Reduced Soil pH Research Articles

Increased stability of a subtropic bamboo forest soil bacterial communities through integration of water and fertilizer management compared to conventional management

BackgroundConventional management (CM), substantial fertilization and flooding irrigation, has led to soil acidification, the decrease in soil bacterial diversity in bamboo forests. Integration of water and fertilizer management (IWF) can effectively improve the efficiency of water and fertilizer use, but its effect on soil environment, especially on microbial community, is still unclear.MethodsHere, we used next-generation high-throughput sequencing to compare soil properties and bacterial communities through different fertilization and irrigation methods under IWF and CM.ResultsCompared to the control group, CM significantly reduced soil pH and bacterial diversity, while IWF improved soil nutrition status, increased soil bacterial diversity and soil pH to a level similar to the control group. Compared with CM, IWF also improved the relative abundance of beneficial bacteria and copiotrophic bacteria community in the soil, and the bacterial community in IWF was similar to CK. The structure of the bacterial community was also significantly correlated with soil organic matter, total nitrogen, hydrolyzable nitrogen, and available potassium, while soil bacterial diversity was mainly associated with soil hydrolyzable nitrogen.ConclusionsIWF can play an important role in preventing soil acidification, the loss of soil bacterial diversity, and improving the structure of the bacterial community under specific conditions.

Sustainable Soil Management in Alkaline Soils: The Role of Biochar and Organic Nitrogen in Enhancing Soil Fertility

Biochar (BC) serves a vital function in sequestering carbon, improving nutrient cycles, and boosting overall soil quality. This research explored the enhancement of the chemical and physical properties of soil (alkaline) using nitrogen and biochar (from organic and inorganic sources) in a semi-arid climate during the autumn seasons of 2015–2016 and 2016–2017. The study involved applying biochar at various rates (0, 10, 20, and 30 t ha⁻1) and nitrogen at different levels (0, 90, 120, and 150 kg ha⁻1) using urea, poultry manure (PM), and farmyard manure (FYM) as nitrogen sources, which were applied to the field in a randomized complete block design with split-plot arrangement. The application of biochar at the highest rate (30 t ha⁻1) resulted in a significant increase of over 120% in soil organic matter (SOM), soil organic carbon (SOC), and soil moisture content (SMC). Additionally, it increased total soil nitrogen (STN) by 14.16% and mineral nitrogen (SMN) by 9.09%. In contrast, applying biochar at this rate reduced soil bulk density (SBD), pH, and electrical conductivity (EC) by 28.52%, 3.38%, and 2.27%, respectively, compared to the control. Similarly, applying nitrogen at 150 kg ha⁻1 using FYM significantly improved SOC, SOM, SMC, and SBD. At the same rate, using PM as a nitrogen source enhanced STN and SMN while reducing soil pH and EC. In conclusion, this study shows that applying biochar at 30 t ha⁻1 combined with nitrogen at 150 kg ha⁻1, sourced from either PM or FYM, offers great potential for improving soil fertility and promoting carbon sequestration in alkaline soils of semi-arid regions. These findings highlight the value of integrating BC and organic N sources for enhancing agroecosystem sustainability. Thus, this study provides a promising pathway to enhance soil quality, improve crop productivity, and support sustainable agricultural practices in challenging environments.

Long-term rice cultivation enhances root development and yields by improving the structural properties of soil aggregates in saline–alkaline environments

Rice cultivation has the ability to improve saline soils. However, the effects of long-term rice cultivation on saline soil chemistry, salt ions, root characteristics, and aggregate formation remain unclear. In this study, the impact of different planting durations (1, 3, 5, 8, and 10 years) on the spatial and temporal transport of soil salts, soil chemical properties, distribution and stability of aggregates, root characteristics, and yields, were assessed. Long-term rice cultivation reduced soil pH, exchangeable sodium percentage (ESP), and EC in the 0-60cm soil layer compared to 1Y (5.45%, 61.57%, and 81.87% reduction in topsoil (0-20cm) and 8.54%, 72.82%, and 71.94 in subsoil (20-60cm), respectively). However, the soil organic matter (OM), alkaline nitrogen (AN), phosphorus (AP), and potassium (AK) increased (217.09%, 90.18%, 89.23%, and 179.18% increase in topsoil and 223.72%, 81.24%, 174.28%, and 172.57% increase in subsoil, respectively). Additionally, the Cl-, K+, and Na+ in the soil gradually leached downward with the increase in the duration of rice cultivation (55.87%、36.08%、59.80%). Simultaneously, the increased duration markedly elevated the soil macroaggregate content (11.43%-20.04% by dry-sieving and 53.48%-288.09% by wet-sieving), clayey grain content (59.17%-198.33%), and soil aggregate stability, especially for 8Y and 10Y. The improved soil structure and root characteristic under long-term rice cultivation conditions increased the yield (28.89-54.81%). Partial least squares path model displayed that rice cultivation affected the aggregate stability, root characteristics, and rice yield via the corresponding chemical properties (pH, EC, and ESP), nutrient contents (AN, AP, AK, and SOM), and salt ion contents (Cl-, K+, and Na+). These findings are critical to understanding aggregate formation in saline soils.

