Phosphorus Losses Research Articles

Chitosan and Zinc Oxide Nanoparticle-Enhanced Tripolyphosphate Modulate Phosphorus Leaching in Soil

Phosphorus (P) loss from agro-ecosystems impinges upon P use efficiency by plants and thereby constitutes both agronomic and environmental nuisances. Herein, we report on the potential for controlling P leaching loss and application in crop fertilization through repurposing and nano-functionalizing tripolyphosphate (TPP) as a sole P source. The developed TPP-Chitosan and TPP-Chitosan-ZnO nanofertilizers exhibited positive surface charges, 5.8 and 13.8 mV, and hydrodynamic sizes of 430 and 301 nm, respectively. In soil, nanoformulations of TPP-Chitosan and TPP-Chitosan-ZnO significantly reduced cumulative P leaching during 72 h, reaching 91 and 97% reductions, respectively, compared to a conventional fertilizer, monoammonium phosphate (MAP). Cumulative P leaching after 72 h from these nanofertilizers was, respectively, 84 and 95% lower than from TPP alone. TPP-Chitosan-ZnO was, overall, 65% more effective in reducing P leaching, compared to TPP-Chitosan. Relative to MAP, the wheat plant height was significantly increased by TPP-Chitosan-ZnO by 33.0%. Compared to MAP, TPP-Chitosan and TPP-Chitosan-ZnO slightly increased wheat grain yield by 21 and 30%, respectively. Notably, TPP-Chitosan-ZnO significantly decreased shoot P levels, by 35.5, 47, and 45%, compared to MAP, TPP, and TPP-Chitosan, respectively. Zn release over 72 h from TPP-Chitosan-ZnO was considerably lower, compared to a control, ZnO nanoparticles, and averaged, respectively, 34.7 and 0.065 mg/L, which was 534 times higher for the former. Grain Zn was significantly higher in the TPP-Chitosan treatment, relative to MAP. TPP-Chitosan also significantly mobilized the resident K, S, Mg, and Ca from soil into the plant, helping to improve the overall nutritional quality and supporting the role of chitosan in nutrient mobilization. Taken together, our data highlight the potential for repurposing a non-fertilizer P material, TPP, for agricultural and environmental applications and the effect of applying nanotechnology on such outcomes. Broadly speaking, the reduction in P loss is critical for controlling the eutrophication of water bodies due to nutrient overload and for sustaining the dwindling global P resources.

Effects of Different Feeding Durations on Ileum Length and Weight and Basal Endogenous Loss of Phosphorus in Broiler Chickens Fed a Phosphorus-Free Diet.

The study investigated the effects of feeding duration on the length and weight of the ileum, and basal endogenous loss (BEL) of phosphorus (P) on broiler chickens fed a P-free diet (PFD). A standard starter diet was fed to 384 birds for 15 days. On day 15, they were weighed and randomly allocated to one of three treatment groups in a randomized complete block design, with eight replicate cages per treatment and 16 birds per cage. The birds in each treatment group were fed the PFD for 2, 3, or 4 days. There was an increase in growth performance (p < 0.05) as the PFD feeding duration increased from 2 to 4 days. Although the relative dry weight of the ileum (mg/100 g of body weight) decreased linearly (p < 0.05) as the PFD feeding duration increased, the amount of dried ileal digesta (g/bird) was not affected. The BEL of P was 110.2, 128.2, and 133.6 mg/kg of dry matter intake in birds fed the PFD for 2, 3, and 4 days, respectively. Feeding a PFD to broiler chickens for 2, 3, or 4 days did not change P BEL.

