Soil application potential of post-sorbents produced by co-sorption of humic substances and nutrients from sludge anaerobic digestion reject water.

This study introduces a novel soil conditioning approach using humic substances (HSs) and nutrients co-recovered from reject water from sewage sludge anaerobic digestion. For the first time, HSs and nutrients were simultaneously recovered through sorption on low-cost, environmentally inert materials: natural rock opoka (OP) and waste autoclaved aerated concrete (WAAC). This innovative application of OP and WAAC as carriers and delivery agents for soil-relevant substances offers potential for resource recovery and soil conditioning. Results indicate that the post-sorption opoka (PS-OP) and post-sorption waste autoclaved aerated concrete (PS-WAAC) effectively release retained HSs at 350-480 µg g⁻1 d⁻1, respectively. These materials also show potential as NPK fertilizers, releasing 280-430 µg g⁻1 d⁻1 N-NH4⁺, 80-150 µg g⁻1 d⁻1 P-PO4³â», and 270-350 µg g⁻1 d⁻1 K⁺. Additionally, PS-OP demonstrated promising fungicide properties, reducing P. diachenii growth by 31% at a concentration of 1 g L⁻1. A two-way ANOVA indicated that the effects of PS-OP and PS-WAAC on soil physicochemical and biological parameters varied with plant species. Both post-sorbents improved the quality of soil collected from sand mining area, increasing cation exchange capacity by 7%-85% and organic matter content by 10%-58%. They also enhanced the functional potential of soil microbial communities, increasing their metabolic activities by 23%-36% in soils sown with clover and by 33%-39% in soils sown with rapeseed. An opposite effect was observed in soils sown with sorghum, suggesting these amendments may not universally act as plant biostimulants. The effectiveness of these post-sorbents in enhancing plant growth varied depending on plant species and the mineral base of the post-sorbent. PS-OP increased the total length of clover and sorghum by 41% and 36%, and their fresh biomass by 82% and 80%, respectively. In turn, PS-WAAC increased the total length of clover and sorghum by 76% and 17%, and their fresh biomass by 29% and 15%, respectively. It was notably more effective than PS-OP for rapeseed. This study proposes a strategy to decrease reliance on non-renewable resources and costly sorbents while minimizing environmental impact. It shows that PS-OP and PS-WAAC can enhance soil quality, microbial activity, and plant growth. Given their origins, these amendments are recommended for soil remediation, particularly in degraded areas. Future research should focus on optimizing their application across various plant species to maximize effectiveness.

Microbial- and seaweed-based biopolymers: Sources, extractions and implications for soil quality improvement and environmental sustainability - A review.

Improving soil quality without creating any environmental problems is an unescapable goal of sustainable agroecosystem management, according to the United Nations 2030 Agenda for Sustainable Development. Therefore, sustainable solutions are in high demand. One of these is the use of biopolymers derived from microbes and seaweed. This paper aims to provide an overview of the sources of extraction and use of microbial (bacteria and cyanobacteria) and seaweed-based biopolymers as soil conditioners, the characteristics of biopolymer-treated soils, and their environmental concerns. A preliminary search was also carried out on the entire Scopus database on biopolymers to find out how much attention has been paid to biopolymers as biofertilizers compared to other applications of these molecules until now. Several soil quality indicators were evaluated, including soil moisture, color, structure, porosity, bulk density, temperature, aggregate stability, nutrient availability, organic matter, and microbial activity. The mechanisms involved in improving soil quality were also discussed.

Comparative efficacy of Parthenium hysterophorus (L.) derived biochar and iron doped zinc oxide nanoparticle on heavy metals (HMs) mobility and its uptake by Triticum aestivum (L.) in chromite mining contaminated soils.