Accumulation of coumaric acid is a key factor in tobacco continuous cropping obstacles.

Phenolic acids are believed to play a significant role in tobacco continuous cropping obstacles, but the strength and potential mechanisms of different phenolic acids remain unclear. This study evaluated the allelopathic effects of six phenolic acids that exhibited cumulative effects in our previous research. Different concentrations of phenolic acids with the strongest allelopathic effects were added to potting soil to explore their impacts on tobacco growth and physiological characteristics, as well as on soil chemical properties and microbial community structure. The results showed that coumaric acid exhibited the strongest direct allelopathic effect. Exogenous coumaric acid significantly reduced soil pH and shifted the soil microbial community from bacteria-dominated to fungi-dominated. Simultaneously, the abundance of bacteria related to nutrient utilization (e.g., Flavisolibacter, Methylobacterium) and fungi related to disease resistance (e.g., Fusicolla, Clonostachys) gradually decreased, along with a reduction in soil catalase, urease, invertase, and acid phosphatase activities. Leaf MDA levels increased continuously with higher concentrations of coumaric acid, while the root resistance hormone (jasmonic acid and the jasmonate-isoleucine complex) levels show the opposite trend. Coumaric acid may inhibit tobacco growth by influencing the physiological processes in tobacco plants directly and the broader soil microecological balance indirectly. This study provides theoretical guidance for precise mitigation of continuous cropping obstacles in future tobacco cultivation.

Nitrogen induced soil carbon gains are resistant to loss after the cessation of excess nitrogen inputs

Nitrogen (N) deposition has increased soil carbon (C) storage across eastern US temperate forests by reducing microbial decomposition. However, the fate of these N-induced soil C gains are uncertain given strong declines in N-deposition rates and rising soil temperatures. As N deposition has reduced soil pH and plant C investments into the rhizosphere, we compared the extent to which removing limitations to microbial decomposition by increasing soil pH, adding artificial root exudates, or elevating soil temperature would increase microbial decomposition in soils that have and have not received excess N inputs. We hypothesized that alleviating these microbial decomposition limitations would prime soil C losses from soils that have received excess N inputs. To test this hypothesis, we conducted a soil microcosm experiment where we compared microbial respiration, microbial biomass, and soil enzyme activity in soils from an unfertilized watershed and a previously N-fertilized watershed 4 years after the end of a 30-year N deposition experiment at the Fernow Experimental Forest in West Virginia. In both watersheds, we found that removing pH, plant carbon, or temperature limitations to decomposition stimulated microbial respiration. However, microbial decomposition and soil C losses were consistently lower in the previously N-fertilized watershed across all treatments. This response, coupled with a lack of differences in microbial biomass between watersheds and treatments, suggests that long-term N fertilization has fundamentally altered soil microbial communities and has led to a sustained impairment of the ability of the microbial community to decompose soil organic matter. Collectively, our results indicate that the legacy effect of N deposition on microbial communities may influence the persistence of soil C stocks in the face of global change.

