Humic Research Articles

Restoring degraded lands: the role of sewage sludge in modulating soil carbon and nitrogen dynamics

Sewage sludge presents significant amounts of organic matter and nutrients and is frequently considered an alternative input for recovering degraded soils. In this scenario, this study aimed to evaluate the impacts of disposing of increasing doses of sewage sludge on the dynamics of C and N in the soil of a degraded area. After the application of five doses of sewage sludge (0, 50, 100, 200, and 400 t ha-1) were evaluated over time (30, 90, 180, 270, and 360 days), the contents of soil C and N, microbial biomass, light organic matter, and humic fractions of soil organic matter. The results showed that sewage sludge contributed to the quality and recovery of degraded soil by providing increases in soil organic C, total N, nitrate, and ammonia contents, microbial biomass C and N, light organic matter, as well as in the C and N stocks in humic substances, especially in humin. Most of the increases in these variables associated with C and N dynamics remained even one year after the application of sewage sludge. The soil quality improvement demonstrates the potential of using sewage sludge in projects to recover degraded areas as an alternative for its final disposal.

Soil Recycling of Waste Biomass in the Production of Malus domestica Fruit Tree Seedlings

The production of fruit tree seedlings generates waste wood biomass, which results from the pruning of budded rootstocks in the first year of the two-year production cycle. This study proposes a new method of managing this biomass by recycling the wood chips (2, 3 and 5 t ha−1) back into the soil. The impact of different wood chip doses on selected physicochemical soil properties after the production process (especially soil organic carbon content (SOC), as well as the quantity and quality of the produced Malus domestica fruit tree seedlings, was determined. The recycling of waste biomass contributed to enriching the soil with additional components, mainly organic carbon with the potential for biotransformation into humic substances. The applied doses of wood chips, in amounts of 2, 3, and 5 t ha−1, resulted in an increase in SOC content compared to the control by 21.5%, 22.5%, and 35.8%, respectively. Additionally, the recycling of waste biomass introduced other compounds important for plant growth and development into the soil, particularly iron, zinc, magnesium, and manganese. It should be noted that the proposed method of managing waste biomass generated during the apple tree seedling production stage resulted in reduced production costs while maintaining high production indices.

A highly capacitive Graphene/Multiholed N‐CNTs hybrid evolved from black humate‐Co‐melamine precursor

Black humic acid (BA) is a black mixture of organic macromolecules isolated from humic acid, which has a greater potential for graphene transformation than fulvic acid and ulmic acid because of more and larger aromatic units and higher molecular weights exceeding 5000 Dalton. Here, chemically bonded BA‐Co‐Melamine precursors are initially constructed using different BA fractions as substrate, Co2+ as bridge bond and melamine as ligand. A series of Graphene/N‐CNTs hybrids (GNCs) is eventually synthesized after the precursor pyrolysis. Resultantly, Fraction Ⅰ, separated at a pH value of 4.16, plays a significant role on constructing the BA‐Co‐Melamine precursor and further producing multiholed GNCs. Due to abundant CNTs, rich mesopores, moderate nitrogen incorporation and a certain graphitized assembly structure, the prepared GNC‐Ⅰ‐b has high capacitance performances. The assembled AC//GNC‐Ⅰ‐b supercapacitor has high specific capacitance (147 F g‐1 at 0.5 A g‐1), rate capability, cycling stability and energy density (16.8 Wh kg‐1 at 14.4 KW kg‐1). The 2032 coin‐type Li//GNC‐Ⅰ‐b half‐cell has high initial discharge capacity (759 mAh g‐1 at 0.03 A g‐1), initial Coulombic efficiency (81.8%), rate performance and cycling stability. Hence, the GNC is a favorable high‐performance carbon material hopefully applied as electrode materials of supercapacitors and LIBs.

