Tracking phosphorus security: indicators of phosphorus vulnerability in the global food system

How do high phosphate concentrations affect soil microbial communities after a century of ecosystem self-reclamation?

The use of rock phosphate (RP) instead of soluble phosphate fertilizers is preferred for the development of more sustainable agriculture. However, the impact of high concentrations in RP on bacterial and fungal communities remains poorly documented. Thus, next-generation sequencing was used to characterize bacterial and fungal communities in the soils and roots of four plant species growing naturally in a self-restored ecosystem, on former open-pit phosphate mines where past exploitation generated locally a substantial phosphate enrichment of the soil. Our results show that bacterial communities are dominated by Actinobacteria and Proteobacteria phyla, while the Ascomycota and Basidiomycota phyla predominate in the fungal community. The alpha and beta diversities of both bacterial and fungal communities differ significantly between the root and soil compartments but are not significantly affected by RP inputs. However, Amplicon Sequence Variants (ASVs) indicative of RP-enriched soils have been identified; among them are bacteria representative of Streptomyces, Bacillus, Mycobacterium or Agromyces. Implications of these results open new ways of reflection to understand the microbial response following RP-inputs and long-term soil restoration, as well as to formulate microbial-based bioinoculants for sustainable agriculture applications based on microorganisms better adapted to high concentrations of RP.

Combining life-cycle assessment and linear programming to optimize social fertilizer costs

This paper focuses on the role of fertilizers within regional nutrient cycles. Bio-based fertilizers can contribute to regional nutrient circularity, but the question remains whether production and consumption of bio-based fertilizers is beneficial to the farmer and the environment. Therefore, both farmers' private costs and environmental externalities should be taken into account. We formulate a farm-level multi-objective optimization model by considering a range of fertilizers, their costs and the environmental consequences associated with their production and use. The cost-minimization approach is applied to a conceptualized Flemish leek farmer aiming to safeguard nutrient uptake while being constrained by nutrient standards and the availability of on-farm residues. Our results suggest that mineral fertilizers have an important role in the fertilizer mix despite their environmental externalities. Nevertheless, there is also a role for bio-based fertilizers. These results have implications for farmers and policymakers wishing to internalize fertilizer externalities.

Early exposure to phosphorus starvation induces genetically determined responses in Sorghum bicolor roots

KEY MESSAGE

We identified novel physiological and genetic responses to phosphorus starvation in sorghum diversity lines that augment current knowledge of breeding for climate-smart crops in Europe. Phosphorus (P) deficiency and finite P reserves for fertilizer production pose a threat to future global crop production. Understanding root system architecture (RSA) plasticity is central to breeding for P-efficient crops. Sorghum is regarded as a P-efficient and climate-smart crop with strong adaptability to different climatic regions of the world. Here we investigated early genetic responses of sorghum RSA to P deficiency in order to identified genotypes with interesting root phenotypes and responses under low P. A diverse set of sorghum lines (n = 285) was genotyped using DarTSeq generating 12,472 quality genome wide single-nucleotide polymorphisms. Root phenotyping was conducted in a paper-based hydroponic rhizotron system under controlled greenhouse conditions with low and optimal P nutrition, using 16 RSA traits to describe genetic and phenotypic variability at two time points. Genotypic and phenotypic P-response variations were observed for multiple root traits at 21 and 42 days after germination with high broad sense heritability (0.38-0.76). The classification of traits revealed four distinct sorghum RSA types, with genotypes clustering separately under both low and optimal P conditions, suggesting genetic control of root responses to P availability. Association studies identified quantitative trait loci in chromosomes Sb02, Sb03, Sb04, Sb06 and Sb09 linked with genes potentially involved in P transport and stress responses. The genetic dissection of key factors underlying RSA responses to P deficiency could enable early identification of P-efficient sorghum genotypes. Genotypes with interesting RSA traits for low P environments will be incorporated into current sorghum breeding programs for later growth stages and field-based evaluations.

Tradeoffs among root functional traits for phosphorus acquisition in 13 soybean genotypes contrasting in mycorrhizal colonization

BACKGROUND AND AIMS

Plants have adapted to acquire phosphorus (P) primarily through advantageous root morphologies, responsive physiological pathways and associations with mycorrhizal fungi. Yet, to date, little information exists on how variation in arbuscular mycorrhizal (AM) colonization is coordinated with root morphological and physiological traits to enhance P acquisition.

METHODS

Thirteen root functional traits associated with P acquisition were characterized at full bloom stage in pot cultures under low soil P availability conditions for 13 soybean genotypes contrasting in AM colonization.

KEY RESULTS

Significant variation in root functional traits was observed in response to low P stress among the 13 tested soybean genotypes contrasting in AM colonization. Genotypes with low AM colonization exhibited greater root proliferation but with less advantageous root physiological characteristics for P acquisition. In contrast, genotypes with high AM colonization exhibited less root growth but higher phosphatase activities and carboxylate content in the rhizosheath. Root dry weights, and contents of carbon and P were positively correlated with root morphological traits of different root orders and whole root systems, and were negatively correlated with AM colonization of fine roots and whole root systems, as well as rhizosheath phosphatase activities and carboxylate contents. These results taken in combination with a significant positive correlation between plant P content and root morphological traits indicate that root morphological traits play a primary role in soybean P acquisition.

CONCLUSIONS

The results suggest that efficient P acquisition involves tradeoffs among carbon allocation to root proliferation, mycorrhizal symbiosis or P-mobilizing exudation. Complementarity and complexity in the selection of P acquisition strategies was notable among soybean genotypes contrasting in AM colonization, which is closely related to plant C budgeting.

Recovering Phosphate from Complex Wastewater Using Macroporous Cryogel Composited Calcium Silicate Hydrate Nanoparticles

Since currently used natural, nonrenewable phosphorus resources are estimated to be depleted in the next 30-200 years, phosphorus recovery from any phosphorus-rich residues has attracted great interest. In this study, phosphorus recovery from complex wastewater samples was investigated using continuous adsorption on cryogel column composited calcium silicate hydrate nanoparticles (CSH columns). The results showed that 99.99% of phosphate was recovered from a synthetic water sample (50 mg L-1) using a 5 cm CSH column with a 5 mL min-1 influent flow rate for 6 h while 82.82% and 97.58% of phosphate were recovered from household laundry wastewater (1.84 mg L-1) and reverse osmosis concentrate (26.46 mg L-1), respectively. The adsorption capacity decreased with an increasing flow rate but increased with increasing initial concentration and column height, and the obtained experimental data were better fitted to the Yoon-Nelson model (R2 = 0.7723-0.9643) than to the Adams-Bohart model (R2 = 0.6320-0.8899). The adsorption performance of phosphate was decreased 3.65 times in the presence of carbonate ions at a similar concentration, whereas no effect was obtained from nitrate and sulfate. The results demonstrate the potential of continuous-flow phosphate adsorption on the CSH column for the recovery of phosphate from complex wastewater samples.

Leaf surface features of maize cultivars and response to foliar phosphorus application: effect of leaf stage and plant phosphorus status

Soil phosphorus (P) application is the most common fertilisation technique but may involve constraints due to chemical fixation and microbial immobilisation. Furthermore, excessive P fertilisation leads to P runoff into water bodies, threatening ecosystems, so targeted foliar P fertilisation is an interesting alternative. This study aimed to determine the importance of leaf surface characteristics for foliar P uptake in P-deficient maize (Zea mays L.). The leaf surface of four maize cultivars was characterised by electron microscopy, Fourier transform infrared spectroscopy and contact angle measurements. Uptake of foliar-applied P by maize cultivars was estimated, measuring also leaf photosynthetic rates after foliar P spraying. Plants of cultivar P7948 were found to be wettable from the 4th leaf in acropetal direction, whereas other cultivars were unwettable until the 6th leaf had developed. Minor variations in stomatal number and cuticle composition were recorded, but no differences in foliar P absorption were observed between cultivars. Nevertheless, cultivars showed variation in the improvement of photosynthetic capacity following foliar P application. Phosphorus deficiency resulted in ultrastructural disorganisation of mesophyll cells and chloroplasts, which impaired photosynthetic performance, yet there was no effect on stomatal frequency and leaf wettability. This study provides new insights into the influence of P deficiency and cultivar on leaf surface characteristics, foliar P uptake and its effect on physiological processes. Understanding the relationships between leaf characteristics and P uptake allows a more targeted evaluation of foliar P fertilisation as an application technique and contributes to the understanding of foliar uptake mechanisms.