Effect of Liquid Microbial Consortium on Physio Chemical Properties of Rice Field (Oryza Sativa) in a Vertisol

A study was conducted during kharif 2020 on "Effect of liquid microbial consortium (Azotobacter, Azospirillum, PSB (Pseudomonas mallei, Pseudomonas cepaceae, Penicillium sp.) and KSB) on physio chemical properties and microbial population of rice field (Oryza sativa) in a Vertisol" at the Indira Gandhi Krishi Vishwavidyalaya's Research cum instructional farm in Raipur (C.G.). Experiment included seven treatments viz. control (no fertilizer, no liquid NPK microbial consortia), two independent applications of 75 % RDF (90:45:30) and 100% RDF ((120: 60: 40) N, P2O5, and K2O kg ha-1 and four various combinations of seed and soil application of liquid NPK microbial consortia. Seed coating with NPK consortia @5ml kg-1, with 75% and 100% RDF and Seed coating with NPK consortia @5ml kg-1 + Soil application of NPK consortia @3 L ha-1 at 21 DAS with 75%RDF and 100%RDF. In the experiment, liquid biofertilizer products, such as liquid microbial NPK consortia were used. The population of Azotobacter, Azospirillum, phosphorous solubilizing bacteria (PSB), potassium solubilizing bacteria (KSB) and total bacterial population were significantly influenced by application of consortia as seed treatment @ 5ml kg-1 only and by a combination of seed treatment @ 5ml kg-1 seed + soil application @ 3 L ha-1 at 21 DAT with 75 or 100 % recommended dose of fertilizers and showed statistically significant higher microbial population in comparisons with the treatments of untreated alone applications of 75 or 100 % RDF. The results showed that the soil reaction, (pH) salt concentration (Electrical conductivity) and organic carbon status were not significantly influenced by the different treatments of fertilizer levels and microbial consortia applied. Slight decrease in the soil reaction (pH) and slight increase in the OC status after the harvesting of rice were observed from their initial soil values (before application of treatments). It might be due to the addition of organic matter as plant residues (straw and roots) of rice crop gown in the field. As compared to untreated- control (T1) a slight decrease in pH and increase in organic carbon content due to application of fertilizer and microbial consortia were also recorded. The residual available nitrogen in the soil after the harvesting of rice was not significantly influenced by the fertilizer levels and NPK consortia applied. The initial status of the experimental soil was low for available nitrogen (224 kg ha-1), medium for available phosphorus (24.5 kg ha-1) and high for available potassium (384 kg ha-1). Due to the addition of nitrogen through the fertilizer (90-120 kg ha-1) and less uptake of native nitrogen from the soil, a marginal increase in the residual available N in the soil from the initial level was observed in all treatments except the control (no fertilizer, no consortia). The residual status of available potassium was also not significantly influenced by the applied fertilizer doses and NPK consortia. A marginal decrease in the residual available K status after the harvesting of rice was observed in all treatments. A decrease was found in the control plot. A decrease in the K status (from the initial level) was observed less where a full dose of NPK fertilizers (100%) was applied with the NPK consortia. Ramlakshmi et al. [1], also observed slight reduction in soil pH and increase in organic carbon content in biofertilizer inoculated treatments as compared to the un-inoculated control soil [2].

Effects of Restoration Strategies on Soil Health after Lycium chinense Removal in the Qaidam Basin

Ecological restoration of arid land plays a pivotal role in maintaining ecological sustainability and enhancing the resilience of local communities. As an ecologically significant arid land, the Qinghai Qaidam Basin has been severely impacted by human activities such as the widespread planting of Lycium chinense, leading to considerable degradation of vegetation and soil carbon and nutrients. Currently, this vital area is undergoing extensive ecological restoration through the employment of a variety of strategies, but the impact remains inadequately understood. This study seeks to compare the effects of different restoration strategies in the Qinghai Qaidam Basin, focusing on soil properties across five scenarios: a controlled desert area, natural restoration after the removal of L. chinense, continued planting of L. chinense, restoration through the planting of Haloxylon ammodendron, and mixed reseeding after four years of restoration. Our findings indicate that mixed reseeding significantly improved soil water storage to 4.26%, especially in the deep soil layer. The planting of H. ammodendron strategy efficiently reduced soil pH in such an alkaline environment. Soil nutrients, including total nitrogen (TN), total phosphorus (TP), and total potassium (TK), were predominantly concentrated in the top soil layer, with reduced concentrations observed in the medium and deep soil layers. Although soil organic matter remained relatively stable across all restoration strategies, its content was notably lower in the deeper layers. Overall, mixed reseeding proved to be the most efficient strategy for enhancing soil water retention and nutrient levels. In contrast, despite achieving high vegetative coverage to 62.6%, planting of L. chinense was less ecologically beneficial due to its extensive irrigation requirements and adverse effects on soil structure. These findings suggest that restoring degraded areas to an ideal ecological state cannot be achieved within a few years, underscoring the importance of sustained restoration efforts. This study offers valuable insights and practical guidance for the ecological restoration of arid lands, contributing to the development of sustainable land management practices in similar regions.

