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Understanding the behavior of colloidal phosphorus (P coll ) under anoxic conditions is pivotal for addressing soil phosphorus (P) mobilization and transport and its impact on nutrient cycling. Our study investigated P coll dynamics in acidic floodplain soil during a 30-day flooding event. The sudden oxic-to-anoxic shift led to a significant rise in pore-water P coll levels, which exceeded soluble P levels by more than 2.7-fold. Colloidal fractions transitioned from dispersed forms (<220 nm) to colloid-associated microaggregates (>220 nm), as confirmed by electron microscopy. The observed increase in colloidal sizes was paralleled by their heightened ability to form aggregates. Compared to sterile control conditions, anoxia prompted the transformation of initially dispersed colloids into larger particles through microbial activity. Curiously, the 16S rRNA and ITS microbial diversity analysis indicated that fungi were more strongly associated with anoxia-induced colloidal release than bacteria. These microbially induced shifts in P coll lead to its higher mobility and transport, with direct implications for P release from soil into floodwaters.

Soil water-dispersible colloidal phosphorus (WCP) presents high mobility, however, the regulatory effect of biochar-coupled organic fertilizer is rarely known, especially under different cropping patterns. This study investigated the P adsorption, soil aggregate stability, and WCP in three paddy and three vegetable fields. These soils were amended with different fertilizers (chemical fertilizer, CF; substitution of solid-sheep manure or liquid-biogas slurry organic fertilizer, SOF/LOF; substitution of biochar-coupled organic fertilizers, BSOF/BLOF). Results presented that the LOF averagely increased the WCP contents by 50.2% across the sites, but the SOF and BSOF/BLOF averagely decreased their contents by 38.5% and 50.7% in comparison with the CF. The WCP decline in the BSOF/BLOF-amended soils was mainly attributed to the intensive P adsorption capacity and soil aggregate stability. The BSOF/BLOF increased the amorphous Fe and Al contents in the fields in comparison with the CF, which improved the adsorption capacity of soil particles, further improving the maximum absorbed P (Q max ) and reducing the dissolved organic matter (DOC), leading to the improvement of > 2 mm water-stable aggregate (WSA >2mm ) and subsequent WCP decrease. This was proved by the remarkable negative associations between the WCP and Q max (R 2  = 0.78, p < 0.01) and WSA >2mm (R 2  = 0.74, p < 0.01). This study manifests that biochar-coupled organic fertilizer could effectively reduce soil WCP content via the improvement of P adsorption and aggregate stability., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Phosphorus (P) availability and loss risk are linked to P species; however, their alternations in the soil amended with biochar-blended organic fertilizer is not well known, particularly under contrasting soil properties and land management. In this study, the variance of soil P species extracted by sequential chemical extraction (SCE) and 31 P NMR techniques, as well as the degree of P saturation (DPS), were investigated throughout three paddy and three vegetable fields. These fields were amended with three different fertilizers at the same P application rate: chemical fertilizer (CF), organic fertilizer substitution (sheep manure/biogas slurry, SM/BS), and biochar-blended organic fertilizer substitution (BSM/BBS). Results showed that the BSM/BBS and SM increased the total P contents by 7.5% and 5.9% (TP) and available P contents by 30.1% and 19.2% (AP), but decreased the DPS values by 19.4% and 11.7%, compared to the CF treatment. Yet, the BS decreased the TP and AP contents but increased the DPS values across the experimental sites. In the BSM/BBS amended soils, high AP contents were due to the increased inorganic P (NaHCO 3 -P i ), while the increased organic P (monoester and DNA) induced low DPS values and reduced soil P loss risk. Our study highlights that biochar-blended organic fertilizer is an effective agronomic way for improving P availability and decreasing P loss risk via the alteration of soil P species., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The manure fertilizer increases the phosphorus (P) saturation of soils and the colloidal P release to water bodies. Manure of different particle-sizes may have different effects on colloidal P release by soil, and to date there is limited knowledge on colloidal P release from soils amended with different size manures. We produced sheep micro- (S Micro ) and nano-manure (S Nano ), and poultry micro- (P Micro ), nano-manure (P Nano ) from bulk samples by wet fractionation method. The fractionation reduced the P contents of micro- and nano-manures, and enriched them in ash and calcium, iron (Fe), magnesium, and aluminum (Al) phosphate minerals compared with the bulk manures. The degree of P saturation (DPS) in Anthorsol and Cambisol was decreased (S Micro , 17.6 and 17.2 %; S Nano , 14.5 and 13.3 % and P Micro , 19.0 and 19.7 mg kg -1 ; P Nano , 17.0 and 14.3 mg kg -1 ) and released less colloidal P (S Micro , 3.12 and 3.78 mg kg -1 ; S Nano , 3.01 and 3.56 mg kg -1 and P Micro , 3.34 and 3.92 mg kg -1 ; P Nano , 3.21 and 3.65 mg kg -1 ) than the soils receiving the bulk manures. The decrease in colloidal P was correlated with less DPS in both soils amended with micro and nano manures. That is, the only measurable effect of manure particle size on colloidal P release from the amended soils was due to chemical fractionation during separation of the size fractions. It was suggested that nano and micro manures were the effective approach to reduce colloidal P release from manure amended soils., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The agricultural use of manure fertilizer increases the phosphorus (P) saturation of soils and the risk of colloidal P (P coll) release to aquatic ecosystems. Two experiments were conducted to identify whether Pteris vittata plantation can decrease P coll contents in two soils (Cambisol and Anthrosol) amended with various manure P rates (0, 10, 25, and 50 mg P kg−1 of soil). The total P coll contents in manured soil without P. vittata were 1.14–3.37 mg kg−1 (Cambisol), and 0.01–2.83 mg kg−1 (Anthrosol) across manure-P rates. The corresponding values with P. vittata were 0.97–2.33 mg kg−1 (Cambisol) and 0.005–1.6 mg kg−1 (Anthrosol). Experimentally determined colloidal minerals (Fe, Al, Ca), colloidal total organic carbon, Mehlich−3 nutrients (Fe, Al, and Ca), and the degree of P saturation were good predictors of P coll concentrations in both soils with and without P. vittata plantation. In unplanted soils, P adsorption decreased and the degree of P saturation increased which released more P coll. However, P. vittata plantation decreased the P coll release and P loss risk due to the increase of P adsorption and reduced DPS in both soils. The P fractions (NaOH, NH 4 F, and HCl–P) contributed to increase the P pool in planted soils which enhanced the bioavailability of P coll and increased the P. vittata biomass. It suggested that P. vittata plantation was an effective approach to reduce P coll release from manure amended soils. [Display omitted] • Soils with maximum P adsorption capacity reduce colloidal phosphorus release. • Pteris vittata plantation increase bioavailability of colloidal phosphorus. • Maximum Degree of P saturation promoted colloidal phosphorus release. [ABSTRACT FROM AUTHOR]