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Keywords = phosphorus fractionation

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17 pages, 3193 KiB  
Article
Effects of Nitrogen and Phosphorus Additions on the Stability of Soil Carbon Fractions in Subtropical Castanopsis sclerophylla Forests
by Yunze Dai, Xiaoniu Xu and LeVan Cuong
Forests 2025, 16(8), 1264; https://doi.org/10.3390/f16081264 - 2 Aug 2025
Viewed by 163
Abstract
Soil organic carbon (SOC) pool plays an extremely important role in regulating the global carbon (C) cycle and climate change. Atmospheric nitrogen (N) and phosphorus (P) deposition caused by human activities has significant impacts on soil C sequestration potential of terrestrial ecosystem. To [...] Read more.
Soil organic carbon (SOC) pool plays an extremely important role in regulating the global carbon (C) cycle and climate change. Atmospheric nitrogen (N) and phosphorus (P) deposition caused by human activities has significant impacts on soil C sequestration potential of terrestrial ecosystem. To investigate the effects of N and P deposition on soil C sequestration and C-N coupling relationship in broad-leaved evergreen forests, a 6-year field nutrient regulation experiment was implemented in subtropical Castanopsis sclerophylla forests with four different N and P additions: N addition (100 kg N·hm−2·year−1), N + P (100 kg N·hm−2·year−1 + 50 kg P·hm−2·year−1), P addition (50 kg P·hm−2·year−1), and CK (0 kg N·hm−2·year−1). The changes in the C and N contents and stable isotope distributions (δ13C and δ15N) of different soil organic fractions were examined. The results showed that the SOC and total nitrogen (STN) (p > 0.05) increased with N addition, while SOC significantly decreased with P addition (p < 0.05), and N + P treatment has low effect on SOC, STN (p > 0.05). By density grouping, it was found that N addition significantly increased light fraction C and N (LFOC, LFN), significantly decreased the light fraction C to N ratio (LFOC/N) (p < 0.05), and increased heavy fraction C and N (HFOC, HFN) accumulation and light fraction to total organic C ratio (LFOC/SOC, p > 0.05). Contrary to N addition, P addition was detrimental to the accumulation of LFOC, LFN and reduced LFOC/SOC. It was found that different reactive oxidized carbon (ROC) increased under N addition but ROC/SOC did not change, while N + P and P treatments increased ROC/SOC, resulting in a decrease in SOC chemical stability. Stable isotope analysis showed that N addition promoted the accumulation of new soil organic matter, whereas P addition enhanced the transformation and utilization of C and N from pre-existing organic matter. Additionally, N addition indirectly increased LFOC by significantly decreasing pH; significantly contributed to LFOC and ROC by increasing STN accumulation promoted by NO3-N and NH4+-N; and decreased light fraction δ13C by significantly increasing dissolved organic C (p < 0.05). P addition had directly significant negative effect on LFOC and SOC (p < 0.05). In conclusion, six-year N deposition enhances soil C and N sequestration while the P enrichment reduces the content of soil C, N fractions and stability in Castanopsis sclerophylla forests. The results provide a scientific basis for predicting the soil C sink function of evergreen broad-leaved forest ecosystem under the background of future climate change. Full article
(This article belongs to the Section Forest Soil)
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25 pages, 1695 KiB  
Review
Bee Brood as a Food for Human Consumption: An Integrative Review of Phytochemical and Nutritional Composition
by Raquel P. F. Guiné, Sofia G. Florença, Maria João Barroca and Cristina A. Costa
Insects 2025, 16(8), 796; https://doi.org/10.3390/insects16080796 - 31 Jul 2025
Viewed by 453
Abstract
The utilisation of edible insects for human nutrition is a long-standing practice in many parts of the globe, and is being gradually introduced into countries without an entomophagic tradition as well. These unconventional sources of protein of animal origin have arisen as a [...] Read more.
