Effect of various phosphorus levels on the extraction of Cd, the transformation of P, and phosphorus-related gene during the phytoremediation of Cd contaminated soil

Phytoremediation has emerged as a common technique for remediating Cd pollution in farmland soil. Moreover, phosphorus, an essential element for plants, can alter the pectin content of plant cell walls and facilitate the accumulation of Cd in plant tissues, thereby enhancing phytoremediation efficiency. Therefore, pot experiments were conducted in order to investigate the effect of phosphorus levels on Cd extraction, phosphorus transformation and phosphorus-related genes during phytoremediation. The results revealed that an optimal application of suitable phosphate fertilizers elevated the soil's pH and electrical conductivity (EC), facilitated the conversion of soil from insoluble phosphorus into available forms, augmented the release of pertinent enzyme activity, and induced the expression of phosphorus cycling-related genes. These enhancements in soil conditions significantly promoted the growth of ryegrass. When applying phosphorus at a rate of 600 mg/kg, ryegrass exhibited plant height, dry weight, and chlorophyll relative content that were 1.27, 1.26, and 1.18 times higher than those in the control group (P0), while the Cd content was 1.12 times greater than that of P0. The potentially toxic elements decline ratio and bioconcentration factor were 42.86% and 1.17 times higher than those of P0, respectively. Consequently, ryegrass demonstrated the highest Cd removal efficiency under these conditions. Results from redundancy analysis (RDA) revealed a significant correlation among pH, total phosphorus, heavy metal content, phosphorus forms, soil enzyme activity, and phosphorus-related genes. In conclusion, this study suggests applying an optimal amount of suitable phosphate fertilizers can enhance restoration efficiency, leading to a reduction in soil Cd content and ultimately improving the safety of crop production in farmlands.

Parameter evaluation for developing phosphate-solubilizing Bacillus inoculants

Bacterial inoculants have been used in agriculture to improve plant performance. However, laboratory and field requirements must be completed before a candidate can be employed as an inoculant. Therefore, this study aimed to evaluate the parameters for inoculant formulation and the potential of Bacillus subtilis (B70) and B. pumilus (B32) to improve phosphorus availability in maize (Zea mays L.) crops. In vitro experiments assessed the bacterial ability to solubilize and mineralize phosphate, their adherence to roots, and shelf life in cassava starch (CS), carboxymethyl cellulose (CMC), peat, and activated charcoal (AC) stored at 4 °C and room temperature for 6 months. A field experiment evaluated the effectiveness of strains to increase the P availability to plants growing with rock phosphate (RP) and a mixture of RP and triple superphosphate (TS) and their contribution to improving maize yield and P accumulation in grains. The B70 was outstanding in solubilizing RP and phytate mineralization and more stable in carriers and storage conditions than B32. However, root adherence was more noticeable in B32. Among carriers, AC was the most effective for preserving viable cell counts, closely similar to those of the initial inoculum of both strains. Maize productivity using the mixture RPTS was similar for B70 and B32. The best combination was B70 with RP, which improved the maize yield (6532 kg ha-1) and P accumulation in grains (15.95 kg ha-1). Our results indicated that the inoculant formulation with AC carrier and B70 is a feasible strategy for improving phosphorus mobilization in the soil and maize productivity.

Evidence for the accumulation of toxic metal(loid)s in agricultural soils impacted from long-term application of phosphate fertilizer

Phosphate fertilizers may contain elevated concentrations of toxic metals and metalloids and therefore, their excessive application can result in the accumulation of both phosphorus (P) and metal(loid)s in agricultural soils. This study aims to investigate the occurrence, distribution, and potential plant-availability of metal(loid)s originating from phosphate fertilizer in a long-term experimental field at the Tidewater Research Station in North Carolina, where topsoil (10-20 cm deep) and subsoil (up to 150 cm deep) samples were collected from five plots with consistent and individually different application rates of P-fertilizer since 1966. We conducted systematic analyses of P and metal(loid)s in bulk soils, in the plant available fraction, and in four sequentially extracted soil fractions (exchangeable, reducible, oxidizable, and residual). The results show that P content in topsoils were directly associated with the rate of P-fertilizer application (ρ = 1, p < 0.05). Furthermore, P concentrations were highly correlated with concentrations of Cd, U, Cr, V, and As in the bulk topsoil (ρ > 0.58, p < 0.05), as well as the potential plant-available fraction (ρ > 0.67, p < 0.01), indicating the accumulation of the fertilizer-derived toxic metal(loid)s in the topsoil. Significant correlations (p < 0.001) of metal(loid)s concentrations between the bulk soil and the potential plant-available fraction raises the possibility that P-fertilizer application could increase the accumulation of toxic metal(loid)s in plants, which could increase human exposure. Results from sequential leaching experiments revealed that large portions of the trace elements, in particular Cd, occur in the soluble (exchangeable and reducing) fractions of topsoil with higher P-fertilizer input, whereas the levels of redox-sensitive elements (As, V, U, Cr) were higher in the reducible and oxidizable fractions of the soils. Overall, the data presented in this study demonstrate the effect of long-term P-fertilizer application on the occurrence and accumulation of a wide range of toxic metal(loid)s in agricultural topsoil.