Environmental sustainability opportunity and socio-economic cost analyses of phosphorus recovery from sewage sludge

Although phosphorus (P) recovery and management from sewage sludge are practiced in North America and Europe, such practices are not yet to be implemented in China. Here, we evaluated the environmental sustainability opportunity and socio-economic costs of recovering P from sewage sludge by replacing the current-day treatments (CT; sludge treatment and landfill) and P chemical fertilizer application (CF) in China using life cycle assessment and life cycle costing methods. Three potential P recovery scenarios (PR1‒PR3: struvite, vivianite, and treated sludge) and corresponding current-day scenarios (CT1‒CT3 and CF) were considered. Results indicated that PR1 and PR2 have smaller environmental impacts than the current-day scenarios, whereas PR3 has larger impacts in most categories. PR3 has the lowest net costs (sum of internal costs and benefits, 39.1-54.7 CNY per kg P), whereas PR2 has the lowest external costs (366.8 CNY per kg P). Societal costs for production and land use of 1 kg P by P recovery from sewage sludge (e.g., ∼527 CNY for PR1) are much higher than those of P chemical fertilizers (∼20 CNY for CF). However, considering the costs in the current-day treatments (e.g., ∼524 CNY for CT1), societal costs of P recovery scenarios are close to or slightly lower than those of current-day scenarios. Among the three P recovery scenarios, we found that recovering struvite as P fertilizer has the highest societal feasibility. This study will provide valuable information for improved sewage sludge management and will help promote the sustainable supply of P in China.

Abundant bacterial subcommunity is structured by a stochastic process in an agricultural system with P fertilizer inputs

Soil microorganisms play an important role in agroecosystems and are related to ecosystem functioning. Nevertheless, little is understood about their community assembly and the major factors regulating stochastic and deterministic processes, particularly with respect to the comparison of abundant and rare bacterial subcommunities in agricultural systems. Here, we investigated the assembly of abundant and rare bacterial subcommunities in fields with different crops (maize and wheat) and phosphorus (P) fertilizer input at three different growth stages on the Loess Plateau. The high-throughput sequencing dataset was assessed using null and neutral community models. We found that abundant bacteria was governed by the stochastic process of homogenizing dispersal, but rare bacterial subcommunity was predominant by deterministic processes in maize and wheat fields due to broader niche breadths of abundant species. Soil nitrogen (N) and P also determined the assembly of abundant and rare soil subcommunities. The relative abundance and composition of the abundant and rare bacterial subcommunities were also influenced by soil nutrients (soil available P (AP) and NO₃^--N) and agricultural practices (P fertilization and crop cultivation). In addition, the abundant bacterial community was more susceptible to P fertilizer input than that of the rare bacteria, and a higher relative abundance of abundant bacteria was observed in the P70 treatment both in maize and wheat soils. The microbial co-occurrence network analysis indicated that the maize field and low nutrient treatment exhibited stronger associations and that the abundant bacteria showed fewer interconnections. This study provides new insights toward understanding the mechanisms for the assembly of abundant and rare bacterial taxa in dryland cropping systems, enhancing our understanding of ecosystem diversity theory in microbial ecology.

Root exudate-derived compounds stimulate the phosphorus solubilizing ability of bacteria

Low phosphorus (P) availability in soils is a major challenge for sustainable food production, as most soil P is often unavailable for plant uptake and effective strategies to access this P are limited. Certain soil occurring bacteria and root exudate-derived compounds that release P are in combination promising tools to develop applications that increase phosphorus use efficiency in crops. Here, we studied the ability of root exudate compounds (galactinol, threonine, and 4-hydroxybutyric acid) induced under low P conditions to stimulate the ability of bacteria to solubilize P. Galactinol, threonine, and 4-hydroxybutyric acid were incubated with the P solubilizing bacterial strains Enterobacter cloacae, Pseudomonas pseudoalcaligenes, and Bacillus thuringiensis under either inorganic (calcium phosphate) or organic (phytin) forms of plant-unavailable P. Overall, we found that the addition of individual root exudate compounds did not support bacterial growth rates. However, root exudates supplemented to the different bacterial appeared to enhance P solubilizing activity and overall P availability. Threonine and 4-hydroxybutyric acid induced P solubilization in all three bacterial strains. Subsequent exogenous application of threonine to soils improved the root growth of corn, enhanced nitrogen and P concentrations in roots and increased available levels of potassium, calcium and magnesium in soils. Thus, it appears that threonine might promote the bacterial solubilization and plant-uptake of a variety of nutrients. Altogether, these findings expand on the function of exuded specialized compounds and propose alternative approaches to unlock existing phosphorus reservoirs of P in crop lands.

Valorization of Anaerobic-Fermentation Liquid Digestates-Membrane-Based Process Development

Complete valorization of various wastes and effluents, with significant organic content, remains a great challenge in the pursuit of a circular economy. The approach based on anaerobic fermentation, leading to valuable biogas production, has been broadly accepted and employed as an attractive processing scheme. However, despite notable research efforts, complete valorization of the digestates (involving recovery of nutrients/by-products and full recycling/reuse of treated water) requires additional work for sustainable process development. This study aims to make a contribution in this direction by demonstrating a systematic methodology for valorizing the liquid digestate. The proposed membrane-based processing scheme involves UF-membrane pretreatment of the liquid digestate (for sludge separation) and subsequent NF/RO membrane treatment for reuse/recycling of the permeate; the concentrate, enriched in "nutrients" (phosphate and ammonium compounds), can be utilized for soil fertilization, with further conditioning/processing. By performing targeted laboratory experiments and advanced simulations, the membrane-based process was developed to a relatively high technology-readiness level, including a pilot unit design/construction and preliminary testing with satisfactory results. Through pilot testing in industrial environment, further process development and optimization will be pursued, towards practical applications. The demonstrated methodology is also considered appropriate for systematic development of membrane-based processes to valorize/treat a variety of similar effluents.

Phosphorus price spikes: A wake-up call for phosphorus resilience

Food systems depend on reliable supplies of phosphorus to fertilize soils. Since 2020, a pandemic, geopolitical disputes, trade wars and escalating fuel prices have driven a >400% increase in phosphorus commodity prices, contributing to the current food crisis. The Russia-Ukraine conflict has disrupted phosphate trade further. Concurrently, phosphorus losses to freshwaters, through insufficient municipal wastewater treatment and inappropriate fertilizer use and land management practices, are a significant threat to water quality globally. Despite precariously balanced food and water security risks, nations are largely unaware of their “phosphorus vulnerability” and phosphorus is markedly absent in national and global policies addressing food and water security. Phosphorus vulnerability can be described as the degree to which people/systems are susceptible to harm due to the physical, geopolitical and socio-economic dimensions of global phosphorus scarcity and pollution. Here, we bring the current price spike into focus, highlighting the drivers, policy responses and their consequences. We highlight the need for an integrated assessment of phosphorus vulnerability that considers environmental, socio-economic and climate change risks across scales. We illustrate how reducing phosphorus waste, increasing phosphorus recycling, and wider system transformation can reduce national reliance on imported phosphorus, whilst enhancing food and water security. The current crisis in fertilizer prices represents a wake-up call for the international community to embrace the global phosphorus challenge.