Insights into the critical roles of water-soluble organic matter and humic acid within kitchen compost in influencing cadmium bioavailability

Compost has demonstrated potential as a cadmium (Cd) remediation agent, while it still remains unclear about the core components in driving the bioactive transformation of Cd. To address this issue, this study isolated three components—kitchen compost powder (KC), humic acid (HA), and water-soluble organic matter (DOM)—from kitchen compost to regulate soil properties, bacterial community structures and functions, and Cd migration risks. The results revealed that the addition of 20% KC and HA reduced the bioavailability factor of Cd by 47.20% and 16.74%, respectively, with HA contributing 35.47% of the total reduction achieved with KC. Conversely, the application of DOM increased the Cd risk through a reduction in soil pH and an increase in the abundance of Cd-activating bacteria, which adversely affected the stability of Cd complexes. However, the porous structure and organic matter in KC and HA provided adsorption sites for Cd passivation and promoted the growth of Cd-fixing bacteria. This study effectively identifies both the positive and negative effects of key compost components on Cd migration and provides scientific guidance for applying kitchen compost in soil management.

Exploring the insights of bioslurry-Nanoparticle amalgam for soil amelioration.

In response to global agricultural challenges, this review examines the synergistic impact of bioslurry and biogenic nanoparticles on soil amelioration. Bioslurry, rich in N, P, K and beneficial microorganisms, combined with zinc oxide nanoparticles synthesized through eco-friendly methods, demonstrates remarkable soil improvement capabilities. Their synergistic effects include enhanced nutrient availability through increased soil enzymatic activities, improved soil structure via stable aggregate formation, stimulated microbial activity particularly beneficial groups, enhanced water retention due to increased organic matter and modified soil surface properties and reduced soil pH fluctuations. These mechanisms significantly impact soil physico-chemical properties including cation exchange capacity, electrical conductivity and nutrient dynamics. This review analyses these effects and their implications for sustainable agricultural practices, focusing on crop yield improvements, reduced chemical fertilizer dependence and enhanced plant stress tolerance. Knowledge gaps such as long-term nanoparticle accumulation effects and impacts on non-target organisms are identified. Future research directions include optimizing bioslurry-nanoparticle ratios for various soil types and developing "smart" nanoparticle-enabled biofertilizers with controlled release properties. This innovative approach contributes to environmentally friendly farming practices, potentially enhancing global food security and supporting sustainable agriculture transitions. The integration of bioslurry and biogenic nanoparticles presents a promising solution to soil degradation and agricultural sustainability challenges.

Polystyrene influence on Pb bioavailability and rhizosphere toxicity: Challenges for ramie (Boehmeria nivea L.) in soil phytoremediation

Microplastics (MPs) and heavy metals often coexist in soil, however their interactions and effects on the soil–plant system remain largely unclear. In this study, ramie (Boehmeria nivea L.) was exposed to soil contaminated with lead (Pb) and polystyrene (PS) of different sizes, dosages, and surface–charged functional groups. This design aimed to simulate the effects of MPs on phytoremediation. The experimental results revealed that PS exacerbated the damaging effects of Pb on ramie. Compared to the effect of Pb alone, PS–COOH had a greater influence on root vigor, leading to a 15.6 % reduction in the active absorption ratio. Laser scanning confocal microscope showed PS entered the roots. Adsorption/desorption experiments demonstrated that PS had a weaker adsorption capacity for Pb than soil but a greater desorption rate than soil when simulating rhizosphere secretion. Moreover, PS reduced soil pH and increased the reducible state of Pb by 6–12 %. After 100 days of phytoremediation, Pb content in the soil with PS–5 μm was 150 μg g−1 less than that in the soil without PS. These results demonstrated that PS improved Pb bioavailability and enhanced the efficiency of Pb uptake by ramie. The redundancy analysis demonstrated that PS mitigated the toxicity of Pb to rhizosphere microorganisms, potentially via its effects on metal chemical fractions, dehydrogenase activity (S–DHA), cation exchange capacity (CEC), and soil organic matter (SOM). This study indicates that the presence of PS could potentially enhance the phytoremediation efficiency of ramie in Pb–contaminated land by influencing soil microenvironmental properties. This study provides insights into the complex interactions of MPs with soil–plant–microbial systems during metal remediation, thereby enhancing our understanding of their environmental impacts.

