Global actions for a sustainable phosphorus future

TP or Not TP? Successful Comparison of Two Independent Methods Validates Total Phosphorus Inference for Long-Term Eutrophication Studies

Validating paleo total phosphorus (TP) inference methods over long time scales is essential for understanding historic changes in lake P supply and the processes leading up to the present-day global lake eutrophication crisis. Monitored lake water TP time series have enabled us to identify the drivers of eutrophication over recent decades. However, over longer time scales, the lack of reliable TP inference means our understanding of drivers is speculative. Validation of lake water TP reconstruction, therefore, remains the "ultimate aim" of eutrophication studies. Here, we present the first critical comparison of two fully independent paleo TP inference approaches: the well-established diatom method (DI-TP) and a recently developed sediment geochemical method (SI-TP). Using lake sediment records from a small eutrophic U.K. lake (Crose Mere), we find a statistically significant agreement between the two inferred TP records with greater than 60% shared variance. Both records show identical timings, with a 19th century acceleration in TP concentration and subsequent declines following a peak in 1930. This significant agreement establishes the validity of long-term paleo TP inference for the first time. With this, we can now test assumptions and paradigms that underpin understanding of catchment P sources and pathways over longer time scales.

Recalcification stabilizes cadmium but magnifies phosphorus limitation in wastewater-irrigated calcareous soil

Long-term wastewater irrigation leads to the loss of calcium carbonate (CaCO3) in the tillage layer of calcareous land, which irreversibly damages the soil's ability to retain cadmium (Cd). In this study, we selected calcareous agricultural soil irrigated with wastewater for over 50 years to examine the recalcification effects of sugar beet factory lime (SBFL) at doses of 0%, 2.5%, 5%, and 10%. We found that SBFL promoted Cd transformation in the soil from active exchangeable species to more stable carbonate-bonded and residual species, which the X-ray diffraction patterns also confirmed results that CdSO4 reduced while CdS and CaCdCO3 increased. Correspondingly, the soil bioavailable Cd concentration was significantly reduced by 65.6-84.7%. The Cd concentrations in maize roots and shoots were significantly reduced by 11.7-50.6% and 13.0-70.0%, respectively, thereby promoting maize growth. Nevertheless, SBFL also increased the proportion of plant-unavailable phosphorus (P) in Ca8-P and Ca10-P by 4.3-13.0% and 10.7-25.9%, respectively, reducing the plant-available P (Olsen P) content by 5.2-22.1%. Consequently, soil P-acquiring associated enzyme (alkaline phosphatase) activity and microbial (Proteobacteria, Bacteroidota, and Actinobacteria) community abundance significantly increased. Our findings showed that adding SBFL to wastewater-irrigated calcareous soil stabilized Cd, but exacerbated P limitation. Therefore, it is necessary to alleviate P limitations in the practice of recalcifying degraded calcareous land.

A clean and sustainable method for recycling of lithium from spent lithium iron phosphate battery powder by using formic acid and oxygen

With the widespread adoption of lithium iron phosphate (LiFePO4) batteries, the imperative recycling of LiFePO4 batteries waste presents formidable challenges in resource recovery, environmental preservation, and socio-economic advancement. Given the current overall lithium recovery rate in LiFePO4 batteries is below 1 %, there is a compelling demand for an eco-friendly, cost-efficient, and sustainable solution. This study introduces a green and sustainable recycling method that employs environmentally benign formic acid and readily available oxygen as reaction agents for selectively leaching lithium from discarded lithium iron phosphate powder. Formic acid was employed as the leaching agent, and oxygen served as the oxidizing agent. Utilizing a single-factor variable approach, various factors including formic acid concentration, oxygen flow rate, leaching time, liquid-to-solid ratio, and reaction temperature were individually investigated. Moreover, the feasibility of this method was explored mechanistically by analyzing E-pH diagrams of the Li-Fe-P-H2O system. Results demonstrate that under conditions of 2.5 mol/L formic acid concentration, 0.12 L/min oxygen flow rate, 25 mL/g liquid-to-solid ratio, 70 °C reaction temperature, and 3 h reaction time, lithium leaching efficiency exceeds 99.9 %, with iron leaching efficiency only at 1.7 %. Moreover, we also explored using air instead of oxygen as the oxidant and get the excellent lithium leaching rate (97.81 %) and low iron leaching rate (4.81 %), which shows the outstanding selectivity. Furthermore, the environmentally benign composition of the chemical reagents, comprising only C, H, and O elements, establishes it as a genuinely green and sustainable technology for secondary resource recovery. It can be considered as a highly environmentally friendly, cost-effective, and efficient approach. Nevertheless, in the current context of carbon neutrality and sustainable development, this method undoubtedly holds excellent prospects for industrialization.