Effects of chemical fertilizer with rice straw on the carbon compositions of tobacco-planting soil

This study explored the changes in carbon components of tobacco-planting soil by the application of rice straw as organic materials to replace chemical fertilizers partially. Flue-cured tobacco was applied to the soil as base fertilizer to investigate the mineralization of soil organic carbon during its growing period. At 0 d, the humic acid carbon (HA-C), humin carbon (HM-C), HU ratio, PQ value and HM-C/(HA-C + FA-C) are 31.67, 31.40, 60.05, 28.01 and 27.75%, respectively which is higher than those of chemical fertilizer alone. At 30 d, the humus carbon (HE-C), HA-C, and fulvic acid carbon (FA-C) were 29.41, 20.97 and 30.49%, respectively. At 90 d, the A2920/1630 values were 227.43 and 232.32% higher than chemical fertilizer. Application of rice straw and decomposed rice straw with less fertilizer can increase the content of soil organic matter, HA-C, HM-C and FA-C in the tobacco-planting soil. This method increases the content of aliphatic chain hydrocarbons and reduces the amount of aromatic carbon, thus increasing aliphatic properties and decreasing the aromatic properties of soil. The treatment with chemical fertilizer reduction with decomposed rice straw also accelerates the formation and accumulation of stable components such as humic acid and humin and significantly improves the humification of soil humus. Bangladesh J. Bot. 53(3): 811-822, 2024 (September) Special

Clay Minerals/TiO2 Composites—Characterization and Application in Photocatalytic Degradation of Water Pollutants

TiO2 used for photocatalytic water purification is most active in the form of nanoparticles (NP), but their use is fraught with difficulties in separation from solution or/and a tendency to agglomerate. The novel materials designed in this work circumvent these problems by immobilizing TiO2 NPs on the surface of exfoliated clay minerals. A series of TiO2/clay mineral composites were obtained using five different clay components: the Na-, CTA-, or H-form of montmorillonite (Mt) and Na- or CTA-form of laponite (Lap). The TiO2 component was prepared using the inverse microemulsion method. The composites were characterized with X-ray diffraction, scanning/transmission electron microscopy/energy dispersive X-ray spectroscopy, FTIR spectroscopy, thermal analysis, and N2 adsorption–desorption isotherms. It was shown that upon composite synthesis, the Mt interlayer became filled by a mixture of CTA+ and hydronium ions, regardless of the nature of the parent clay, while the structure of Lap underwent partial destruction. The composites displayed high specific surface area and uniform mesoporosity determined by the size of the TiO2 nanoparticles. The best textural parameters were shown by composites containing clay components whose structure was partially destroyed; for instance, Ti/CTA-Lap had a specific surface area of 420 m2g−1 and a pore volume of 0.653 cm3g−1. The materials were tested in the photodegradation of methyl orange and humic acid upon UV irradiation. The photocatalytic activity could be correlated with the development of textural properties. In both reactions, the performance of the most photoactive composites surpassed that of the reference commercial P25 titania.

Higher Stability of Soil Organic Matter near the Permafrost Table in a Peatland of Northeast China

Understanding the stability of soil organic matter (SOM) is essential for making accurate predictions regarding carbon release rates. However, there is limited information on the role of chemical composition of dissolved organic matter (DOM) in SOM stability. To address this gap, the peatland soil profile in the discontinuous frozen soil region of Northeast China was selected as the focus of this research, and a comprehensive analysis was conducted on the differences between the molecular composition of DOM and the stability of SOM. The results indicate a significant carbon accumulation phenomenon near the permafrost table. Through analyses using TG-50, δ13C, and δ15N, it was determined that SOM near the permafrost table exhibits high stability, whereas SOM within the permafrost layer demonstrates poor stability. Investigations utilizing UV-vis, 3D-EEM, FT-IR, and 1H-NMR technologies revealed that DOM near the permafrost table is of high quality and highly aromatic. Furthermore, compared to near the permafrost table, humic acid materials in the permafrost layer decreased by 17%, while protein materials increased by 17%. These findings offer a novel perspective on the understanding of SOM stability in peatland soil profiles within discontinuous permafrost regions.

