niger phytase had 10-fold higher maximum rate for polyP dephosphorylation than the sweet potato PAP, whereas the sweet potato PAP dephosphorylated RNA at a 6-fold faster rate than A. niger phytase. Both enzymes had up to 3 orders of magnitude lower reactivity for RNA than for polyP. We determined a combined phosphodiesterase-monoesterase mechanism for RNA and terminal phosphatase mechanism for polyP using high-resolution mass spectrometry and 31P nuclear magnetic resonance, respectively. Molecular modeling with eight plant and fungal AP structures predicted substrate binding interactions consistent with the relative reactivity kinetics. Our findings implied a hierarchy in enzymatic P recycling from P-polymers by phosphatases from different biological origins, thereby influencing the relatively longer residence time of RNA versus polyP in environmental matrices. This research further sheds light on engineering strategies to enhance enzymatic recycling of biopolymer-derived P, in addition to advancing environmental predictions of this P recycling by plants and microorganisms.

Variations in rhizosphere soil total phosphorus and bioavailable phosphorus with respect to the stand age in Pinus massoniana Lamb.

Phosphorus (P) is a nutrient limiting plant growth in subtropical regions. However, our understanding of how soil P responds to an increase in stand age is rather poor. In particular, little is known about how bioavailable P pools (soluble P, exchangeable P, hydrolyzable P, and ligand P) shift with a change in stand age. Moreover, the P cycle in rhizosphere soil has the most direct and significant influence on plants. The aim of the present study was to determine the concentrations of total P in various rhizosphere soil bioavailable P fractions in 5-, 9-, 19-, 29-, and 35-year-old stands of Pinus massoniana Lamb. According to the results, total P (TP) concentration and N:P ratio in rhizosphere soil first decreased, and then increased with an increase in stand age. Soluble P concentration decreased first, and then increased with an increase in stand age; exchangeable P and ligand P decreased first, and then tended to be stable with an increase in stand age, whereas hydrolyzable P increased first, and then decreased. Structural Equation Model results suggested that ligand P and soluble P were the major factor affecting the TP. In addition, soil microorganisms and acid phosphatase-driven hydrolyzable P play a crucial role in soil bioavailable P cycling. Overall, the results of our study provide a mechanistic understanding of soil bioavailable P cycling under low available P conditions, and a basis for an effective P management strategy for the sustainable development of P. massoniana plantations.

Considering inorganic P binding in bio-based products improves prediction of their P fertiliser value.

Prediction of the relative phosphorus (P) fertiliser value of bio-based fertiliser products is agronomically important, but previous attempts to develop prediction models have often failed due to the high chemical complexity of bio-based fertilisers and the limited number of products included in analyses. In this study, regression models for prediction were developed using independently produced data from 10 different studies on crop growth responses to P applied with bio-based fertiliser products, resulting in a dataset with 69 products. The 69 fertiliser products were organised into four sub-groups, based on the inorganic P compounds most likely to be present in each product. Within each product group, multiple regression was conducted using mineral fertiliser equivalents (MFE) as response variable and three potential explanatory variables derived from chemical analysis, all reflecting inorganic P binding in the fertiliser products: i) NaHCO3-soluble P, ii) molar ratio of calcium (Ca):P and iii) molar ratio of aluminium + iron (Al + Fe):P. The best regression model fit was achieved for sewage sludges with Al-/Fe-bound P (n = 20; R2 = 79.2%), followed by sewage sludges with Ca-bound P (n = 11; R2 = 71.1%); fertiliser products with Ca-bound P (n = 29; R2 = 58.2%); and thermally treated sewage sludge products (n = 9; R2 = 44.9%). Even though external factors influencing P fertiliser values (e.g. fertiliser shape, application form, soil characteristics) differed between the underlying studies and were not considered, the suggested prediction models provide potential for more efficient P recycling in practice.