A slurry approach to identify nutrient critical source areas from subtropical catchment erosion

Targeting catchment nutrient critical source areas (CSAs) (areas contributing most of the nutrients in a catchment) is an efficient way to prioritize remediation sites for reducing nutrient runoff to waterways. We tested if the soil slurry approach – with particle sizes and sediment concentrations representative of those in streams during high rainfall events – can be used to identify potential CSAs within individual land use types, examine fire impacts, and identify the contribution of leaf litter in topsoil to nutrient export in subtropical catchments. We first confirmed the slurry approach met the prerequisite to identify CSAs with relatively higher nutrient contribution (not absolute load estimation) by comparing the slurry sampling with stream nutrient monitoring data. We validated that: 1) differences in slurry total nitrogen to phosphorus mass ratios from different land uses were consistent with stream monitoring data; and 2) our estimated nutrient export contribution from agricultural land, via the slurry approach, was comparable to that derived from monitoring data. Additionally, we found nutrient concentrations in slurries differed across soil types and management practice within individual land uses, correlating with nutrient concentrations in fine particles. These results indicate the slurry approach can be used to identify potential small-scale CSAs. Slurry results from burnt soils were also comparable to other studies showing increased levels of dissolved nutrient loss and higher nitrogen than phosphorus loss, than non-burnt soils. The slurry method also showed the contribution of leaf litter to slurry nutrient concentrations from topsoil was greater for dissolved nutrients than particulate nutrients, indicating different forms of nutrients need to be considered for impacts of vegetation. Our study reveals that the slurry method can be used to identify potential small-scale CSAs within the same land use from erosion and can account for impacts of vegetation and bushfires, providing timely information to guide catchment restoration actions.

Investigation of phosphorus transport dynamics using high-frequency monitoring at a subsurface-drained field in the Western Lake Erie Basin

To minimize the environmental impact of phosphorus (P) loss from subsurface-drained fields to freshwater water bodies like the Great Lakes, a detailed understanding of P transport dynamics is vital. The main objective of this study was to investigate P transport dynamics using high-frequency monitoring. We used the HydroCycle-PO4 instrument to measure total reactive P (TRP) concentration at a high resolution from a subsurface-drained farm with continuous no-till and Blount loam soil. We used a dataset containing hourly TRP concentration and hourly drainage discharge measurements in the analysis. Results showed that there was a good relationship between TRP concentration and drainage discharge (R-squared = 0.60) such that TRP had a transport-limited chemodynamic pattern, that is TRP concentration tended to increase with increase in flow during events. A 1% increase in drainage discharge resulted in a 1.36% increase in TRP load, indicating a significant increase in P concentration during high flows. We found that flow events substantially contributed to P loss (89%) because of capturing the rapid increase in P concentration during high flows. The rate of increase in P concentration during the rising limb ranged from 0.02 to 0.66 mg/L per hour. The highest 7.7% of drainage flow transported 75% of the TRP load during the monitoring period. The hysteresis pattern tended to be positive (clockwise) during the study period, indicating that preferential flow was a pathway for TRP loss. Most flow events (30 out of 36) displayed a flushing effect in which P concentration increased with rise in drainage discharge. In conclusion, high-frequency P sampling showed that management and conservation practices should target flow events to reduce P loss.

Soil chronosequence derived from landslides on the upper reach of Minjiang River, western China

Soil chronosequences derived from landslides with certain time series are the great avenue to elevate our understanding on the processes of pedogenesis, nutrient dynamics, and ecosystem evolution. However, the construction of reliable soil chronosequence from historical landslides remains intricate. Here, we presented a 22,000-year soil chronosequence from multiple landslides on the upper reach of Minjiang River, western China. The variation in a variety of pedogenesis indices and soil nutrients verified the reliability of the chronosequence. The silica-alumina ratio and silica sesquioxide ratio decreased significantly with soil age. This reflected the enrichment of Al/Fe/Ti oxides but the depletion of Si oxides with the soil development. Meanwhile, the values of the Chemical Index of Weathering and the Chemical Index of Alteration increased significantly with soil age, especially from 5 to 89 years. These variations were attributed to the soil weathering, which led to the destruction of soil minerals with the rapid loss of most of cations (e.g., K, Na, Ca, and Mg) during the soil development. The concentrations of carbon and nitrogen in topsoil increased with soil age, and the carbon accumulation rate slowed significantly from 5,500 to 22,000 years. The total phosphorus concentrations decreased with soil age, suggesting the gradual loss of soil phosphorus with soil development. The results indicate that the landslide chronosequence established on the upper reach of Minjiang River is reliable and delineates a long-term soil development process, which will provide a great platform for further improvement of biogeochemical theories and understanding sustainable vegetation restoration.