The utilisation of edible insects for human nutrition is a long-standing practice in many parts of the globe, and is being gradually introduced into countries without an entomophagic tradition as well. These unconventional sources of protein of animal origin have arisen as a sustainable alternative to other animal protein sources, such as meat. This review intends to present the compilation of data in the scientific literature on the chemical composition and nutritional value of the bee brood of A. mellifera species and subspecies as edible foods. For this, a comprehensive search of the scientific literature was carried out using the databases ScienceDirect, Scopus, Pub-Med, BOn, and SciELO. Appropriate keywords were used for the search to reach the research works that addressed the topics of the review. The results showed that bee brood has considerable quantities of protein, fat and carbohydrates. The most abundant amino acids are leucine and lysine (these two being essential amino acids) and aspartic acid, glutamic acid, and proline (these three being non-essential amino acids). As for the fatty acids, bee broods contain approximately equal fractions of saturated and monounsaturated fatty acids, while the polyunsaturated fatty acids are negligible. The dietary minerals present in higher quantities are potassium, phosphorus, and magnesium, and the most abundant vitamins are vitamin C and niacin; choline is also present, although it is not a true vitamin. Although bee brood from A. mellifera has potential for human consumption as a nutrient-rich food, there are still many aspects that need to be further studied in the future, such as safety and hazards linked to possible regular consumption. Full article
(This article belongs to the Special Issue Insects: A Unique Bioresource for Agriculture and Humanity)
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18 pages, 1291 KiB  
Article
Effect of Calcium Addition on Extracellular Enzymes and Soil Organic Carbon in Maize Rhizosphere Soils
by Zhaoquan He, Xue Shang and Xiaoze Jin
Agronomy 2025, 15(7), 1680; https://doi.org/10.3390/agronomy15071680 - 11 Jul 2025
Viewed by 360
Abstract
This study examined the regulatory mechanism of calcium (Ca) amendment on the dynamics of soil organic carbon (SOC) fractions and extracellular enzyme activities, elucidating the role of Ca in soil carbon cycling processes. A field experiment with maize was conducted, comparing treatments of [...] Read more.
This study examined the regulatory mechanism of calcium (Ca) amendment on the dynamics of soil organic carbon (SOC) fractions and extracellular enzyme activities, elucidating the role of Ca in soil carbon cycling processes. A field experiment with maize was conducted, comparing treatments of low calcium (T1), high calcium (T2), and a calcium-free control (CK). Measurements included inter-root SOC fractions—soluble organic carbon (DOC), microbial biomass carbon (MBC), and readily oxidizable organic carbon (ROC)—and the activities of the following extracellular enzymes: β-xylanase, β-glucosidase (β-glu), phenol oxidase (Phox), peroxidase (Pero), phosphatase (Phos), acetylaminoglucosidase (NAG), and urease. The main findings indicated the following: (1) Calcium addition significantly increased SOC content (115.04% and 99.22% higher in T1 and T2, respectively, than CK during the entire reproductive period) and enhanced microbial activity (elevated DOC and MBC). However, SOC decreased by 8.44% (T1) and 16.38% (T2) relative to CK in the late reproductive stage (irrigation–ripening), potentially reflecting microbial utilization (supported by the inverse correlation between SOC and MBC/DOC), and maize carbon reallocation during grain filling. (2) Calcium activated β-glu, Phox, Phos, NAG, and urease (p < 0.05), with pronounced increases in Phox (241.13 IU·L−1) and Phos (1126.65 U·L−1), indicating enhanced organic matter mineralization and phosphorus availability. (3) Calcium-driven MBC and ROC accumulation was associated with the positive regulation of Phox (path coefficient > 0.8) and the negative regulation of Phos. SOC was co-regulated by β-glu and Phos (R2 = 0.753). (4) Calcium dynamically optimized the short-term carbon distribution through enzyme activity while promoting long-term sequestration. Our study provides new evidence supporting multi-pathway interactions through which calcium mediates enzyme networks to influence the soil carbon cycle. The findings provide a theoretical foundation for calcium fertilizer management and soil carbon sequestration strategies in agriculture, advancing academic and practical goals for sustainable development and carbon neutrality. Full article
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15 pages, 2224 KiB  
Article
Estimation of Available Phosphorus Under Phosphorus Fertilization in Paddy Fields of a Cold Region Using Several Extraction Methods: A Case Study from Yamagata, Japan
by Shuhei Tsumuraya, Hisashi Nasukawa and Ryosuke Tajima
Agriculture 2025, 15(13), 1453; https://doi.org/10.3390/agriculture15131453 - 5 Jul 2025
Viewed by 308
Abstract
Assessing available phosphorus (P) in paddy fields is challenging due to waterlogging-induced reducing conditions. This study tested the applicability of the Truog, Bray 2, and Mehlich 3 extraction methods in both air-dried and incubated soils, as well as the ascorbic-acid-reduced Bray 2 (AR [...] Read more.