Influence of monoammonium phosphate on glyphosate adsorption-desorption in tropical soils: Effect of the order of sorbate additions

Glyphosate and phosphate compete for the same adsorption sites in the soil because their adsorption mechanisms are similar as the herbicide contains a phosphate group. However, how this competition occurs in relation to the order of addition of the sorbate and the composition of the soils remains unclear. The effect of the soil clay composition and the order of glyphosate and monoammonium phosphate (MAP) additions on glyphosate sorption-desorption was investigated using three inceptisols collected from Colombian rice fields. Glyphosate adsorption isotherms were evaluated using the batch equilibrium method and were modeled applying the Freundlich equation. The values for glyphosate Kfa, when evaluated alone, ranged from 14.39 to 639.86 mg1-na Lna kg-1. An agreement was found between adsorbed glyphosate, chlorites, and low initial phosphorous soil content. Preadsorbed MAP or simultaneous MAP-glyphosate additions to the soil revealed a drastic reduction in glyphosate Kfa values in soil containing the highest amount of 2 × 1 clays, but kaolinitic soils remained practically unaffected. Low desorption values could be associated with soils with the highest kaolinite content. Glyphosate remobilization was favored when the desorbing MAP solution was used in soils containing preadsorbed glyphosate. This study provides new knowledge on the effect of phosphorus fertilizers on glyphosate bioavailability in soils with different mineral compositions.

Phosphate fertilizers facilitated the Cd contaminated soil remediation by sepiolite: Cd mobilization, plant toxicity, and soil microbial community

In-situ immobilization does not remove Cd from the contaminated soil. It is vital to investigate the effects of fertilizers on soil Cd mobility during remediation with amendments. In the current study, a pot experiment was conducted to investigate the effects of calcium magnesium phosphate (CMP) and calcium superphosphate (SSP) on the remediation of Cd-contaminated soil by sepiolite. We mainly focused on changes in soil Cd immobilization, plant toxicity, and soil microbial communities after applying two phosphates during Cd-contaminated soil remediation by sepiolite. The results demonstrated that sepiolite decreased Cd concentration in brown rice, straw, and roots by 32.66%, 38.89%, and 30.94%, respectively. During soil remediation by sepiolite, the Cd concentrations of brown rice and straw were not affected by CMP or SSP, except for the treatment with sepiolite plus high-dose CMP. Sepiolite significantly decreased HCl-extractable Cd and DTPA-extractable Cd by 32.21% and 10.50%, respectively. During soil remediation by sepiolite, the HCl-extractable and DTPA-extractable Cd further decreased with CMP or SSP. The decreasing amplitude with CMP was 40.57-72.60% and 7.05-14.53%, and that of SSP was 37.68-59.66% and 20.71-25.07%, respectively. The superoxide dismutase, peroxidase, catalase activities, and malondialdehyde concentration in rice roots decreased inordinately with the addition of sepiolite, CMP, and SSP, indicating that the application of sepiolite, CMP, or SSP alleviated Cd-induced rice root stress and protected rice roots from Cd toxicity. Alpha diversity estimators (including the Chao, ACE, and Shannon indices) indicated that sepiolite, CMP, or SSP applications had no adverse effects on soil bacterial richness and diversity. Hierarchical clustering analysis revealed that the two phosphate fertilizers and sepiolite were the main factors affecting changes in the bacterial communities structure. Redundancy analysis revealed that soil pH, Eh, and soil-extractable Cd were critical factors affecting the structure of the bacterial communities.

