Green manure removal with reduced nitrogen improves saline-alkali soil organic carbon storage in a wheat-green manure cropping system

The incorporation of green manure into cropping systems is a potential strategy for sequestering soil carbon (C), especially in saline-alkali soil. Yet, there are still unknown about the substitution impacts of green manure on nitrogen (N) fertilizer in wheat-green manure multiple cropping system. Herein, a five-year field experiment was performed to determine the impact of three levels of N fertilizer inputs [i.e., N fertilizer reduced by 0 % (100N), 10 % (90 N), and 20 % (80 N)] with aboveground biomass of green manure removal (0GM) and return (100GM) on soil organic carbon (SOC) storage and its primary determinants. The results demonstrated that no significant interaction on SOC storage was detected between green manure and N fertilizer management. 80 N enhanced SOC storage in bulk soil by 7.4 and 13.2 % in 0-20 cm soil depth relative to 100 N and 90 N (p < 0.05). Regardless of N fertilizer levels, compared with 100GM, 0GM increased SOC storage in bulk soil by 14.2-34.6 % in 0-40 cm soil depth (p < 0.05). This was explained by an increase in soil macro-aggregates (>2 and 0.25-2 mm) proportion contributing to SOC physical protection. Meanwhile, the improvement of SOC storage under 0GM was due to the decrease of soil C- and N-acquisition enzyme activities, and microbial resource limitation. Alternatively, the variation partitioning analyses (VPA) results further suggested that C- and N-acquisition enzyme activities, as well as microbial resource limitation were the most important factors for SOC storage. The findings highlighted those biological factors played a dominant role in SOC accumulation compared to physical factors. The aboveground biomass of green manure removal with N fertilizer reduced by 20 % is a viable option to enhance SOC storage in a wheat-green manure multiple cropping system.

Combined microbe-plant remediation of cadmium in saline-alkali soil assisted by fungal mycelium-derived biochar

Cadmium contamination in saline-alkali soil is becoming a great concern. Combined microbe-plant remediation is an economic way to treat this contamination, but is compromised by its low cadmium-removing capacity. In this study, the novel fungus-derived biochar was prepared to enhance the salt-tolerant bacterium-plant remediation of cadmium-contaminated saline-alkali soil. This biochar was prepared by pre-incubation of living Trichoderma atroviride hyphae with imidazole and further heating at 500 °C for 1 h. The obtained fungus-derived nitrogen-doped biochar (FBioCN) exhibited the high affinity to bacterial cells, leading to efficient colonization of exogenous salt-tolerant bacteria (e.g., Rhizobacter sp. and Sphingomonas sp.) on Amaranthus hypochondriacus roots. During culturing of the plants in the cadmium-contaminated saline-alkali soil, FBioCN drastically remodeled the rhizosphere microbiome, leading to enhance colonization of the exogeneous salt-tolerant bacteria, and increase bacterial diversity. The combination of FBioCN and the exogeneous bacteria further improved the activity of rhizosphere functional enzymes, protected the plants from the multiple stress, and promoted cadmium transport from the soil to the plants. Consequently, FBioCN together with the salt-tolerant bacteria drastically improved cadmium removal from the saline-alkali soil, with the percent of cadmium removal at the rhizosphere region increasing from 35.1% to 95.1%. This study sheds a light on the application of fungus-derived biochar in combined microbe-plant remediation in saline-alkali soil.

Effective strategies for reclamation of saline-alkali soil and response mechanisms of the soil-plant system