Assessing available phosphorus (P) in paddy fields is challenging due to waterlogging-induced reducing conditions. This study tested the applicability of the Truog, Bray 2, and Mehlich 3 extraction methods in both air-dried and incubated soils, as well as the ascorbic-acid-reduced Bray 2 (AR Bray 2), which simulates reducing conditions, for evaluating rice growth under P fertilization. In addition, to investigate the chemical characteristics of the extraction methods, active Al and Fe and P sequential extractions were measured. Soil samples from four representative regions in Yamagata Prefecture were used. Pot cultivation tests using ‘Haenuki’ and ‘Tsuyahime’ cultivars were conducted with varying P fertilizer levels. Variations in P availability across soil types were influenced by levels of active Al and Fe. Sequential extractions identified NaHCO3-P and NaOH-P fractions as important for P availability. Bray 2 in both soils and AR Bray 2 were the most effective methods, showing a strong saturating exponential correlation with rice growth and P uptake, whereas Mehlich 3 and Truog showed weaker correlations. Bray 2 and AR Bray 2 show potential but require further evaluation for practical application due to the small number of soils. Future efforts should prioritize developing methods that account for P dynamics under reducing conditions, thereby improving P management strategies and supporting sustainable rice production. Full article
(This article belongs to the Special Issue Innovative Conservation Cropping Systems and Practices—2nd Edition)
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22 pages, 4025 KiB  
Article
Effects of Different Land Use Types on Soil Quality and Microbial Diversity in Paddy Soil
by Ximei Zhao, Fengyun Xiang, Xicheng Wang, Mengchen Yang and Jifu Li
Agronomy 2025, 15(7), 1628; https://doi.org/10.3390/agronomy15071628 - 3 Jul 2025
Viewed by 368
Abstract
This study investigated the effects of three land use patterns—rice (Oryza sativa L.)–rapeseed (Brassica napus L.) rotation (Rapeseed), rice–shrimp (Procambarus clarkii G.) rotation (Shrimp), and the conversion of paddy fields to forestland (Forestland)—on aggregate structure, nutrient content, and microbial diversity in [...] Read more.
This study investigated the effects of three land use patterns—rice (Oryza sativa L.)–rapeseed (Brassica napus L.) rotation (Rapeseed), rice–shrimp (Procambarus clarkii G.) rotation (Shrimp), and the conversion of paddy fields to forestland (Forestland)—on aggregate structure, nutrient content, and microbial diversity in rice soils in Chuandian Town, Jingzhou District, Jianghan Plain, central China. The results revealed that the Shrimp treatment significantly increased soil organic matter (SOM), available nitrogen (AN), and available phosphorus (AP) content in the surface soil (0–10 cm) while reducing soil bulk density and improving pore structure. Forestland exhibited higher aggregate stability in deeper soil layers (20–40 cm), particularly in the 0.053–0.25 mm size fraction. Microbial diversity analysis showed that bacterial richness (Chao1 index) and diversity (Shannon index) were significantly higher in the Shrimp and Rapeseed treatments compared to those in the Forestland treatment, with Proteobacteria and Chloroflexi being the dominant bacterial phyla. Fungal communities were dominated by Ascomycota, withfForestland showing greater fungal richness in deeper soil. Soil depth significantly influenced aggregates, nutrients, and microbial diversity, with surface soil exhibiting higher values for these parameters than deeper layers. Redundancy analysis indicated that SOM, AP, and pH were the key drivers of bacterial community variation, while fungal communities were more influenced by nitrogen and porosity. Path analysis further demonstrated that land use patterns indirectly affected microbial diversity via altering aggregate structure and nutrient availability. Overall, the Shrimp treatment outperformed others in improving soil structure and nutrient supply, whereas the Forestland treatment was more conducive to promoting aggregate stability in deeper soil. Land use patterns indirectly regulated microbial communities through modifying soil aggregate structure and nutrient status, thereby influencing soil ecosystem health and stability. This study provides a theoretical basis for the sustainable management of rice soils, suggesting the optimization of rotation patterns in agricultural production to synergistically enhance soil physical, chemical, and biological properties. Full article
(This article belongs to the Section Agroecology Innovation: Achieving System Resilience)
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14 pages, 1278 KiB  
Article
High Ratio of Manure Substitution Enhanced Soil Organic Carbon Storage via Increasing Particulate Organic Carbon and Nutrient Availability
by Xiaoyu Hao, Xingzhu Ma, Lei Sun, Shuangquan Liu, Jinghong Ji, Baoku Zhou, Yue Zhao, Yu Zheng, Enjun Kuang, Yitian Liu and Shicheng Zhao
Plants 2025, 14(13), 2045; https://doi.org/10.3390/plants14132045 - 3 Jul 2025
Viewed by 430
Abstract
Replacing partial chemical fertilizers with organic fertilizer can increase organic carbon input, change soil nutrient stoichiometry and microbial metabolism, and then affect soil organic carbon (SOC) storage. A 6-year field experiment was used to explore the mechanism of SOC storage under different ratios [...] Read more.