Earthworm mucus contributes significantly to the accumulation of soil cadmium in tomato seedlings

Whether earthworm mucus affects Cd transport behavior in soil-plant systems remains uncertain. Consequently, this study thoroughly assessed the impacts of earthworm mucus on plant growth and physiological responses, plant Cd accumulation, translocation, and distribution, as well as soil characteristics and Cd fractionation in a soil-plant (tomato seedling) system. Results demonstrated that the earthworm inoculation considerably enhanced plant Cd uptake and decreased plant Cd translocation, the effects of which were appreciably less significant than those of the earthworm mucus. This suggested that earthworm mucus may play a crucial role in the way earthworms influence plant Cd uptake and translocation. Moreover, the artificial mucus, which contained identical inorganic nitrogen contents to those in earthworm mucus, had no significant effect on plant Cd accumulation or translocation, implying that components other than inorganic nitrogen in the earthworm mucus may have contributed significantly to the overall effects of the mucus. Compared with the control, the earthworm mucus most substantially increased the root Cd content, the Cd accumulation amount of root and whole plant, and root Cd BCF by 93.7 %, 221.3 %, 72.2 %, and 93.7 %, respectively, while notably reducing the Cd TF by 48.2 %, which may be ascribed to the earthworm mucus's significant impacts on tomato seedling growth and physiological indicators, its considerable influences on the subcellular components and chemical species of root Cd, and its substantial effects on the soil characteristics and soil Cd fractionation, as revealed by correlation analysis. Redundancy analysis further suggested that the most prominent impacts of earthworm mucus may have been due to its considerable reduction of soil pH, improvement of soil DOC content, and enhancement of the exchangeable Cd fraction in soil. This work may help better understand how earthworm mucus influences the transport behavior of metals in soil-plant systems.

Companion interference and symbiotic matching phenomenon occurred in saline-alkali habitats

Salinization has emerged as a worldwide concern hampering the progression of agriculture and husbandry. Arbuscular mycorrhizal (AM) fungi, which abundantly distributed in the Songnen Plain, was considered to possess great potential for combating salinity. To elucidate the relationship between AM fungal community and saline-alkali ecological remediation, a 70-days pot experiment, with the soil in the late succession stage of Songnen saline-alkali habitat was taken as substrate, the dominant plant in the latter as research object, and the rhizosphere soil from three stages as inoculants, was conducted. Simultaneously, Chloris virgate was cultivated to ascertain the accompanying role on mycorrhizal effects and soil improvement. The results revealed that AM fungi effectively regulated the botanical morphogenesis, photosynthesis, osmotic concentration, and antioxidant enzymatic activity under saline-alkali conditions. Specifically, the net photosynthetic rate increased by 1.11–2.44 μmol·(m2)−1·s−1, and the total root length grew by 41.15–148.98 cm after inoculation. Furthermore, the soil salinization and nutrient sequestration were modulated by AM fungi, and that leaded to a notable reduction in soil pH by 0.3 %-1.64 % and an increase in nitrogen content by 52.17 %-118.84 %. In a comprehensive assessment, the utmost ecological advantage appeared in the group inoculated AM fungi procured from the identical stage as the host, with a peak mycorrhizal dependency of 2.93. Additionally, despite enhancing salinization restoration compared to the non-companion group, the associated plants reduced the mycorrhizal dependency of neighbour by a range of 27.04–51.46 %, and significantly decreased the dry weight by 0.09–0.28 g. These results confirmed the occurrence of symbiotic matching phenomenon in saline-alkali habitats and suggested that the mechanism should be considered as utilizing AM fungi for ecological restoration. However, the introduction of companion should be cautious due to their complex effects.