The combination of amendments has emerged as a potential strategy to efficiently alleviate salt stress in saline-alkali soil. However, knowledge regarding how to optimize the proportion of different amendment materials, comprehensively assess the contribution of each component, and clarify the response mechanisms of the amendment-saline-alkali soil-plant system is incomplete. Based on this, we conducted a pot experiment to evaluate the improvement effect of the combined application of different amendment materials at varying levels and the contribution of the amendment components to alleviating salt stress. Overall, T6 exhibited the most significant improvement effect on the physicochemical and biological properties of the saline-alkali soil and promoted the growth of oilseed rape, with the levels of 2.0 % phosphogypsum, 2.0 % humic acid, 0.25 % bentonite, and 0.03 % sodium carboxymethyl cellulose. Compared with the control group, the EC decreased by 1.51 % to 33.49 %, the soil salt content dropped by 11.40 % to 35.46 %, and the soil soluble Na + concentration significantly declined by 39.47 % to 63.20 %. Additionally, the soil nutrient content and soil microbial community structure were enhanced in treatment groups. Meanwhile, amendments alleviated salt stress in the oilseed rape plant by activating anti-oxidative enzymes and osmoregulatory substances such as soluble sugar and proline, thus improving their ability to remove reactive oxygen species (ROS). The anti-oxidative enzymes such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were significantly increased, with an increase of 10.68 % (SOD, T2) ∼207.31 % (CAT, T6) compared to the control group. The structural equation modeling (SEM) analysis and simulation experiments indicated that the amendment components synergically promoted the amelioration effect on salt stress, and effectively improved soil properties, which affected the response of oilseed rape to soil environment. This research paper provides the relevant reference for the combined application of different amendment materials for soil reclamation.

Comprehensive evaluation of the risk system for heavy metals in the rehabilitated saline-alkali land

A comprehensive assessment of the heavy metal system in the rehabilitated saline-alkali land holds significant importance, as the in-situ remediation process utilizing amendments substantially alters the initial physicochemical properties of the soil, which could lead to the migration or reactivation of previously stabilized heavy metals. In this context, the present study aims to evaluate the heavy metal content and health risk within the improved saline-alkali soil-plant system. Moreover, a comprehensive evaluation based on the TOPSIS-RSR method is carried out to accurately gauge the soil health status. The findings indicate that the modification process has an impact on the concentrations of heavy metals in the soil and crops, causing either an increase or decrease. However, the level of heavy metal pollution in the improved saline-alkali soil and rape remains within safe limits. The results of the migration of heavy metals after amendment application indicated that the migration of heavy metals in the soil was influenced by the properties of the heavy metals, the composition of the amendment, and leaching. Furthermore, the total non-carcinogenic hazard quotients in the soil and rape were within the safe threshold for all populations. The findings provided novel insights into the status and risk assessment of the pollution of improved saline-alkali soil.

Biochar and Chlorella increase rice yield by improving saline-alkali soil physicochemical properties and regulating bacteria under aquaculture wastewater irrigation

The combined effects of biochar and Chlorella under aquaculture wastewater irrigation in improving saline-alkali soil physicochemical properties, microbial communities, and rice yield, is not yet clear. This study utilized soil physicochemical indicators and gene sequencing to examine the effect of salinity stress, biochar and Chlorella under aquaculture wastewater irrigation on soil properties, bacterial community compositions, and rice production. Treatments included three factors in a randomized complete block design with three replications: (i) Biochar - 40 tons ha -1 (BW) versus no-biochar (BN); (ii) Salinity - 3‰ salinity (SH) versus 1‰ salinity (SL); and (iii) Chlorella - with 107 cells mL -1 Chlorella (CW) versus no-Chlorella (CN). The results revealed that increased salinity adversely affected the soil nutrients (TOC, NO3⁻-N, NH4+-N, Olsen-P), and enzyme activity (urease, sucrase, catalase), resulting in a 9.67% reduction in rice yield compared to SL treatment. However, the close correlation between alterations in soil bacterial communities, functions, and soil physicochemical properties, as well as rice yield, indicated that biochar and Chlorella promoted rice yield by enhancing the physicochemical properties of saline-alkali soil and bacterial community when irrigated with aquaculture wastewater: (1) addition of biochar increased the146.05% rice yield by increasing TOC content, the complexity of bacterial co-occurrence patterns, nitrogen fixation potential, and nitrification potential, (2) addition of Chlorella increased TOC, NO3⁻-N, NH4+-N, enhanced urease, sucrase, catalase activity, and nitrification potential to increased rice yield by 60.29%, and (3) compared with the treatment T3 (SHBNCN), the treatments with biochar (BW) and Chlorella (CW) increased the yield by 561.30% and 445.03% under 1‰ and 3‰ salinity, respectively. These findings provide novel perspectives on the capacity of biochar and Chlorella to improve saline-alkali soil properties and increase rice yield irrigated with aquaculture wastewater.