Replacing partial chemical fertilizers with organic fertilizer can increase organic carbon input, change soil nutrient stoichiometry and microbial metabolism, and then affect soil organic carbon (SOC) storage. A 6-year field experiment was used to explore the mechanism of SOC storage under different ratios of manure substitution in northeast China, with treatments including chemical fertilizer application alone (nitrogen, phosphorus, and potassium, NPK) and replacing 1/4 (1/4M), 2/4 (2/4M), 3/4 (3/4M), and 4/4 (4/4M) of chemical fertilizer N with manure N. Soil nutrients, enzymatic activity, and SOC fractions were analyzed to evaluate the effect of different manure substitution ratios on SOC storage. A high ratio of manure substitution (>1/4) significantly increased soil total N, total P, total K, and available nutrients (NO3-N, available P, and available K), and the 4/4M greatly decreased the C/N ratio compared to the NPK. Manure incorporation increased microbial biomass carbon (MBC) by 18.3–53.0%. Treatments with 50%, 75%, and 100% manure substitution (2/4M, 3/4M, and 4/4M) enhanced bacterial necromass carbon (BNC), fungal necromass carbon (FNC), and total microbial necromass carbon (MNC) by 31.9–63.5%, 25.5–107.1%, and 27.4–94.2%, respectively, compared to the NPK treatment. Notably, the increase in FNC was greater than that of BNC as the manure substitution ratio increased. The increasing manure substitution significantly enhanced particulate organic C (POC) and total SOC but did not affect mineral-associated organic C (MAOC). High soil N and P supplies decreased leucine aminopeptidases (LAPs) and alkaline phosphatase activities but increased the activity ratio of β-glucosidase (BG)/(N-acetyl-glucosaminidase (NAG) + LAP). Treatments with 25% manure substitution (1/4M) maintained maize and soybean yield, but with increasing manure rate, the maize yield decreased gradually. Overall, the high ratio of manure substitution enhanced SOC storage via increasing POC and MNC, and decreasing the decomposition potential of manure C and soil C resulting from low N- and P-requiring enzyme activities under high nutrient supplies. This study provides empirical evidence that the rational substitution of chemical fertilizers with manure is an effective measure to improve the availability of nutrients, and its effect on increasing crop yields still needs to be continuously observed, which is still a beneficial choice for enhancing black soil fertility. Full article
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29 pages, 2767 KiB  
Article
Closed-Loop Valorization of Annatto Seed Waste into Biochar: A Sustainable Platform for Phosphorus Adsorption and Safe Nutrient Recycling in Agro-Industries
by Diana Guaya, Camilo Piedra and Inmaculada Carmona
Molecules 2025, 30(13), 2842; https://doi.org/10.3390/molecules30132842 - 2 Jul 2025
Viewed by 462
Abstract
Valorizing agro-industrial waste into functional materials for environmental remediation and resource recovery is essential for advancing circular economy models. This study presents a novel closed-loop strategy to convert annatto (Bixa orellana) seed residues into biochar for phosphate recovery from aqueous solutions [...] Read more.
Valorizing agro-industrial waste into functional materials for environmental remediation and resource recovery is essential for advancing circular economy models. This study presents a novel closed-loop strategy to convert annatto (Bixa orellana) seed residues into biochar for phosphate recovery from aqueous solutions and real agro-industrial wastewater. A novel ternary modification with Fe, Zn, and Mn metals was applied to enhance the phosphate adsorption performance of the biochar. Materials were synthesized via pyrolysis at 600 °C and 700 °C, with ABC-M700 exhibiting the highest performance. Comprehensive characterization (FTIR, SEM–EDS, and XRF) confirmed the successful incorporation of metal (oxy)hydroxide functional groups, which facilitated phosphate binding. Adsorption studies revealed that ABC-M700 achieved a maximum phosphate removal capacity of 6.19 mg·g−1, representing a 955% increase compared to unmodified ABC-N700 (0.59 mg·g−1), and a 31% increase relative to ABC-M600 (4.73 mg·g−1). Physicochemical characterization indicated increased surface area, well-developed mesoporosity, and the formation of metal (oxy)hydroxide functionalities. ABC-M700 achieved a maximum adsorption capacity of 73.22 mg·g−1 and rapid kinetics, removing 95% of phosphate within 10 min and reaching equilibrium at 30 min. The material exhibited notable pH flexibility, with optimal performance in the range of pH 6–7. Performance evaluations using real wastewater from the same agro-industry confirmed its high selectivity, achieving 80% phosphate removal efficiency despite the presence of competing ions and organic matter. Phosphate fractionation revealed that 78% of adsorbed phosphate was retained in stable, metal-associated fractions. Although the material showed limited reusability, it holds potential for integration into nutrient recycling strategies as a slow-release fertilizer. These findings demonstrate a low-cost, waste-derived adsorbent with strong implications for circular economy applications and sustainable agro-industrial wastewater treatment. This study establishes a scalable model for agro-industries that not only reduces environmental impact but also addresses phosphorus scarcity and promotes resource-efficient waste management. Full article
(This article belongs to the Special Issue Porous Carbon Materials: Preparation and Application)
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18 pages, 1684 KiB  
Article
The Effect of Warming and Nitrogen Addition on Soil Aggregate Enzyme Activities in a Desert Steppe
by Xin Zhang and Guodong Han
Sustainability 2025, 17(13), 6031; https://doi.org/10.3390/su17136031 - 1 Jul 2025
Viewed by 401
Abstract
Soil enzymes secreted by microorganisms play a key role in carbon (C), nitrogen (N), and phosphorus (P) metabolism in soil organic matter. As major drivers of climate change, warming and nitrogen addition affect soil physicochemical properties and enzyme activity, but their combined effects [...] Read more.