Subsurface phosphorus and nitrogen loss following liquid dairy manure and commercial fertilizer application on a clay soil in northwest Ohio.

Nutrient source has been the focus of much debate regarding the re-eutrophication of Lake Erie, despite that only 20% of nutrients applied to crops in the Western Lake Erie Basin (WLEB) originate from organic sources. However, limited data and assessments exist on the subsurface tile drainage water quality comparison between organic (liquid dairy manure) and commercial (mono-ammonium phosphate [MAP]) sources in crop production systems. Subsurface tile drainage, dissolved reactive phosphorus (DRP) and total phosphorus (TP) losses in tile drainage discharge following equal phosphorus (P) based applications of liquid dairy manure and MAP were assessed using a before-after control-impact design and four years of data from a paired field system located in northwest Ohio, USA. Nitrate-nitrogen (NO3--N) and total nitrogen (TN) losses were also examined to supplement the P findings; however, due to dissimilar nitrogen application rates, losses were assessed in a different context. No significant differences (p > 0.05) were detected in drainage discharge volumes or TP loads between the control and impact sites. However, statistically significant increases (p < 0.05) were measured for mean daily DRP, NO3--N, and TN loads from the dairy manure site. While significant, mean daily DRP differences between commercial (MAP) and liquid dairy manure treatments were only on the order of 0.01 g DRP/ha. Assuming current manure application extent and rates, when accumulated annually across the WLEB watershed, these losses are equivalent to less than 1% of target loads. These findings also help to inform nutrient management stewardship as it relates to nutrient source. Furthermore, additional research across a range of soil characteristics and cropping managements should be explored as well as the impacts of other livestock manure nutrients. This article is protected by copyright. All rights reserved.

Crop Residue Removal Effects on Soil Erosion and Phosphorus Loss in Purple Soils Region, Southwestern China

Background: Purple soil has a fragile structure and is highly vulnerable to soil erosion and phosphorus (P) loss risks. Despite this, the region is endowed with abundant crop residue resources. To ensure sustainable agricultural development in this area, we conducted a study to investigate the impact of crop residue removal on soil aggregate structure, soil erosion, and the risk of P loss. Methods: We conducted a three-year on-farm experiment and analyzed various soil parameters. These parameters include mean weight diameter (MWD), geometric mean diameter (GMD), soil aggregates with a diameter greater than 0.25 mm (R&gt;0.25mm), saturated hydraulic conductivity, soil erosion estimated by RUSLE 2, total soil phosphorus (TP) concentration, geometric mean concentration of TP (GMC), and geometric mean concentration of TP adjusted for aggregate size (GMCd). Results: Retaining all crop residue can significantly improve soil saturated hydraulic conductivity, which was 2.56 times higher than the complete removal treatment. After three years of experimentation, compared to four months, the 50% residue removal treatment increased the GMCd by 32.7%, while the 0% removal treatment increased the GMCd by 16.6%. Both improvements were higher than the complete removal treatment. Partial or complete removal of the crop residue can reduce the soil aggregate stability and increase the risk of soil erosion and P loss. Conclusions: The GMC and GMCd have the potential to serve as indicators for evaluating soil P loss risk. Removing crop residues can cause the degradation of the structure of purple soil aggregates, thus resulting in increased soil erosion and P loss. It is not recommended to remove crop residues in the purple soil region to ensure sustainable agricultural development.