Interactions between flue gas desulfurization gypsum and biochar on water infiltration characteristics and physicochemical properties of saline-alkaline soil

The application of flue gas desulfurization gypsum (FGDG) improves the soil structure, reduces soil pH, and accelerates soil salt leaching. Biochar amendment to soil can affect the soil infiltration rate, increase soil porosity, decrease soil bulk density, and enhance the water retention capacity. This study investigated the interactive effect of FGDG and biochar on water infiltration characteristics and physicochemical properties as well as determined the optimal amendment rate as a saline-alkaline soil conditioner. Seven experimental schemes were designed, and the newly reclaimed cultivated soil from Pingtan Comprehensive Experimental Zone in Fujian Province, China, was used in an indoor soil column experiment to simulate soil infiltration. Five models were employed to describe the infiltration process. The power function was used to represent the dynamic process of the wetting front. The conclusions of this study are as follows: (1) there was a reduction in the infiltration capacity of saline-alkaline soil (sandy soil) in each treatment, and the application of FGDG alone had the highest inhibition effect compared to the control (CK). The Kostiakov model provides the best fit for the experimental data of soil cumulative infiltration. (2) All treatments increased the total porosity and water content of saline-alkali soil, with the combined application of FGDG and biochar found to be more effective. (3) The application of FGDG alone or in combination with biochar decreased the pH and increased the electrical conductivity of the saline-alkali soil significantly, with the combined application having the most significant effect. In contrast, soil amended with biochar alone had minimal effect on the pH and EC of the soil. (4) The best improvement ratio was achieved with the F1B2 combination (75 g/kg FGDG + 30 g/kg biochar).

Bioremediation of phenanthrene in saline-alkali soil by biochar- immobilized moderately halophilic bacteria combined with Suaeda salsa L

Polycyclic aromatic hydrocarbon (PAH) contaminated saline-alkali soil is commonly salinized and hardened, which leads to low self-purification efficiency, making it difficult to reuse and remediate. In this study, pot experiments were conducted to investigate remediation of PAH contaminated saline-alkali soil using biochar-immobilized Martelella sp. AD-3, and Suaeda salsa L (S. salsa). Reduction in phenanthrene concentration, PAH degradation functional genes, and the microbial community in the soil were analyzed. The soil properties and plant growth parameters were also analyzed. After a 40-day remediation, the removal rate of phenanthrene by biochar-immobilized bacteria combined with S. salsa (MBP group) was 91.67 %. Additionally, soil pH and electrical conductivity (EC) reduced by 0.15 and 1.78 ds/m, respectively. The fresh weight and leaf pigment contents increased by 1.30 and 1.35 times, respectively, which effectively alleviated the growth pressure on S. salsa in PAH-contaminated saline-alkali soil. Furthermore, this remediation resulted in abundance of PAH degradation functional genes in the soil, with a value of 2.01 × 10³ copies/g. The abundance of other PAH degraders such as Halomonas, Marinobacter, and Methylophaga in soil also increased. Furthermore, the highest abundance of Martelella genus was observed after the MBP treatment, indicating that strain AD-3 has a higher survival ability in the rhizosphere of S. salsa under the protection of biochar. This study provides a green, low-cost technique for remediation of PAH-contaminated saline-alkali soils.

The various effect of cow manure compost on the degradation of imazethapyr in different soil types