Phosphorus Fertilizers from Sewage Sludge Ash and Animal Blood as an Example of Biobased Environment-Friendly Agrochemicals: Findings from Field Experiments.

Wastes of biological origin from wastewater treatment systems and slaughterhouses contain substantial amounts of phosphorus (P) with high recovery potential and can contribute to alleviating the global P supply problem. This paper presents the performance of fertilizer (AF) and biofertilizer (BF) from sewage sludge ash and animal blood under field conditions. BF is AF incorporated with lyophilized cells of P-solubilizing bacteria, Bacillus megaterium. In the experiments with spring or winter wheat, the biobased fertilizers were compared to commercial P fertilizer, superphosphate (SP). No P fertilization provided an additional reference. Fertilizer effects on wheat productivity and on selected properties of soil were studied. BF showed the same yield-forming efficiency as SP, and under poorer habitat conditions, performed slightly better than AF in increasing yield and soil available P. Biobased fertilizers applied at the P rate up to 35.2 kg ha-1 did not affect the soil pH, did not increase As, Cd, Cr, Ni, and Pb content, and did not alter the abundance of heterotrophic bacteria and fungi in the soil. The findings indicate that biobased fertilizers could at least partially replace conventional P fertilizers. Research into strain selection and the proportion of P-solubilizing microorganisms introduced into fertilizers should be continued.

An Investigation into the Growth of Lolium perenne L. and Soil Properties Following Soil Amendment with Phosphorus-Saturated Bauxite Residue.

Reuse options for bauxite residue include treatment of phosphorus (P)-enriched wastewaters where the P-saturated media offers fertiliser potential. However, few studies have assessed the impact on soil properties. Two types of spent P-saturated bauxite residue were applied to soil and compared to conventional superphosphate fertiliser as well as a control soil. Soil physico-chemical properties, worm Eisenia fetida L. choice tests, and Lolium perenne L. growth and elemental uptake were examined. Comparable biomass and plant content for L. perenne in the P-saturated bauxite residue treatments and those receiving superphosphate, indicated no phytotoxic effects. E. fetida L. showed a significant preference for the control soil (58 %± 2.1%) over the amended soils, indicating some form of salt stress. Overall, P-saturated bauxite residue was comparable to the superphosphate fertiliser in terms of the plant performance and soil properties, indicating the potential recycling of P from wastewaters using bauxite residue as a low-cost adsorbent.

Mechanisms for improving phosphorus utilization efficiency in plants.

BACKGROUND: Limitation of plant productivity by phosphorus (P) supply is widespread and will probably increase in the future. Relatively large amounts of P fertilizer are applied to sustain crop growth and development and to achieve high yields. However, with increasing P application, plant P efficiency generally declines, which results in greater losses of P to the environment with detrimental consequences for ecosystems. SCOPE: A strategy for reducing P input and environmental losses while maintaining or increasing plant performance is the development of crops that take up P effectively from the soil (P acquisition efficiency) or promote productivity per unit of P taken up (P utilization efficiency). In this review, we describe current research on P metabolism and transport and its relevance for improving P utilization efficiency. CONCLUSIONS: Enhanced P utilization efficiency can be achieved by optimal partitioning of cellular P and distributing P effectively between tissues, allowing maximum growth and biomass of harvestable plant parts. Knowledge of the mechanisms involved could help design and breed crops with greater P utilization efficiency.

Assessing and predicting phosphorus phytoavailability from sludge incineration ashes.