Mitigating the detrimental impacts of low- and high-density polyethylene microplastics using a novel microbial consortium on a soil-plant system: Insights and interactions

The accumulation of polyethylene microplastics (PE-MPs) in soil has raised considerable concerns; however, the effects of their persistence and mitigation on agroecosystems have not been explored. This study aimed to assess the detrimental effects of PE-MPs on a soil-plant system and evaluate their mitigation using a novel microbial consortium (MC). We incorporated low-density polyethylene (LDPE) and high-density polyethylene (HDPE) at two different concentrations, along with a control (0 %, 1 %, and 2 % w/w) into the sandy loam soil for a duration of 135 days. The samples were also treated with a novel MC and incubated for 135 days. The MC comprised three bacterial strains (Ralstonia pickettii (MW290933) strain SHAn2, Pseudomonas putida strain ShA, and Lysinibacillus xylanilyticus XDB9 (T) strain S7–10F), and a fungal strain (Aspergillus niger strain F1–16S). Sunflowers were subsequently cultivated, and physiological growth parameters were measured. The results showed that adding 2 % LDPE significantly decreased soil pH by 1.06 units compared to the control. Moreover, adding 2 % HDPE resulted in a more significant decrease in soil electrical conductivity (EC) relative to LDPE and the control. A dose-dependent increase in dissolved organic carbon (DOC) was observed, with the highest DOC found in 2 % LDPE. The addition of higher dosages of LDPE reduced soil bulk density (BD) more than HDPE. The addition of 2 % HDPE increased the water drop penetration time (WDPT) but decreased the mean weight diameter of soil aggregates (MWD) and water-stable aggregates (WSA) compared to LDPE. The results also revealed that higher levels of LDPE enhanced soil basal respiration (BR) and microbial carbon biomass (MBC). The interaction of MC and higher MP percentages considerably reduced soil pH, EC, BD, and WDPT but significantly increased soil DOC, MWD, WSA, BR, and MBC. Regarding plant growth, incorporating 2 % PE-MPs significantly reduced physiological responses of sunflower: chlorophyll content (Chl; −15.2 %), Fv/Fm ratio (-25.3 %), shoot dry weight (ShD; −31.3 %), root dry weight (RD; −40 %), leaf area (LA; −38.4 %), and stem diameter (StemD; −25 %) compared to the control; however, the addition of novel MC considerably reduced and ameliorated the harmful effects of 2 % PE-MPs on the investigated plant growth responses.

Soil properties and nutrient uptake of maize (Zea mays) as influenced by mixed manure and blended inorganic fertilizer in Haramaya district, eastern Ethiopia

The deteriorating state of soil fertility and low agricultural productivity in Ethiopia can be traced to the lack of equivalent consideration given to the soil's biological, chemical, and physical properties. A pot experiment was conducted to investigate the effect of mixed manure and blended nitrogen, phosphorus, sulfur and boron (NPSB) fertilizer on phosphorus adsorption, and other properties of Vertisols, nutrient uptake, and growth performance of maize. The study findings indicate that the combined application of mixed manure and blended NPSB significantly reduced soil pH from 7.87 to 7.68, phosphorus adsorption efficiency from 93 to 88.5 %, and Freundlich adsorption capacity from 194 to 100.75 mg kg−1 , intensity from 1.96 to 1.27 compared to control. However, combined application of these two treatments significantly increased the organic carbon from 0.81 to 1.64 %, total nitrogen from 0.04 to 0.13 %, and available phosphorus from 6.96 to 73.82 g kg−1. The study further revealed that mixed manure and blended NPSB resulted in significantly (p ≤ 0.05) higher contents of nitrogen and phosphorus in the maize leaves as well as their uptake compared to their sole application and control. The highest values of these parameters were observed in plots treated with a combined application of 15 t ha−1 mixed manure with each rate of 100 and 150 kg ha−1 blended NPSB. Additionally, the maize plant height (p ≤ 0.05) and above-ground biomass (p ≤ 0.01) also exhibited significant increase. Compared to the control and full dose of NPSB, all the treatments that received a combined application of 15 t ha−1 mixed manure with blended NPSB ranging from 50 to 150 kg ha−1 resulted in significantly higher above-ground biomass of maize. The results suggest that the combined use of mixed manure and blended NPSB could be a practical and effective approach to improve soil properties and maize above-ground biomass yield.