Adding compost to soil is an effective strategy to promote the degradation of organic pollutants and reduce ecological risks. However, the effect of compost on the degradation of imazethapyr (IMET) in different soil types is not clear. To address this issue, a pot experiment was conducted, and high-throughput sequencing and mass spectrometry technology were used to identify the influence of cow manure compost on the degradation efficiency of IMET in black soil and saline-alkali soil and the role of key microorganisms. The results showed that adding compost to black soil increased the degradation rate of IMET by 12.58% and shortened the half-life by 53.37%, while in saline-alkali soil, the degradation rate of IMET decreased by 6.99% with no significant change in the half-life. High-throughput sequencing results showed that adding cow manure compost (mass ratio of 4%) significantly increased the abundance of bacterial families capable of degrading organic pollutants in black soil, but had an inhibitory effect on this bacterial community in saline-alkali soil. Redundancy analysis (RDA) results showed that total organic carbon (TOC), alkali-hydrolyzable nitrogen (AN), ammonia nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^--N) were the main factors driving microbial community variation. Mass spectrometry analysis indicated that IMET generated three metabolites during the degradation process. Sphingomonadaceae and Vicinamibacteraceae could accelerate the breaking of side-chain alkyl groups, while Chitinophagaceae could cause the rearrangement of the imidazole ring structure, gradually metabolizing IMET into small organic molecules. The application of appropriate cow manure compost can promote the development of IMET-degrading bacteria by adjusting the organic carbon and dissolved nitrogen content in black soil. In the future, the quantitative effects of organic fertilizer application on the IMET degradation process in different soil types should be further analyzed, and microbial isolation and purification should be used to enhance the ability of microorganisms to degrade herbicides.

Nitrogen migration and transformation in a saline-alkali paddy ecosystem with application of different nitrogen fertilizers

With the increasing transformation of saline-alkali land into paddy, the nitrogen (N) loss in saline-alkali paddy fields becomes an urgent agricultural-environmental problem. However, N migration and transformation following the application of different N fertilizers in saline-alkali paddy fields remains unclear. In this study, four types of N fertilizers were tested to explore the N migration and transformation among water-soil-gas-plant media in saline-alkali paddy ecosystems. Based on the structural equation models, N fertilizer types can change the effects of electrical conductivity (EC), pH, and ammonia-N (NH₄⁺-N) of surface water and/or soil on ammonia (NH₃) volatilization and nitrous oxide (N₂O) emission. Compared with urea (U), the application of urea with urease-nitrification inhibitors (UI) can reduce the potential risk of NH₄⁺-N and nitrate-N (NO₃^--N) loss via runoff, and significantly (p < 0.05) reduce the N₂O emission. However, the expected effectiveness of UI on NH₃ volatilization control and total N (TN) uptake capacity of rice was not achieved. For organic-inorganic compound fertilizer (OCF) and carbon-based slow-release fertilizer (CSF), the average TN concentrations in surface water at panicle initiation fertilizer (PIF) stage were reduced by 45.97% and 38.63%, respectively, and the TN contents in aboveground crops were increased by 15.62% and 23.91%. The cumulative N₂O emissions by the end of the entire rice-growing season were also decreased by 103.62% and 36.69%, respectively. Overall, both OCF and CSF are beneficial for controlling N₂O emission and the potential risks of N loss via runoff caused by surface water discharge, and improving the TN uptake capacity of rice in saline-alkali paddy fields.

Integrated microbiological and metabolomics analyses to understand the mechanism that allows modified biochar to affect the alkalinity of saline soil and winter wheat growth

In order to understand the mechanism that allows modified biochar (BC) to enhance the salt tolerance and growth of crops in saline-alkali soil, we tested the effects of ordinary BC, nanoparticle-size BC, acidified BC (HBC), and acidified nanoparticle-size BC on winter wheat growth and the soil properties by combining microbiological and metabolomics analyses. The results showed that compared with the control with no BC, the plant height increased by 17.33 % under HBC and the proportion of large soil aggregates increased by 1.25-2.83 times. HBC increased the relative abundances of some dominant genera of bacteria (e.g., Streptococcus) and fungi (e.g., Mycothermus), as well as functions such as bacterial metabolic genetic information processing and cellular processes, and reduced the abundance of pathotrophic fungi. Metabolomics analysis showed that HBC upregulated various metabolites (including amino acids and their derivatives, lipids, flavonoids, and organic acids) and five main metabolic pathways. Among the KEGG pathways, the pyrimidine metabolism pathway was significantly upregulated, as well as crop leaf metabolism, β-alanine metabolism, and valine, leucine, and isoleucine metabolism, and the antioxidant levels and resistance to salt-alkali stress were enhanced in winter wheat leaves. Partial least squares-path modeling suggested that HBC affected the growth of winter wheat by significantly changing the soil physicochemical properties and microbial structure (path coefficients of 0.566 and 0.512, respectively).