Interfaces between biodegradable organic matrices coating and MAP fertilizer for improve use efficiency

Improving phosphorus (P) use efficiency is a challenge to promote a circular economy and greening the phosphorus cycle towards planetary sustainability. The disruptive innovation for phosphate fertilizers may help to reduce some unwelcome reactions that occur to P in soils. Monoammonium phosphate (MAP) coating with biodegradable organic polymers and the addition of magnesium (Mg) - a nutrient with a synergistic effect on the uptake of P, zinc (Zn), and boron (B) - emerge as a smart strategy to applying these micronutrients uniformly in soils. The objectives of this study were: to characterize the coated-MAP with biodegradable organic polymers, quantify the diffusion and availability of P in the soil, and evaluate the corn crop nutrition and yield during two crop seasons. The treatments were: MAP, MAP coated with biodegradable organic polymer (BOP), MAP + BOP + 1.3% of Zn + 0.33% of B, and MAP + BOP + 1.76% of Mg. The laboratory tests showed that the diffusion of MAP-based fertilizers was: MOMg (7.86 mm) = MO (8.82 mm) = MAP (8.84 mm) = MOM (8.51 mm) after 432 h. Coatings did not cause delays in the P-release in water at 25 °C since more than 95% of P was released within 24 h. In the field trials, the application of Mg, Zn, and B in the MAP coating did not increase nutrient leaf concentration. In the summer crop season, grain yield increased up to the P-rates of 85 kg of P₂O₅ ha^-1, reaching the value of 6731 kg ha^-1. Physical and chemical characteristics of MAP-fertilizers tend to improve with the coatings. The addition of biodegradable organic polymers, Mg, B, and Zn, as MAP-coatings did not enhance P diffusion, release, and availability in the soil and the crop nutrition. Coated-MAP improved corn yield only in the 2^nd crop season.

Distribution, behavior, and erosion of uranium in vineyard soils

Phosphate fertilization contributes to an input of uranium (U) in agricultural soils. Although its accumulation and fate in agricultural soils have been previously studied, its colloidal transport and accumulation along slopes through erosion have been studied to a lesser extent in viticulture soils. To bridge this gap, the contents and potential mobility of U were investigated in vineyard model soils in the Rhineland-Palatinate region, Germany. In addition to elevated U contents, U was expected to associate with colloids and subject to erosion, thus accumulating on slope foots and in soils with fine structure, and reflecting a greater variability. Moreover, another expectation was the favorable erosion/mobility of U in areas with greater carbonate content. This was tested in three regional locations, at different slope positions and through soil horizon depths, with a total of 57 soil samples. The results show that U concentrations (0.48-1.26 ppm) were slightly higher than proximal non-agricultural soils (0.50 ppm), quite homogenous along slope positions, and slightly higher in topsoils. Assuming a homogeneous fertilization, the vertical translocation of U in soil was most probably higher than along the slope by erosion. In addition, carbonate content and soil texture correlated with U concentrations, whereas other parameters such as organic carbon and iron contents did not. The central role of carbonate and soil texture for the prediction of U content was confirmed using decision trees and elastic net, although their limited prediction power suggests that a larger sample size with a larger range of U content is required to improve the accuracy. Overall, we did not observe neither U nor colloids accumulating on slope foots, thus suggesting that soils are aggregate-stable. Lastly, we suggested considering further soil parameters (e.g., Ca²⁺, phosphorus, alkali metals) in future works to improve our modelling approach. Overall, our results suggest U is fortunately immobile in the studied locations.

Assessment of cadmium and lead contamination in rice farming soils and rice (Oryza sativa L.) from Guayas province in Ecuador

Rice is the world's most consumed and in-demand grain. Ecuador is one of the main rice-consuming countries in Latin America, with an average per capita consumption of 53.2 kg per year. Rice cultivation takes place under flooding conditions, which favors the mobilization and subsequent accumulation of heavy metals in the plant. This study's principal objective was to evaluate the contamination of cadmium (Cd) and lead (Pb) in the rice cultivation system in the province of Guayas. To this end, extensive sampling of water, soil and rice grains was carried. Water samples were analyzed to determine physicochemical properties and concentrations of dissolved Cd and Pb. Physicochemical properties, total organic carbon (TOC), total content of nitrogen (N), iron (Fe), manganese (Mn), phosphorus (P), bioavailable phosphorus (P mehlich), Cd and Pb were determined in soil samples. In addition, to understand the dynamics of Cd and Pb mobility and bioavailability, an extraction of six randomly selected soil samples was carried out. The concentration values of the total Cd and Pb content in the rice cultivation system did not exceed the maximum recommended limit for soil, water and rice grains. However, 85% of the total Cd was in the soluble or exchangeable fraction of the soil, while the Pb was strongly bound to crystalline iron oxyhydroxides. It was established that the TOC, N, Fe, and P mehlich have a significant correlation (p < 0.05) with the overall concentration of Cd and Pb in the rice farming soil. The Cd and Pb present in rice do not represent a dietary health risk to the population of Ecuador.