Dynamic variation of nutrient absorption, metabolomic and transcriptomic indexes of soybean (Glycine max) seedlings under phosphorus deficiency

The dynamic trajectory of metabolites and gene expression related to phosphorus absorption and utilization in soybean seedling roots were determined under short- and long-term phosphorus deficiency stress. The metabolome results showed that TCA and GS/GOGAT cycles were enhanced after 2 days of phosphorus deficiency stress; however, they were inhibited after 15 days. GC-TOF-MS showed that phosphorus deficiency increased the accumulation of amino acids significantly after 2 days, whereas organic acids and lipid substances increased significantly after 15 days. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) showed that transcriptional levels of five key genes related to phosphorus activation and phosphorus starvation signal transduction increased continuously with phosphorus deficiency. The expression of GmPHT1 and GmSPX triggered the phosphorus starvation signal pathway and induced the expression of the GmPS and GmPAP genes to enhance the synthesis and secretion of organophosphorus hydrolase and organic acid in soybean roots under phosphorus deficiency. The phospholipid metabolism was enhanced significantly after 15 days of stress and when GmSQD, a crucial enzyme in lipid biosynthesis, was up-regulated. Thus, we propose that future investigations on stress caused by phosphorus deficiency should include more organs obtained at different developmental stages.

Recent Advances of Enzyme-Free Electrochemical Sensors for Flexible Electronics in the Detection of Organophosphorus Compounds: A Review

Emerging materials integrated into high performance flexible electronics to detect environmental contaminants have received extensive attention worldwide. The accurate detection of widespread organophosphorus (OP) compounds in the environment is crucial due to their high toxicity even at low concentrations, which leads to acute health concerns. Therefore, developing rapid, highly sensitive, reliable, and facile analytical sensing techniques is necessary to monitor environmental, ecological, and food safety risks. Although enzyme-based sensors have better sensitivity, their practical usage is hindered due to their low specificity and stability. Therefore, among various detection methods of OP compounds, this review article focuses on the progress made in the development of enzyme-free electrochemical sensors as an effective nostrum. Further, the novel materials used in these sensors and their properties, synthesis methodologies, sensing strategies, analytical methods, detection limits, and stability are discussed. Finally, this article summarizes potential avenues for future prospective electrochemical sensors and the current challenges of enhancing the performance, stability, and shelf life.

Nematophagous Fungi: A Review of Their Phosphorus Solubilization Potential

Nematophagous fungi (NF) are a group of diverse fungal genera that benefit plants. The aim of this review is to increase comprehension about the importance of nematophagous fungi and their role in phosphorus solubilization to favor its uptake in agricultural ecosystems. They use different mechanisms, such as acidification in the medium, organic acids production, and the secretion of enzymes and metabolites that promote the bioavailability of phosphorus for plants. This study summarizes the processes of solubilization, in addition to the mechanisms of action and use of NF on crops, evidencing the need to include innovative alternatives for the implementation of microbial resources in management plans. In addition, it provides information to help understand the effect of NF to make phosphorus available for plants, showing how these biological means promote phosphorus uptake, thus improving productivity and yield.

Effect of phosphorus fertilizer on phytoextraction using Ricinus communis L. in Cu and Cd co-contaminated soil

Mining activities have led to Cu and Cd contaminated of surrounding agricultural soil. To decrease the Cu and Cd accumulation in crops, the Ricinus communis L. (castor) has been used for phytoremediation. A pot experiment was served to investigate the effect of phosphate fertilizer (Ca(H₂PO₄)₂) on the growth and Cu/Cd uptake of castor in contaminated soil. The results showed that the application of P fertilizer improved the leaf cell morphology, decreased the malonaldehyde (MDA) content of castor leaves, and increased the plant biomass (28.2-34.2%). Besides, phosphate fertilizer still facilitated accumulation Cu and Cd by castor. The addition of phosphate fertilizer increased the contents of Cu in the root of castor, improved the bioconcentration factor (BCF) of Cu, and observably enhanced the accumulation of Cu (up to 201 μg/plant) in castor. Applying phosphorus increased the percentage of residual Cd, diminished the percentage of acid extractable Cd in soil, and the accumulation of Cd in castor was not significantly increased. These results suggest that phosphorus alleviated the stress of heavy metals on castor leaves and enhanced the accumulation of Cu and Cd in castor by promoting the growth of castor.

Phosphorus availability drives mycorrhiza induced resistance in tomato

Arbuscular mycorrhizal (AM) symbiosis can provide multiple benefits to the host plant, including improved nutrition and protection against biotic stress. Mycorrhiza induced resistance (MIR) against pathogens and insect herbivores has been reported in different plant systems, but nutrient availability may influence the outcome of the interaction. Phosphorus (P) is a key nutrient for plants and insects, but also a regulatory factor for AM establishment and functioning. However, little is known about how AM symbiosis and P interact to regulate plant resistance to pests. Here, using the tomato-Funneliformis mosseae mycorrhizal system, we analyzed the effect of moderate differences in P fertilization on plant and pest performance, and on MIR against biotic stressors including the fungal pathogen Botrytis cinerea and the insect herbivore Spodoperta exigua. P fertilization impacted plant nutritional value, plant defenses, disease development and caterpillar survival, but these effects were modulated by the mycorrhizal status of the plant. Enhanced resistance of F. mosseae-inoculated plants against B. cinerea and S. exigua depended on P availability, as no protection was observed under the most P-limiting conditions. MIR was not directly explained by changes in the plant nutritional status nor to basal differences in defense-related phytohormones. Analysis of early plant defense responses to the damage associated molecules oligogalacturonides showed primed transcriptional activation of plant defenses occurring at intermediate P levels, but not under severe P limitation. The results show that P influences mycorrhizal priming of plant defenses and the resulting induced-resistance is dependent on P availability, and suggest that mycorrhiza fine-tunes the plant growth vs defense prioritization depending on P availability. Our results highlight how MIR is context dependent, thus unravel molecular mechanism based on plant defence in will contribute to improve the efficacy of mycorrhizal inoculants in crop protection.

Impacts of the Green Revolution on Rhizosphere Microbiology Related to Nutrient Acquisition

The Green Revolution (GR) involved selective breeding of cereals and the use of high fertilizer inputs with the goal of increasing crop yields to alleviate hunger. As a result of both greater use of inorganic fertilizers and the introduction of semi-dwarf cultivars, grain yield increased globally and hunger was alleviated in certain areas of the world. However, these changes in varietal selection and fertilization regimes have impacted soil fertility and the root-associated microbiome. Higher rates of inorganic fertilizer application resulted in reduced rhizosphere microbial diversity, while semi-dwarf varieties displayed a greater abundance of rhizosphere microbes associated with nitrogen utilization. Ultimately, selection for beneficial aboveground traits during the GR led to healthier belowground traits and nutrient uptake capabilities.

Foliar P Application Cannot Fully Restore Photosynthetic Capacity, P Nutrient Status, and Growth of P Deficient Maize (Zea mays L.)

The essential plant nutrient phosphorus (P) is key for numerous structures and processes in crops and its deficiency can severely restrict yield and quality. As soil P availability for plant uptake is often limited, foliar P application can be an alternative means of supplying P to the plants during the growth period. This study was aimed at investigating the effect of foliar P application on photosynthetic parameters, P nutritional status, and growth of P deficient maize over time. Plants of Zea mays L. cv. Keops were grown with deficient and sufficient amounts of P in hydroponics. Foliar P treatments were applied to P deficient plants and several physiological parameters were monitored for 21 days. The variables measured were leaf gas exchange parameters, SPAD values, foliar P absorption, re-translocation rates, and plant biomass production. Foliar P application significantly increased CO₂-assimilation and SPAD values and additionally enhanced biomass production in all plant components. Elemental analysis revealed increased tissue P concentrations following foliar P application compared to P deficient plants. While increased growth of P-deficient plants was steadily promoted by foliar P spraying for the entire experimental period, the positive effect on CO₂ assimilation and P concentration was transient and vanished some days after the foliar treatment. P deficiency markedly impaired the efficiency of physiological processes of maize plants. As a conclusion, foliar P fertilisation improved physiological and agronomical plant parameters over time, but failed to restore plant functionality of P deficient maize plants during a prolonged experimental period.