Soil enzymes secreted by microorganisms play a key role in carbon (C), nitrogen (N), and phosphorus (P) metabolism in soil organic matter. As major drivers of climate change, warming and nitrogen addition affect soil physicochemical properties and enzyme activity, but their combined effects on these parameters across different soil aggregate size scales in desert steppes remain unclear. This study used a 2 × 2 factorial split-plot design (control; warming; nitrogen addition: warming + nitrogen addition) conducted from 2006 in Inner Mongolia’s desert steppe. Soil samples were collected in 2018–2019, and aggregates were fractionated into >2000 μm, 250–2000 μm, and <250 μm sizes using a modified dry-sieving method. Physicochemical properties and enzyme activities were measured. Our results show that warming significantly reduced the total nitrogen (TN) and organic carbon (SOC) content in aggregates, while nitrogen addition significantly decreased the pH value in aggregates but had no significant impact on other soil nutrient content indicators. For soil enzyme activity, warming significantly reduced the activity of Urease and Alkaline Phosphatase (ALP) in soil aggregates, and nitrogen addition significantly reduced the activity of Urease, ALP, and β-glucosidase (BG) in aggregates. However, the size of the aggregates had a significant impact on the activity of Urease and BG. The influence of soil physicochemical properties on different enzyme activities varied across different years. These findings indicate that under the global change scenario, the physicochemical properties and enzyme activity of desert steppe soils are affected by warming and nitrogen addition to varying degrees, and the impact of these two factors shows significant differences across different years. Moreover, the interactive effects of warming and nitrogen addition did not simply result in an additive effect influenced by single factors. Full article
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21 pages, 3801 KiB  
Article
Age-Specific Effects of Nitrogen Addition on Soil Aggregate Dynamics in Chinese Evergreen Forests
by Yunze Dai, Xiaoniu Xu and LeVan Cuong
Forests 2025, 16(7), 1082; https://doi.org/10.3390/f16071082 - 29 Jun 2025
Viewed by 325
Abstract
In the context of China’s ecosystem facing a high intensity of nitrogen loads, carbon–nitrogen interactions are receiving increasing attention. Physical protection by soil aggregates is critical for soil carbon and nitrogen sequestration in terrestrial ecosystems; however, there is currently limited information on how [...] Read more.