Biochar improves soil quality and wheat yield in saline-alkali soils beyond organic fertilizer in a 3-year field trial

The objective of this study was to examine the effects of biochar compared to organic fertilizer on soil quality and wheat yield in the saline-alkaline lands. A 3-year field trial was conducted on moderately saline-alkaline land in the Yellow River Delta region (YRD) with six treatments: biochar (B1: 5 t, B2: 10 t, B3: 20 t ha^-1 year^-1) and organic fertilizer (OF1: 5 t, OF2: 7.5 t ha^-1 year^-1) as well as control (CK). The results showed that both biochar and organic fertilizer increased total organic carbon (TOC), total nitrogen (TN), NH₄⁺-N, and NO₃^--N, and reduced pH, thereby increasing soil microbial biomass carbon (MBC) and nitrogen (MBN), MBC/TOC ratio, and MBN/TN ratio, but organic fertilizer increased soil nutrients and microbial biomass better than biochar. Correlation analysis revealed that soil water content (SWC), soil salt content (SSC), and Na⁺ were the most important factors influencing wheat yield. When compared to CK, the SSC and Na⁺ decreased by 5.55-7.52% and 3.86-9.39%, respectively, and SWC increased by 5.14-5.62% in the biochar treatment, while they increased by 1.07-10.19%, 1.08-7.58%, and 2.96-3.84% in the organic fertilizer treatment, respectively. Accordingly, wheat yield of biochar treatment was 0.90-14.71% higher than that of organic fertilizer treatment (4.49-4.80 t ha^-1) and CK (4.47 t ha^-1). Collectively, B2 had the lowest SSC and Na⁺ and the highest yield and was significantly better than the organic fertilizer treatment, as well as efficiently increasing soil nutrients and microbial biomass, suggesting that it may be a better agricultural practice for improving soil quality and increasing wheat yield in the YRD.

Dephenolization pyrolysis fluid improved physicochemical properties and microbial community structure of saline-alkali soils

Saline-sodic soil is widely distributed around the world and has induced severe impacts on ecosystems and agriculture. Biomass pyrolysis fluid (BPF), as a substance rich in organic acids, has been proposed as a saline-alkali soil conditioner. One of the main problems with BPF applications is the potential contamination of the phenolic substances it contains. Therefore, the purpose of this study is to reduce the phenolic substances in BFP and study the improvement effect of BFP on saline-alkali soil. Firstly, we explored the physicochemical properties of BPF prepared at different temperatures (300 °C, 400 °C, 500 °C, 600 °C, and 700 °C). Then BPF was separated into upper phases (UP) and lower phases (LP) by a simple one-step salting-out extraction method. We found that phenolic substances were mainly concentrated in the UP (average content was 193.27 mg/g), and the content of phenolic substances in the LP was effectively reduced (average content was 64.52 mg/g). Next, we added the LP diluted at different times (0, 50, 100, 200, 400) into saline-alkali soil for improvement experiments. The experimental results show that the lower phase diluted 400 times at the pyrolysis temperature of 500℃ was added into saline-alkali soil, which greatly increased the content of soil available nutrients. Under the action of organic acids, soil pH (the average was 7.43) and total salt content could be reduced effectively, and soil enzyme activities can be increased. Microbial community analysis showed that the addition of LP could increase the proportion of Actinomycetes, which played a beneficial role in improving soil fertility and then improved the growth of Chinese cabbage.

