Bioavailable Phosphorus Research Articles

Enhanced phosphorus bioavailability of biochar derived from sewage sludge co-pyrolyzed with K, Ca-rich biomass ash

Sewage sludge has great potential for phosphorus (P) recovery. However, sewage sludge-derived biochar suffers from low P bioavailability in land application. K, Ca-rich biomass ash was used to co-pyrolyze with sewage sludge to enhance P bioavailability of synthesized biochar. Phase transformation mechanism of P during the co-pyrolysis process was studied. When sunflower straw ash (SSA) was used as an additive (50 wt%) for co-pyrolysis with sludge at 600°C, the ratio of bioavailable P (Bio-P, determined by 2 wt% citric acid) to total P (TP) of the co-pyrolyzed biochar could achieve 92.1 wt%, which was remarkably higher than that of biochar pyrolyzed by sludge alone (9.5 wt%). The K and Ca elements in SSA significantly contributed to the conversion of the Fe-phosphate phase (FePO4) in sludge into K, Ca-phosphates (KCaPO4, K2CaP2O7 and K2CaP2O7·4H2O) and Ca-phosphate (Ca5(PO4)3OH) phases, therefore enhancing the Bio-P content in the co-pyrolyzed biochar. Model compound pyrolysis results indicate that KCl/K2CO3 and CaCO3 phases in SSA play a synergistic role in enhancing the P bioavailability of co-pyrolyzed biochar. Based on the DFT calculations, the absolute value of the adsorption energy (|ΔEads|) of CH3COO- presented an order: K2CaP2O7 (2.43 eV) > KCaPO4 (1.70 eV) > Ca5(PO4)3OH (1.64 eV)> FePO4 (1.08 eV), indicating that K2CaP2O7, KCaPO4, and Ca5(PO4)3OH are more likely to interact with organic acid and have higher bioavailability than FePO4. Furthermore, the co-pyrolyzed biochar reaches the release rate standard for P, K-slow-release fertilizer. This study proposes a promising and sustainable solution to simultaneously realize sludge utilization and P resource recycling.

Rational eucalypt logging site management patterns enhance soil phosphorus bioavailability and reshape phoD-harboring bacterial community structure

Continuous planting of eucalypt plantations negatively affects soil nutrient effectiveness, especially soil phosphorus (P) availability. Therefore, exploring the response characteristics of soil P-mineralising microbial communities and the distribution mechanism of soil P fractions under different transformation patterns on eucalypts logging sites holds great practical significance for improving soil nutrient effectiveness in plantations. This experiment investigated the effects and correlations between four different transformation patterns on soil phoD-harboring bacterial communities, alkaline phosphatase (ALP) activity, and P fractions. Management patterns mainly included non-forest area formed upon eucalypt stump germination suppression after two generations of Eucalyptus afforestation (TWE), the third generation of pure plantation planting (THE), mixing of Eucalyptus with Manglietia glauca (EM), and rotation of pure M. glauca plantation (MM), with previous mixed coniferous and broadleaf forest (CK) as the control. The results showed that, TWE and THE significantly reduced soil (0–10 cm and 10–20 cm) organic carbon (SOC), total nitrogen (TN), bioavailable P, and labile Po, and increased the occluded P and ALP activity compared to CK; however, SOC, TN, bioavailable P, and labile Po indices improved in plantations of EM or MM compared to TWE and THE. Meanwhile, the four management patterns on the logging site caused significant differences in phoD gene community structure and diversity. TWE and THE significantly increased the relative abundances (RAs) of Pseudomonadaceae and Comamonadaceae, which correlated negatively with soil bioavailable P and HCl-P and positively with ALP activity, suggesting a positive effect on Po mineralization and insoluble P mobilization. In contrast, Streptomycetaceae and Oxalobacteraceae were significantly enriched in EM or MM, implying that not all microorganisms carrying phoD genes play important roles in synthesizing ALP. The structure equation model showed that TN, resin-Pi, NaHCO3-Pi, and HCl-P had indirect effects on ALP through phoD-harbouring bacterial diversity and community composition. These findings provide a basis for understanding the soil P cycling mechanism after eucalypt plantations logging site transformation.