In the context of China’s ecosystem facing a high intensity of nitrogen loads, carbon–nitrogen interactions are receiving increasing attention. Physical protection by soil aggregates is critical for soil carbon and nitrogen sequestration in terrestrial ecosystems; however, there is currently limited information on how nitrogen addition influences carbon and nitrogen dynamics across different stages of forest ageing. Herein, a field nitrogen manipulation experiment over 6 years was established in subtropical forests (46, 78, and about 200 years old) in China. Aggregate fractions and stable isotope analyses were used to assess the effects of nitrogen addition. The results show that forest soil was dominated by macroaggregates, and these increased with forest ageing (p > 0.05). The macroaggregates’ carbon content decreased with forest ageing (p > 0.05), while the macroaggregates’ nitrogen content was highest in the 200-year-old forest. Nitrogen addition increased the aggregates’ carbon and nitrogen concentrations in the 46- and 200-year-old forests. The macroaggregates, under nitrogen addition in the 78- and 200-year-old forests, were relatively weak, while forest age and nitrogen addition mainly affected macroaggregate carbon and nitrogen concentrations to promote their carbon and nitrogen storage, and the macroaggregates were the main storage unit for fixing and protecting new carbon in soils. Nitrogen addition increased the macroaggregates’ δ13C abundance in the 78- and 200-year-old forests and decreased it in the 46-year-old forest (p > 0.05); significantly increased the macroaggregates’ δ15N in the 46-year-old forest (p < 0.05), and decreased the macroaggregates’ δ15N in the 200-year-old forest (p > 0.05). Considering the distribution of δ13C and δ15N in the aggregates, the effect of nitrogen addition on the dynamic mechanism of soil aggregate carbon and nitrogen fractions varied based on forest age and aggregate size. Correlation analysis further revealed that soil total phosphorus, NH4+-N, NO3-N, dissolved organic nitrogen, pH, texture, etc., were the primary predictors explaining most of the variation in aggregate fractions and their δ13C distribution. In summary, the effect of nitrogen deposition on the carbon and nitrogen stability of soil aggregates in broad-leaved forests depends on forest age. Full article
(This article belongs to the Section Forest Soil)
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17 pages, 1618 KiB  
Article
A Phosphorus Microfractionation (P-MF) Method for Measuring Phosphorus Fractions in Small Quantities of Suspended Solids and Sediments: Detailed Method and Example Application
by Jacob B. Taggart, Rebecca L. Ryan, A. Woodruff Miller, Theron G. Miller and Gustavious P. Williams
Environments 2025, 12(7), 218; https://doi.org/10.3390/environments12070218 - 26 Jun 2025
Viewed by 369
Abstract
The standard methods for sediment phosphorus (P) fractionation are impractical for use with suspended solids due to the inherent difficulties associated with collecting sufficient sample quantities for analysis. To allow the fractionation analysis of small quantities of suspended solids or sediment, we developed [...] Read more.
The standard methods for sediment phosphorus (P) fractionation are impractical for use with suspended solids due to the inherent difficulties associated with collecting sufficient sample quantities for analysis. To allow the fractionation analysis of small quantities of suspended solids or sediment, we developed a P-microfractionation (P-MF) method and evaluated the minimum sample size threshold. The dry mass threshold is likely <1.0 g for Utah Lake suspended solids and between 0.35 and 0.99 g for Utah Lake sediments, though we recommend experimentation to refine these thresholds for other locations, as Utah Lake sediment P concentrations are high (~1000 mg kg−1). We estimated dry mass using duplicate samples, as drying a sample changes the P fractions. We show that Utah Lake suspended solids have a significantly higher P content across most P fractions compared to those in sediments, emphasizing the importance of considering suspended solids when managing water nutrient levels in eutrophic water bodies. P-MF has the potential to enable researchers to use reasonably sized water samples to assess the P sorption behavior of suspended solids, a measurement not typically performed. Full article
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18 pages, 2348 KiB  
Article
Sedimentary Differentiation Characteristics of Organic Matter and Phosphorus in Eutrophic Lake Special Zones
by Ya-Ping Liu, Di Song, Li-Xin Jiao, Jin-Long Zheng, Miao Zhang, Bo Yao, Jing-Yi Yan, Jian-Xun Wu and Xin Wen
Water 2025, 17(13), 1899; https://doi.org/10.3390/w17131899 - 26 Jun 2025
Viewed by 362
Abstract
Lake eutrophication, often driving harmful algal blooms (HABs) and ecosystem degradation, involves complex biogeochemical shifts within sediments. Changes in the sedimentary dissolved organic matter (DOM) composition during transitions from macrophyte to algal dominance are thought to critically regulate internal phosphorus (P) loading, yet [...] Read more.