Beyond Triphenylphosphine: Advances on the Utilization of Triphenylphosphine Oxide

Triphenylphosphine oxide is a well-known industrial waste byproduct, and thousands of tons of it are generated every year. Due to its chemical stability and limited applications, settlement of this waste issue has drawn extensive attention from chemists. The reduction of triphenylphosphine oxide to triphenylphosphine is heretofore the most employed solution, and is well reviewed. In view of our recent studies on the selective and efficient conversion of Ph3P(O) to other valuable organophosphorus chemicals by using sodium, the present perspective mainly highlights the advances on the utilization of Ph3P(O) to prepare a diverse range of functional organophosphorus compounds, except Ph3P, via selective P-C, C-H, and P-O bond cleavages.

Effects of microplastic properties and dissolved organic matter on phosphorus availability in soil and aqueous mediums

Plastic mulching films and phosphate fertilizers have been widely used to improve agricultural soil productivity. Microplastics (MP) and phosphorus (P) significantly accumulate in agricultural soil and water bodies. However, the effects of residual MP on P availability in soil and aqueous mediums remain unclear. In this study, available P (Olsen-P) in soils and P adsorption capacity in aqueous medium were determined to examine the influence of MP properties on P availability in laboratory. In agricultural soils, Olsen-P was significantly affected by MP types. Conventional MP (mulching film particles), such as polyethylene (PE) and polyvinyl chloride (PVC), and biodegradable MP, such as polylactic acid (PLA), substantially reduced soil Olsen-P by 9.7-38.6% and 38.4-73.6%, respectively. The size and concentration of MP strongly affected soil Olsen-P, with smaller (25 μm) and more concentrated (5%) MP causing greater reductions in Olsen-P. In the soil contaminated with MP, increased fulvic acid content significantly increased Olsen-P levels. Microplastics exhibited strong P adsorption capacities, leading to decreased P availability in aqueous medium. Conventional MP exhibited a higher P adsorption capacity than biodegradable MP, with P distribution coefficients (Kd values) ordered as PVC (5.19 L kg-1) > PE (4.23 L kg-1) > PLA (2.48 L kg-1). Notably, the Kd values increased with decreasing sizes of conventional MP, whereas the opposite trend was observed for PLA. The presence of fulvic acid affected the adsorption of P by MP in aqueous medium. Increased fulvic acid content reduced P adsorption capacity of MP, thus enhancing P availability. Our findings contribute to a better understanding of P dynamics in MP-contaminated agricultural soil and aqueous medium, which could aid in formulating sustainable agricultural practices and effective environmental management strategies for plastic mulching films and P contamination.

Unraveling spatial patterns and source attribution of nutrient transport: Towards optimal best management practices in complex river basin

A comprehensive understanding of nutrient transport patterns and clarification of pollutant sources' load contributions are critical prerequisites for developing scientific pollution control strategies in complex river basins. Here, we focused on the Minjiang River Basin (MRB) and employed the Soil and Water Assessment Tool (SWAT) model to systematically investigate the nitrogen (N) and phosphorus (P) loads from both point and non-point sources. Results revealed that the key source areas of N and P pollution in the MRB were predominantly located along the riverbanks, influenced by a combination of sediment, precipitation, agricultural activities such as fertilization. Our analysis indicated that soil nutrient loss, fertilization, and livestock farming were the major contributors to N and P inputs, accounting for over 70 % of the total input, followed by rural residential and urban point sources. Based on the identification of non-point source pollution as the primary load source, a multi-objective optimization was conducted using response surface methodology (RSM) coupled with the non-dominated sorting genetic algorithm-II (NSGA-II), resulting in the identification of optimal best management practices (BMPs) that achieve a reduction of 40.04 % in N load, 39.22 % in P load, and a net economic benefit of -1.13 billion yuan per year. Compared to the RSM and automated optimization results, the proposed management measures exhibited significant improvements in N and P load reduction and net benefits. Overall, the findings provide important insights for formulating agricultural management policies in the MRB and offering valuable implications for pollution management in other complex river basins.