Prospects of genetics and breeding for low-phosphate tolerance: an integrated approach from soil to cell

Improving phosphorus (P) crop nutrition has emerged as a key factor toward achieving a more resilient and sustainable agriculture. P is an essential nutrient for plant development and reproduction, and phosphate (Pi)-based fertilizers represent one of the pillars that sustain food production systems. To meet the global food demand, the challenge for modern agriculture is to increase food production and improve food quality in a sustainable way by significantly optimizing Pi fertilizer use efficiency. The development of genetically improved crops with higher Pi uptake and Pi-use efficiency and higher adaptability to environments with low-Pi availability will play a crucial role toward this end. In this review, we summarize the current understanding of Pi nutrition and the regulation of Pi-starvation responses in plants, and provide new perspectives on how to harness the ample repertoire of genetic mechanisms behind these adaptive responses for crop improvement. We discuss on the potential of implementing more integrative, versatile, and effective strategies by incorporating systems biology approaches and tools such as genome editing and synthetic biology. These strategies will be invaluable for producing high-yielding crops that require reduced Pi fertilizer inputs and to develop a more sustainable global agriculture.

Phosphorus flow analysis in maize cultivation: a case study in Thailand

Phosphorus (P) is an essential element for plant cultivation, where the demand for agricultural products as food and feed are the main drivers of aggravated agricultural production systems. Maize is one of the main feedstocks for animal feed production in Thailand. Therefore, this study investigated P flows, using the conservation of mass-balanced concept to identify the major P flows in maize cultivation during rainy and dry seasons based on a survey of 131 plantation land plots. The result indicated that total amount of P input to maize fields during upland rainy and lowland dry season cultivation was determined as 27.76 and 34.96 kg P/ha, respectively, approximately 97% of which was in chemical fertilizers. P output in grain products accounted for 31.7 and 37.3% of the total P input or 32.9 and 38.0% of the applied fertilizer during maize cultivation in rainy and dry seasons, respectively. Agricultural soils were the main stock of P in maize cultivation systems. From the amount of applied P in rainy and dry seasons of maize cultivation, 43.9 and 41.3% remained in the soil, respectively, whereas 6.0 and 4.5% of those input during rainy and dry season were lost through runoff to the hydrosphere, respectively. This result indicated that seasonal and geographical factors may affect P flow pattern in maize cultivation. This revealed that P accumulation in soils and P loss occurring in rainy season were greater than those of dry season. Therefore, optimizing P flows through improved nutrient management should carefully consider helping reduce P loss during maize cultivation in Thailand.

Stimulation of Distinct Rhizosphere Bacteria Drives Phosphorus and Nitrogen Mineralization in Oilseed Rape under Field Conditions

Advances in DNA sequencing technologies have drastically changed our perception of the structure and complexity of the plant microbiome. By comparison, our ability to accurately identify the metabolically active fraction of soil microbiota and its specific functional role in augmenting plant health is relatively limited. Important ecological interactions being performed by microbes can be investigated by analyzing the extracellular protein fraction. Here, we combined a unique protein extraction method and an iterative bioinformatics pipeline to capture and identify extracellular proteins (metaexoproteomics) synthesized in the rhizosphere of Brassica spp. We first validated our method in the laboratory by successfully identifying proteins related to a host plant (Brassica rapa) and its bacterial inoculant, Pseudomonas putida BIRD-1. This identified numerous rhizosphere specific proteins linked to the acquisition of plant-derived nutrients in P. putida. Next, we analyzed natural field-soil microbial communities associated with Brassica napus L. (oilseed rape). By combining metagenomics with metaexoproteomics, 1,885 plant, insect, and microbial proteins were identified across bulk and rhizosphere samples. Metaexoproteomics identified a significant shift in the metabolically active fraction of the soil microbiota responding to the presence of B. napus roots that was not apparent in the composition of the total microbial community (metagenome). This included stimulation of rhizosphere-specialized bacteria, such as Gammaproteobacteria, Betaproteobacteria, and Flavobacteriia, and the upregulation of plant beneficial functions related to phosphorus and nitrogen mineralization. Our metaproteomic assessment of the “active” plant microbiome at the field-scale demonstrates the importance of moving beyond metagenomics to determine ecologically important plant-microbe interactions underpinning plant health.

IMPORTANCE Plant-microbe interactions are critical to ecosystem function and crop production. While significant advances have been made toward understanding the structure of the plant microbiome, learning about its full functional role is still in its infancy. This is primarily due to an incomplete ability to determine in situ plant-microbe interactions actively operating under field conditions. Proteins are the functional entities of the cell. Therefore, their identification and relative quantification within a microbial community provide the best proxy for which microbes are the most metabolically active and which are driving important plant-microbe interactions. Here, we provide the first metaexoproteomics assessment of the plant microbiome using field-grown oilseed rape as the model crop species, identifying key taxa responsible for specific ecological interactions. Gaining a mechanistic understanding of the plant microbiome is central to developing engineered plant microbiomes to improve sustainable agricultural approaches and reduce our reliance on nonrenewable resources.

Hyperspectral and genome-wide association analyses of leaf phosphorus status in local Thai indica rice

Phosphorus (P) is an essential mineral nutrient and one of the key factors determining crop productivity. P-deficient plants exhibit visual leaf symptoms, including chlorosis, and alter spectral reflectance properties. In this study, we evaluated leaf inorganic phosphate (Pi) contents, plant growth and reflectance spectra (420–790 nm) of 172 Thai rice landrace varieties grown hydroponically under three different P supplies (overly sufficient, mildly deficient and severely deficient conditions). We reported correlations between Pi contents and reflectance ratios computed from two wavebands in the range of near infrared (720–790 nm) and visible energy (green-yellow and red edge) (r > 0.69) in Pi-deficient leaves. Artificial neural network models were also developed which could classify P deficiency levels with 85.60% accuracy and predict Pi content with R² of 0.53, as well as highlight important waveband sections. Using 217 reflectance ratio indices to perform genome-wide association study (GWAS) with 113,114 SNPs, we identified 11 loci associated with the spectral reflectance traits, some of which were also associated with the leaf Pi content trait. Hyperspectral measurement offers a promising non-destructive approach to predict plant P status and screen large germplasm for varieties with high P use efficiency.

Integrated microbiology and metabolomics analysis reveal responses of soil microorganisms and metabolic functions to phosphorus fertilizer on semiarid farm

Localized fertilization of phosphorus has potential benefits in achieving higher crop productivity and nutrient use efficiency, but the underlying biological mechanisms of interactions between soil microorganisms and related metabolic cycle remain largely to be recognized. Here, we combined microbiology with non-target metabolomics to explore how P fertilizer levels and fertilization patterns affect wheat soil microbial communities and metabolic functions based on high-throughput sequencing and UPLC-MS/MS platforms. The results showed P fertilizer decreased the diversity of bacterial 16S rRNA genes and fungal ITS genes, and it did significantly change both soil bacterial and fungal overall community structures and compositions. The P levels and patterns also interfered with complexity of soil bacterial and fungal symbiosis networks. Moreover, metabolomics analysis showed that P fertilizer significantly changed soil metabolite spectrum, and the differential metabolites were significantly enriched to 7 main metabolic pathways, such as arginine and proline metabolism, biosynthesis of plant hormones, amino acids, plant secondary metabolites, and alkaloids derived from ornithine. Additionally, microbes also were closely related to the accumulation of metabolites through correlation analysis. Our results indicated that localized appropriate phosphorus fertilizer plays an important role in regulating soil microbial metabolism, and their interactions in soil providing valuable information for understanding how the changed phosphorus management practices affect the complex biological processes and the adaption capacity of plants to environments.

