Different facets of alpha and beta diversity of benthic diatoms along stream watercourse in a large near-natural catchment.

Understanding the processes and mechanisms that shape the distribution patterns and variations of biodiversity along spatial gradients continues to be a priority for ecological research. We focused on the biodiversity of benthic diatom communities within a large near-natural watershed. The objectives are: (1) to explore the overall spatial patterns of benthic diatom biodiversity; (2) to investigate the effects associated with watercourse position and environmental variables, as well as both common and rare species on two facets (i.e., taxonomic and functional) of alpha and beta diversity; and (3) to unveil the mechanisms underlying their spatial variations. Alpha diversity indices along the stream watercourse showed a clear increasing trend from upstream to downstream sites. Results of random forest regression identified conductivity as the primary factor influencing functional alpha diversity, while elevation emerged as the predominant factor for taxonomic alpha diversity. Beta diversity partitioning revealed that taxonomic beta diversity generally exceeded functional beta diversity. These diversity measures exhibited different patterns along the watercourse position: taxonomic beta diversity remained relatively consistent along the watercourse, whereas functional total beta diversity and its two components of middle stream sites were lower than those of upstream and downstream sites. Functional beta diversity was sustained by dominant and common species, while rare species made significant contributions to taxonomic beta diversity. Both taxonomic and functional beta diversity and its components displayed a stronger influence from spatial factors than from local environmental, geo-climatic, and nutrient variables. Collectively, taxonomic and functional alpha and beta diversity demonstrated distinct responses to the main environmental gradients and spatial factors within our catchment, highlighting their different insights into diatom diversity. Furthermore, research is required to assess the generalizability of our findings to similar ecosystems. In addition, this study presents opportunities for expansion to include other taxa (e.g., macroinvertebrates and fish) to gain a comprehensive understanding of the driving mechanisms behind stream biodiversity.

Comparison of different macroinvertebrates bioassessment indices in a large near-natural watershed under the context of metacommunity theory.

The metacommunity theory proposes that community structure and biodiversity are influenced by both local processes (such as environmental filtering) and regional processes (such as dispersal). Despite the extensive use of traditional bioassessments based on species-environment relationships, the impact of dispersal processes on these assessments has been largely overlooked. This study aims to compare correlations between various bioassessment indices, including Shannon Weiner (H'), Biological Monitoring Working Party (BMWP), average score per taxon (ASPT), biotic index (BI), and EPT taxa index (EPT), based on macroinvertebrates collected from 147 sampling sites in a subtropical Chinese near-natural catchment. Modified indices were calculated by removing species strongly influenced by dispersal processes to address the influence of dispersal processes. Their relationship with environmental factors was then compared to the original indices. The study employed random forest regression (RFR) to compare the explanatory power of environmental factors using the two sets of indices. The spearman rank correlation analysis was conducted to examine the correlation between indices and environmental factors. The river health assessment was performed based on both modified and original indices. The results reveal significant differences between original and modified indices (especially H' and BI) providing a more accurate reflection of environmental conditions. Furthermore, the sensitivity of the different indices to various environmental factors varied, leading to differences in the bioassessment results between the modified and the original indices. Notably, original H', BMWP, and ASPT overestimated the bioassessment results, whereas the original BI underestimated them. These findings offer valuable insights into bioassessment and river health assessment evaluation within the catchment and other interconnected freshwater ecosystems, such as lakes, reservoirs, and wetlands. Our study underscores the importance of assessing and mitigating the impact of dispersal processes on bioassessment to obtain a more precise representation of the status of freshwater ecosystems.

Seed nano-priming with multiple nanoparticles enhanced the growth parameters of lettuce and mitigated cadmium (Cd) bio-toxicity: An advanced technique for remediation of Cd contaminated environments.