Valorisation of Deinking Paper Sludge for Fertiliser Purposes: New Perspective in Sustainable Agriculture

The growth of the global population, coupled with concomitant economic development, has resulted in the generation of a substantial quantity of waste. The transition of the European Union’s economy towards a closed-loop model is prompting a comprehensive search for waste management concepts across a range of industrial sectors. The objective of this study is to valorise deinking paper sludge, which has a high potential for soil formation due to its high organic matter content. To produce organic–mineral fertiliser, the deinking sludge was subjected to acid hydrolysis, then neutralised with KOH solution and enriched with poultry litter ash. The final products were characterised in terms of their nutrient and heavy metal content. The bioavailability of phosphorus, along with the forms in which it occurs in fertilisers, was determined through the implementation of a five-step fractionation procedure. Furthermore, an eight-week incubation period was conducted to assess the fertilisers’ performance in soil. Soil samples were tested on a weekly basis for pH, water-soluble and bioavailable phosphorus content using the spectroscopic method after previous extraction in water and Bray’s solution, and catalase activity using the titrimetric method. The resulting fertilisers were found to meet the requirements for organo-mineral fertilisers and were categorised as PK-type fertilisers with a total nutrient content of 24.6–39.3%. Fractionation studies demonstrated that the fertilisers contained 20–30% of the total potentially bioavailable phosphorus. Furthermore, the long-term release of phosphorus from the fertilisers was confirmed through incubation studies. Additionally, the fertilisers were observed to contribute to an increase in catalase activity in the soil.

Enhanced phosphorus bioavailability and reduced water leachability in dairy manure through hydrothermal carbonization: effect of processing temperature and CaO additive

ABSTRACT Dairy manure, a significant source of phosphorus (P), can potentially cause environmental risk due to P runoff when dairy manure is directly applied to cropland. Thus, there is an increasing interest in mitigating P loss from manure prior to land applications. This study aimed to investigate the potential of hydrochar produced by hydrothermal carbonization (HTC) for P recycling from dairy manure with and without the addition of CaO, focusing on the plant bioavailability, stabilization, and transformation of P in the resultant hydrochar. Hydrochar was prepared under different temperatures (180–240°C). The effect of CaO addition (0–10% of raw manure on dry wt. basis) was also evaluated at 220°C. Results showed that water-soluble P (WSP), a key indicator of P runoff loss, was significantly reduced in hydrochar, particularly with CaO addition. In addition, the plant available P in hydrochar increased with HTC temperature increase till 220°C, which accounted for ∼90% of total P content, then decreased with temperatures higher than 220°C. The addition of CaO slightly reduced plant bioavailability when compared to hydrochar produced at 220°C without additive. The P fractionation and speciation analyses indicated the transformation of P into Ca-associated apatite P. Hydrochar produced at 220°C with 10% CaO addition resulted in a high P recovery (∼85%) and a reduced runoff risk by 97%. The results demonstrate the efficacy of P recycling through hydrochar produced from dairy manure through HTC, which offers a sustainable approach to managing dairy waste while mitigating the potential environmental risks of P runoff.

Pseudomonas putida triggers phosphorus bioavailability and P-transporters under different phosphate regimes to enhance maize growth

The decline of available phosphorus in soil due to anthropogenic activities necessitates utilizing soil microorganisms that influence soil phosphorus levels. However, the specific mechanisms governing their interaction in Zea mays under diverse phosphate regimes remain largely unknown. The present study investigated the dynamics of phosphorus solubilization and the impact of organic acid supplementation in combination with the beneficial rhizobacterium Pseudomonas putida (RA) on maize growth under phosphorus-limiting and unavailable conditions. HPLC analysis revealed gluconic acid as the primary organic acid (OA) produced by P. putida across all three conditions (P-sufficient, P-limiting, and P-unavailable), with the highest production occurring under P-limiting conditions. The study evaluates the effects of RA, OA, and OA + RA on plant growth parameters under P-limiting and insufficient conditions, revealing significant alterations in growth and biochemical parameters (P = 0.05) compared to their respective untreated controls. Additionally, plants treated with organic acids and bacterial inoculation show increased phosphorus concentrations in both roots and shoots. Gene expression analysis of key phosphorus transporter genes (PHT1, PHO1, PTF, PHF1) further supports the role of organic acids and bacterial inoculation in enhancing phosphorus uptake. In conclusion, our study affirms that the secretion of gluconic acid by RA and its plant growth-promoting properties boost phosphorus uptake and maize growth by increasing phosphorus availability and influencing the expression of phosphorus transport-related genes.