Insight into the co-hydrothermal humification of corn stalk and sewage sludge for enhanced nitrogen-rich humic acid production

Insight into the co-hydrothermal humification of corn stalk and sewage sludge for enhanced nitrogen-rich humic acid production

Impact of humic acid on iron (oxyhydr)oxide transport in the presence of phosphate in saturated porous media

The subsurface flow of particular phosphate (P) has been recently regarded as a vital P transport path. Humic acid (HA) and P usually coexist in the natural environment and show a strong affinity to iron (Fe) (oxyhydr)oxide. The impact of P and HA on Fe (oxyhydr)oxide stability and transport is critical for evaluating the vertical transport of particular P and biogeochemical processes of Fe and P. This study investigated the effect of inorganic (IP) and organic (OP) phosphate on the stability and transport of ferrihydrite and goethite with HA through stability tests and column experiments. The adsorption of IP or OP on Fe (oxyhydr)oxide enhanced the stability and transport of Fe (oxyhydr)oxide, and OP showed a stronger enhancement than IP due to its stronger binding capacity and more negative surface. Compared with ferrihydrite, goethite had fewer adsorption sites for IP or OP and showed strong stability and transport at low IP (50 μM) or OP (10 μM) concentration. HA decreased IP or OP adsorption on Fe (oxyhydr)oxide through competition adsorption and electrostatic repulsion. The formed ternary phosphate-Fe (oxyhydr)oxide-HA complex showed a more negative surface and strong stability and transport. Our findings provide direct insights into the distinct role of IP and OP on Fe (oxyhydr)oxide stability and transport in the presence of HA, which provides essential information for evaluating the transport of particular Fe (oxyhydr)oxide-facilitated P in soils and subsurface environments rich in iron, phosphate, and dissolved carbon.

The role of the application of nanosilver and humic acid on the physiological and yield traits of corn (Zea Mays L.) under deficit irrigation conditions

Water deficit is the most common abiotic stress and at least 75% of corn fields in Iran are exposed to drought stress during different stages of growth. humic acid (HA) and nanosilver (NS) can help mitigate abiotic stresses in plants; especially drought stress. A field experiment was conducted to study the effect of humic acid and nanosilver on the physiological traits and yield of corn during two crop years. Experimental treatments were including deficit irrigation (100%, 80%, 60% of crop water requirement (CWR)) and nanosilver (0 (NS0), 60 (NS60), 80 (NS80) and 100 (NS100) microliters/liter/ha) and humic acid (control (HA0), 500 (HA500) and 1000 (HA1000) g/ha). The highest amount of chlorophyll a, b and total in 100% CWR+NS60+HA1000 was obtained. The highest amount of proline in 60% CWR + NS60 +HA1000 as well as treatment NS0 +HA1000 were observed. In all irrigation levels, the application of NS100 has reduced chlorophyll a and total. The yield components were affected by HA and nanosilver foliar spraying. The highest grain yield was observed in 100% CWR with the application of NS60 +HA500 at the rate of 10,582 kg/ha. In conditions of 100% CWR, nanosilver concentrations had a positive effect on plant growth and yield, and with increasing stress, high concentrations of nanosilver had a negative effect on growth and yield, but with the combined application of nanosilver and HA, the effect of drought stress decreased, which indicates the positive effect of HA in improving plant growth and yield.

Lysozyme coupling protease pretreatment to relieve the humic acid inhibition on excess sludge anaerobic fermentation

The asynchronous dosed protease and lysozyme combination pretreatment was proved to be effective in enhancing the anaerobic fermentation of waste activated sludge (WAS). However, humic acid (HA) in the sludge could interact with hydrolase and restrain the hydrolysis efficiency, thus inhibiting short-chain fatty acids (SCFAs) production. This study investigated the effectiveness and mechanism of enzymatic pretreatment against HA. Results showed that the enzyme cocktail method increased the extracellular bioavailable contents by 34 %, which raised SCFAs production by 89.69 % (1269.65 mg COD /L). The balanced ratio of hydrolysis and fermentation communities suggested that the small molecular organics generated by the hydrolysis community could be sufficiently utilized by fermentation communities. The metabolism of amino acids and glucose was facilitated, and the activities of key enzymes were enhanced. These results clarified the effect of asynchronous enzyme cocktail pretreatment against HA inhibition and contributed to SCFAs production, which offered fresh perspectives on carbon recovery.