Seed nano-priming can be used as an advanced technology for enhancing seed germination, plant growth, and crop productivity; however, the potential role of seed nano-priming in ameliorative cadmium (Cd) bio-toxicity under Cd stress has not yet been sufficiently investigated. Therefore, in this study we investigated the beneficial impacts of seed priming with low (L) and high (H) concentrations of nanoparticles including nSiO2 (50/100 mg L-1), nTiO2 (20/60 mg L-1), nZnO (50/100 mg L-1), nFe3O4 (100/200 mg L-1), nCuO (50/100 mg L-1), and nCeO2 (50/100 mg L-1) on lettuce growth and antioxidant enzyme activities aiming to assess their efficacy for enhancing plant growth and reducing Cd phytotoxicity. The results showed a significant increase in plant growth, biomass production, antioxidant enzyme activities, and photosynthetic efficiency in lettuce treated with nano-primed nSiH + Cd (100 mg L-1), nTiH + Cd (60 mg L-1), and nZnL + Cd (50 mg L-1) under Cd stress. Moreover, nano-priming effectively reduced the accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA) in lettuce shoots. Interestingly, nano-primed nSiH + Cd, nTiH + Cd, and nZnL + Cd demonstrated efficient reduction of Cd uptake, less translocation factor of Cd with high tolerance index, ultimately reducing toxicity by stabilizing the root morphology and superior accumulation of critical nutrients (K, Mg, Ca, Fe, and Zn). Thus, this study provides the first evidence of alleviating Cd toxicity in lettuce by using multiple nanoparticles via priming strategy. The findings highlight the potential of nanoparticles (Si, Zn, and Ti) as stress mitigation agents for improved crop growth and yield in Cd contaminated areas, thereby offering a promising and advanced approach for remediation of Cd contaminated environments.

Assessing the effectiveness of 3, 4-dimethylpyrazole phosphate (DMPP) inhibitor in mitigating N2O emissions from contrasting Cd-contaminated soils.

Improving nitrogen use efficiency of chemical fertilizers is essential to mitigate the negative environmental impacts of nitrogen. Nitrification, the conversion of ammonium to nitrate via nitrite by soil microbes, is a prominent source of nitrogen loss in soil systems. The effectiveness of nitrification inhibitors in reducing nitrogen loss through inhibition of nitrification is well-documented, however, their efficacy in heavy metals-contaminated soils needs thorough investigations. The current study assessed the efficacy of nitrification inhibitor 3, 4-dimethylpyrazole phosphate (DMPP) in reducing nitrous oxide (N2O) emissions in cadmium (Cd) contaminated paddy and red soils under lab-controlled environment. Obtained results indicated the substantial reduction in N2O emissions with DMPP in paddy and red soil by 48 and 35 %, respectively. However, Cd contamination resulted in reduced efficacy of DMPP, thus decreased the N2O emissions by 36 and 25 % in paddy and red soil, respectively. It was found that addition of DMPP had a significant effect on the abundance of ammonia oxidizing bacteria (AOB) and archaea (AOA). Notably, the reduction in N2O emissions by DMPP varied with the abundance of AOB. Moreover, Cd pollution resulted in a significant (P < 0.05) reduction in the abundance of archaeal and bacterial amoA genes, as well as bacterial nirK, nirS, and nosZ genes. The combined treatment of Cd and DMPP had a detrimental impact on denitrifiers, thereby influencing the overall efficiency of DMPP. These findings provide novel insights into the application of DMPP to mitigate nitrification and its potential role in reducing N2O emissions in contaminated soils.

A critical review on selenium removal capacity from water using emerging non-conventional biosorbents.