Lake eutrophication, often driving harmful algal blooms (HABs) and ecosystem degradation, involves complex biogeochemical shifts within sediments. Changes in the sedimentary dissolved organic matter (DOM) composition during transitions from macrophyte to algal dominance are thought to critically regulate internal phosphorus (P) loading, yet the underlying mechanisms, especially in vulnerable plateau lakes like Qilu Lake, require further elucidation. This study investigated the coupled cycling of carbon (C) and P in response to historical ecosystem succession and anthropogenic activities using a 0–24 cm sediment core from Qilu Lake. We analyzed the total organic carbon (TOC), total phosphorus (TP), sequential P fractions, and DOM fluorescence characteristics (EEM-PARAFAC), integrated with chronological series data. The results revealed an asynchronous vertical distribution of TOC and TP, reflecting the shift from a submerged macrophyte-dominated, oligotrophic state (pre-1980s; high TOC, low TP, stable Ca-P dominance) to an algae-dominated, eutrophic state. The eutrophication period (~1980s–2010s) showed high TP accumulation (Ca-P and NaOH85 °C-P enrichment), despite a relatively low TOC (due to rapid mineralization), while recent surface sediments (post-2010s) exhibited a high TOC, but a lower TP following input controls. Concurrently, the DOM composition shifted from microbial humic-like dominance (C1) in deeper sediments to protein-like dominance (C3) near the surface. This study demonstrates that the ecosystem shift significantly regulates P speciation and mobility by altering sedimentary DOM abundance and chemical characteristics (e.g., protein-like DOM correlating negatively with Ca-P), reinforcing a positive feedback mechanism that sustains internal P loading and potentially exacerbates HABs. DOM molecular characteristics emerged as a key factor controlling the internal P cycle in Qilu Lake, providing critical insights for managing eutrophication in plateau lakes. Full article
(This article belongs to the Special Issue Water Environment Pollution and Control, 4th Edition)
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41 pages, 9366 KiB  
Article
Soil Bioindicators and Crop Productivity Affected by Legacy Phosphate Fertilization and Azospirillum brasilense Inoculation in No-Till Systems
by Naiane Antunes Alves Ribeiro, Aline Marchetti Silva Matos, Viviane Cristina Modesto, Nelson Câmara de Souza Júnior, Vitória Almeida Moreira Girardi, Iêda de Carvalho Mendes and Marcelo Andreotti
Appl. Sci. 2025, 15(13), 7146; https://doi.org/10.3390/app15137146 - 25 Jun 2025
Viewed by 363
Abstract
Pressure on agroecosystems is increasing with rising agricultural demand, pushing Brazilian agriculture toward more sustainable systems that prioritize soil health. This study aimed to evaluate whether long-term no-till management and inoculation with Azospirillum brasilense influenced soil bioindicators; chemical, biological, and enzymatic attributes; and [...] Read more.
Pressure on agroecosystems is increasing with rising agricultural demand, pushing Brazilian agriculture toward more sustainable systems that prioritize soil health. This study aimed to evaluate whether long-term no-till management and inoculation with Azospirillum brasilense influenced soil bioindicators; chemical, biological, and enzymatic attributes; and how these attributes correlated with crop productivity in a rotational system. The experiment also assessed the residual effects of phosphate fertilization (initially applied in 2013 and reapplied in 2020) and its interaction with inoculation on soil phosphorus fractions and crop performance. This study was conducted on Dystrophic Red Oxisol in the low-altitude Cerrado region under 20 years of no-tillage management, using a randomized block design in a 5 × 2 factorial scheme: five phosphorus doses (0, 30, 60, 120, and 240 kg ha−1 P2O5) and inoculated or non-inoculated grasses, with four replicates. The results showed that inoculation influenced dry matter (DM) production and nutrient cycling, improving soil health despite lower fertility and total DM. The correlation between bioindicators and productivity suggests that soil health indicators can be used to monitor system sustainability. No consistent effects of inoculation or phosphate fertilization were observed for some crop components, indicating complex interactions under long-term conservationist systems. Full article
(This article belongs to the Special Issue Soil Health and Soil Microbiology)
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13 pages, 1908 KiB  
Article
Effect of Crop Type Shift on Soil Phosphorus Morphology and Microbial Functional Diversity in a Typical Yellow River Irrigation Area
by Zijian Xie, Rongbo Zhao, Bo Bo, Chunhua Li, Yang Wang, Yu Chu and Chun Ye
Microorganisms 2025, 13(7), 1458; https://doi.org/10.3390/microorganisms13071458 - 23 Jun 2025
Viewed by 341
Abstract
The Hetao irrigation area is one of the largest irrigation areas in the Yellow River Basin and a typical salinized agricultural area. Crop type shifts in this area can alter soil phosphorus (P) morphology and microbial functional diversity, thereby influencing soil P losses. [...] Read more.