Incineration of municipal sludge and agri-food by-products generates large quantities of ash that can be used in agriculture as phosphorus fertilizer. The fertilizing potential of sludge incineration ash (SIA) from 12 cities in Canada and the United States was tested in a greenhouse experiment against a synthetic fertilizer (TSP: triple superphosphate), a natural fertilizer (RP: rock phosphate), and a control without any P fertilizer. Two soil types were used: clay and sandy loam. A reliable a priori indicator of SIA P bioavailability was determined using the random forest method. SIA application increased ryegrass P uptake. The SIA relative P effectiveness (RPE), compared to the TSP, varied from 5.1% to 46.2% depending on the sludge origin and P solubility. SIA RPE was greater than RP for the clay soil but similar for the sandy loam soil. The neutral ammonium citrate (NAC) extraction, sometimes inappropriately used to characterize P availability of sludge and by-products, explained only 53% of the RPE variation. The random forest analysis showed that the oxalate extraction (Al, P, and Fe) is a better indicator (R2 = 0.94) of relative availability of SIA than the NAC P solubility (R2 = 0.86), and that Al content is the factor that influences most SIA P solubility. Based on our findings, we recommend the use of the Al, Fe, and P oxalate extraction to predict the SIA P availability, instead of the widely used NAC method which extracts only P.

Filter-feeding fish (Hypophthalmichthys molitrix) mediated phosphorus recycling versus grazing pressure as drivers of the trophic cascade in large enclosures subsidized by allochthonous detritus.

Stocking of filter-feeding fish is a common tool used in (sub)tropical Chinese reservoirs to control phytoplankton. However, field investigations have showed that such stocking would enhance instead of controlling phytoplankton in these reservoirs. Reservoirs generally receive a considerable amount of detritus from their catchments which may constitute an important carbon source to filter-feeding fish. Whether direct consumption of detritus increases the availability of dissolved inorganic phosphorus (P) to phytoplankton and thereby provides resilience against the control of phytoplankton biomass is debated. We conducted an enclosure experiment in a (sub)tropical Chinese reservoir (Liuxihe Reservoir) to assess how a gradient of filter-feeding fish (Silver Carp Hypophthalmichthys molitrix) biomass affected P dynamics and fish grazing and predation when subsidized by allochthonous detritus. Fish had strong effects on the dynamics and fluxes of P. TP concentration in the water column increased over time in all enclosures, but the presence of fish slowed its increase. Thus, TP decreased with increasing fish biomass. Fish were a net sink of P to the water column, because they gained mass during the experiment. Moreover, P sequestered by fish could largely account for the lower TP concentrations observed in enclosures with fish compared to fishless enclosures. Fish presence at high biomass strongly reduced the abundance of large zooplankton species and P excretion by zooplankton. However, the negative effect of fish predation on zooplankton was negligible when fish was present at low biomass. Increasing fish biomass increased the relative role of fish in P cycling but decreased the overall P excretion by fish and zooplankton. Compared to enclosures with high fish biomass, both zooplankton grazing effect on phytoplankton (zooplankton: phytoplankton biomass ratio as a proxy) and the overall P excretion were much higher, whereas fish grazing effect on phytoplankton (fish: phytoplankton biomass ratio as a proxy), chlorophyll a and the yield of chlorophyll a per TP were much lower in enclosures with low fish biomass. This suggested that phytoplankton limitation might shift from one of zooplankton control to one of limitation by P availability with increasing fish biomass. Relative to fish mediated P recycling and fish grazing, zooplankton grazing appeared to be more important as a driver of trophic cascades in systems subsidized by allochthonous detritus. Silver Carp stocked at high biomass would strongly reduce zooplankton grazing pressure and increase the yield of phytoplankton per TP.

Phosphorus circular economy of disposable baby nappy waste: Quantification, assessment of recycling technologies and plan for sustainability.