Trace metal elements vaporization and phosphorus recovery during sewage sludge thermochemical treatment - A review

Phosphorus (P) plays essential roles in crops growth. Natural mineral sources of phosphate are non-renewable, overexploited and unevenly distributed worldwide, making P a strategic resource for agricultural systems. The search for sustainable ways to secure P supply for fertilizer production has therefore become a critical issue worldwide. Sewage sludge (SS) is an organic waste material considered as a key alternative source of P. Switzerland and the European Union are about to make it mandatory to recover P from SS or its treatment residues. Among the many technical options to achieve this objective, SS thermochemical treatments spiked with Cl-donors appear as a promising approach to recover P from SS and separate it from mineral pollutants such as trace metal elements (TME). The purpose of Cl-donor additives is to fix P within the mineral residues, possibly in bioavailable P species forms, while promoting TME vaporization by chlorination mechanisms. This review paper compares the various thermochemical treatments investigated worldwide over the past two decades. The influence of process conditions and Cl-donor nature is discussed. The presented results show that, except for nickel and chromium, most TME can be significantly vaporized during a high temperature treatment (over 900 °C) with Cl addition. In addition, the fixation rate and solubility of P is increased when a Cl-donor such as MgCl₂ is added.

Controlled release fertilizer: A review on developments, applications and potential in agriculture

Controlled release fertilizer (CRF) plays a crucial yet necessary part in the sustainable agriculture industry. An alarming rise in call for crop production directly influences the increasing need for synthetically derived fertilizers and pesticides production. The application of CRF has been a gamechanger as an environmentally sustainable pathway to increase crop yields by paving desired phase of plant growth via a direct or indirect mechanism. The mechanism of CRF does not only decreases nutrient dissipation due to volatilization and leaching, but also provides a precisely appropriate nutrient release design that is suitable in the physiological and biochemical aspect of the plant growth. However, CRF is not deployed on larger scale of commercial agriculture practices due to being expensive, has relatively low efficiency in releasing nutrients and its coatings are largely composed of petroleum-based synthetic polymers. Alternatively, there are many polymers derived from renewable and biodegradable sources that can be used as coating material for CRF in the form of bio-nanocomposites. Having said that, there is an apparent gap between the mechanism of the CRFs for promoting plant growth and the prominent role of the nanocomposites especially bio-nanocomposites as coating material for CRF synthesis, thus the importance of nanotechnology application in enhancing the effectiveness of CRF. Therefore, this review attempts to bridge the stated gap and summarizes the comprehensive developments, application mechanisms and future potential of CRF as a fertilizer for crop sustainability.

Recirculating treated sewage sludge for agricultural use: Life cycle assessment for a circular economy

The objective of this study is to assess the environmental value of recirculating nutrients from treated sewage sludge by application to agricultural soils to grow forage as opposed to landfilling and incineration. The methodological choices are aligned to the circular economy framework using life cycle assessment. Consequential modeling and open loop modeling were adopted and adhere to ISO 14044 and International Reference Life Cycle Data System (ILCD) standards. The functional unit is defined in terms of the amounts of nitrogen (N), phosphorus (P) and potassium (K) recirculated from the treated sewage sludge produced annually in Kuwait. The results indicate a reduction in environmental burden with respect to fossil fuel depletion, metal depletion and climate change. A total of 95% of the reduction is realized by avoiding virgin nitrogen production and instead using its recirculated counterpart. Considerable amounts of natural gas, coal, dinitrogen monoxide (nitrous oxide, N₂O) and copper are consumed during virgin N fertilizer production.

Rhizosphere Microbial Communities Are Significantly Affected by Optimized Phosphorus Management in a Slope Farming System

Soil rhizosphere microorganisms play crucial roles in promoting plant nutrient absorption and maintaining soil health. However, the effects of different phosphorus (P) managements on soil microbial communities in a slope farming system are poorly understood. Here, rhizosphere microbial communities under two P fertilization levels-conventional (125 kg P2O5 ha-1, P125) and optimal (90 kg P2O5 ha-1, P90)-were compared at four growth stages of maize in a typical sloped farming system. The richness and diversity of rhizosphere bacterial communities showed significant dynamic changes throughout the growth period of maize, while different results were observed in fungal communities. However, both the P fertilization levels and the growth stages influenced the structure and composition of the maize rhizosphere microbiota. Notably, compared to P125, Pseudomonas, Conexibacter, Mycobacterium, Acidothermus, Glomeromycota, and Talaromyces were significantly enriched in the different growth stages of maize under P90, while the relative abundance of Fusarium was significantly decreased during maize harvest. Soil total nitrogen (TN) and pH are the first environmental drivers of change in bacterial and fungal community structures, respectively. The abundance of Gemmatimonadota, Proteobacteria, and Cyanobacteria showed significant correlations with soil TN, while that of Basidiomycota and Mortierellomycota was significantly related to pH. Additionally, P90 strengthened the connection between bacteria, but reduced the links between fungi at the genus level. Our work helps in understanding the role of P fertilization levels in shaping the rhizosphere microbiota and may manipulate beneficial microorganisms for better P use efficiency.

Could biochar amendment be a tool to improve soil availability and plant uptake of phosphorus? A meta-analysis of published experiments

As one of the most important nutrients for plant growth, phosphorus was often poorly available in soil. While biochar addition induced improvement of soil structure, nutrient and water retention as well as microbial activity had been well known, and the effect of biochar soil amendment (BSA) on soil phosphorus availability and plant P uptake had been not yet quantitatively assessed. In a review study, data were retrieved from 354 peer-reviewed research articles on soil available P content and P uptake under BSA published by February 2019. Then a database was established of 516 data pairs from 86 studies with and without BSA in agricultural soils. Subsequently, the effect size of biochar application was quantified relative to no application and assessed in terms of biochar conditions, soil conditions, as well as experiment conditions. In grand mean, there was a significant and great effect of BSA on soil available P and plant P uptake by 65% and 55%, respectively. The effects were generally significant under manure biochar, biochar pyrolyzed under 300 °C, soil pH <5 and fine-textured soil, and soils that are very low in available P. Being significantly correlated to soil P availability (R²=0.29), plant P uptake was mostly enhanced with vegetable crops of high biomass yield. Overall, biochar amendment at a dosage up to 10 t ha^-1 could be a tool to enhance soil availability and plant uptake of phosphorus, particularly in acid, heavy textured P-poor soils.

More efficient phosphorus use can avoid cropland expansion

Global projections indicate that approximately 500 Mha of new arable land will be required to meet crop demand by 2050. Applying a dynamic phosphorus (P) pool simulator under different socioeconomic scenarios, we find that cropland expansion can be avoided with less than 7% additional cumulative P fertilizer over 2006-2050 when comparing with cropland expansion scenarios, mostly targeted at nutrient-depleted soils of sub-Saharan Africa. Additional P fertilizer would replenish P withdrawn from crop production, thereby allowing higher productivity levels. We also show that further agronomic improvements such as those that allow for better (legacy) P use in soils could reduce both P outflows to freshwater and coastal ecosystems and the overall demand for P fertilizer.

Effect of protein concentrate mixtures and dietary addition of exogenous phytase on major milk minerals and proteins, including casein phosphorylation

Variations in major milk minerals, proteins, and their posttranslational modifications are largely under genetic influence, whereas the effect of nongenetic factors is less studied. Through a controlled feeding experiment (incomplete balanced Latin square design), the effect of concentrate mixtures, based on fava beans, rapeseed meal, or soybean meal as main P and protein sources, on milk composition was examined under typical Danish management conditions. Concentrations of P, Ca, and Mg, together with proteomics for relative quantification of major milk proteins and their isoforms, were analyzed in milk samples from 24 cows sampled in 4 periods. Each cow was fed 1 of the 3 diets in each period with or without addition of exogenous phytase. Cows were blocked by lactation stage into early and mid-lactation (23.3 ± 6.7 and 176 ± 15 d in milk, respectively, at the beginning of the experiment, mean ± standard deviation). Significant effects of feed concentrate mixture were observed for milk protein concentration, milk urea nitrogen, citrate, and the percentage of mixed and preformed fatty acids as well as mineral composition, and their distributions within micellar or serum phases. Furthermore, relative contents of α_S1-casein (CN) 9P form and unglycosylated κ-CN and thereby phosphorylation degree of α_S1-CN (PD) and the glycosylation degree of κ-CN were found to be significantly affected by these diets. To our knowledge, we are the first to document that feed concentrate mixture can affect the relative concentrations of α_S1-CN phosphorylation isoforms in milk, and the results suggested an effect on α_S1-CN 9P and PD, but not on α_S1-CN 8P. Furthermore, although only significant for α_S1-CN 8P, we found a lower relative concentration of α_S1-CN 8P and higher α_S1-CN 9P (and thus higher PD) in milk from cows in mid compared with early lactation. Also, protein concentration and concentration of Mg in skim milk and serum as well as relative concentration of α-lactalbumin were found to be significantly affected by lactation stage. Addition of dietary exogenous phytase only had a minor effect on milk composition or functionality with significant effect detected for α-lactalbumin and micellar Mg concentration.