In this study we investigated the efficacy of a novel material parthenium weed (Parthenium hysterophorus L.) biochar (PBC), iron doped zinc oxide nanoparticles (nFe-ZnO), and biochar modified with nFe-ZnO (Fe-ZnO@BC) to adsorb heavy metals (HMs) and reduce their uptake by wheat (Triticum aestivum L.) in a highly chromite mining contaminated soil. The co-application of the applied soil conditioners exhibited a positive effect on the immobilization and restricted the HMs uptake below their threshold levels in shoot content of wheat. The maximum adsorption capacity was because of large surface area, cation exchange capacity, surface precipitation, and complexation of the soil conditioners. The scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) showed porous smooth structure of parthenium weed derived biochar that helped in HMs adsorption, increase the efficiency of soil fertilizers and nutrients retention which help in the enhancement soil condition. Under different application rates the highest translocation factor (TFHMs) was obtained at 2 g nFe-ZnO rate followed the descending order: Mn > Cr > Cu > Ni > Pb. The overall TFHMs was found <1.0 indicating that low content of HMs accumulation in roots from soil slight transferred to shoot, thus satisfying the remediation requirements.

Wheat is considered as an important staple food which is grown in a chromite mining contaminated soil containing toxic HMs releasing from weathering of mafic and ultramafic rocks in the study area. The present research work is significantly beneficial in identifying the efficiency of treatment technologies to immobilize toxic HMs in soil. Parthenium weed derived biochar and biochar modified with nFe-ZnO (Fe-ZnO@BC) reduce the HMs uptake by wheat plant.

Influence of the production environment on the cultivation of lettuce and arugula with spent mushroom substrate.

After mushroom production, the substrate plus the cultivated mycelium represents a byproduct, the so-called "spent mushroom substrate" (SMS). We evaluated different SMS types in fresh form, recently taken from the cultivation rooms, for the production of lettuce and arugula in the open field, greenhouse and greenhouse in pot. Three kinds of SMS were used (i - SMS of ABL (Agaricus subrufescens), ii - SMS of POS (Pleurotus ostreatus) and iii - 50% SMS of ABL + 50% SMS of POS) at three doses (1, 2 and 4 kg m-2). For comparison purposes, two commercial soil conditioners, Forth Condicionador® and Visa Fértil Orgânico®, were used. Finally, chicken manure with reference as international organic material was used. A control treatment consisted of a soil plot without any organic material. The application of fresh SMS in the production of LE (lettuce) and AR (arugula) is feasible considering several agronomic parameters evaluated, therefore that in F (field) the superior results were obtained by the ABL dose of 4 kg m-2, in the GR (green house) at a lower dose ABL with 1 kg m-2, POS with 2 kg m-2 and mix with ABL + POS at doses of 2-4 kg m-2, and finally in GR/P (greenhouse pot) it was proved that in a protected environment by rain the combination ABL + POS at dose of 4 kg m-2 is recommended.

Amendment of vanadium-contaminated soil with soil conditioners: A study based on pot experiments with canola plants (Brassica campestris L.).

We performed pot experiments with canola plants (Brassica campestris L.) to evaluate the effect of eight soil conditioners on the amendment of vanadium (V)-contaminated soil based on analysis of the growth of canola plants and the uptake, bioaccumulation, and translocation of heavy metals. Tested soil conditioners included polyacrylamide (PAM), sepiolite, humic acid (HAC), peat, sludge compost (SC), bentonite, lime, and fly ash. Results from the analysis of the growth of canola plants and the analysis of variance showed that the best soil conditioners for V-contaminated soil were 0.05-0.1 wt% PAM, 1 wt% peat, 1 wt% HAC, and 1 wt% SC; moderately effective soil conditioners included sepiolite and lime. The best combination of soil conditioners was 0.1 wt% PAM, 1 wt% HAC, and 0.15 wt% lime, in addition of 1% ZVI, which increased the biomass and height of canola plants by 1.18-fold and 59.49%, respectively. We conclude that the best combination of soil conditioners determined from this study is promising for mitigating V contamination in soil.

Geochemical fractions and phytoavailability of Zinc in a contaminated calcareous soil affected by biotic and abiotic amendments.