Improving phosphorus availability in sewage sludge ash through a novel microwave‐based technology

AbstractThis work is connected with the increasing demand for fertilizers and the associated supply risks and market volatility in the European Union (EU). It highlights the reliance on phosphorus from Moroccan phosphate rocks and the environmental issues stemming from the overuse of phosphate‐based fertilizers. The paper suggests a shift in perspective, viewing waste as a valuable resource. Specifically, it explores the potential of recycling phosphorus from sewage sludge ash, which contains a high phosphorus concentration. The focus is on comparing two methods of phosphorus extraction from sewage sludge ashes: classical wet‐chemical extraction and a new microwave‐based technology. There is an increase in phosphorus bioavailability with the microwave treatment, making it a promising approach for waste management. An initial economic evaluation suggests that the microwave method is highly competitive, especially when compared with wet‐chemical extraction technologies. The resulting material from the microwave treatment is classified as a straight solid inorganic macronutrient fertilizer according to EU regulations.

A three-stage oxidation method improves sludge dewaterability by achieving sustained oxidation and phased enhanced coagulation: Ingeniously using H2O2 as a “converter”

Sludge reduction is essential for mitigating the environmental hazards associated with sludge. The use of ferric chloride (Fe(III)) catalyzed ferrate (Fe(VI)) can significantly enhance sludge dewaterability by increasing the Fe(VI) oxidation rate and maintaining in-situ enhanced coagulation. However, its weak oxidation ability at the sludge’s original pH limits its practical application. To address this, hydrogen peroxide (H2O2) strengthened Fe(VI)/Fe(III) was employed to efficiently improve sludge dewaterability without pH adjustment, thereby enhancing the environmental utilization capacity of sludge. Compared to raw sludge, the treatment of Fe(VI)/Fe(III)–H2O2 resulted in approximately the 95% reduction in specific resistance to filtration (SRF) and increased the bioavailable phosphorus (P) content in dewatered sludge. During the oxidation process, highly reactive species such as tetravalent iron (Fe(IV)) and hydroxyl radicals (OH) were generated, facilitating the release of tightly bound water in extracellular polymeric substances (EPS). Importantly, the oxidation process was divided into three stages (persistent moderate oxidation — fast strong oxidation — sustained weak oxidation) based on the predominant reactive species (Fe(IV) or OH). This division promoted more robust and more durable oxidation processes. Phased enhanced coagulation occurred during the oxidation process. The gradual increase in Fe(III) content led to the re-flocculation of damaged EPS, enlarging the size of sludge drainage pores/channels and improving water discharge efficiency. Additionally, the costs and carbon emissions of chemicals for the Fe(VI)/Fe(III)–H2O2 process were 18% and 52% lower than those of the traditional Fenton method. This study not only achieves the goals of sludge reduction and resource collection but also provides insights into selecting sludge conditioning methods that meet pollution reduction and carbon emission reduction requirements.

Sedimentary geochemistry in P-limited freshwater drained marshes (Charente-Maritime, France): Original drivers for phosphorus mobilization

Phosphorus bioavailability is a major issue in aquatic environments, where it generally limits primary production. In this work, the analysis of the pore water and the solid phase of the sediment was carried out over a 9-month monitoring period between February 2020 and April 2021 in two drained marshes (Marans and Genouillé, France) distinct by their uses and management tools. Soluble reactive phosphorus (SRP) enrichment in the sediment was intimately controlled by iron oxide dissolution. The latter seemed highly controlled by seasonal nitrate inputs (winter and early spring) that favoured denitrification as a major benthic mineralization process promoting iron curtain development and stability. Following benthic mitigation of nitrate other anaerobic metabolisms developed such as iron dissolutive reduction promoting P recycling and planktic bioavailability. Surprisingly, sulphur cycle seemed to affect P dynamics, especially in the absence of nitrate. The absence of NO3− triggered high sulphate reduction rates in the two first centimeters depth, reaching −8.9 E−03 ± 0.5 E−03 and -5.0 E−03 ± 0.2 E−03 nmol cm−3 s−1 in August and July at Marans and Genouillé respectively. These values placed this process at higher rates than the denitrification (maximum in May at Marans with −5.0 E−03 ± 1.1 E−03 nmol cm−3 s−1) and reduced iron production (maximum in July at Genouillé with 0.5 E−03 ± 0.1 E−03 nmol cm−3 s−1). The rapidity with which process changes occur (monthly scale) testified to the dynamism of these systems. The similarity in geochemical patterns regarding NO3− pressure at both sites underlines the importance of diffuse pollution in coastal systems for nitrogen mitigation and phosphorus trapping. The results obtained in this study could lead to the development of a generalized diagenetic operating model for temperate systems with high agricultural pressure. This would enable to target management efforts to both optimize the purification function and limit eutrophication risks in these systems.