Microbial fertilizers improve soil quality and crop yield in coastal saline soils by regulating soil bacterial and fungal community structure

Salinization is a global problem affecting agricultural productivity and sustainability. The application of exogenous microbial fertilizer harbors great potential for improving saline-alkali soil conditions and increasing land productivity. Yet the responses to microbial fertilizer application rate in terms of rhizosphere soil biochemical characteristics, soil microbial community, and crop yield and their interrelationships and underlying mechanisms are still unclear. Here, we studied changes to rhizosphere soil-related variables, soil enzyme activity (catalase, sucrase, urease), microbial community diversity, and sweet sorghum (Sorghum bicolor (L.) Moench) yield under four fertilization concentration levels (0, 0.12, 0.24, and 0.36 kg m−2) in a saline-alkali ecosystem (Shandong, China). Our results showed that the best improvement effect on soil when the microbial fertilizer was applied at a rate of 0.24 kg m−2. Compared with the control (sweet sorghum + no fertilizer), it significantly increased soil organic carbon (21.50 %), available phosphorus (26.14 %), available potassium (36.30 %), and soil urease (38.46 %), while significantly reducing soil pH (2.21 %) and EC (12.04 %). Meanwhile, the yield of sweet sorghum was increased by 24.19 %. This is mainly because microbial fertilizers enhanced the diversity and the network complexity of bacterial and fungal communities, and influenced catalase (CAT), urease (UE), and sucrase (SC), thereby facilitating nutrient release in the soil, enhancing soil fertility, and indirectly influencing sweet sorghum productivity. Among them, Gemmatimonadota and Verrucomicrobiota may be the key microbial factors affecting sweet sorghum yield, while available potassium, soil urease and available phosphorus are the main soil factors. These findings provide valuable theoretical insights for preserving the health of coastal saline-alkali soils and meeting the agricultural demand for increased yield per unit of land area.

Efficacy of various amendments for immobilization of potentially toxic elements in wastewater contaminated soils

Farmers are using municipal wastewater either treated or untreated for irrigation because of limited fresh water resources. Wastewater extensively used for irrigation purposes is enriched with many nutrients. The reuse of wastewater is imposing a negative impact on human health and the ecosystem. It is a need of the day to identify and assess issues of the reuse of wastewater. In the current experiment, impact of organic/inorganic amendments was studied to mitigate the toxic effects of pollutants present in wastewater. Soil was brought from the site having consistent use of wastewater and different treatments were applied as per plan. The experiment has 28 treatments with 04 replications. Nine different amendments were used at 3 varying levels. Incubation time of 30 days was given after the addition of all treatments. The results of the study showed the application of FYM @ 5.0% w/w soil reduced soil pH (7.44), EC (2.16 dS m−1), SAR (8.14), lead (8.48 mg kg−1), cadmium (1.14 mg kg−1), nickel (10.55 mg kg−1) and arsenic (2.03 mg kg−1) when compared with control and other treatments. Usage of compost and horse waste followed FYM. On the basis of this study, it is recommended that wastewater can be used for irrigation purpose after treating with FYM preferably and compost in general.

Impact of low molecular weight organic acids on heavy metal(loid) desorption in biochar-amended paddy soil.

Low molecular weight organic acids (LMWOAs) are important soil components and play a key role in regulating the geochemical behavior of heavy metal(loid)s. Biochar (BC) is a commonly used amendment that could change LMWOAs in soil. Here, four LMWOAs of oxalic acid (OA), tartaric acid (TA), malic acid (MA), and citric acid (CA) were evaluated for their roles in changing Cd and SB desorption behavior in contaminated soil with (S1-BC) or without BC (S1) produced from Paulownia biowaste. The results showed that OA, TA, MA, and CA reduced soil pH with rising concentrations, and biochar partially offset the pH reduction by LMWOAs. The LMWOAs reduced Cd desorption from the soil at low concentrations but increased Cd desorption at high concentrations, and CA was the most powerful in this regard. The LMWOAs had a similar effect on Sb desorption, and CA was the most effective species of LMWOAs. Adding BC to the soil affects Cd and Sb dynamics by reducing the Cd desorption but increasing Sb desorption from the soil and increasing the distribution coefficient (Kd) values of Cd but lowering the Kd values of Sb. This study helped understand the effects of LMWOAs on the geochemical behavior of Cd and Sb in the presence of biochar, as well as the potential risks of biochar amendment in enhancing Sb desorption from contaminated soil.