Many studies have conducted to determine the best management practice to reduce the mobility and phytoavailability of the trace metals in contaminated soils. In this study, geochemical speciation and phytoavailability of Zn for sunflower were studied after application of nanoparticles (SiO2 and zeolite, with an application rate of 200 mg kg-1) and bacteria [Bacillus safensis FO-036b(T) and Pseudomonas fluorescens p.f.169] to a calcareous heavily contaminated soil. Results showed that the biotic and abiotic treatments significantly reduced the Zn concentration in the aboveground to non-toxicity levels compared to the control treatment, and the nanoparticle treatments were more effective than the bacteria and control treatments. The concentration of CaCl2-extractable Zn in the treated soils was significantly lower than those of the control treatment. The results of sequential extraction showed that the maximum portion of total Zn belonged to the fraction associated with iron and manganese oxides. On the contrary, the minimum percent belonged to the exchangeable and water-soluble Zn (F1). From the environmental point of view, the fraction associated with iron and manganese oxides is less bioavailable than the F1 and carbonated fractions. On the basis of plant growth promotion, simultaneous application of the biotic and abiotic treatments significantly increased the aboveground dry biomass yield and also significantly reduced the CaCl2-extractable form, uptake by aboveground and translocation factor of Zn compared to the control treatment. Therefore, it might be suggested as an efficient strategy to promote the plant growth and reduce the mobile and available forms of toxic metals in calcareous heavily contaminated soils.

Distribution of seven heavy metals among hot pepper plant parts.

The main objective of this investigation was to monitor concentrations of seven metals (Cd, Pb, Ni, Mo, Cu, Zn, and Cr) in the fruits, leaves, stem, and roots of Capsicum annuum L. (cv. Xcatic) plants grown under four soil management practices: yard waste (YW), sewage sludge (SS), chicken manure (CM), and no-much (NM) bare soil. Elemental analyses were conducted using inductively coupled plasma mass spectrometer. Pb and Cd concentrations in soil amended with YW, SS, and CM were not significantly different (P < 0.05) compared to NM soil, whereas Mo and Cu concentrations were significantly greater in YW compared to SS, CM, and NM treatments. Concentrations of Cd in the fruits of plants grown in NM soil were greater compared to the fruits of plants grown in other treatments. Total Ni concentration (sum of Ni in all plant parts) in plants grown in NM bare soil was greater than in plants grown in SS-, YW-, and CM-amended soils. Values of the bioaccumulation factor indicated that pepper fruits of plants grown in YW, SS, and CM did not show any tendency to accumulate Pb, Cr, and Ni in their edible fruits.

Soil conditioner improves soil properties, regulates microbial communities, and increases yield and quality of Uncaria rhynchophylla.

Uncaria rhynchophylla is an important traditional herbal medicine in China, and the yield and quality of Uncaria rhynchophylla can be improved by suitable soil conditioners because of changing the soil properties. In this paper, Uncaria rhynchophylla associated alkaloids and soil microbial  communities were investigated. The field experiment was set up with the following control group: (M1, no soil conditioner) and different soil conditioner treatment groups (M2, biomass ash; M3, water retention agent; M4, biochar; M5, lime powder and M6, malic acid). The results showed that M2 significantly increased the fresh and dry weight and the contents of isorhynchophylline, corynoxeine, isocorynoxeine, and total alkaloids. Acidobacteria, Proteobacteria, Actinobacteria, and Chloroflexi were major bacterial phyla. Correlation analysis showed that fresh and dry weight was significantly positively correlated with Acidobacteria, while alkali-hydrolyzable nitrogen, phosphatase activity, fresh and dry weight, corynoxeine, and isocorynoxeine were significantly negatively correlated with Chloroflexi. The application of soil conditioner M2 increased the abundance of Acidobacteria and decreased the abundance of Chloroflexi, which contributed to improving the soil nutrient content, yield, and quality of Uncaria rhynchophylla. In summary, biomass ash may be a better choice of soil conditioner in Uncaria rhynchophylla growing areas.

Improved microbial-plant soil bioremediation of PAHs and heavy metal through in silico methods.