Structure liming reduces draught requirement on clay soil

Liming with ‘structure lime’, comprising approximately 80–85% ground limestone and 15–20% slaked lime, has been promoted in subsidised environmental schemes in Sweden since 2010 to increase clay aggregate stability and mitigate particulate phosphorus losses to surface waters. To date, approximately 65,000 ha have been structure-limed. Apart from stabilising aggregates, liming may also improve other physical properties, such as soil strength. This study examined the effect of increasing application rate (0–16 t ha-1) of structure lime on soil strength, approximated by horizontal (draught requirement) and vertical (penetrometer resistance) measurements, in eight field soils (clay content 26–38%) to which structure lime had been applied two, three, four or six years previously. Draught requirement when cultivating with a multipurpose cultivator significantly decreased (by 11%) with the highest application rate of structure lime (16 t ha-1) compared with an unlimed control. This reduced the wheel power requirement by 7.1 kW and diesel consumption by 1.2–1.4 L ha-1, and lowered CO2 emissions by 3–4 kg ha-1. To clarify the general effect of structure liming, the mean value of all limed treatments was compared with that of the unlimed control. This showed that structure liming in general significantly reduced the draught requirement (by 7%). However, penetrometer resistance measurements revealed no significant effects of structure liming and no relation between draught requirement and penetrometer resistance measurements. Overall, the results indicate that structure liming can reduce fuel consumption, due to easier soil tillage, and thus lower CO2 emissions.

Phosphorus diffusion and deactivation during SiGe oxidation

Dopant profiles near the semiconductor–oxide interface are critical for microelectronic device performance. As the incorporation of Si1−xGex into transistors continues to increase, it is necessary to understand the behavior of dopants in Si1−xGex. In this paper, the diffusion and electrical activation of phosphorus within a strained, single-crystal Si0.7Ge0.3 layer on Si during oxidation are reported. Both layers were uniformly doped, in situ, with an average phosphorus concentration of 4 × 1019 atoms/cm3. After high-temperature oxidation, secondary ion mass spectrometry measurements revealed that the bulk of the phosphorus diffuses out of only the SiGe layer and segregates at the oxidizing SiGe–SiO2 interface. Hall effect measurements corroborate the observed phosphorus loss and show that the phosphorus diffusing to the oxidizing interface is electrically inactive. Through density functional theory (DFT) calculations, it is shown that phosphorus interstitials prefer sites near the SiGe–SiO2 interface. Finally, based on a combination of experimental data and DFT calculations, we propose that the phosphorus atoms are displaced from their lattice sites by Ge interstitials that are generated during SiGe oxidation. The phosphorus atoms then migrate toward the SiGe–SiO2 interface through a novel mechanism of hopping between Ge sites as P–Ge split interstitials. Once they reach the interface, they are electrically inactive, potentially in the form of interstitial clusters or as part of the reconstructed interface or oxide.

Soil health tradeoffs may be minimal in phosphorus‐enriched Coastal Plain soils

AbstractSoil health practices can improve soil conditions and provide ecosystem services, but increased risk of phosphorus (P) loss can be an unintended consequence. We investigated conservation tillage and cover crops effects on soil P stratification, P accumulation at depth, and soil aggregation for sandy Coastal Plain soils from the Mid‐Atlantic United States soil cores from 10 agricultural fields with 0–15 years of conservation tillage or cover cropping were analyzed for Mehlich‐3 P and dry aggregate stability. We found no evidence that conservation tillage or cover cropping caused P stratification or accumulation in study fields that were already enriched with P prior to soil health implementation. Annual particulate, dissolved runoff, and leachate P loads decreased when estimated using the North Carolina Phosphorus Loss Assessment Tool assuming no‐till and cover crops (soil health) compared to conventional till and winter fallow (conventional). We suggest that soil health practices are unlikely to exacerbate P losses from high P Coastal Plain soils beyond their initial risk profile.

Alum reduced phosphorus release from flooded soils under cold spring weather conditions.