Screening bacterial phosphate solubilization with bulk-tricalcium phosphate and hydroxyapatite nanoparticles

Phosphate-solubilizing bacteria can release phosphorus (P) from insoluble minerals and benefit either soil fitness or plant growth. Bulk sized P compounds have been suggested but little is known about solubilization of nanosized materials such as hydroxyapatite nanoparticles (HANP). A screening of the initial 43 strains from vanilla rhizospheres for phosphate solubilization with bulk Ca₃(PO₄)₂ was carried out. Subsequently, 6 strains were selected on bulk rock phosphate (RP) and HANP. Two kinetics experiments were run out regarding evaluation at 5, 10 and 20 days after inoculation (dai). Bacterial biomass production was similar in both experiments; the lowest biomass was found at 20 dai. In all cases, bacteria reduced the original culture medium pH; which was related with phosphate solubilization from the production of organic acids. Citric acid was produced by all strains. Enterobacter cloacae CP 31 was the most interesting bacterium: produced the lowest culture pH at 20 dai (4) with both Ca₃(PO₄)₂ and RP, and 3.7 at 10 dai with HANP correlating with high soluble P concentration (536, 64 and 13 mg L^-1 with these P sources, respectively). This bacterium should be tested as an inoculant in plants to reveal its potential as plant promoter growth and HANP to suggest its role in the potential use of nano-P fertilizers.

Inputs of rare earth elements in Brazilian agricultural soils via P-containing fertilizers and soil correctives

The mineral exploration of rare earth elements (REEs) and their entry into the soil via fertilizers has generated concern about environmental impacts and human health risks. We evaluated 60 samples of limestone, gypsum and phosphate fertilizers marketed in Brazil in order to characterize their contents, signature and solubility of REEs. The fertilizers from igneous origin presented the largest accumulation of REEs. Accumulation of the light REEs Ce, La, Nd, Pr, Sm and Eu were larger than the heavy REEs (Y, Dy, Gd, Er, Yb, Ho, Tb and Lu). The solubility of fertilizers produced from sedimentary sources was greater than that of igneous sources. The mean annual REEs contribution of SSP and organo-mineral + phosphate rock (both of igneous origin) to soils was > 4000 t year^-1, with highest additions for Ce, La, Nd and Y. Thus, phosphate fertilization and liming were considered to be significant sources of REEs and soils receiving continuously high doses of these inputs are likely to be enriched in REEs. Risk assessment studies are necessary to evaluate the impact of these REEs additions to soils on human health.

Soil to plant transfer of alpha activity in potato plants: impact of phosphate fertilizers

BACKGROUND

Radionuclides in the phosphate fertilizers belonging to (232)Th and (238)U and (40) K are the major contributors to the outdoor terrestrial natural radiation. These radionuclides are transferred from fertilizer to food through soil.

MATERIALS AND METHODS

Present work deals with the alpha activity in the different parts of the potato (Solanum Tuberosum) plants grown under controlled pots experiment using different amounts of phosphate fertilizers and urea. Alpha activities have been measured by track etch technique using the solid-state nuclear track detectors (LR-115).

RESULTS

Translocation factor for the fruit (edible Part) varied from 0.13 (for DAP) to 0.73 (for PF) with an average of 0.40 ± 0.26 for the plant grown with 20 g of fertilizers. Translocation factors increased with the increase in amount of fertilizers having value 0.51 ± 0.31 for the plant grown with 50 g of fertilizers. The translocation factor for the lower and the upper part of leaves varied from 0.44 to 0.67 and 0.22 to 0.83 with an average value 0.55 ± 0.15 and 0.45 ± 0.23 respectively. The transfer factor (TF's) for the potato plants varied from 1.5 × 10(-2) to 1.03 × 10(-1) for root, from 1.3 × 10(-2) to 1.23 × 10(-1) for stem, from 2.1 × 10(-3) to 4.5 × 10(-2) for fruit and from 5.4 × 10(-3) to 5.8 × 10(-3) for lower part of the leaves after 105 days of the plantation.

CONCLUSIONS

The results revealed that the alpha activity in the potato plants was higher in case of the plants grown with the use of phosphate fertilizers than with other fertilizers.