The combined pollution of polycyclic aromatic hydrocarbons (PAHs) and organic cadmium (Cd) in farmland soils, and the field controlling strategy need to be studied urgently. In this study, 5 PAHs, 5 Cd and 11 soil conditioners were selected to explore the co-exposure risk and remediation efficiency. Firstly, a significant combination Fl-alkylalkoxy cadmium was obtained using forward and reverse methods coupling variation coefficient methods (the combined pollution value was 0.173). Secondly, the interaction energy of microbial degradation / plant absorption of Fl under Cd stress, and microbial mineralization / plant absorption of alkylalkoxy cadmium under PAHs stress were characterized using factorial experimental design, molecular docking and molecular dynamics simulation. The combined pollution of alkylalkoxy cadmium and dialkyl cadmium, phenanthrene and Benzo [a] pyrene was significant (synergistic contribution rates were 17.58 % and 19.22 %, respectively). In addition, 6 soil conditioners with significant efficiency were selected to design Taguchi orthogonal experimental schemes, indicating the microbial degradation / mineralization and plant absorption were significantly effective (the maximum increase of remediation efficiency was 93.81 %) under the combinations (i.e., trratone, coumarol, fulvamic acid, potassium fertilizer and others, etc.). Finally, it was found that the soil conditioners affected the hydrophobic groups and forces, and the efficiency was proportional to the highest peak value and minimum distance in the RDF curve. This study identifies the risk characteristics of co-exposure of PAHs and Cd and screens effective soil conditioners, providing theoretical guidance for risk controlling.

Lemongrass (Cymbopogon flexuosus) growth rate, essential oil yield and composition as influenced by different soil conditioners under two watering regimes.

The vast cultivation of lemongrass (Cymbopogon flexuosus) as an essential oil-bearing plant worldwide relies heavily on its compound citral that holds immense industrial potential. Soil fertility practices greatly affect the growth and quality of these plants, with a majority of the agricultural land globally grappling with water scarcity. In this respect, field experiments were conducted at the University of Embu research farm during the November 2021-September 2022 growing period and aimed to investigate the influence of two different factors, namely; (i) two watering regimes (rainfed and irrigated) and (ii) four soil conditioner levels (control (T1), cow manure (T2), cow manure plus NPK fertilizer (T3), and NPK fertilizer alone (T4)) on the growth and essential oil parameters of C. flexuosus. The field trials were arranged in a split-plot design with three replicates for each treatment. The essential oil from C. flexuosus was obtained using steam distillation method and analyzed for quality using gas chromatography with mass spectrometry (GC-MS) technique. Results revealed that treatments T4 and T3 improved the growth of C. flexuosus under rain-fed conditions, implying the plant's sensitivity to soil fertility practices and watering regimes. Herbage from rain-fed plants harvested after 120 days had high oil content, ranging from 0.17 to 0.23 %, while herbage from irrigated plants harvested after 180 days had the lowest oil content, ranging from 0.11 to 0.17 %. Using GC-MS, the main components of C. flexuosus oil were citral (75.97-87.70 %), geranyl acetate (0.80-4.91 %), geraniol (0.80-4.26 %), isogeranial (1.83-3.45 %), and isoneral (1.29-2.78 %). Notably, citral, a racemic mixture of geranial and neral, was found in a high concentration (87.70 %), meeting the acceptable international market standards for its use. Altogether, the major oil compounds, oil yield and growth properties of C. flexuosus in this experiment differed as a function of different soil conditioners under the two watering regimes, and so with the time scale. The outcomes of this research highlight implications for enhancing and bolstering the production of high-value lemongrass oil in Kenya, where it holds potential significance as a vital economic and export-oriented crop.

Bauxite residue valorization - Soil conditioners production through composting with palm oil mill residual biomass.