Sustainable Agri-Food Systems: Environment, Economy, Society, and Policy

Agri-food systems (AFS) have been central in the debate on sustainable development. Despite this growing interest in AFS, comprehensive analyses of the scholarly literature are hard to find. Therefore, the present systematic review delineated the contours of this growing research strand and analyzed how it relates to sustainability. A search performed on the Web of Science in January 2020 yielded 1389 documents, and 1289 were selected and underwent bibliometric and topical analyses. The topical analysis was informed by the SAFA (Sustainability Assessment of Food and Agriculture systems) approach of FAO and structured along four dimensions viz. environment, economy, society and culture, and policy and governance. The review shows an increasing interest in AFS with an exponential increase in publications number. However, the study field is north-biased and dominated by researchers and organizations from developed countries. Moreover, the analysis suggests that while environmental aspects are sufficiently addressed, social, economic, and political ones are generally overlooked. The paper ends by providing directions for future research and listing some topics to be integrated into a comprehensive, multidisciplinary agenda addressing the multifaceted (un)sustainability of AFS. It makes the case for adopting a holistic, 4-P (planet, people, profit, policy) approach in agri-food system studies.

Phosphorus fertilization induces nectar secretion for honeybee visitation and cross-pollination of almond trees

Precise phosphorus (P) application requires a mechanistic understanding of mineral effects on crop biology and physiology. Photosynthate assimilation, metabolism, and transport require phosphorylation, and we postulated that P is critical for the bloom and fruit-set of almond trees that rely on stored carbohydrate reserves. Hence, we studied the growth, physiology and carbohydrate dynamics in 2-year-old almond trees irrigated with P concentrations between 1 mg l-1 and 20 mg l-1. Almond trees attained maximal photosynthesis, transpiration, and growth by 6 mg P l-1 irrigation. Nevertheless, almond trees continued to extract P in 10 mg P l-1 and 15 mg P l-1 irrigations, which corresponded to larger yields. We attributed the augmented productivity to increased fruit-set (59% between 6 mg P l-1 and 15 mg P l-1), caused by more frequent (29%) honeybee visits. High P improved pollinator visitation by enabling almond trees to utilize more of their starch reserves for nectar secretion (which increased by ~140% between 6 mg P l-1 and 15 mg P l-1). This work elucidates the benefits of P fertilization to plant-pollinator mutualism, critical to almond productivity, and reveals novel indices for optimal P application in almond orchards.

Niche-adaptation in plant-associated Bacteroidetes favours specialisation in organic phosphorus mineralisation

Bacteroidetes are abundant pathogen-suppressing members of the plant microbiome that contribute prominently to rhizosphere phosphorus mobilisation, a frequent growth-limiting nutrient in this niche. However, the genetic traits underpinning their success in this niche remain largely unknown, particularly regarding their phosphorus acquisition strategies. By combining cultivation, multi-layered omics and biochemical analyses we first discovered that all plant-associated Bacteroidetes express constitutive phosphatase activity, linked to the ubiquitous possession of a unique phosphatase, PafA. For the first time, we also reveal a subset of Bacteroidetes outer membrane SusCD-like complexes, typically associated with carbon acquisition, and several TonB-dependent transporters, are induced during Pi-depletion. Furthermore, in response to phosphate depletion, the plant-associated Flavobacterium used in this study expressed many previously characterised and novel proteins targeting organic phosphorus. Collectively, these enzymes exhibited superior phosphatase activity compared to plant-associated Pseudomonas spp. Importantly, several of the novel low-Pi-inducible phosphatases and transporters, belong to the Bacteroidetes auxiliary genome and are an adaptive genomic signature of plant-associated strains. In conclusion, niche adaptation to the plant microbiome thus appears to have resulted in the acquisition of unique phosphorus scavenging loci in Bacteroidetes, enhancing their phosphorus acquisition capabilities. These traits may enable their success in the rhizosphere and also present exciting avenues to develop sustainable agriculture.

Engineering rhizobacteria for sustainable agriculture

Exploitation of plant growth promoting (PGP) rhizobacteria (PGPR) as crop inoculants could propel sustainable intensification of agriculture to feed our rapidly growing population. However, field performance of PGPR is typically inconsistent due to suboptimal rhizosphere colonisation and persistence in foreign soils, promiscuous host-specificity, and in some cases, the existence of undesirable genetic regulation that has evolved to repress PGP traits. While the genetics underlying these problems remain largely unresolved, molecular mechanisms of PGP have been elucidated in rigorous detail. Engineering and subsequent transfer of PGP traits into selected efficacious rhizobacterial isolates or entire bacterial rhizosphere communities now offers a powerful strategy to generate improved PGPR that are tailored for agricultural use. Through harnessing of synthetic plant-to-bacteria signalling, attempts are currently underway to establish exclusive coupling of plant-bacteria interactions in the field, which will be crucial to optimise efficacy and establish biocontainment of engineered PGPR. This review explores the many ecological and biotechnical facets of this research.

Toxicity of the sawdust used for phosphorus recovery in a eutrophic reservoir: experiments with Lactuca sativa and Allium cepa

Eutrophication is one of the environmental problems arising from the increase of essential nutrient concentrations, mainly phosphorus and nitrogen. In contrast to excess phosphorus, the depletion of phosphate rock deposits used for the production of fertilizers compromises the food supply. Therefore, the development of technologies that propose the recovery of the phosphorus contained in eutrophic environments for its later use for agricultural fertilization purposes is very important to ensure global food security. This work aimed to evaluate the toxic potential of the sawdust (biosorbent previously used for phosphorus adsorption) in order to enable its application in agriculture. For this, toxicity experiments with Lactuca sativa (lettuce) and Allium cepa (onion) seeds were performed. The phytotoxic potential was assessed by means of the seed germination index and physiological parameters such as radicle and hypocotyl growth. Cytotoxicity, genotoxicity, and mutagenicity tests were also performed on onion seeds. From statistical tests, it was possible to affirm that the sawdust did not promote inhibition of seed germination and radicle and hypocotyl growth. No genotoxicity, cytotoxicity and, mutagenicity were observed, which allowed to state that the sawdust is not toxic to the onion species, which reinforces the possibility of application of the biosorbent for soil fertilization purposes. Therefore, the use of sawdust for phosphorus biosorption with the subsequent agricultural application is promising and quite important from a global food security point of view.

Role of Silicon in Mediating Phosphorus Imbalance in Plants

The soil bioavailability of phosphorus (P) is often low because of its poor solubility, strong sorption and slow diffusion in most soils; however, stress due to excess soil P can occur in greenhouse production systems subjected to high levels of P fertilizer. Silicon (Si) is a beneficial element that can alleviate multiple biotic and abiotic stresses. Although numerous studies have investigated the effects of Si on P nutrition, a comprehensive review has not been published. Accordingly, here we review: (1) the Si uptake, transport and accumulation in various plant species; (2) the roles of phosphate transporters in P acquisition, mobilization, re-utilization and homeostasis; (3) the beneficial role of Si in improving P nutrition under P deficiency; and (4) the regulatory function of Si in decreasing P uptake under excess P. The results of the reviewed studies suggest the important role of Si in mediating P imbalance in plants. We also present a schematic model to explain underlying mechanisms responsible for the beneficial impact of Si on plant adaption to P-imbalance stress. Finally, we highlight the importance of future investigations aimed at revealing the role of Si in regulating P imbalance in plants, both at deeper molecular and broader field levels.