The Hetao irrigation area is one of the largest irrigation areas in the Yellow River Basin and a typical salinized agricultural area. Crop type shifts in this area can alter soil phosphorus (P) morphology and microbial functional diversity, thereby influencing soil P losses. However, few studies have elucidated the underlying mechanisms. In this study, soil samples were collected from four different crop planting areas: sunflower field (SF), corn field (CF), wheat land (WL), and vegetable and fruit land (VFL). Subsequently, the physicochemical properties, P fractions, and phosphate-solubilizing microorganisms (PSMs) were analyzed. The results indicated that when other lands shifted to SF, the soil pH increased significantly. Simultaneously, SOM, TN, and TP decreased significantly during the crop type conversion. Analysis of P fraction revealed that moderately active P, including NaOH-Pi, NaOH-Po, and HCl-Pi, were the dominant fractions in the tested soils. Among them, HCl-Pi was the major component of moderately active P. The soil P leaching change point in the tested are was 6.25 mg Olsen-P kg−1. The probabilities of P leaching in WL, VFL, CF, and SF were 91.7%, 83.8%, 83.8%, and 66.7%, respectively. Additionally, the sum of the relative abundances of the three PSMs in SF, VFL, WL, and CF were 8.81%, 11.88%, 8.03%, and 10.29%, respectively. The shift in crop type to SF exacerbated the soil degradation process. Both TP and residual P in the soil decreased. However, the NaHCO3 slightly increased, which may have been due to the increased abundance of Thiobacillus and Escherichia. Full article
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15 pages, 1190 KiB  
Article
Sustainable Phosphate Capture from Urban Wastewater Treatment Plants Towards a Nutrient Recovery and Water Reuse Strategy
by Andreia F. Santos, Paula Alvarenga, Licínio M. Gando-Ferreira and Margarida J. Quina
Appl. Sci. 2025, 15(12), 6761; https://doi.org/10.3390/app15126761 - 16 Jun 2025
Viewed by 321
Abstract
This study proposes and evaluates a two-step phosphorus (P) recovery strategy that combines chemical precipitation with adsorption to comply with the updated EU Urban Wastewater Treatment Directive (Directive (EU) 2024/3019), which sets stricter limits on nutrient discharge and promotes resource recovery. The objective [...] Read more.
This study proposes and evaluates a two-step phosphorus (P) recovery strategy that combines chemical precipitation with adsorption to comply with the updated EU Urban Wastewater Treatment Directive (Directive (EU) 2024/3019), which sets stricter limits on nutrient discharge and promotes resource recovery. The objective was to enhance the P removal efficiency beyond that achieved by conventional precipitation. A laboratory-scale design of experiments was conducted using real wastewater with an initial P concentration of 10 mg P/L post-precipitation and was extended to 1 and 40 mg P/L to assess broader applicability. The optimal lab-scale conditions (30 cm bed height and 5 mL/min flow rate) resulted in a saturated bed fraction (FSB) of 0.425 and a breakthrough time of 126 min. The process was successfully scaled up to a column with a height of 60 cm and a diameter of 4 cm, achieving a higher FSB (0.764), improved adsorption capacity (84.1 mg P/kg), and reduced unused bed (40%). The integrated system maintained effluent P levels below 0.5–0.7 mg P/L for over 400 min, demonstrating regulatory compliance and operational reliability. These findings confirmed the feasibility and scalability of combining precipitation with adsorption for enhanced P recovery in wastewater treatment systems. Full article
(This article belongs to the Section Applied Biosciences and Bioengineering)
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15 pages, 2854 KiB  
Article
Effects of Biochar on the Temporal Dynamics and Vertical Distribution of Iron and Phosphorus Under Soil Submergence
by Ying-Ren Lai and Shan-Li Wang
Agronomy 2025, 15(6), 1394; https://doi.org/10.3390/agronomy15061394 - 5 Jun 2025
Viewed by 496
Abstract
Biochar is considered a promising amendment for improving phosphorus (P) availability in agricultural soils; however, its effects on the chemical transformation and long-term immobilization of P in submerged soils across soil depth and over time remain unclear. This study conducted a 98-day column [...] Read more.
Biochar is considered a promising amendment for improving phosphorus (P) availability in agricultural soils; however, its effects on the chemical transformation and long-term immobilization of P in submerged soils across soil depth and over time remain unclear. This study conducted a 98-day column incubation experiment to investigate the effects of rice straw biochar (RSB) on the spatial and temporal dynamics of iron (Fe) and P under soil submergence. Soils with and without biochar addition were mixed with water homogeneously and then added into each PVC column with an additional standing water layer above the soil surface. The results revealed a two-stage shift in soil redox potential (Eh), with more rapid changes observed at deeper depths. RSB addition accelerated the decline in Eh and increased the soil pH. The rise in pH by submergence and biochar addition promoted the release of soluble and exchangeable P from soil to pore water during incubation. Ca-associated P precipitation and re-adsorption resulted in relatively low phosphate concentrations in pore water. RSB addition increased P availability in the early stage by releasing soluble and exchangeable P and promoting phosphate desorption through pH elevation, which increased the negative surface charge of soil constituents, thereby reducing their affinity for phosphate and enhancing its release into the pore water. However, prolonged submergence led to the transformation of soluble and exchangeable P into more stable Ca-P precipitates, limiting long-term P availability. These findings provide new insights into the temporal and spatial dynamics of P in submerged soils and highlight the short-term benefits and long-term limitations of biochar for sustaining P availability in paddy rice systems. Full article
(This article belongs to the Section Soil and Plant Nutrition)
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