Grouper bone nano-calcium and substitution long-chain triglyceride (LCT) into medium-chain triglyceride (MCT) enhanced calcium bioavailability and rat’s bone density

BACKGROUND: The most effective strategy to prevent osteopenia or osteoporosis in the old life is to consume an adequate amount of calcium from childhood through adulthood. OBJECTIVE: This study compared the bioavailability of CaCO3 which is the standard non-dairy calcium supplementation with grouper bone nano-calcium (GBN) combined with various percentages of Long-Chain Triglyceride (LCT) into Medium-Chain Triglyceride (MCT) on calcium bioavailability and rat’s bones density. METHODS: This study was carried out during the rat’s growth period, from the weaning until the rats reached 16 weeks. Thirty-five weaned rats were separated into seven groups and fed varied feeds for 12 weeks. The seven groups of feed were (1) CCa: standard feed AIN-93G, (2) C0: standard calcium deficient feed (without calcium), (3) G0: GBN + MCT:LCT 0 : 100%, (4) G25: GBN + MCT:LCT 25 : 75%, (5) G50: GBN + MCT:LCT 50 : 50%, (6) G75: GBN + MCT:LCT 75 : 25%, and (7) G100: GBN + MCT:LCT 100 : 0%. Parameters observed were serum levels of calcium, phosphorus, and alkaline phosphatase, femur bone characteristics, bone microarchitecture by histomorphometry, micro computed-tomography (μCT), and mechanical strength. RESULTS: The CCa and G100 groups had the best dietary results based on all parameters. The G100 group was superior to CCa in calcium and phosphorus bioavailability, rat’s bone strength and density. CONCLUSIONS: G100: GBN + MCT:LCT 100 : 0% group feed beneficially affected the bioavailability of calcium, was letting he rat’s bones to develop properly, had high density, and been strong throughout the growth phase.

Mobility, Bioavailability, and Enrichment of Soil-Bound Phosphorus in Flood-Prone Paddy Fields: A Case Study of Kunnukara, South India.

Bioavailability, enrichment, and risk of phosphorus (P) and its fraction composition were monitored in the paddy soils of Kunnukara during the pre-cultivation and post-harvest periods in the years 2020 and 2021. Iron-bound P (≥ 105.56 ± 0.05mg/kg) was found highest among the P fractions. The bioavailability of P was recorded at peak value during the post-harvest period, contributed by organic P, Iron bound P, and loosely bound P. Principal component analysis inferred that loosely bound P was pH-dependent and significantly influenced by cation exchange, particle density, soil aggregate stability, and total organic carbon (TOC) in the post-harvest soil, whereas TOC, aluminium-bound P, and calcium-bound P in the pre-cultivation soils. Additionally, physico-chemical parameters like electrical conductivity, bulk density, specific gravity, TOC, and soil aggregate stability have a significant impact on the composition of P fractions in the soil. Bioavailable phosphorus (BAP) ranged from 642.78 ± 0.49 to 594.20 ± 1.23mg/kg during the post-harvest period. Moreover, the contribution of BAP to total P ranged from 99.45 to 99.54%, indicating the fact that soil is sufficient in BAP. Pollution indices revealed that the paddy soils are at risk of eutrophication. Phosphorus Pollution Index (PPI) > 1 exhibited moderate pollution (1.06 to 1.07) at the topsoil (0-15cm) and PPI < 1, mild pollution (0.92 to 0.99) at 15-30cm depths. The organic nitrogen index ≥ 0.133 indicates severe soil pollution in the study site. An extended fertilizer application in the field contributes to nutrient enrichment and warrants the risk of contamination in nearby riverine systems (River Periyar and River Chalakkudy).