The role of fulvic acid in feeding heifers of reproductive age in the conditions of the Novgorod region

Many domestic and foreign researchers have drawn attention to humic and fulvic acids, which are successfully used in animal husbandry, poultry farming and aquaculture. In search of new ways to increase livestock productivity, as well as the quality of livestock products, the number of scientific studies on the use of humic substances of various origins in animal husbandry has increased significantly, which emphasizes the role of feed additives obtained from local resources. In the article the effectiveness of the use of fulvic acid in the diets of young cattle is presented. Experimental studies were conducted in the Ilyich Agricultural Cooperative of the Starorussky district of the Novgorod region on heifers of the Holstein breed of Dutch breeding older than a year (repair heifers of reproductive age). The animals of the control group consumed a nutritionally balanced basic diet (HR), the first experimental group – HR + fulvic acid (10 ml/head / day), the second experimental group - HR + fulvic acid (15 ml/head /day), 10 heads in each group. As a result of the conducted studies, the positive effect of the use of fulvic acid in the diets of young animals was determined, its effect on the digestibility of nutrients in diets, biochemical parameters of blood, reproductive function was studied, the optimal dose of fulvic acid feeding in this age period was determined. The use of fulvic acid in the diet of young animals allowed to increase the absorption of nutrients from the diet, improve blood biochemical parameters, and improve the reproductive qualities of heifers by 15.5–20.2 %. The results obtained allow us to recommend fulvic acid for use in the diets of repair heifers of reproductive age on farms in the Northwestern region in the amount of 10 ml per head per day.

Preparation of artificial humic acid from corn straw and its high-efficiency adsorption on norfloxacin

In this study, the biomass artificial humic acid (AHA) with efficient adsorption performance for norfloxacin (NOR) was prepared by ultrasonic-assisted acid-alkaline combined hydrothermal method with corn straw as raw material. Characterization analysis showed that AHA was a typical amorphous structure, and the oxygen content of AHA prepared by ultrasonic-assisted hydrothermal method was obviously improved compared with that without ultrasonic-assisted method. The saturated adsorption capacity of AHA was 551.53 mg/g, which was higher than that of other reported materials, such high-efficiency adsorption is due to the abundant oxygen-containing groups (–OH, –C=O, etc.) in AHA, which were functional groups that can be π-π stacked, hydrogen bonded and electrostatically bonded with NOR. It had good selective adsorption for NOR, with less interference from acidity of environmental water, coexisting inorganic ions and common antibiotics. When it was applied to adsorb NOR with concentration of 10.0 mg/L in simulated water prepared by environmental water, the highest removal rate was 91%, which indicated that AHA could not only remove all the NOR in the polluted water with complex components at the highest concentration of 630 μg/L, but also its adsorption capacity far exceeded the pollution amount. The research had important practical significance in realizing the recycling of agricultural wastes and the removal of environmental pollution.

Efficient Degradation of Ofloxacin by Magnetic CuFe2O4 Coupled PMS System: Optimization, Degradation Pathways and Toxicity Evaluation.

Magnetic CuFe2O4 was prepared with the modified sol-gel method and used for enhanced peroxymonosulfate (PMS) activation and ofloxacin (OFL) degradation. The OFL could almost degrade within 30 min at a catalyst dosage of 0.66 g/L, PMS concentration of 0.38 mM, and initial pH of 6.53 without adjustment, using response surface methodology (RSM) with Box-Behnken design (BBD). In the CuFe2O4/PMS system, the coexisting substances, including CO32-, NO3-, SO42-, Cl- and humic acid, have little effect on the OFL degradation. The system also performs well in actual water, such as tap water and surface water (Mei Lake), indicating the excellent anti-interference ability of the system. The cyclic transformation between Cu(II)/Cu(I) and Fe(III)/Fe(II) triggers the generation of active radicals including SO4•-, •OH, •O2- and 1O2. The OFL degradation pathway, mainly involving the dehydrogenation, deamination, hydroxylation, decarboxylation and carboxylation processes, was proposed using mass spectroscopy. Moreover, the toxicity assessment indicated that the end intermediates are environmentally friendly. This study is about how the CuFe2O4/PMS system performs well in PMS activation for refractory organic matter removal in wastewater.