Biomass-derived carbon dots with light conversion and nutrient provisioning capabilities facilitate plant photosynthesis

Carbon dots (CDs)-enabled agriculture has been developing rapidly, but small-scale synthesis and high costs hinder the agricultural application of CDs. Herein, biomass-derived carbon dots (B-CDs) were prepared on a gram-level with low cost, and these B-CDs significantly improved crop photosynthesis. The B-CDs, exhibiting small size and blue fluorescence, were absorbed by crops and enhanced photosynthesis via light-harvesting. Foliar application of B-CDs (10 mg·kg-1) could promote chlorophyll synthesis (30-100 %), Ferredoxin (Fd, 40-80 %), Rubisco enzyme (20-110 %) and upregulated gene expression (20-70 %), resulting in higher net photosynthetic rates (130-300 %), dry biomass (160-300 %) and fresh biomass (80-150 %). Further, the B-CDs could increase crop photosynthesis under nutrient deficient conditions, which was attributed to the release of nutrients from B-CDs. Therefore, the B-CDs enhanced the photosynthesis via enhancing light conversion and nutrient supply. This study provides a promising material capable of enhancing photosynthesis for sustainable agriculture production.

Cannabis Hunger Games: nutrient stress induction in flowering stage - impact of organic and mineral fertilizer levels on biomass, cannabidiol (CBD) yield and nutrient use efficiency

Indoor medicinal cannabis cultivation systems enable year-round cultivation and better control of growing factors, however, such systems are energy and resource intensive. Nutrient deprivation during flowering can trigger nutrient translocation and modulate the production of cannabinoids, which might increase agronomic nutrient use efficiency, and thus, a more sustainable use of fertilizers. This experiment compares two fertilizer types (mineral and organic) applied in three dilutions (80, 160 and 240 mg N L-1) to evaluate the effect of nutrient deprivation during flowering on biomass, Cannabidiol (CBD) yield and nutrient use efficiency of N, P and K. This is the first study showing the potential to reduce fertilizer input while maintaining CBD yield of medicinal cannabis. Under nutrient stress, inflorescence yield was significantly lower at the final harvest, however, this was compensated by a higher CBD concentration, resulting in 95% of CBD yield using one-third less fertilizer. The higher nutrient use efficiency of N, P, and K in nutrient-deprived plants was achieved by a larger mobilization and translocation of nutrients increasing the utilization efficiency of acquired nutrients. The agronomic nutrient use efficiency of CBD yield - for N and K - increased 34% for the organic fertilizers and 72% for the mineral fertilizers comparing the dilution with one-third less nutrients (160) with the highest nutrient concentration (240). Differences in CBD yield between fertilizer types occurred only at the final harvest indicating limitations in nutrient uptake due to nutrient forms in the organic fertilizer. Our results showed a lower acquisition and utilization efficiency for the organic fertilizer, proposing the necessity to improve either the timing of bio-availability of organic fertilizers or the use of soil amendments.

Competitive adsorption of heavy metals between Ca-P and Mg-P products from wastewater during struvite crystallization