Bauxite residue (BR) is a by-product of Bayer process, which is applied for alumina production. Due to its inherent alkalinity and sodicity, the use of BR is globally limited to 23% of the 150 million tons (Mt) produced annually. Maximizing alternative and large-scale uses of BR is a game changer to promote the sustainability of the aluminum production chain. As a strategy for BR valorization, a soil conditioner composed of BR and palm oil residual biomass was proposed. Here we evaluate the BR (25%, 50% and 75%) batch composting with raw palm oil mill waste (POMW) and palm oil compost (POC). The pH, EC, total N and organic carbon, C:N ratio, water holding capacity (WHC), cation exchange capacity (CEC), granulometry and elemental composition were determined after 90 days of composting. Changes in temperature, pH and EC curves were observed during composting of soil conditioners for 90 days. Composting reduced the alkalinity and sodicity of BR, increasing CEC, moisture, organic carbon and total nitrogen. The formulation containing 25% of BR and 75% of POC showed WHC ≥ 60% and CEC ≥ 200 mmolc·kg-1, meeting the Brazilian legislation for production and commercialization of soil conditioners. This strategy could potentially consume 7.6% of all BR produced annually in the largest Brazilian alumina refinery. Concentrations of potentially toxic elements were far below the allowable levels in all formulations. Major and minor plant nutrients were present and the composting aggregated small particles in BR. Composting of BR is a new alternative for the valorization of mining tailings, allowing the development of an environmentally friendly and zero-waste product, which can be applied on a large scale in agriculture to improve soil fertility.

Postharvest quality of yellow passion fruit produced in soil with bovine biofertilizer and nitrogen.

The use of soil conditioners as bovine biofertilizer associated with mineral fertilization affect the physical and physicochemical quality of passion fruit. For fruit growth, post-harvest quality is crucial for production chain development, as it is the characteristic most used by the fresh consumption market for this fruit. In this sense, an experiment was carried out to investigate the effects of doses of bovine biofertilizer in the soil with and without nitrogen fertilization in the cultivation of yellow passion fruit. A randomized block design was adopted, with three replications in a 5×2 factorial scheme, referring to five doses of liquid bovine biofertilizer (B) diluted in water (A): 0% - control (0B + 4A); 25% (1B + 3A); 50% (2B + 2A); 75% (3B + 1A); and 100% (4B + 0A) with and without nitrogen fertilization applied to the soil. Urea was the nitrogen source used in this study. A total of 10 g plant-1 of N was applied monthly at 30 and 60 days after transplanting, and after that age, 20 g plant-1 was applied until the end of harvest. During the final phase of production and ripening, twelve fruits were harvested from each treatment in physiological maturation for physical and physicochemical characterization. The following analyses were performed: longitudinal diameter, transversal diameter, number of seeds per fruit, peel firmness, pulp yield, fruit peel percentage, pulp pH, soluble solids content; titratable acidity and soluble solids content/titratable acidity ratio. Data underwent analysis of variance by the F test means for nitrogen were compared by Tukey's test and means for bovine biofertilizer, by regression. Nitrogen enhances the positive effect of bovine biofertilizer on the postharvest quality of yellow passion fruit. The association of biofertilizer and nitrogen improves fruit quality in comparison to plants without these inputs, except for pulp yield and fruit peel percentage, which suffered isolated effects from the factors. High doses of biofertilizer, above 75 and 100%, reduce soluble solids content and increase titratable acidity. The bovine biofertilizer has promising effects, but it does not replace nitrogen fertilization on the postharvest quality of yellow passion fruit.

Bio-oil and char obtained from cassava rhizomes with soil conditioners by fast pyrolysis.

We studied the properties of the bio-oil and char from fast pyrolysis of cassava rhizomes in a free-fall reactor, catalyzed by adding various soil conditioners (or improvers) as catalysts to the reactor at 500 °C and 200 g/h feed rate. Four conditioners were evaluated - granular TPI pH11 soil conditioner, volcanic rock, TPI pelletized organic fertilizer and super dolomite - and added at 50% (w/w) of the rhizomes. Bio-oil and gas yields decreased, whereas char yields increased, yielding bio-oil 57-59%, gas 14-20% and char 23-28%. With the catalysts, the bio-oil higher heating value increased, while that of char decreased: for cassava rhizomes with volcanic rock the bio-oil high heating value increased from 19.4 to 23.6 MJ/kg, whereas rhizomes with dolomite led to an increased viscosity from 27 to 34 × 10-3 mm2/s.