This study assessed the potential for minimizing human excreta bound phosphorus (P) loss through used disposable baby nappies, an area that remained unexplored for nations. Accordingly, it performed a substance flow analysis to assess the national P loss through used disposable baby nappies in the case of Australia. The analysis revealed that approximately 308 tonne P is lost through used baby nappies to landfills in Australia in 2019, which is nearly 2.5% of the overall P excreta as human waste. Although the quantity seems small in percentage term, it could result in the loss of a significant amount of P over several years, as assessed 5452 tonne P over the 2001-2019 period, which is concerning in the context of anticipated future global P scarcity. The review of peer-reviewed literature on available technologies/methods for recycling disposable baby nappy waste indicates that there are some technologies for recycling P particularly through co-composting with food and other organic wastes, while the majority of these are still at the lab/pilot scale. There are also various recycling techniques with purpose ranging from energy recovery to volume reduction, generation of pulp, hydrogel, cellulose, and polymer as well as to increase yield stress and viscosity of concrete, however, these are not effective in P recovery. The study implies that compost made of nappy waste can be used as fertilizer to produce bamboo, cotton, and maize plants to supply raw materials for producing biodegradable nappies, hence, to close the loop. The various product and system design options e.g., designing for flushing, designing for disassembling the excreta containing part, and designing for community composting suggested in this study could be further researched for identifying best suitable option to achieve P circular economy of disposable baby nappies. This study also recommends necessary interventions at various stages of the nappy life cycle to ensure sustainable management of phosphorus.

Legacy effect of green manure crops fertilized with calcium phosphite on maize production and soil properties.

Recycling phosphorus (P) is crucial to meet future P demand for crop production. We investigated the possibility to use calcium phosphite (Ca-Phi) waste, an industrial by-product, as P fertilizer following the oxidation of phosphite (Phi) to phosphate (Pi) during green manure (GM) cropping in order to target P nutrition of subsequent maize crop. In a greenhouse experiment, four GM crops were fertilized (38 kg P ha-1) with Ca-Phi, triple super phosphate (TSP) or without P (Control) in sandy and clay soils. The harvested GM biomass (containing Phi after Ca-Phi fertilization) was incorporated into the soil before maize sowing. Incorporation of GM residues containing Phi slowed down organic carbon mineralization in clay soil and mass loss of GM residues in sandy soil. Microbial enzymatic activities were affected by Ca-Phi and TSP fertilization at the end of maize crop whereas microbial biomass was similarly influenced by TSP and Ca-Phi in both soils. Compared to Control, Ca-Phi and TSP increased similarly the available P (up to 5 mg P kg-1) in sandy soil, whereas in clay soil available P increased only with Ca-Phi (up to 6 mg P kg-1), indicating that Phi oxidation occurred during GM crops. Accordingly, no Phi was found in maize biomass. However, P fertilization did not enhance aboveground maize productivity and P export, likely because soil available P was not limiting. Overall, our results indicate that Ca-Phi might be used as P source for a subsequent crop since Phi undergoes oxidation during the preliminary GM growth.

Evidence of a rapid phosphorus-induced regime shift in a large deep reservoir.

Ecological regime shift studies in freshwater systems are mainly limited to shallow lakes and reservoirs, while abrupt changes in deeper lakes are often attributed to climate change. Here, we demonstrate the application of regime shift theory to one of California's newest and deepest reservoirs, Diamond Valley Lake (DVL), which in recent years showed an unexpected rapid departure from its water quality conditions of the previous decade. The reservoir shifted from a well oxygenated condition with low phytoplankton growth to a hypoxic, phytoplankton-dominated turbid system. We statistically identified the critical stressor (phosphorus (P)), switch points, and its load threshold and characterized its transition to an alternative stable state and the stabilizing mechanisms contributing to hysteresis. We analyzed long-term environmental, chemical and flow data, conducted a hydrographic survey, and developed a hydrodynamic model to characterize the factors that contributed to regime shift and to evaluate different management strategies that might reverse this shift. Our findings indicate that large deep systems exhibit different transition dynamics in the presence of an acute stressor compared to regime shifts in shallow systems. A cumulative external TP load threshold of 4.6 mg m-2 d-1 added to the reservoir over nearly 11 months was identified as the critical stressor. For large deep systems, inherent morphometric features such as large relative depth combine with external stressors to drive regime shifts. Light winds, morphometric conditions impeding deep mixing, and a stable stratification that lasts up to 9 months makes DVL more susceptible to hypolimnetic hypoxia, an intrinsic factor accelerating regime shift. Results also suggest regime shift occurred in 2013, when new limnological processes were established to reinforce the new alternative stable state and existing ecosystem services were impaired. Interactions between hypoxia, internal P loading (~2.1 mg m-2 d-1), and seasonal cyanobacterial blooms were identified as mechanisms perpetuating the new alternative state.