Influence of composted manures and co-composted biochar on growth performance of saffron and soil nutrients under varying electrical conductivity soil conditions: A two-year field study

The stigmas of saffron (Crocus sativus L.) are known as “red gold” for being the most expensive spice of the world. This medicinal crop grows well in the regions with cold winter Mediterranean climate. However, salinity can be one of the limiting factors for its cultivation in these regions. Composted manures and their co-compost with wood-derived biochar as fertilizers in saline soil can reduce the salinity stress on saffron. In this study, the composted manures from dairy farms (FYM), sheep and goats (SG) and poultry (PM) and their co-compost with wood-derived biochar (FYM-B, SG-B and PM-B) were amended in non-saline (EC1:2 0.25 dS m−1, SOM; 9.9 g kg−1) and soil with natural slight salinity (EC1:2; 1.95 dS m−1, SOM; 30.9 g kg−1) soil for two consecutive years with the total amendment rate of 65 t ha−1 for each fertilizer. The saline soil was transported from an agricultural farm (30 km away from research field); whereas, the non-saline soil was not transported and was not cultivated before. The amendment of fertilizers and sowing of corms were conducted at the same time in the mid of August. The stigma yield in saline control soil was significantly lower than non-saline control in both cropping years. In non-saline soil, all fertilizers reduced stigma yield of first-year crop by 14–60 % (P < 0.05). No differences between treatments for the stigma yield of second year crop in non-saline and of first year crop in saline soil were observed. In saline soil, FYM and PM fertilizers increased stigma yield of second year crop by 44 % and 41 %, respectively (P < 0.05). The two-year cumulative agronomic efficiencies for nitrogen and phosphorus and the nitrogen use efficiency for leaf biomass were lower under fertilizer treatments than control in non-saline and saline soil. In non-saline soil the PM-B; whereas, in saline soil all fertilizers (except SG) increased the phosphorus use efficiency of leaves (P < 0.05). The two-year amendment of composted manures and FYM-B in non-saline soil resulted in high uptake of sodium in leaves (P < 0.05); whereas, such effect was not observed for saline soil. Almost all fertilizers increased ∼2–5 fold the concentration of bioavailable phosphorus and ∼2–3 fold the concentration of potassium in non-saline and saline soil (P < 0.05). The positive influence of fertilizers on stigma yield and PUE of leaves of second year crop was observed only for saline soil. Furthermore, contrary to the results for non-saline soil, these fertilizers did not cause an increased uptake of Na in leaves in saline soil. We attribute this effect to the high concentration of SOM and gradual decline in EC (0.94–1.71 dS m−1) over time in saline soil. The gradual improvement in yield (from negative to neutral in non-saline and from neutral to positive in saline soil) was observed over time. Amendment of fertilizers and sowing of corms at same time may be the reason for their negative influence on stigma yield in low SOM-containing non-saline soil.

Cascaded reservoirs promote phosphorus bioavailability of surface sediments in the Upper Mekong River

As a key nutrient for primary productivity in freshwater ecosystems, the effect of upper cascade reservoirs on the downstream phosphorus (P) loading is subject to an ongoing scientific debate in the Mekong River. To investigate the effects of cascade reservoirs on the forms of P and its bioavailability in surface sediment, two rounds of field research were carried out both in a free-flowing river (Nu River) and in the Upper Mekong River (Lancang River) during winter and summer. Results showed that while the P was trapped with sediments and environmental parameters changed significantly, high relative abundance of bioavailable phosphorus (BioP, generally include Fe-bound P, Al-bound P, and Organic P) in sediment was detected in reservoirs and at near the border between China and Myanmar. The increased Bio-P in reservoirs may be caused by sediments sorting, anaerobic surface sediments, appropriate temperature, longer residence time and algae-nutrient positive feedback loops. Accumulated Bio-P in sediments may elevate the phosphorus release to overlying water and exacerbate eutrophication in reservoirs. Considered the intense anthropogenic phosphorus loading, nutrients enrichment risk in the lower Mekong River should receive more attention in further research.