Anthropogenic-driven selenium (Se) contamination of natural waters has emerged as severe health and environmental concern. Lowering Se levels to safe limits of 40 µg-L-1 (recommended by WHO) presents a critical challenge for the scientific community, necessitating reliable and effective methods for Se removal. The primary obectives of this review are to evaluate the efficiency of different biosorbents in removing Se, understand the mechanism of adsorption, and identify the factors influencing the biosorption process. A comprehensive literature review is conducted to analyze various studies that have explored the use of modified biochars, iron oxides, and other non-conventional biosorbents for selenium removal. The assessed biosorbents include biomass, microalgae-based, alginate compounds, peats, chitosan, and biochar/modified biochar-based adsorbents. Quantitative data from the selected studies analyzed Se adsorption capacities of biosorbents, were collected considering pH, temperature, and environmental conditions, while highlighting advantages and limitations. The role of iron impregnation in enhancing the biosorption efficiency is investigated, and the mechanisms of Se adsorption on these biosorbents at different pH levels are discussed. A critical literature assessment reveals a robust understanding of the current state of Se biosorption and the effectiveness of non-conventional biosorbents for Se removal, providing crucial information for further research and practical applications in water treatment processes. By understanding the strengths and limitations of various biosorbents, this review is expected to scale-up targeted research on Se removal, promoting the development of innovative and cost-effective adsorbents, efficient and sustainable approaches for Se removal from water.

Effect of foliar application of nanoparticles on growth, physiology, and antioxidant enzyme activities of lettuce (Lactuca sativa L.) plants under cadmium toxicity.

Nanotechnology has attracted the interest of scientists due to its wide range of application specifically in agriculture. Nanoparticles (NPs) may act as a promising materials to alleviate cadmium (Cd) stress in plants. This study aims to assess the impact of multiple nanoparticles including nSiO2 (50 mg L-1:100 mg L-1), nTiO2 (20 mg L-1:60 mg L-1), nZnO (50 mg L-1:100 mg L-1), nFe3O4 (100 mg L-1:200 mg L-1), nCuO (50 mg L-1:100 mg L-1), and nCeO2 (50 mg L-1:100 mg L-1) in combination with CdCl2 (5 µM) to mitigate Cd toxicity in lettuce through foliar application in hydroponic solution. Current findings indicate that foliar application of nSiL + Cd (50 mg L-1), nZnL + Cd (50 mg L-1), and nTiL + Cd (20 mg L-1) is more effective in improving growth, biomass, root architecture, and elevated photosynthetic efficiency, which might be attributed to the increasing uptake of essential micronutrient (K, Mg, Ca, Fe, Zn) under Cd stress. Similarly, treatment with nanoparticles leads to reduced accumulation of ROS and MDA in lettuce, while enhancing the SOD, POD, CAT, and APX activities. The results showed that nanoparticles have high tolerance against Cd as depicted by the inhibition in Cd accumulation by 3.2-58% and 10-72% in roots as well as edible parts of lettuce, respectively. In addition, Cd alone reduces the morphological traits, antioxidant enzyme activity, and photosynthetic activity, while increasing the ROS, MDA, and Cd accumulation in lettuce. This comprehensive study suggests the role of nanoparticles in reducing Cd toxicity in lettuce, signifying their importance as stress mitigation agents. However, long-term pot, priming, and field trials are needed to identify the optimal nanoparticle for the lettuce under variable environmental conditions.

Biochar-coupled organic fertilizer reduced soil water-dispersible colloidal phosphorus contents in agricultural fields.

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 (Qmax) 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 Qmax (R2 = 0.78, p < 0.01) and WSA>2mm (R2 = 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.

Improved phosphorus availability and reduced degree of phosphorus saturation by biochar-blended organic fertilizer addition to agricultural field soils.

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 31P 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 (NaHCO3-Pi), 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.

Prediction of nano, fine, and medium colloidal phosphorus in agricultural soils with machine learning.