The effectiveness of amendments such as alum [Al2 (SO4 )3 ·18H2 O] in reducing phosphorus (P) loss to floodwater has been reported under summer conditions and laboratory-controlled environments, but not under actual spring weather conditions in cold climate regions with high diurnal temperature variations when potential for P losses is high. The effectiveness of alum in reducing P release under Manitoba spring weather conditions was evaluated in a 42-day experiment using 15-cm soil monoliths from eight agricultural soils, which were unamended or alum-amended (5 Mg ha-1 ) and flooded to a 10-cm head. Dissolved reactive P (DRP) concentrations and pH of porewater and floodwater were determined on flooding day and every 7 days after flooding (DAF). Porewater and floodwater DRP concentrations in unamended soils increased 1.4- to 4.5-fold, and 1.8- to 15.3-fold, respectively, from 7 to 42 DAF. In alum-amended soils, DRP concentrations averaged across soils was 43%-73% (1.0-2.0mg L-1 ) lower in porewater, and 27%-64% (0.1-1.2mg L-1 ) lower in floodwater than unamended soils during the flooding period. The reduction of DRP by alum was more pronounced under high fluctuating diurnal spring air temperature than with controlled air temperature (4°C) in a previous similar study. Acidic pH in porewater and floodwater due to alum did not persist over 7 days. This study showed that alum application is a viable option in reducing P released to floodwater in agricultural soils of cold regions where flooding-induced P loss is prevalent in the spring.

Field-scale nutrient loss assessment following cover crop and manure rate change

Eutrophication due to elevated nitrogen (N) and phosphorus (P) loss from croplands remains one of the most pressing water quality issues throughout the world. Understanding the effect of implementing conservation management practices is critical for meeting nutrient reduction goals as well as informing conservation programs and policies. A before-after-control-impact (BACI) analysis was used to evaluate the individual and combined effect of cover crops and manure application rate on discharge and nutrient loss using six water years (WY2014-WY2019) of measured data across four distinct drainage zones (1X–NCC; 1X–CC; 2X–NCC; 2X–CC) within an Ohio, USA, crop production field. White mustard significantly reduced mean monthly nitrate (NO3−-N) concentration regardless of manure application rate (i.e., 65 m3 ha−1 and 130 m3 ha−1). However, neither the use of white mustard, doubling manure rate, or the combination of the two had a significant impact on mean monthly drainage discharge, dissolved-reactive P (DRP), or total P (TP) loss. Seasonal analysis confirmed that NO3−-N concentration in the cover crop zones was signficantly less in fall, winter, and spring. However, significant increases in spring discharge, NO3−-N, DRP, and TP loads as well as TP concentration were noted with cover crop and greater manure rate treatments. These findings confirm that cover crops have a reducing effect on NO3−-N concentration but may not have any effect on addressing P concerns. Further research is warranted; however, this study highlights that the resource concern (e.g., N or P) should be considered prior to implementing cover crops as a conservation management practice.

Influence of broiler litter band positioning on cotton growth and yield in a Blackland Prairie soil

AbstractSubsurface band application of broiler litter in soil is being evaluated across the United States as a potential management practice for curbing phosphorus loss and improving nutrient retention. This management practice also shows promise for increasing yields of row crop systems. Determining the optimum plant distance from the subsurface banded broiler litter (BL) could be useful to optimize crop yields. Thus, a cotton (Gossypium hirsutum L.) experiment was established to investigate the distance of a subsurface BL band from the planted row on cotton growth and yield. Treatments consisted of subsurface banding BL at 0, 10, 20, 30 cm from the crop row plus a non‐fertilized check, broadcast BL, and banding of urea‐ammonium nitrate (UAN) at 20 cm to the side of rows as controls. Subsurface band placement of BL and UAN occurred just prior to sowing at a depth of 10 cm. Placing BL in subsurface bands tended to increase cotton yield compared to surface broadcasting the litter. When comparing BL band positions, cotton lint yield was generally greatest when BL was placed in subsurface bands 20 cm or less from the planted row. Minimal differences in cotton fiber quality were observed among treatments. Results suggest the reduced distance between the cotton row and a subsurface BL band can increase cotton growth and yield.

Study on non-point source pollution characteristics under different spatial scales: a case study of Hanjiang River Basin, China.