Riverine nutrient impact on global ocean nitrogen cycle feedbacks and marine primary production in an Earth system model

Abstract. Riverine nutrient export is an important process in marine coastal biogeochemistry and also impacts global marine biology. The nitrogen cycle is a key player here. Internal feedbacks are shown to regulate not only nitrogen distribution, but also primary production and thereby oxygen concentrations. Phosphorus is another essential nutrient and interacts with the nitrogen cycle via different feedback mechanisms. After a previous study of the marine nitrogen cycle response to riverine nitrogen supply, here we include phosphorus from river export with different phosphorus burial scenarios and study the impact of phosphorus alone and in combination with nitrogen in a global 3D ocean biogeochemistry model. Again, we analyse the effects on near-coastal and open-ocean biogeochemistry. We find that riverine export of bioavailable phosphorus alone or in conjunction with nitrogen affects marine biology on millennial timescales more than riverine nitrogen alone. Biogeochemical feedbacks in the marine nitrogen cycle are strongly influenced by additional phosphorus. Where bioavailable phosphorus increases with river input, nitrogen concentration increases as well, except for in regions with diminishing oxygen concentrations. High phosphorus burial rates decrease biological production significantly. Globally, the addition of riverine phosphorus in the modelled ocean leads to elevated primary production rates in the coastal and open oceans.

Toward Cross-Species Crop Se Content Prediction Using Random Forest Modeling

Selenium is an indispensable trace element in the human body that plays an important role in maintaining life activities. The consumption of Se-rich crops provides a practical and effective way for the body to supplement Se. However, the Se content in crops is affected by the soil Se content and the interactions between other elements in the soil. In this study, the Tibetan Plateau of China was chosen as the study area. The random forest algorithm was applied to select four key indicators—selenium (Se), bioavailable phosphorus (P), cadmium (Cd), and bioavailable copper (Cu)—from 29 soil variables to predict the Se content in rapeseed, wheat, potato, pasture, and chrysanthemum crops. The results showed that, despite the rich soil Se resources in the Tibetan Plateau, only 20% of the crop samples met the national Se enrichment standard (&gt;0.07 mg kg−1). Compared with the traditional multiple linear regression method, the random forest model is more accurate, efficient, and reliable in predicting the Se content of crops. In cross-species crop prediction, which refers to the simultaneous cultivation and analysis of multiple distinct crop species within the same agricultural setting, the random forest model demonstrated superior performance, marking a significant breakthrough in cross-species crop research. This approach effectively eliminates the tedious process of conducting repetitive individual evaluations for different crop types in the same region, highlighting its innovative significance. Meanwhile, the Tibetan Plateau, known as the “Roof of the World”, is also of great research value. These results provide valuable references for the planning and management of Se-enriched farmlands, which will help improve the yield and quality of Se-enriched crops and promote the growth of farmers’ interests.

Biochar-based phosphate fertilizer improve phosphorus bioavailability, microbial functioning, and citrus seedling growth

Phosphorus is essential for plant growth but often becomes immobilized in soils, reducing its availability to plants. This study explored the enhancement of phosphorus bioavailability through the co-pyrolysis of rice straw with magnesium oxide (MgO) at 800 °C, resulting in a novel biochar-based phosphate fertilizer, termed MRS8-P. The treatment involved enriching biochar with MgO to increase phosphorus loading and evaluating its effects on soil physicochemical properties and citrus seedling growth. Soil analysis revealed improved physicochemical properties, including increased available phosphorus (AP), enhanced soil pH, higher electrical conductivity (EC), and rapidly increased available potassium (RAK); however, a temporary immobilization of alkaline hydrolytic nitrogen (AHN) was noticed by biochar application. Notably, soil microbiota dynamics shifted with an increase in beneficial taxa, such as Proteobacteria and Actinobacteria, which enhanced phosphorus solubilization and organic matter decomposition, and a decrease in taxa, such as Methylomirabilota and Desulfobacterota. These microbial changes significantly contribute to soil fertility and nutrient availability. The application of MRS8-P significantly enhanced nitrogen, phosphorus, and potassium (NPK) uptake in citrus seedlings, as demonstrated by increased growth metrics, such as plant height, stem coarseness, and chlorophyll content measured by the SPAD index. These findings underscore the potential of MRS8-P in reducing reliance on traditional phosphate fertilizers, which are linked to environmental degradation through runoff and pollution. The study confirms that biochar-based phosphate fertilizers, such as MRS8-P, can promote more sustainable agricultural practices and improve crop health and soil management while minimizing environmental impacts.