Soil colloids have been shown to play a critical role in soil phosphorus (P) mobility and transport. However, identifying the potential mechanisms behind colloidal P (Pcoll) release and the key influencing factors remains a blind spot. Herein, a machine learning approach (random forest (RF) coupled with partial dependence plot analyses) was applied to determine the effects of different soil physicochemical parameters on Pcoll content in three colloidal subfractions (i.e., nano- (NC): 1-20 nm, fine- (FC): 20-220 nm and medium-sized colloids (MC): 220-450 nm) based on a regional dataset of 12 farmlands in Zhejiang Province, China. RF successfully predicted Pcoll content (R2 = 0.98). Results showed that colloidal- organic carbon (OCcoll) and minerals were the major determinants of total Pcoll content (1-450 nm); their critical values for increasing Pcoll release were 87.0 mg L-1 for OCcoll, 11.0 mg L-1 for iron (Fecoll) or aluminium (Alcoll), 2.6 mg L-1 for calcium (Cacoll), 9.0 mg L-1 for magnesium (Mgcoll), 2.5 mg L-1 for silicon (Sicoll), and 1.4 mg L-1 for manganese (Mncoll). Among three colloidal subfractions, the major factors determining Pcoll were soil Olsen-P (POlsen; 125.0 mg kg-1), Cacoll (2.5 mg L-1), and colloidal P saturation (21.0%) in NC; Mncoll (1.5 mg L-1), Mgcoll (6.8 mg L-1), and POlsen (135.0 mg kg-1) in FC; while Mncoll (1.5 mg L-1), Alcoll (2.5 mg L-1), and Fecoll (3.8 mg L-1) in MC, respectively. OCcoll had a considerable effect in the three fractions, with critical values of 80.0 mg L-1 in NC or FC, and 50.0 mg L-1 in MC. Our study concluded that the information gleaned using the RF model can be used as crucial evidence to identify the key determinants of different size fractionated Pcoll contents. However, we still need to discover one or more easy-to-measure parameters that can help us better predict Pcoll.

Nano and fine colloids suspended in the soil solution regulate phosphorus desorption and lability in organic fertiliser-amended soils.

Mobile colloids impact phosphorus (P) binding and transport in agroecosystems. However, their relationship to P-lability and their relative importance to P-bioavailability is unclear. In soils amended with organic fertilisers, we investigated the effects of nano (NC; 1-20 nm), fine (FC; 20-220 nm), and medium (MC; 220-450 nm) colloids suspended in soil solution on soil P-desorption and lability. The underlying hypothesis is that mobile colloids of different sizes, i.e., NC, FC, and MC, may contribute differently to P-lability in soils enriched with organic fertiliser. NC- and FC-bound Pcoll were positively correlated with P-lability parameters from diffusive gradient in thin films (DGTA-labile P concentration, r ≥ 0.88; and DGTA-effective P concentration, r ≥ 0.87). The corresponding relations with MC-bound Pcoll are weaker (r values of 0.50 and 0.51). NC- and FC-bound Pcoll were also strongly correlated with soil P-resupply (r ≥ 0.64) and desorption (r ≥ 0.79) parameters during DGTA deployment, and the mobility of these colloids was corroborated by electron microscopy of DGTA gels. MC-bound Pcoll was negatively correlated with the solid-to-solution distribution coefficient (r = -0.42), indicating this fraction is unlikely to be the source of P-release from the solid phase after P-depletion from the soil solution. We conclude that NC and FC mainly contribute to regulating soil desorbable-P supply to the soil solution in the DGTA depletion zone (in vitro proxy for plant rhizosphere), and consequently may act as critical conditioners of P-bioavailability, whereas MC tends to form complexes that lead to P-occlusion rather than lability.

Nano and micro manure amendments decrease degree of phosphorus saturation and colloidal phosphorus release from agriculture soils.

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- (SMicro) and nano-manure (SNano), and poultry micro- (PMicro), nano-manure (PNano) 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 (SMicro, 17.6 and 17.2 %; SNano, 14.5 and 13.3 % and PMicro, 19.0 and 19.7 mg kg-1; PNano, 17.0 and 14.3 mg kg-1) and released less colloidal P (SMicro, 3.12 and 3.78 mg kg-1; SNano, 3.01 and 3.56 mg kg-1 and PMicro, 3.34 and 3.92 mg kg-1; PNano, 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.

Qualitative and quantitative investigation on adsorption mechanisms of Cd(II) on modified biochar derived from co-pyrolysis of straw and sodium phytate.