In recent years, the research on non-point source (NPS) pollution has been deepening, but it is focused on the large-scale watershed or region. There are a few studies on the scales of small watershed and runoff plot, and it is even less to analyze the characteristics and mechanism of non-point source pollution in certain watershed by combining three different scales. Based on the combination of natural rainfall monitoring and MIKE model simulation, the Shaanxi section of Hanjiang River Basin in China was taken as an example to study the characteristics of NPS pollution at different spatial scales. The results showed that there was an obvious correlation between rainfall and runoff/sediment yield. The order of runoff yield/sediment yield per unit area was as follows: woodland > forested and grassy land > arable land. There was a significant relationship between the loss of total phosphorus and the sediment yield in the runoff plots. The total nitrogen pollution was serious, with an average concentration of 3.8mg/L. The nutrient loss was in the form of nitrate nitrogen, with an average proportion of 63.06%. For small watershed scale, the characteristics of rainfall runoff pollution generation were like runoff plot scale, both have obvious initial scour phenomenon. However, compared with runoff plot scale, the pollutant loss concentration increases with a strong lag. The MIKE model based on the coupling of hydrology, hydrodynamics, and pollution load had a strong applicability in the basin. The critical source areas of NPS pollution were identified, and five scenarios were laid out in the areas for the control of NPS pollution. Centralized livestock and poultry farming had the best reduction effect.

Effect of fertilization on farmland phosphorus loss via surface runoff in China: A meta-analysis

Fertilization inevitably induces phosphorus (P) loss via runoff from farmland causing aquatic eutrophication. A current challenge is estimating farmland P loss induced by fertilization under different conditions of soil hydroclimate, field managements and soil properties. Thus, we synthesized 1636 observations from 69 studies in China to analyze how multiple factors influence P loss in surface runoff from upland and paddy fields. The results showed that P fertilization increases P loss in surface runoff from farmland, and that P loss is lower from upland than paddy fields. The amount of P fertilization (P2O5 in fertilizer) had significantly positive correlations with the effect size of P loss in upland and paddy fields. The rise of P application rate (times of fertilization during study period) significantly decreased P loss in upland fields, but increased P loss in paddy fields. The expansion of crop acreage decreased P loss in upland fields compared to paddy fields. P loss from upland fields is more sensitive to temperature and precipitation than paddy fields, although the responses of P loss differed among fertilizers, crops and soil types. The value of soil pH was significantly positive correlated with P loss in upland and paddy fields. Overall, our study examined the effects of P fertilization on P loss in surface runoff from farmland and estimated the potential variations of P loss under various conditions from the perspective of increasing air temperature and precipitation, providing reference data for field management activities to reduce P output from upland and paddy fields.

Periphyton Phosphorus Uptake in Response to Dynamic Concentrations in Streams: Assimilation and Changes to Intracellular Speciation.

Effective modeling and management of phosphorus (P) losses from landscapes to receiving waterbodies requires an adequate understanding of P retention and remobilization along the terrestrial-aquatic continuum. Within aquatic ecosystems, the stream periphyton can transiently store bioavailable P through uptake and incorporation into biomass during subscouring and baseflow conditions. However, the capacity of stream periphyton to respond to dynamic P concentrations, which are ubiquitous in streams, is largely unknown. Our study used artificial streams to impose short periods (48 h) of high SRP concentration on stream periphyton acclimated to P scarcity. We examined periphyton P content and speciation through nuclear magnetic resonance spectroscopy to elucidate the intracellular storage and transformation of P taken up across a gradient of transiently elevated SRP availabilities. Our study demonstrates that the stream periphyton not only takes up significant quantities of P following a 48-h high P pulse but also sustains supplemental growth over extended periods of time (10 days), following the reestablishment of P scarcity by efficiently assimilating P stored as polyphosphates into functional biomass (i.e., phospho-monoesters and phospho-diesters). Although P uptake and intracellular storage approached an upper limit across the experimentally imposed SRP pulse gradient, our findings demonstrate the previously underappreciated extent to which the periphyton can modulate the timing and magnitude of P delivery from streams. Further elucidating these intricacies in the transient storage potential of periphyton highlights opportunities to enhance the predictive capacity of watershed nutrient models and potentially improve watershed P management.