Bioremediation of a saline-alkali soil polluted with Zn using ryegrass associated with Fusariumincarnatum

Biotechnological strategies have become effective in the remediation of polluted soils as they are cost-effective and do not present a risk of secondary pollution. However, using a single bioremediation technique (microorganism or plant) is not suitable for achieving a high remediation rate of polluted saline-alkali soils with heavy metals. Therefore, the present study aims to assess the effects and mechanisms of combined ryegrass and Fusarium incarnatum on the zinc (Zn)-polluted saline-alkali soil over 45 days. According to the obtained results, the combined Fusarium incarnatum-ryegrass showed the highest remediation rate of 49.35% after 45 days, resulting in a significantly lower soil Zn concentration than that observed in the control group. In addition, the inoculation of Fusarium incarnatum showed a positive effect on the soil EPS secretion. The soil protein contents ranged from 0.035 to 0.055 mg/kg, while the soil polysaccharide contents increased from 0.25 to 0.61 mg/g. The soil microbial flora and ryegrass showed resistance to saline and alkaline stresses through the secretion of extracellular polysaccharides. The three-dimensional fluorescence spectrum (3D-EEM) confirmed that EPS in the soil was mainly a fulvic acid-like substance. The fluorescein diacetate (FDA) hydrolase activity in the saline-alkali soil was first increased due to the effect of Fusarium incarnatum and then decreased to a minimum value of 96 μg/(g·h). In addition, the Fusarium incarnatum inoculation improved the diversity and richness of soil fungi. Although the Fusarium incarnatum inoculation had a slight effect on the germination of ryegrass, it increased the biomass and enrichment coefficient. The results revealed a translocation factor (TF) value of 0.316 at 45 days after ryegrass sowing, showing significant enrichment of the soil Zn heavy metal zinc in the ryegrass roots.

Functional carbon nanodots improve soil quality and tomato tolerance in saline-alkali soils

High salinity and alkalinity of saline-alkali soil lead to soil deterioration, the subsequent osmotic stress and ion toxicity inhibited crops growth and productivity. In this research, 8 mg kg^-1 and 16 mg kg^-1 functional carbon nanodots (FCNs) can alleviate the adverse effects of saline-alkali on tomato plant at both seedling and harvest stages, thanks to their up-regulation effects on soil properties and plant physiological processes. On one hand, FCNs stimulate the plant potential of tolerance to saline-alkali and disease resistance through triggering the defense response of antioxidant system, enhancing the osmotic adjustment, promoting the nutrient uptake, transportation and utilization, and up-regulating the photosynthesis, thereby improve tomato growth and productivity in saline-alkali soils. On the other hand, FCNs application contributes to the improvement of soil physicochemical properties and fertilities, as well as decline soil salinity and alkalinity, which are related to plant growth and fruit quality. This research also focuses on the dose-dependent effects of FCNs on their regulation effects and toxicity to tomato growth under stress or non-stress. These findings recommend that FCNs could be applied as potential amendments to ameliorate the saline-alkali soil and improve the tomato tolerance and productivity in the Yellow River Delta.

Elaeagnus angustifolia can improve salt-alkali soil and the health level of soil: Emphasizing the driving role of core microbial communities

Saline-alkali environments are widely distributed in China and significantly hinder the development of agriculture. This study characterizes the long-term effects of planting Elaeagnus angustifolia (E. angustifolia) on the physical and chemical properties, enzyme activities and microbial community characteristics of saline-alkali soil in the Songnen Plain (1, 2 and 3 years). The results showed that planting E. angustifolia reduced soil pH and electrical conductivity (EC) and increased soil total phosphorus (TP), total nitrogen (TN), nitrate nitrogen (Nni), total potassium (TK), dissolved organic C (DOC), dissolved organic matter (DOM) and available potassium (AK) content and catalase, urease, polyphenol oxidase, phosphatase, sucrase and cellulase enzyme activities, and the results peaked in the 3 year. High-throughput sequencing showed that the bacterial abundance and diversity were as follows (from high to low) y3 > y2 > y1 > CK. E. angustifolia resulted in an increase in the relative abundance of the dominant bacteria. Proteobacteria and Pseudomonas were the major phylum and genus, respectively. Redundancy analysis showed that changes in the soil microbial community significantly affect the physical and chemical properties of the soil, with Proteobacteria members being the key microorganisms that reduce soil salinity. Network analysis showed that Pseudomonas (Proteobacteria) participated in the synthesis of key soil enzymes. 16S rRNA sequencing predicted that the expression of genes related to carbon (rbcL, acsA, acsB, Pcc and accA) and nitrogen (amoA/B, nxrA, hao, gdh, ureC and nosZ) transformation increased, and Pseudomonas members were key regulators of carbon and nitrogen dynamics. In conclusion, the planting of E. angustifolia could improve the physical and chemical properties of the soil by releasing root exudates into the soil and increasing the diversity and richness of soil microbial communities to improve saline-alkali soil, providing a theoretical basis for improving saline-alkali soil and promoting the sustainable development of modern agriculture.