Wastewater usually contains high concentration of calcium (Ca), posing a competitive reaction with magnesium (Mg) on phosphorus (P) recovery during the struvite crystallization. The differences in the adsorption of heavy metals by Ca-P and Mg-P (struvite) generated are still unclear. Herein, we analyzed the residues of four kinds of common heavy metals (Cu, Zn, Cd, Pb) in Ca-P and Mg-P (struvite) under varying conditions (solution pH, N/P ratio, Mg/Ca ratio) in the swine wastewater and explored their possible competitive adsorption mechanisms. The experiments using synthetic wastewater and real wastewater have similar experimental patterns. However, under the same conditions, the metal (Pb) content of struvite recovered from the synthetic wastewater (16.58 mg/g) was higher than that of the real wastewater (11.02 mg/g), as predicted by the Box-Behnken Design of Response Surface Methodology (BBD-RSM). The results demonstrated that Cu was the least abundant in the precipitates compared to Zn, Cd, and Pb of almost all experimental groups with an N/P ratio greater than or equal to 10. The fact might be mainly attributed to the its stronger binding capacity of Cu ion with NH₃ and other ligands. Compared with struvite, the Ca-P product had a higher adsorption capacity for heavy metals and a lower P recovery rate. In addition, the higher solution pH and N/P ratio were favorable to obtain qualified struvite with lower heavy metal content. It can be applied to reduce the incorporation of heavy metals by modulating pH and N/P ratio through RSM, which is suitable for different Mg/Ca ratios. It is anticipated that the results obtained would offer support for the safe utility of struvite from wastewater containing Ca and heavy metals.

Perspective: Phosphorus monitoring must be rooted in sustainability frameworks spanning material scale to human scale

Phosphorus (P) is a finite resource, and its environmental fate and transport is complex. With fertilizer prices expected to remain high for years and disruption to supply chains, there is a pressing need to recover and reuse P (primarily as fertilizer). Whether recovery is to occur from urban systems (e.g., human urine), agricultural soil (e.g., legacy P), or from contaminated surface waters, quantification of P in various forms is vital. Monitoring systems with embedded near real time decision support, so called cyber physical systems, are likely to play a major role in the management of P throughout agro-ecosystems. Data on P flow(s) connects the environmental, economic, and social pillars of the triple bottom line (TBL) sustainabilty framework. Emerging monitoring systems must account for complex interactions in the sample, and interface with a dynamic decision support system that considers adaptive dynamics to societal needs. It is known from decades of study that P is ubiquitous, yet without quantitative tools for studying the dynamic nature of P in the environment, the details may remain elusive. If new monitoring systems (including CPS and mobile sensors) are informed by sustainability frameworks, data-informed decision making may foster resource recovery and environmental stewardship from technology users to policymakers.

Optimized multilateral crop trade patterns can effectively mitigate phosphorus imbalance among the involved countries

Phosphorus imbalance for cropland can greatly influence environmental quality and productivity of agricultural systems. Resolving cropland phosphorus imbalance may be possible with more efficient multilateral crop trade within the involved trading countries; however, the driving mechanisms are unclear. This study calculates phosphorus budgets in China and five central Asian countries and proposes two optimal multilateral crop trade models to mitigate the phosphorus imbalance. Results show that the current trading pattern between China and Central Asia is causing a phosphorus imbalance intensification. Phosphorus surpluses in China and Uzbekistan are 41.7 and 8.9 kg/ha, while Kazakhstan, Kyrgyzstan, Tajikistan, and Turkmenistan exhibit phosphorus deficits with the negative value of -0.7, -1.2, -0.8, and -0.8 kg/ha, respectively. However, under the optimal multilateral crop trade patterns, phosphorus budget of China and Central Asia will become balanced. Phosphorus imbalance intensification for China is reduced to -2525 and -2472 kt under the single- and bilevel-objective-based crop trades. In Kyrgyzstan, it will drop 61.5 % and 50.0 % and change to 321 and 417 kt under the two optimal crop trades. Moreover, changes of phosphorus imbalance mitigations for other central Asian countries range from 11.9 % to 28.2 %. This provides a scientific basis when establishing policies for strengthening optimal multilateral crop trading across the world to promote global phosphorus management.