A Global Database of Soil Plant Available Phosphorus

Soil phosphorus drives food production that is needed to feed a growing global population. However, knowledge of plant available phosphorus stocks at a global scale is poor but needed to better match phosphorus fertiliser supply to crop demand. We collated, checked, converted, and filtered a database of c. 575,000 soil samples to c. 33,000 soil samples of soil Olsen phosphorus concentrations. These data represent the most up-to-date repository of freely available data for plant available phosphorus at a global scale. We used these data to derive a model (R2 = 0.54) of topsoil Olsen phosphorus concentrations that when combined with data on bulk density predicted the distribution and global stock of soil Olsen phosphorus. We expect that these data can be used to not only show where plant available P should be boosted, but also where it can be drawn down to make more efficient use of fertiliser phosphorus and to minimise likely phosphorus loss and degradation of water quality.

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 &amp;gt;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.

Weighted risk assessment of critical source areas for soil phosphorus losses through surface runoff mechanisms

In intensive livestock areas, soils commonly contain elevated nutrients above the agronomic optimum which increases the risk of nutrient losses and contributing to poor ecological status waterbodies. Large within-field variability in soil nutrient content exists, and at-risk phosphorus (P) hotspots are rarely quantified due to sub-optimal soil sampling regimes. This study aims to address this issue by developing and evaluating an improved classification of P transfer risk at a sub-field scale through a weighted risk assessment model that combines gridded soil sampling data with modelled in-field surface runoff pathways. Within-field soil P variability was quantified at six field-scale sites in Northern Ireland using two different sampling techniques; traditional bulked field soil sampling (i.e. bulk analysis of W pattern sampling) and gridded sampling (at 35 m resolution) alongside interpolation. Results show that traditional bulked sampling failed to account for the sub-field scale spatial variability in soil P content. This may contribute to the poor chemical and ecological status of surface waters by frequently under-predicting soil nutrient content, and failing to identify potential contributing sources of soil P losses. In contrast, higher intensity gridded sampling and interpolation revealed wide in-field spatial variability in soil P content, facilitating the identification of contributing sources of P losses to poor water quality and aiding in the characterisation of risk for nutrient losses to waterways. Hydrological modelling of in-field runoff pathways indicated several P sources potentially contributing to runoff-based P losses. Our weighted risk assessment model was successful in identifying P hotspots and transfer potential to water courses, illustrating that a similar approach could be applied anywhere in the world where excess P poses a problem for water quality. Model validation took place using instream water quality sampling data, which showed that higher risk weighting model results correlated to poorer water quality conditions. This methodology could be a useful management tool to help countries meet their national water quality targets.

Effects of forage phosphorous content on faecal phosphorous excretion and possible markers of low phosphorous intake in foals fed forage-only diets.

Knowledge of endogenous nutrient losses is important when estimating the nutrient requirements of animals. It has been suggested that faecal endogenous phosphorus (P) losses differ between growing and adult horses, but studies on foals are scarce. In addition, studies on foals on forage-only diets with different P contents are lacking. Thus this study: (1) assessed faecal endogenous P losses in foals fed a grass haylage-only diet close to or below estimated P requirements; (2) evaluated use of serum cross-linked carboxyterminal telopeptides of type-I collagen (CTx) as a marker of bone resorption secondary to low-P intake; and (3) examined whether analysis of faecal P concentration on a dry matter (DM) basis could be used as an indicator of P intake. Six foals were fed three grass haylages (fertilised to contain different amounts of P: 1.9, 2.1, 3.0 g/kg DM) for 17-day periods in a Latin square design. Total collection of feaces was performed by the end of each period. Faecal endogenous P losses were estimated using linear regression analysis. There was no difference in the concentration of CTx in plasma between diets in samples collected on the last day of each period. A correlation was found (y = 0.64x - 1.51; r2 = 0.75, p < 0.0001) between P intake and faecal P content, but regression analysis indicated that underestimation as well as overestimation of intake is likely if faecal P content is used to assess intake. It was concluded that faecal endogenous P losses in foals are low, probably no higher than in adult horses. It was also concluded that plasma CTx cannot be used to assess short-term low-P intake in foals and that faecal P content cannot be used to assess differences in P intake, at least not when P intake is close to or below estimated P requirements.