Diversity of bacterium communities in saline-alkali soil in arid regions of Northwest China

BACKGROUND

The saline-alkali soil area accounts for over 1/4-1/5 of the land area in Gansu Province of China, which are mainly distributed in the north of Hexi corridor and Jingtai basin. The unique ecological environment contains unique and diverse microbial resources. The investigation of microbial diversity in saline environment is vital to comprehend the biological mechanisms of saline adaption, develop and utilize microbial resources.

RESULTS

The Illumina MiSeq sequencing method was practiced to investigate the bacterial diversity and composition in the 5 subtypes and 13 genera of saline-alkali soil in Gansu Province, China. The results from this study show that Proteobacteria, Bacteroidetes, Actinobacteria, Firmicutes, and Gemmatimonadetes were the dominant bacterial groups in 13 saline soil. Proteobacteria had the greatest abundance in sulfate-type meadow solonchaks and orthic solonchaks, chloride-type orthic solonchaks and bog solonchaks, sulfate-chloride-type, chloride-sulfate-type, and sulfate-type dry solonchaks. Halobacteria was the dominant bacterial class in soil samples except for sulfate-type meadow solonchaks and orthic solonchaks, chloride-type orthic solonchaks and bog solonchaks. The richness estimators of Ace and Chao 1 and the diversity indices of Shannon and Simpson revealed the least diversity in bacterial community in sulfate-chloride-type orthic solonchaks.

CONCLUSIONS

The sulfate anion was the most important driving force for bacterial composition (17.7%), and the second most influencing factor was pH value (11.7%).

Evaluation of coastal farming under salinization and optimized fertilization strategies in China

Nitrogen (N) application and salinity are key factors influencing crop yield and net economic benefit in coastal saline-alkali soils. Integrated analysis and optimization of the benefits of wheat-corn cropping under different nitrogen applications in saline soils could provide lay the scientific basis for sustainable development of agriculture in coastal farmlands. A total of 571 pair-reviewed literature data on two-factor cross-over trials, involving soil salinity and nitrogen application, were integratively analyzed. Based on multi-objective optimization of crop yield, agronomic and net economic benefits, and soil nitrate residue in coastal saline-alkali soils, area-specific nitrogen application strategies were developed. The results showed that increasing the N application rate under 1.8-2.9‰ salinity can increase crop yield and economic benefits. The net economic benefit of crops was negative under 3.5‰ salinity. Above that threshold of 3.5‰, it is not suitable for planting food crops. Consequently, it is necessary to strengthen the management of saline-alkali soils. While the application rate of 2.78 × 10⁸ kg N in winter wheat/summer corn cropping ensured environmental protection, farmers preferred 3.08 × 10⁸ kg of nitrogen dose. These were respectively 40.4% and 33.9% lower than the traditional dose and with relatively higher benefits too.

Optimizing biochar application to improve soil physical and hydraulic properties in saline-alkali soils

Biochar application has been a promising approach to improve soil quality but their optimal amount in improving physical and hydraulic properties remains contradictory and inconclusive. The objective of this study was to examine and propose an optimal biochar application amount in saline alkali soil considering their impact on soil physical and hydraulic properties. A three-year field experiment was conducted in the saline-alkali soils under plastic film-mulched drip irrigation in Xinjiang, China. The studied physical and hydraulic properties included bulk density, soil porosity, saturated soil water content (θ_s), permanent wilting point (PWP), field capacity (FC), plant available water (PAW), spatial distribution of soil water content, planar soil water storage (PSWS), and soil evaporation. The treatments included biochar application amounts of 0 (CK), 10 (B10), 50 (B50), and 100 t ha^-1 (B100) in 2018. Additional two treatments with 25 t ha^-1 (B25) and 30 t ha^-1 (B30) were added in 2019 and 2020, respectively. A four-parameter Gaussian function was fitted to the single-peak curves of the studied hydraulic properties vs. biochar application amounts to determine the most optimal biochar application amount. The results indicated that: (1) All of the biochar treatments significantly decreased bulk density and increased soil porosity over CK; (2) B10 and B25 treatments significantly increased θ_s, FC, PAW, PWP, and PSWS of root zones in the film-mulched zones over CK, but reverse results were observed in the B50 and B100 treatments; (3) Daily and cumulative soil evaporation were increased in no mulch zones of all biochar treatments over CK; (4) A dose of 21.9 t ha^-1 was recommended as the most optimal biochar application amount for improving physical and hydraulic properties of saline-alkali soil. This research provided useful information on biochar application amounts for improving physical and hydraulic properties in saline-alkali soil.