Design and development of guar gum based novel, superabsorbent and moisture retaining hydrogels for agricultural applications.

The novel hydrogels were synthesized by grafting guar gum with acrylic acid and cross-linking with ethylene glycol di methacrylic acid (EGDMA). The synthesis of hydrogel was confirmed by characterization through 13C NMR, FTIR spectroscopy, SEM micrography, thermo-gravimetric analysis and water absorption studies under different solutions. Synthesized hydrogel (GG-AA-EGDMA) was confirmed to be biodegradable with half-life period of 77 days through soil burial biodegradation studies. The effects of hydrogel treatment on soil were evaluated by studying various physico-chemical properties of soil like bulk density, porosity, water absorption and retention capacity etc. The hydrogel which could absorb up to 800 ml water per gram, after addition to soil, improved its porosity, moisture absorption and retention capacity significantly. Water holding capacity of water increased up to 54% of its original and porosity also increased up to 9% of its original. The synthesized hydrogel revealed tremendous potential as soil conditioning material for agricultural applications.

The effect of Hydropolymers on soil microbial activities in Mediterranean areas / El efecto de los polímeros absorbentes en la actividad microbiológica del suelo bajo condiciones mediterráneas

ABSTRACT Objectives. The aim of this study was to evaluate the effect of the hydropolymer TerraCottem on soil microbial activity by measuring soil respiration and leaching of mineral nitrogen. Materials and methods. The incubation experiment contained control variants with natural soil of Nerja area (South Spain, inside the Sierra Tejeda, Almijara and Alhama Natural Park, 36.7985173° N 3.8511693° W; WCGS84), variants with the addition of easy available nitrogen compounds (kg N ha-1), easy accessible carbon compounds (1% glucose solution) and a combinations of both. Within each variant, the recommended amount of control hydropolymers (1.5 kg/m3) and a double dose of 3.0 kg/m3 were compared. Results. Showed that respiration activity of the soil in this Mediterranean area was not eliminated by the lack of ready available nitrogen or carbon substrates. Furthermore, differences in CO2 production between the variants containing different amounts of hydropolymers were not significant. A statistically significant difference in the CO2 production was found in the first week compared to longer time periods. Conclusions. The mineral nitrogen leaching measurement showed that the biological activity of the studied is not affected by nitrogen dynamics which is balanced regardless of the amount of applied hydropolymer. On the other hand, leaching processes occurred when soil was doped only with nitrogen compounds or only carbonaceous, a problem that can appear after fertilizers application.

RESUMEN Objetivo. El objetivo de este estudio pasa por evaluar el efecto del-Terracottem- en la actividad microbiana del suelo mediante la medida de la respiración edáfica y la pérdida de nitrógeno mineral por lixiviación. El ensayo se ha realizado en condiciones de laboratorio controladas y con suelos naturales. Materiales y métodos. Para el experimento, se han diseñado varios tratamientos: i) suelos naturales a los que se les ha adicionado compuestos nitrogenados de libre disponibilidad (Kg N ha-1); ii) suelos naturales a los que se les ha adicionado carbohidratos de libre disponibilidad (1% de solución de glucosa); iii) suelos naturales a los que se les ha adicionado una mezcla de compuestos nitrogenados de libre disponibilidad (Kg N ha-1) con carbohidratos (1% de solución de glucosa). En cada variante se han testeado diferentes dosis del polímero. Resultados. Los resultados han demostrado que la actividad respiratoria del suelo es independiente de la disponibilidad de compuestos como el nitrógeno o carbono. Tampoco se han observado diferencias significativas entre las diferentes dosis del polímero. Por el contrario, si se observaron diferencias en la producción de CO2. Conclusiones. La lixiviación únicamente se producía cuando los suelos eran enmendados con compuestos únicamente nitrogenados o únicamente sólo carbonosos.