Mechanistic insights into the selective adsorption of phosphorus from wastewater by MgO(100)-functionalized cellulose sponge

Metal oxides have remained state-of-the-art adsorbents for recovering phosphorus from aqueous solutions, but their practical application is still limited by their unsatisfactory adsorption capacities and selectivities in wastewater. Here, using MgO as a model metal oxide, the strategy of employing porous cellulose sponge to support metal oxides featuring exposed specific crystal facets was proposed to develop promising phosphate adsorbents. The phosphate adsorption isotherms and kinetics were measured and the phosphate adsorption mechanism was explored. The results show that cellulose sponge-supported MgO(100) (C-MgO(100)) has a saturation capacity of 28.3 mg P/g, over ten times higher than MgO(100) particles. Importantly, the phosphate adsorption properties of C-MgO(100) are almost not affected in wastewater, demonstrating its exceptional selectivity for phosphate adsorption. In contrast, the saturation capacity of MgO(111)-functionalized cellulose sponge is obviously declined in wastewater. Experimental together with theoretical analyses indicate that phosphate is chemically adsorbed on C-MgO(100) with obvious electrons transfer from the p-orbital of phosphate, and the adsorption energy of C-MgO(100) towards phosphate is maintained in the presence of coexisting anions. Ultimately, regeneration experiments reveal that a regenerant formulation composed of KOH (wt.1 %) and tap water is suitable for the regeneration of C-MgO(100) with >82.6 % phosphate desorption efficiencies after 5 cycles, further confirming its potential in practical application for the treatment of real water.

Morphology-Tailored Hydroxyapatite Nanocarrier for Rhizosphere-Targeted Phosphorus Delivery

High hydrophilicity and soil fixation collectively hamper the delivery of phosphorus (P) released from conventional chemical phosphorus fertilizers (CPFs) to plant rhizosphere for efficient uptake. Here, a phosphorus nutrient nanocarrier (PNC) based on morphology-tailored nanohydroxyapatite (HAP) is constructed. By virtue of kinetic control of building blocks with designed calcium phosphate intermediates, rod-like and hexagonal prism-like PNCs are synthesized, both having satisfactory hydrophobicity (water contact angle of 105.4^- 132.9°) and zeta potential (-17.43 to -58.4 mV at pH range from 3 to 13). Greenhouse experiments demonstrate that the P contents increase by up to 183% in maize rhizosphere and up to 16% in maize biomass when compared to the CPF. Due to the water potential gradient driven by photosynthesis and transpiration, both PNCs are stably transported to maize rhizosphere, and they are capable to counteract soil fixation prior to uptake by plant roots. Within the synergies of the HAP morphological characteristics and triggered phosphate starvation response, root anatomy confirms that two pathways are elucidated to enhance plant P replenishment from the PNCs. Together with structure tunability and facile synthesis, our results offer a new nanodelivery prototype to accommodate plant physiological traits by tailoring the morphology of HAP.

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.

A new direction for tackling phosphorus inefficiency in the UK food system

The UK food system is reliant on imported phosphorus (P) to meet food production demand, though inefficient use and poor stewardship means P is currently accumulating in agricultural soils, wasted or lost with detrimental impacts on aquatic environments. This study presents the results of a detailed P Substance Flow Analysis for the UK food system in 2018, developed in collaboration with industry and government, with the key objective of highlighting priority areas for system interventions to improve the sustainability and resilience of P use in the UK food system. In 2018 the UK food system imported 174.6 Gg P, producing food and exportable commodities containing 74.3 Gg P, a P efficiency of only 43%. Three key system hotspots for P inefficiency were identified: Agricultural soil surplus and accumulation (89.2 Gg P), loss to aquatic environments (26.2 Gg P), and waste disposal to landfill and construction (21.8 Gg P). Greatest soil P accumulation occurred in grassland agriculture (85% of total accumulation), driven by loadings of livestock manures. Waste water treatment (12.5 Gg P) and agriculture (8.38 Gg P) account for most P lost to water, and incineration ashes from food system waste (20.3 Gg P) accounted for nearly all P lost to landfill and construction. New strategies and policy to improve the handling and recovery of P from manures, biosolids and food system waste are therefore necessary to improve system P efficiency and reduce P accumulation and losses, though critically, only if they effectively replace imported mineral P fertilisers.