Archaeal community diversity in different types of saline-alkali soil in arid regions of Northwest China

High-throughput sequencing was used to investigate the archaeal community structure and diversity, and associated influencing factors in the 5 subtypes and 13 genera of saline-alkali soil in Gansu Province, China. The results indicated the analysis of chemical parameters demonstrated statistically significant differences in these soils. Operational taxonomic units (OTUs), Chao 1, ACE, Simpson, and Shannon indexes of the archaeal community varied significantly in the 5 subtypes and 12 genera of soil except for chloride-type orthic solonchaks. The abundance was highest for sulfate-chloride-type meadow solonchaks and lowest for chloride-sulfate-type dry solonchaks. The diversity was highest for chloride-sulfate-type orthic solonchaks and lowest for sulfate-type orthic solonchaks. The archaeal community was dominated by the Euryarchaeota and Crenarchaeota. Except chloride-type orthic solonchaks; Halomicrobium in chloride-type meadow solonchaks (12.7%); Halobacterium in sulfate-chloride-type and chloride-sulfate-type dry solonchaks (11.1% and 9.2%, respectively); Candidatus Nitrososphaera in sulfate-chloride-type, chloride-sulfate-type, and sulphate-type meadow solonchaks; sulfate-type orthic solonchaks; and chloride bog solonchaks (9.0%, 21.6%, 27.0%, 45.3%, and 30.0%, respectively); Halorhabdus in sulfate-chloride-type orthic solonchaks, magnesium alkalized solonchaks, chloride-type dry solonchaks (15.7%, 11.5%, and 5.9%, respectively); and Haloarcula in chloride-sulfate-type orthic solonchaks (8.1%) were the most dominant archaea. Redundancy analysis showed that archaeal diversity was influenced by soil organic matter, total salt, sulfate anion, and zinc contents and pH. These results will lead to more comprehensive understanding of how 5 subtypes and 13 soil genera of saline-alkali soil affects microbial distribution.

Application of Vis-NIR spectroscopy for determination the content of organic matter in saline-alkali soils

Visible and near-infrared diffuse reflectance spectroscopy (Vis-NIR) has been recognized as a fast method to evaluate the content of soil organic matter (SOM) in various types of soil. The accuracy of Vis-NIR is comparable to conventional laboratory methods for estimating SOM. However, very few studies have applied Vis-NIR to estimate SOM in saline-alkali soil. This study aimed to investigate the efficiency of spectral data for evaluating SOM in saline-alkali soil. Soil samples (n = 291) were collected from the five major saline-alkali soil regions in Shaanxi. SOM was measured using standard methods and the samples were scanned using ASD Fieldspec4 at wavelength of 350-2500 nm to obtain spectral data. Twenty-six pre-processing methods were tested and partial least squares regression (PLSR) was used to estimate SOM. The best preprocessing was R + SG + SNV + FD. The calibration results were Pc = 15, Rc² = 0.92, RMSEC = 1.11, SEC = 1.12, Slope = 0.92, Offset = 0.45; the validation results were Rv² = 0.97, RPD = 5.21, RMSEP = 0.38, SEP = 0.38, Slope = 0.97, Offset = 0.17. Therefore, this main objective of the study was to propose an effective approach based on Vis-NIR spectroscopy and Chemometrics for predicting saline-alkali SOM contents in the center of Shaanxi, China.