Valorization of calcium phosphite waste as phosphorus fertilizer: Effects on green manure productivity and soil properties.

The potential to use calcium phosphite (Ca-Phi) as phosphorus (P) fertilizer may represent an effective recycling of P-containing by-products. A greenhouse experiment was conducted to investigate the effect of Ca-Phi (38 kg P ha-1) on soil properties and the growth parameters of four green manure species in clay and sandy soils using Ca-Phi, TSP (triple superphosphate) and control (no fertilization) as treatments. Eight weeks after sowing, we measured aboveground biomass yield, phosphite (Phi) concentration in plant biomass, different soil P pools as well as microbial biomass nutrients. Compared to control, the addition of Ca-Phi did not negatively affect green manure yield, except for lupine (Lupinus albus L.) in clay soil. The Phi concentration in plant biomass varied across species and soil type with a maximum concentration of about 400 mg Phi kg-1 for mustard (Brassica juncea L.) in clay soil. Compared to control, TSP and Ca-Phi fertilization had a similar effect on different P pools and microbial biomass nutrients (C, N and P) although the response was soil-type dependent. In the sandy soil, after Ca-Phi addition the amount of available P (PNHCO3) increased to the same extent as in the TSP treatment (i.e. around 6 mg P kg-1) suggesting that Ca-Phi was, at least partly, oxidized. In the clay soil with high P fixing capacity, Ca-Phi promoted higher PNaHCO3 than TSP likely due to different solubility of chemical P forms. Additional studies are however required to better understand soil microbial responses and to quantify the P agronomical efficiency for the following crop under Ca-Phi fertilization.

Co-composts of sewage sludge, farm manure and rock phosphate can substitute phosphorus fertilizers in rice-wheat cropping system.

In the present study, various co-composts of sewage sludge (SS), farm manure (FM) and rock phosphate (RP) were prepared and their influence on phosphorus (P) uptake, soil P restoration and growth of rice crop and residual effect on wheat crop were investigated. The treatments comprised of T1 (control, no amendment), T2 (452 kg Nitrophos ha-1, T3 (724 kg SS50:FM50 ha-1), T4 (594 kg SS100:FM0 ha-1), T5 (728 kg SS25:FM25:RP50 ha-1), T6 (726 kg SS5O:FM25:RP25 ha-1), T7 (508 kg SS75:FM0:RP25 ha-1), and T8 (546 kg SS50:FM0:RP50 ha-1). The post-experimental soil samples were analyzed for pH, EC, OM, Olsen's P. The plant samples (grains and straw of both crops) were analyzed for concentrations of P, and heavy metals. The P adsorption by post-wheat composts-amended soil was tested through Langmuir, and Freundlich adsorption isotherms. The investigated parameters (biomass, grain and straw yield, plant height and P concentrations in plant parts) were significantly increased in all composts as compared to the control treatment. The P uptake by the plants was higher in compost treatments as compared to the control and NP that shows long-term residual effect of applied composts. The maximum grain yield (1.63 Mg ha-1) was obtained in T5 followed by T6 (1.52 Mg ha-1). The P concentration in rice grains were recorded in the trend as T8 (2.55%) > T6 (2.24%) > T4 (1.92%) = T3 (1.88%) > T7 (1.62%). It is evident that the combined application of FM (25%) and RP (50%) enhanced the effect of SS (25%) in terms of P bioavailability and yield parameters and can be effectively used as P fertilizer.