Efficiency of Combining Strains Ag87 (Bacillus megaterium) and Ag94 (Lysinibacillus sp.) as Phosphate Solubilizers and Growth Promoters in Maize

Increasing phosphorus (P) use efficiency in agricultural systems is urgent and essential to significantly reduce the global demand for this nutrient. Applying phosphate-solubilizing and plant growth-promoting bacteria in the rhizosphere represents a strategy worthy of attention. In this context, the present work aimed to select and validate bacterial strains capable of solubilizing phosphorous and promoting maize growth, aiming to develop a microbial inoculant to be used in Brazilian agriculture. Bacterial strains from the maize rhizosphere were evaluated based on their ability to solubilize phosphate and produce indole acetic acid. Based on these characteristics, 24 strains were selected to be further evaluated under laboratory, greenhouse, and field conditions. Among the selected strains, four (I04, I12, I13, and I17) showed a high potential to increase maize root growth and shoot P content. Strains I13 (Ag87) and I17 (Ag94) were identified by genomic sequencing as Bacillus megaterium and Lysinibacillus sp., respectively. These strains presented superior yield increments relative to the control treatment with 30% P. In addition, combining Ag87 and Ag94 resulted in even higher yield gains, indicating a synergistic effect that could be harnessed in a commercial inoculant for Brazilian agriculture.

Are stakeholders ready to transform phosphorus use in food systems? A transdisciplinary study in a livestock intensive system

Food systems worldwide are vulnerable to Phosphorus (P) supply disruptions and price fluctuations. Current P use is also highly inefficient, generating large surpluses and pollution. Global food security and aquatic ecosystems are in jeopardy if transformative action is not taken. This paper pivots from earlier (predominantly conceptual) work to develop and analyse a P transdisciplinary scenario process, assessing stakeholders potential for transformative thinking in P use in the food system. Northern Ireland, a highly livestock-intensive system, was used as case study for illustrating such process. The stakeholder engagement takes a normative stance in that it sets the explicit premise that the food system needs to be transformed and asks stakeholders to engage in a dialogue on how that transformation can be achieved. A Substance Flow Analysis of P flows and stocks was employed to construct visions for alternative futures and stimulate stakeholder discussions on system responses. These were analysed for their transformative potential using a triple-loop social learning framework. For the most part, stakeholder responses remained transitional or incremental, rather than being fundamentally transformative. The process did unveil some deeper levers that could be acted upon to move the system further along the spectrum of transformational change (e.g. changes in food markets, creation of new P markets, destocking, new types of land production and radical land use changes), providing clues of what an aspirational system could look like. Replicated and adapted elsewhere, this process can serve as diagnostics of current stakeholders thinking and potential, as well as for the identification of those deeper levers, opening up avenues to work upon for global scale transformation.

Using knowledge-based management for sustainable phosphorus use in China

Sustainable phosphorus (P) management presents challenges in crop production and environmental protection; the current understanding of chemical P-fertilizer manufacturing, rock phosphate (RP) mining, P loss within supply chains, and strategies to mitigate loss is incomplete because of a fragmented understanding of P in the crop production supply chain. Therefore, we develop a knowledge-based management theoretical framework to analyze P supply chains to explore ways to mitigate China's P crisis. This framework connects upstream P industries and crop production, addressing knowledge gaps and stakeholder involvement. We demonstrate the potential to improve P use efficiency in the supply chain, thereby mitigating the P crisis using optimized P management. Our results showed that P footprint and grain production demand for RP can be reduced without yield penalty using a crop-demand-oriented P supply chain management that integrates P use in crop production, P-fertilizer manufacturing, and RP mining. Food security and P-related environment sustainability can be achieved by sharing responsibility and knowledge among stakeholders.

A loss function to evaluate agricultural decision-making under uncertainty: a case study of soil spectroscopy

Modern sensor technologies can provide detailed information about soil variation which allows for more precise application of fertiliser to minimise environmental harm imposed by agriculture. However, growers should lose neither income nor yield from associated uncertainties of predicted nutrient concentrations and thus one must acknowledge and account for uncertainties. A framework is presented that accounts for the uncertainty and determines the cost-benefit of data on available phosphorus (P) and potassium (K) in the soil determined from sensors. For four fields, the uncertainty associated with variation in soil P and K predicted from sensors was determined. Using published fertiliser dose-yield response curves for a horticultural crop the effect of estimation errors from sensor data on expected financial losses was quantified. The expected losses from optimal precise application were compared with the losses expected from uniform fertiliser application (equivalent to little or no knowledge on soil variation). The asymmetry of the loss function meant that underestimation of P and K generally led to greater losses than the losses from overestimation. This study shows that substantial financial gains can be obtained from sensor-based precise application of P and K fertiliser, with savings of up to £121 ha^-1 for P and up to £81 ha^-1 for K, with concurrent environmental benefits due to a reduction of 4-17 kg ha^-1 applied P fertiliser when compared with uniform application.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11119-022-09887-2.