Self-Assembled Anion-Binding Cryptand for the Selective Liquid-Liquid Extraction of Phosphate Anions

The ligands L1 and L2 form trinuclear self-assembled complexes with Cu2+ (i.e. [(L1 )2 Cu3 ]6+ or [(L2 )2 Cu3 ]6+ ) both of which act as a host to a variety of anions. Inclusion of long aliphatic chains on these ligands allows the assemblies to extract anions from aqueous media into organic solvents. Phosphate can be removed from water efficiently and highly selectively, even in the presence of other anions.

Alternate wetting and drying irrigation increases water and phosphorus use efficiency independent of substrate phosphorus status of vegetative rice plants

Sustainable approaches to rice cultivation that apply less irrigation and chemical fertilisers are required to increase crop resource use efficiency. Although alternate wetting and drying (AWD) has been widely promoted as a water-saving irrigation technique, its interactions with phosphorus (P) nutrition have attracted little attention. Vegetative rice plants were grown with two phosphorus levels, fertilised (HP) or un-fertilised (LP), and either continuous flooding (CF) or AWD irrigation. Treatment effects on substrate P bioavailability (measured by Diffusive Gradients in Thin films - DGT-P), plant and substrate water relations, and foliar phytohormone status, were assessed along with P partitioning in planta. Shoot biomass and leaf area under different irrigation treatments depended on substrate P status (significant P x irrigation interaction), since LP decreased these variables under CF, but had no significant effect on plants grown under AWD. AWD maintained DGT-P concentrations and increased maximal root length, but decreased root P concentrations and P offtake. Substrate drying decreased stomatal conductance (g_s) and leaf water potential (Ψ_leaf) but re-flooding increased g_s. AWD increased foliar abscisic acid (ABA), isopentenyl adenine (iP) and 1-aminocyclopropane-1-carboxylic acid (ACC) concentrations, but decreased trans-zeatin (tZ) and gibberellin A1 (GA1) concentrations. Low P increased ACC and jasmonic acid (JA) concentrations but decreased gibberellin A4 (GA4) concentrations. Across all treatments, stomatal conductance was negatively correlated with foliar ABA concentration but positively correlated with GA1 concentration. Changes in shoot phytohormone concentrations were associated with increased water and phosphorus use efficiency (WUE and PUE) of vegetative rice plants grown under AWD.

Phosphorus recovery from sewage sludge - phosphorus leaching behavior from aluminum-containing tertiary and anaerobically digested sludge

Systematic investigations of the acidic dissolution of phosphorus (P), aluminum (Al), iron (Fe), and calcium (Ca) from Al-containing tertiary sludge were carried out in this work. The results were compared with the dissolution behavior of Al-containing anaerobically digested sludge to evaluate the P recovery potential in the form of struvite from tertiary sludge versus anaerobically digested sludge. Additional investigations of synthetically produced Al sludge served as a comparison for the dissolution behavior of P and Al without the influence of other contaminants (metals, biomass). In addition, the acid consumption was analyzed as a function of the target pH during the dissolution. The dissolution efficiency of ortho-phosphate in tertiary and anaerobically digested sludge after acid treatment at pH 2 was ∼90%. The dissolution efficiency of Al and Ca in tertiary sludge was also ∼90% at pH 2, while the release efficiency of Al and Ca in anaerobically digested sludge was lower, ∼70% at pH 2. In tertiary sludge, about 75% of Fe was found dissolved at pH 2, whereas in anaerobically digested sludge this value was higher, ∼90%. Based on the experimental data, it can be concluded that significant dissolution of phosphorus from Al-containing tertiary sludge can take place at pH < 3. The highest sulfuric acid consumption for P dissolution was observed in the case of tertiary sludge at pH 2.

Full-scale increased iron dosage to stimulate the formation of vivianite and its recovery from digested sewage sludge

The recovery of phosphorus from secondary sources like sewage sludge is essential in a world suffering from resources depletion. Recent studies have demonstrated that phosphorus can be magnetically recovered as vivianite (Fe(II)₃(PO₄)₂∗8H₂O) from the digested sludge (DS) of Waste Water Treatment Plants (WWTP) dosing iron. To study the production of vivianite in digested sludge, the quantity of Fe dosed at the WWTP of Nieuwveer (The Netherlands) was increased (from 0.83 to 1.53 kg Fe/kg P in the influent), and the possible benefits for the functioning of the WWTP were evaluated. Higher Fe dosing is not only relevant for P-recovery, but also for maximal recovery of organics from influent for e.g. biogas production. The share of phosphorus present as vivianite in the DS increased from 20% to 50% after the increase in Fe dosing, making more phosphorus available for future magnetic recovery. This increase was directly proportional to the increase of Fe in DS, suggesting that vivianite could be favored not only thermodynamically, but also kinetically. Interestingly, analyses suggest that several types of vivianite are formed in the WWTP, and could differ in their purity, oxidation state or crystallinity. These differences could have an impact on the subsequent magnetic separation. Following the Fe dosing increase, P in the effluent and H₂S in the biogas both decreased: 1.28 to 0.42 ppm for P and 26 to 8 ppm for H₂S. No negative impact on the nitrogen removal, biogas production, COD removal or dewaterability was observed. Since quantification of vivianite in DS is complicated, previous studies were reviewed and we proposed a more accurate Mössbauer spectroscopy analysis and fitting for sludge samples. This study is important from a P recovery point of view, but also because iron addition can play a crucial role in future resource recovery wastewater facilities.

A green process for phosphorus recovery from spent LiFePO4 batteries by transformation of delithiated LiFePO4 crystal into NaFeS2

Recovery of high-content and valuable elements including phosphorus (P) is critical for recycling of spent LiFePO₄ battery, but P recovery is challengeable due to the poor solubility of lithium phosphate and iron phosphate. This study compared two strategies to recover P by adopting sulfide salt to induce P dissolution, i.e., recovery of P directly from LiFePO₄, and step-by-step recovery of Li then P. The results revealed that the second strategy was more efficient because of the higher recovering efficiency and selectivity. Accordingly, an acid-free process to recover P was successfully demonstrated. Li-recovery efficiency of 97.5 % was reached at a leaching time of 65 min, and nearly 100 % P-recovery efficiency was reached at 5 h. Mechanism analysis revealed that the transforming of delithiated LiFePO₄ crystal to NaFeS₂ was mainly responsible for P dissolution. Thermodynamic analysis and density functional theory calculation further proved the transformation reaction, and a stepwise-transformation mechanism was proposed. In addition, P was reclaimed in the form of soluble phosphate salts. The process is especially appealing due to its environmental and economic benefits for recycling spent LiFePO₄ batteries.

Increasing the organic carbon stocks in mineral soils sequesters large amounts of phosphorus

Despite the fact that phosphorus (P) is critical for plant biomass production in many ecosystems, the implications of soil organic carbon (OC) sequestration for the P cycle have hardly been discussed yet. Thus, the aims of this study are, first, to synthesize results about the relationship between C and P in soil organic matter (SOM) and organic matter inputs to soils, second, to review processes that affect the C:P ratio of SOM, and third, to discuss implications of OC storage in terrestrial ecosystems for P sequestration. The study shows that the storage of OC in mineral soils leads to the sequestration of large amounts of organic phosphorus (OP) since SOM in mineral soils is very rich in P. The reasons for the strong enrichment of OP with respect to OC in soils are the mineralization of OC and the formation of microbial necromass that is P-rich as well as the strong sorption of OP to mineral surfaces that prevents OP mineralization. In particular, the formation of mineral-associated SOM that is favorable for storing OC in soil over decadal to centennial timescales sequesters large amounts of OP. Storage of 1,000 kg C in the clay size fraction in the topsoils of croplands sequesters 13.1 kg P. In contrast, the OC:OP ratios of wood and of peatlands are much larger than the ones in cropland soils. Thus, storage of C in wood in peatlands sequesters much less P than the storage of OC in mineral soils. In order to increase the C stocks in terrestrial ecosystems and to lock up as little P as possible, it would be more reasonable to protect and restore peatlands and to produce and preserve wood than to store OC in mineral soils.