Developing effective modification methods and obtaining a comprehensive understanding of adsorption mechanisms are essential for the practical application of biochars for the removal of heavy metals from solutions. In this study, rice straw was impregnated with sodium phytate and pyrolyzed at 350 °C, 450 °C, and 550 °C to synthesize modified biochars (i.e., MBC350, MBC450, and MBC550). The Cd(II) adsorption capacities and contributions of different mechanisms, including the effects of biochar-derived dissolved organic matter (BDOM), were investigated using batch sorption experiments and characterization analyses. The modification of sodium phytate promoted the pyrolysis of biomass, thereby increasing the BDOM content and aromatic structures at low and high pyrolysis temperatures, respectively. Moreover, the modification also increased the exchangeable Na+ and carbonate contents in the modified biochars. Compared with the raw biochars, the Cd(II) adsorption capacities of modified biochars increased by 3.3-4.3 times, and MBC550 had the highest Cd(II) adsorption capacity (126.5 mg/g), of which precipitation with minerals and interaction with π-electrons contributed 41.7% and 45.8%, respectively. However, at a lower pyrolysis temperature, the Cd(II) adsorption attributed to ion exchange and co-deposition with BDOM significantly increased, especially on MBC350 (33.9 and 12.6 mg/g, respectively). These results indicate that modification by sodium phytate effectively enhanced various adsorption mechanisms, thereby increasing the Cd(II) adsorption capacity. In addition, the contribution of co-deposition with BDOM to adsorption was unneglectable for the biochars pyrolyzed at low temperatures.

Phytate exudation by the roots of Pteris vittata can dissolve colloidal FePO4.

Phosphorus (P) is limiting nutrient in many soils, and P availability may often depend on iron (Fe) speciation. Colloidal iron phosphate (FePO4coll) is potentially present in soils, and we tested the hypothesis that phytate exudation by Pteris vittata might dissolve FePO4coll by growing the plant in nutrient solution to which FePO4coll was added. The omission of P and Fe increased phytate exudation by P. vittata from 434 to 2136 mg kg-1 as the FePO4coll concentration increased from 0 to 300 mM. The total P in P. vittata tissue increased from 2880 to 8280 mg kg-1, and the corresponding increases in the trichloroacetic acid (TCA) extractable P fractions were inorganic P (860-5100 mg kg-1), soluble organic P (250-870 mg kg-1), and insoluble organic P (160-2030 mg kg-1). That is, FePO4-solubilizing activity was positive correlated with TP, TCA P fractions in P. vittata, TP in growth media, and root exudates. This study shows that phytate exudation dissolved FePO4coll due to the chelation effect of phytic acid on Fe; however, the wider question of whether phytic acid excretion was prompted by deprivation of P, Fe, or both remains to be answered.

Pteris vittata plantation decrease colloidal phosphorus contents by reducing degree of phosphorus saturation in manure amended soils.

The agricultural use of manure fertilizer increases the phosphorus (P) saturation of soils and the risk of colloidal P (Pcoll) release to aquatic ecosystems. Two experiments were conducted to identify whether Pteris vittata plantation can decrease Pcoll 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 Pcoll 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 Pcoll 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 Pcoll. However, P. vittata plantation decreased the Pcoll release and P loss risk due to the increase of P adsorption and reduced DPS in both soils. The P fractions (NaOH, NH4F, and HCl-P) contributed to increase the P pool in planted soils which enhanced the bioavailability of Pcoll and increased the P. vittata biomass. It suggested that P. vittata plantation was an effective approach to reduce Pcoll release from manure amended soils.

Synthesis of a novel Fe-Mn binary oxide-modified lava adsorbent and its effect on ammonium removal from aqueous solutions.