Comprehensive evaluation of bioavailable phosphorus in biochar synthesized by co-pyrolysis of sewage sludge and straw ash

The world's phosphorus (P) resources are gradually depleting. Sewage sludge is an important secondary P resource, and sludge-derived biochar for land use is an effective way to achieve P recovery. However, P in biochar synthesized by direct pyrolysis of sludge usually shows comparatively low bioavailability. In this study, biomass ash from different types of straw was used as an additive for co-pyrolysis with sludge. The distribution of different P fractions in the obtained co-pyrolyzed biochar was investigated. The P bioavailability of the co-pyrolyzed biochar was comprehensively evaluated by three methods, including chemical extraction, diffusive gradients in thin films (DGT) technology and pot experiments. The results indicate that the bioavailable P in co-pyrolyzed biochar is significantly positively correlated with the contents of K, Ca, and Mg elements in straw ash, which facilitate the transformation of P in sludge into forms that are more easily utilized by plants, including monetite (CaHPO4), hydroxyapatite (Ca5(PO4)3OH) and pyrocoproite (K2MgP2O7). Moreover, pot experiments show that the P contents in ryegrass shoots and roots cultivated in co-pyrolyzed biochar-added soils increased by 11.98–114.97 % and 28.90–69.70 %, respectively, compared to the control soil. The DGT technology could better reflect the uptake of P by plants with a Pearson correlation coefficient as high as 0.94. This study provides references for P resource recovery, and the collaborative reutilization of sewage sludge and straw ash.

Dietary phosphorus and renal disease in cats: where are we?

Phosphorus is an essential nutrient required for the normal function of every cell in the body and a deficiency in dietary phosphorus may lead to adverse effects. Conversely, high dietary phosphorus may cause kidney damage in otherwise healthy adult cats, particularly when provided in highly bioavailable forms and when the calcium-to-phosphorus ratio is low. For cats that have chronic kidney disease (CKD), phosphorus is the most important mineral in its pathogenesis and morbidity. As the disease progresses, elevated phosphorus may increase the risk of complications such as soft tissue mineralization, which can lead to a further decrease in renal function. Additionally, the hormones secreted in response to increased circulating phosphorus have harmful effects, such as bone resorption, and can cause cardiovascular pathology. Very low phosphorus diets can also be problematic in cats with early CKD, potentially leading to hypercalcemia. There is currently a lack of maximum safety limits for dietary phosphorus in accepted nutritional guidelines in North American and Europe, which makes it difficult to assess the safety of some higher phosphorus cat foods. Additionally, information regarding phosphorus bioavailability is unknown for many diets and there are no commercially available tests. Similarly, there is no consensus regarding phosphorus requirement and recommended intake in cats with International Renal Interest Society stage 1-4 CKD despite there being targets for serum phosphorus. This review evaluates dietary phosphorus in healthy cats and cats with renal disease, and describes how newer research is informing evolving clinical approaches in feline nutrition. The article is aimed at general practitioners, internal medicine specialists and veterinary nutritionists. Information provided in this article is drawn from the published literature.

Enhancing nutrient bioavailability in distillery wastewater through electrochemical oxidation for microalgal growth: Insights on biomass yield, nutrient utilisation, and VFA-assisted carbon capture

Two-stage treatment of distillery wastewater (DWW) via electrochemical oxidation (EO) using Ti-RuO2 anodes (35 cm2 area) followed by mixotrophic microalgal treatment was investigated. In the first-stage, EO of DWW has improved the bioavailability of nitrogen and phosphorus at 3.95–5.14 mg/Ah and 0.43–1.02 mg/Ah, respectively, which had strong correlation with current density. EO also reduced ∼30 % TOC, 53 % COD and ∼44 % TN. In the second-stage, the ability of a novel microalgae, Asterarsys quadricellulare to mitigate the toxicity of electrochemically oxidised DWW (EO-DWW) while utilising the nutrients effectively was investigated. The mixotrophic algal growth effectively utilised 85 % phosphate and 91 % nitrate present in EO-DWW at a corresponding growth rate of 0.73 d−1. The algal biomass was found to have ∼15 % carbohydrates, ∼12 % lipids and ∼33 % proteins. Subsequently, a bench-scale bubble column photobioreactor investigation was carried out to understand the carbon dynamics during the growth of Asterarsys quadricellulare. The metabolic uptake of monocarboxylic volatile fatty acids (VFA) and nitrate were found to release OH− ions, which eventually helped in dissolving CO2 in the reactor through a diffusion-limited process. The total energy spent in bench-scale EO system was 840 kWh (3024 kJ) per L of DWW, and the energy recovery potential of second-stage algal reactor was ∼8.7 %. The microtoxicity experiments with Alivibrio fischeri revealed that two-stage treated DWW was found to be safe for reuse as the microalgal growth has abated the toxicity of EO-DWW.