Opening access to the black box: The need for reporting on the global phosphorus supply chain

Phosphorus (P) is an essential macronutrient in agriculture; however, lack of reporting makes its supply chain a black box. By using literature synthesis on the P challenge, we identify four areas where the reporting process is problematic: P reserves and resources; P losses along the supply chain; P externalities; and access to data. We find that in these areas, the reporting system is inconsistent, inaccurate, incomplete, fragmented and non-transparent. We use systems analysis to discuss implications of reporting on the sustainability of the P supply chain. We find that reporting is essential for the achievement of global P governance and the human right to adequate food. It can also inform decision makers and other impacted stakeholders on policies on agriculture, food security, pollution and international conflict. An improved P reporting process also allows a better evaluation of global sustainability commitments such as the United Nations Sustainable Development Goals.

Anthropogenic global shifts in biospheric N and P concentrations and ratios and their impacts on biodiversity, ecosystem productivity, food security, and human health

The availability of carbon (C) from high levels of atmospheric carbon dioxide (CO2 ) and anthropogenic release of nitrogen (N) is increasing, but these increases are not paralleled by increases in levels of phosphorus (P). The current unstoppable changes in the stoichiometries of C and N relative to P have no historical precedent. We describe changes in P and N fluxes over the last five decades that have led to asymmetrical increases in P and N inputs to the biosphere. We identified widespread and rapid changes in N:P ratios in air, soil, water, and organisms and important consequences to the structure, function, and biodiversity of ecosystems. A mass-balance approach found that the combined limited availability of P and N was likely to reduce C storage by natural ecosystems during the remainder of the 21st Century, and projected crop yields of the Millennium Ecosystem Assessment indicated an increase in nutrient deficiency in developing regions if access to P fertilizer is limited. Imbalances of the N:P ratio would likely negatively affect human health, food security, and global economic and geopolitical stability, with feedbacks and synergistic effects on drivers of global environmental change, such as increasing levels of CO2 , climatic warming, and increasing pollution. We summarize potential solutions for avoiding the negative impacts of global imbalances of N:P ratios on the environment, biodiversity, climate change, food security, and human health.

In Vitro Regeneration Potential of White Lupin (Lupinus albus) from Cotyledonary Nodes

The tissue culture regeneration system of Lupinus albus has always been considered as recalcitrant material due to its genotype-dependent response and low regeneration efficiency that hamper the use of genetic engineering. Establishment of repeatable plant regeneration protocol is a prerequisite tool for successful application of genetic engineering. This aim of this study was to develop standardized, efficient protocol for successful shoot induction from cotyledonary node of white lupin. In this study, 5 day old aseptically cultured seedlings were used to prepare three explants (half cotyledonary node, HCN; whole cotyledonary node, WCN; and traditional cotyledonary node, TCN), cultured on four concentrations of M519 medium (M519, ½ M519, 1/3 M519, and ¼ M519), containing four carbohydrate sources (sucrose, fructose, maltose, and glucose), and stimulated with various combinations of KT (kinetin), and NAA (naphthalene acetic acid) for direct shoot regeneration. High frequency of 80% shoot regeneration was obtained on ½ M519 medium (KT 4.0 mg L-1 + NAA 0.1 mg L-1) by using HCN as an explant. Interestingly, combinations of (KT 4.0 mg L-1 + NAA 0.1 mg L-1 + BAP 1.67 mg L-1), and (KT 2.0 mg L-1 + NAA 0.1 mg L-1) showed similar shoot regeneration frequency of 60%. Augmentation of 0.25 g L-1 activated charcoal (AC) not only reduced browning effect but also improved shoot elongation. Among the all carbohydrate sources, sucrose showed the highest regeneration frequency with HCN. Additionally, 80% rooting frequency was recorded on ½ M519 containing IAA 1.0 mg L-1 + KT 0.1 mg L-1 (indole acetic acid) after 28 days of culturing. The present study describes establishment of an efficient and successful protocol for direct plant regeneration of white lupin from different cotyledonary nodes.

Chemical production of acidified activated carbon and its influences on soil fertility comparative to thermo-pyrolyzed biochar

Biochar (BC) is gaining attention day by day due to its potential benefits for the improvement in degraded soil health. During its production by pyrolysis, carbon sequestration is an important aspect that makes it environment-friendly amendment. However, 100% anaerobic combustion of waste at such a high temperature decreases its adaptability to produce BC at commercial scale. On the other hand, the alkaline nature of BC also causes adverse effects on soil health when used in alkaline soils. Keeping in mind the problem of BC production and its high pH, current experiment was conducted to introduce chemical production of acidified activated carbon (AAC) and its effects on soil nutrients status comparative to high temperature pyrolyzed BC. As compared to thermal pyrolysis, sulphuric acid produce acidified activated carbon in minimum time and large in quantity. Sulphuric acid produces acidified activated carbon, fix higher carbon as compared to thermal pyrolyzed BC. Results also showed that application of 2% AAC was far better for decreasing alkaline soil pHs (3.52 and 4.71%) and ECe (45.2 and 71.4%) as compared to control in clay and sandy clay loam. A significant maximum increase in available P (117.5 and 25.9%), extractable Zn (42.0 and 52.2%), B (111.4 and 46.2%) and Fe (59.5 and 34.4%) in clay and sandy clay texture soils also validated the efficacious functioning of AAC over BC and control. It is concluded that sulphuric acid use is an easier and adaptable method to produce activated carbon at commercial scale. As compared to thermal pyrolyzed BC, application of AAC could be more effective in the improvement of soil health and fertility status.

Phosphorus recovery from municipal wastewater treatment: Critical review of challenges and opportunities for developing countries

The aim of this paper is to provide guidance in selecting phosphorus recovery options within the municipal wastewater treatment sector regarding developing countries. This critical review includes a brief contextualization of the resource-oriented sanitation paradigm, the discussion of processes for phosphorus recovery based on methods at full-scale, pilot-scale and laboratory-scale, and a concise discussion of the environmental impacts and benefits associated with phosphorus recovery strategies. Finally, the main challenges related to the implementation of resource recovery strategies, especially for phosphorous, were identified and discussed. According to the results, some of the main drivers for phosphorus recovery are the limited availability of phosphorus, increasing cost of phosphate fertilizers and reduction of maintenance costs. Currently, most of the operational processes are based on crystallization or precipitation from the digester supernatant. Struvite is the most common recovered product. The recovery rate of phosphorus from the liquid phase is lower (10-60% from wastewater treatment plant influent), than from sludge (35-70%) and from sludge ashes (70-98%). Phosphorus recovery remains challenging, and some barriers identified were the integration between stakeholders and institutions, public policies and regulations as well as public acceptance and economic feasibility. In developing countries, the implementation of nutrient recovery systems is challenging, because the main concern is on the expansion of sanitation coverage. Resource recovery approaches can provide benefits beyond the wastewater treatment sector, not only improving the sustainability of wastewater treatment operations, but generating revenue for the utility provider.

Assessing national vulnerability to phosphorus scarcity to build food system resilience: The case of India

The scarcity of phosphorus worldwide led researchers to develop indicators of national vulnerability to phosphorus scarcity, however this has not been applied at a national level so far. A systematic approach is described here to identify country-specific indicators of such vulnerability, in this case for India, based on literature and stakeholder engagement. The indicators are then aggregated to compute a phosphorus vulnerability index (PVI) to help policymakers formulate strategies towards building national resilience towards scarcity of phosphorus. For India, the key indicators include import dependence, soil fertility, purchasing power of farmers, and their access to credit. A PVI of 37.29 puts India in the 'highly vulnerable' category. Existing schemes targeted for agricultural sector in India are assessed for their ability to manage phosphorus vulnerability and for building resilience. Other developing countries with similar challenges can easily replicate the approach.