Ammonium is strongly related to eutrophication and a key control of eutrophication in aquatic systems, especially in agricultural runoff. In this study, a novel Fe-Mn binary oxide-modified lava (FMML) granular adsorbent was synthesized for ammonium removal from aqueous solutions by co-precipitation method. The kinetic data were described by pseudo-second-order kinetic model well and intraparticle diffusion had effects on ammonium adsorption. For pH between 4.0 and 10.0, the adsorption efficiency was >80%, and its optimum was recorded at pH 7.0. FMML exhibited strong ammonium adsorption selectivity under the single presence of cations like Na+ , K+ , Ca2+ , and Mg2+ . The optimum adsorbent dose and particle size were 4 g/L and 3-5 mm, respectively, for an aqueous solution containing 10 mg/L of ammonium under normal conditions (298 K and pH 7.0). Furthermore, the adsorption process was endothermic, following both the Langmuir (R2  > 0.98) and Freundlich (R2  > 0.96) models. Compared with other adsorbents, the FMML can be prepared following a simpler protocol. After 30 times of adsorption-regeneration cycle, the FMML also had a relatively high ammonium adsorption capacity; hence, we see it as a prospective adsorbent for ammonium adsorption from aqueous solutions. PRACTITIONER POINTS: Fe-Mn binary oxide-modified lava with Fe/Mn ratio 3:1 was prepared using co-precipitation method. Adsorption maximum of modified lava was 20.8 mg/g (298 K and pH 7.0). Adsorption was sensitive to changes in adsorbent dose, particle size, and pH. Inorganic cations decreased ammonium adsorption in order of Na+  > K+  > Ca2+  > Mg2+ . Mechanisms for ammonium removal by FMML include diffusion, electrostatic attraction, oxidation, and complexation reaction.

Effect of sheep manure-derived biochar on colloidal phosphorus release in soils from various land uses.

Colloidal phosphorus (CP) as an additional route of P mobilization in soil solution has gained much attention. A batch experiment was conducted to investigate the effect of sheep manure-derived biochar (SMB) on CP release from various land uses (paddy, vegetable, tea, and citrus) at a rate of 0% as a control treatment (CK), 1% as a low (L) level, 2% as a middle (M) level, and 4% as a high (H) level of SMB application. The CP and MRPcoll in the solution increased from 30.58 to 88.97% and from 2.45 to 55.54% of total P (TP), respectively. The SMB enhanced CP release in all the soils and all the treatments (except CK and L levels in tea soil; CK, L, and M levels in vegetable soil; and L and M levels in citrus soil). Multiple linear regression revealed a significant correlation between CP and MRPcoll and between colloidal iron, aluminum, calcium, and total organic carbon (Fecoll, Alcoll, Cacoll, and TOCcoll) and pH, which may play an important role as CP carriers that could depend on the pH. This study suggests that the application of SMB in the soil at an appropriate rate of 1 and 2% for tea and vegetable soils, respectively, could be beneficial to avoid the risk of CP release in water bodies.

Synergistic effects of anionic polyacrylamide and gypsum to control phosphorus losses from biogas slurry applied soils.

Excessive application of phosphorus (P) fertilizer to the agriculture soil can lead to the P loss to the aquatic ecosystem. Three soils from different land use (tea, paddy, and vegetable soils) were treated with biogas slurry (BS) at rate of 79.8 kg ha-1, anionic polyacrylamide (PAM) at rate of 12.5, 25 and 50 kg ha-1, Gypsum (Gy) at rate of 5t ha-1, and the control (Ck) without treatment, to control P losses in a laboratory batch experiment. The soil solution was analyzed for total P (TP), dissolved reactive P (DRP) and total dissolved P (TDP). Particulate P (PP) and dissolved unreactive P (DURP) were calculated by subtracting DRP from TP and TDP, respectively. The DRP was within a range of 68-98% of TP whereas PP varied in a range of 2-32% of TP and DURP was within a range of 0.1-19% of TP, depending on soil types and different treatments. The addition of PAM at a high rate and Gy together on the soil after BS application reduced the release of TP by 54, 46, and 51% and that of DRP by 61, 49, and 53% for tea, paddy and vegetable soils, respectively. However, the application of BS with PAM alone promoted the release of DRP by 77, 86, 70% for tea, paddy, and vegetable soils, respectively. This study suggests that the synergic application of PAM and Gy on soils after BS addition can be a good strategy to reduce P losses.