Spectroscopic analysis reveals that soil phosphorus availability and plant allocation strategies impact feedstock quality of nutrient-limited switchgrass

The perennial native switchgrass adapts better than other plant species do to marginal soils with low plant-available nutrients, including those with low phosphorus (P) content. Switchgrass roots and their associated microorganisms can alter the pools of available P throughout the whole soil profile making predictions of P availability in situ challenging. Plant P homeostasis makes monitoring of P limitation via measurements of plant P content alone difficult to interpret. To address these challenges, we developed a machine-learning model trained with high accuracy using the leaf tissue chemical profile, rather than P content. By applying this learned model in field trials across two sites with contrasting extractable soil P, we observed that actual plant available P in soil was more similar than expected, suggesting that adaptations occurred to alleviate the apparent P constraint. These adaptations come at a metabolic cost to the plant that have consequences for feedstock chemical components and quality. We observed that other biochemical signatures of P limitation, such as decreased cellulose-to-lignin ratios, were apparent, indicating re-allocation of carbon resources may have contributed to increased P acquisition. Plant P allocation strategies also differed across sites, and these differences were correlated with the subsequent year’s biomass yields.

Hao et al. develop a machine learning approach to spectroscopy data of the tissue biochemistry of the switchgrass Panicum virgatum L. Using field and lab data with phosphorus-limited conditions, the authors show how soil phosphorus availability and nutrient allocations strategies may impact feedstock chemical components and quality.

Differential Root Exudation and Architecture for Improved Growth of Wheat Mediated by Phosphate Solubilizing Bacteria

Phosphorous (P) deficiency is a major challenge faced by global agriculture. Phosphate-solubilizing bacteria (PSB) provide a sustainable approach to supply available phosphates to plants with improved crop productivity through synergistic interaction with plant roots. The present study demonstrates an insight into this synergistic P-solubilizing mechanism of PSB isolated from rhizosphere soils of major wheat-growing agro-ecological zones of Pakistan. Seven isolates were the efficient P solubilizers based on in vitro P-solubilizing activity (233-365 μg ml-1) with a concomitant decrease in pH (up to 3.5) by the production of organic acids, predominantly acetic acid (∼182 μg ml-1) and gluconic acid (∼117 μg ml-1). Amplification and phylogenetic analysis of gcd, pqqE, and phy genes of Enterobacter sp. ZW32, Ochrobactrum sp. SSR, and Pantoea sp. S1 showed the potential of these PSB to release orthophosphate from recalcitrant forms of phosphorus. Principal component analysis indicates the inoculation response of PSB consortia on the differential composition of root exudation (amino acids, sugars, and organic acids) with subsequently modified root architecture of three wheat varieties grown hydroponically. Rhizoscanning showed a significant increase in root parameters, i.e., root tips, diameter, and surface area of PSB-inoculated plants as compared to uninoculated controls. Efficiency of PSB consortia was validated by significant increase in plant P and oxidative stress management under P-deficient conditions. Reactive oxygen species (ROS)-induced oxidative damages mainly indicated by elevated levels of malondialdehyde (MDA) and H2O2 contents were significantly reduced in inoculated plants by the production of antioxidant enzymes, i.e., superoxide dismutase, catalase, and peroxidase. Furthermore, the inoculation response of these PSB on respective wheat varieties grown in native soils under greenhouse conditions was positively correlated with improved plant growth and soil P contents. Additionally, grain yield (8%) and seed P (14%) were significantly increased in inoculated wheat plants with 20% reduced application of diammonium phosphate (DAP) fertilizer under net house conditions. Thus, PSB capable of such synergistic strategies can confer P biofortification in wheat by modulating root morphophysiology and root exudation and can alleviate oxidative stress under P deficit conditions.