Effect of 3-year amendment measures on coastal saline–alkali soil conditions during the growing season

Seawater intrusion and fluctuations in the water table in coastal areas lead to seasonal variations in soil salinity and pH, which greatly limit the development of coastal protection forests. In a 3-year field study, the impact of five soil amendment measures were evaluated on soil conditions in coastal areas. Amendments included biochar, biochar with arbuscular mycorrhizal fungi (AMF), straw with AMF, straw alone, and AMF alone, compared to a control (CK) with no additive. Results indicated that combinations of straw, biochar, and AMF reduced soil pH across various layers and seasons, with electrical conductivity mainly decreasing in spring. During the summer, at the 0–20 cm soil depth, microbial biomass carbon notably increased due to these mixtures. Additionally, AMF alone and biochar with AMF significantly improved enzyme activities in the 0–40 cm layer in spring, while in fall, AMF alone notably increased nutrient availability in the same layer. Linear regression analysis revealed a negative correlation between electrical conductivity, microbial biomass carbon, enzyme activity, and nutrient availability with pH. The biochar–AMF mixture emerged as the most effective soil amendment, suggesting that using it in conjunction with seasonal management could optimize soil health and promote silviculture in coastal regions.

Improving the enrichment of Cd and Zn in leaf mustard (Brassica juncea) by using metal-activating probiotics

Microbial-assisted phytoremediation is of great significance for the remediation of soil contaminated with heavy metals (HMs). Probiotics are beneficial microorganisms that can improve soil structure and fertility and promote plant growth. This study aimed to investigate the effect of two kinds of probiotics, including Lactobacillus casei (L) and Bacillus licheniformis (B), on activating the remediation potentiality of leaf mustard [Brassica juncea (L.) Czerniak.] for mining soil contaminated by Cd and Zn. The results showed that addition of two probiotics significantly reduced soil pH (with 0.05–0.32 units) and improved the available contents of soil HMs (16.0%–59.9% for Cd and 7.1%–23.9% for Zn) in the indoor-incubation experiment. After probiotic treatments, available Cd and Zn in potting soil treated with 1×109 cfu mL-1 of B were 1.65-fold and 1.66-fold of the control, respectively. Meanwhile, soil alkaline phosphatase, urease and sucrose activities were increased, indicating that soil microbial metabolic activities were also motivated. Addition of L and B significantly improved the biomass and chlorophyll contents of leaf mustard. The contents of Cd, Zn in shoot and root were significantly increased with 1×105 cfu mL-1 of L treatment (shoot: 75.2%, 71.9%; root: 36.8%, 61.2%). Furthermore, the activity of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) and the level of malondialdehyde (MDA) were increased or inhibited, indicating that the resistance of plants to HMs was enhanced. These results indicated that two kinds of probiotics could improve the activities of Cd and Zn directly in mining soil and promote the growth of leaf mustard, thus increasing the efficiency of phytoremediation for HMs. The study provides a reference value for probiotic-assisted phytoremediation of soil contaminated with HMs.

Effects of Polyethylene Microplastics on Soil Nutrients and Enzyme Activities

The threat of microplastic pollution in soil ecosystems has caused widespread concern. In order to clarify the effect of polyethylene microplastics on soil properties, a 4-month soil incubation experiment was conducted in this study to investigate the effect of different mass fraction (1 %, 2.5 %, and 5 %) and particle sizes (30 mesh and 100 mesh) of polyethylene microplastics on soil chemical properties, nutrient contents, and enzyme activities. The results showed that:① When the particle size was 100 mesh, microplastics at the mass concentrations of the 2.5 % and 5 % treatments significantly reduced soil pH, and the exposure of polyethylene microplastics had no significant effect on soil conductivity. ② Compared to that in CK, the addition of microplastics reduced soil available potassium, available phosphorus, and nitrate nitrogen to varying degrees. The addition of 100 mesh microplastics significantly increased soil organic matter and ammonium nitrogen. ③ When the particle size was 100 mesh, compared to that in CK, treatments of all concentrations significantly increased soil catalase activity and alkaline phosphatase, showing an increasing but not significant trend, and the 5 % concentration treatment significantly decreased soil sucrase activity. ④ Changes in soil properties were influenced by the addition of microplastics of different concentrations and sizes, with higher concentrations and smaller particle sizes having more significant effects. In conclusion, the effects of microplastics on soil properties were not as pronounced as expected, and future research should focus on the mechanisms involved in the different effects.