Biochar and wood vinegar altered the composition of inorganic phosphorus bacteria community in saline-alkali soils and promoted the bioavailability of phosphorus

As an important part of the ecosystem, saline-alkali soils are in urgent need of efficient and environmentally friendly soil conditioners. Biochar and wood vinegar are regarded as organic soil improvement and plant growth regulators to improve soil physicochemical properties and promote crop growth. However, the mechanism of how inorganic phosphorus bacteria increase phosphorus when biochar and wood vinegar applied to saline-alkali soils is not clear. Herein, the present study was designed to investigate the effects of biochar and wood vinegar with different rates on physicochemical properties of saline-alkali soils and inorganic phosphorus bacteria diversities and to discuss the mechanism of biochar and wood vinegar on available phosphorus by pot experiments. The application of biochar and wood vinegar exhibited an effect on the decrease in pH and salt contents and the increase in soil porosity, soil nutrients, and hundred-grain weight of rice. The 600 kg ha−1 biochar and 1800 kg ha−1 wood vinegar group showed the most significant increment in available phosphorus, alkaline phosphatase, acid phosphatase, and neutral phosphatase activities, with the increases of 49.24%, 40.35%, 48%, and 149%, respectively. The 600 kg ha−1 biochar and 1200 kg ha−1 wood vinegar group significantly enhanced microbial biomass phosphorus concentrations by 41.29%. Moreover, biochar and wood vinegar shifted inorganic phosphorus bacteria composition structure and promoted its diversities, more so at a higher rate of wood vinegar application. The dominant species of inorganic phosphorus bacteria were Proteobacteria, Gammaproteobacteria, Alphaproteobacteria, Pseudomonas, and Rhizobium in saline-alkali soils. The Alphaproteobacteria and Hydrogenophaga were the key microorganisms reducing pH and salt contents and increasing available phosphorus contents in saline-alkali soils. In conclusion, the application of biochar and wood vinegar was a useful strategy to improve saline-alkali soils.

Unveiling wheat growth promotion potential of phosphate solubilizing Pantoea agglomerans PS1 and PS2 through genomic, physiological, and metagenomic characterizations.

Phosphorus is an abundant element in the earth's crust and is generally found as complex insoluble conjugates. Plants cannot assimilate insoluble phosphorus and require external supplementation as chemical fertilizers to achieve a good yield. Continuous use of fertilizers has impacted soil ecology, and a sustainable solution is needed to meet plant elemental requirements. Phosphate solubilizing microbes could enhance phosphorus bioavailability for better crop production and can be employed to attain sustainable agriculture practices. The current study unveils the biofertilizer potential of wheat rhizospheric bacteria through physiological, taxonomic, genomic, and microbiomics experimentations. Culture-dependent exploration identified phosphate-solubilizing PS1 and PS2 strains from the wheat rhizosphere. These isolates were rod-shaped, gram-negative, facultative anaerobic bacteria, having optimum growth at 37°C and pH 7. Phylogenetic and phylogenomic characterization revealed their taxonomic affiliation as Pantoea agglomerans subspecies PS1 & PS2. Both isolates exhibited good tolerance against saline (>10% NaCl (w/v), >11.0% KCl (w/v), and >6.0% LiCl (w/v)), oxidizing (>5.9% H2O2 (v/v)) conditions. PS1 and PS2 genomes harbor gene clusters for biofertilization features, root colonization, and stress tolerance. PS1 and PS2 showed nitrate reduction, phosphate solubilization, auxin production, and carbohydrate utilization properties. Treatment of seeds with PS1 and PS2 significantly enhanced seed germination percentage (p = 0.028 and p = 0.008, respectively), number of tillers (p = 0.0018), number of leaves (p = 0.0001), number of spikes (p = 0.0001) and grain production (p = 0.0001). Wheat rhizosphere microbiota characterizations indicated stable colonization of PS1 and PS2 strains in treated seeds at different feek stages. Pretreatment of seeds with both strains engineered the wheat rhizosphere microbiota by recruiting plant growth-promoting microbial groups. In vitro, In vivo, and microbiota characterization studies indicated the biofertilizer potential of Pantoea sp. PS1 & PS2 to enhance wheat crop production. The employment of these strains could fulfill plant nutrient requirements and be a substitute for chemical fertilizers for sustainable agriculture.