Composted biochar versus compost with biochar: effects on soil properties and plant growth

Biochar is widely recognized as an amendment that enhances soil properties and sequesters carbon, particularly in degraded soils. However, biochar applied solely to soil may also hinder plant development due to toxic by-products generated during pyrolysis or nutrient retention. To mitigate these adverse effects, it has been suggested to either mix biochar with compost or to process it by composting with fresh organic materials. To date, there is a lack of comparative studies evaluating the performance of these two approaches. In this study, three types of biochar, differing in their initial feedstocks (beech wood, hornbeam/beech/oak mixture, and digestate/cereal straw mixture), were investigated. These biochars were applied solely, mixed with green waste compost, or processed as composted biochar in two soils of different fertility (a Luvisol and a gleyic Fluvisol). A pot experiment was conducted under controlled conditions where lettuce was grown for three months. After harvesting, plant biomass, and soil microbial and physicochemical properties were measured. Composted biochar and compost additives maintained a neutral soil pH, contrary to biochar applied solely or mixed with compost. The dissolved organic carbon and total nitrogen were higher in composted biochar treatments, leading to a higher proportion of humified material with a high degree of condensed aromatic groups compared to other treatments. Microbial activities were higher in the composted biochar treatments compared to those in the compost with biochar, and more specifically in the less fertile Luvisol. Finally, composted biochar increased plant growth by almost six times compared to the control without amendments, whereas the mix of biochar and compost increased it by only three times. Solely applied biochars did not affect lettuce growth. This study demonstrates that biochar composting is more beneficial than mixing biochar with compost in terms of improving soil fertility and mitigating the negative effects associated with pure biochar application.Graphical

Fulvic Acid Enhances Nitrogen Fixation and Retention in Paddy Soils through Microbial-Coupled Carbon and Nitrogen Cycling.

Fulvic acid, the most soluble and active humic substance, is widely used as an agent to remediate contaminated soils and improve soil fertility. However, the influence of fulvic acid (FA), as a microbial carbon source, on carbon and nitrogen cycles in paddy soils remains elusive. Therefore, to investigate it, an incubation experiment was conducted. Gas analyses indicated that the carbon dioxide and methane emissions were enhanced in FA treatment, which increased up to 94.08-fold and 5.06-fold, respectively. 15N-labeling experiments revealed that nitrogen fixation capability was promoted (1.2-fold) to reduce the carbon and nitrogen imbalance due to fulvic acid amendment. Metagenomic analysis further revealed that gene abundances of degradation of lignin-like compounds, gallate degradation, methanogenesis, nitrogen fixation, and urea hydrolysis increased, while the bacterial ammonia oxidation and anaerobic ammonium oxidation decreased, caused by FA application. Metabolic reconstruction of metagenome-assembled genomes revealed that Azospirillaceae, Methanosarcinaceae, and Bathyarchaeota, with higher abundance in FA treatment, were the key microorganisms to maintain the carbon and nitrogen balance. The metabolic pathways of fulvic acid degradation and coupled nitrogen fixation and retention were constructed. Collectively, our results provided novel insights into the theoretical basis of the use of humic substances for reducing nitrogen fertilization and climate change.

Ultraviolet/dielectric barrier discharge enhanced ultrafiltration for treating natural water: Performance, mechanism and iodinated disinfection by-product fate

This study employed ultraviolet (UV)/ dielectric barrier discharge (DBD) pre-treatment to mitigate ultrafiltration membrane fouling and enhance the purification efficiency of natural surface water. Moreover, as an emerging contaminant, the iodinated disinfection by-products’ fate and degradation performance were discussed. The investigation revealed that the generation of numerous active species (⋅OH, ⋅O2−, 1O2, etc) under high input voltage and low pH conditions were advantageous for augmenting membrane flux, with sodium sulfate electrolyte playing a role in promoting the formation of selective sulfate radicals. Fluorescence excitation-emission matrix spectroscopy indicated that the UV/DBD system at 5.5 kV can effectively degrade proteins and humic substances in surface water, leading to an enhancement in water quality. With the assistance of UV radiation, macromolecular organic matter underwent extensive decomposition into smaller molecules, thus creating an ideal environment for controlling membrane fouling in the UV/DBD system. Additionally, it was identified the intermediate products and degradation pathways during iopamidol degradation by UV/DBD. It also affirmed the minimal risk of disinfection by-product generation with this strategy. The study provides a viable and efficient pre-treatment approach for mitigating membrane fouling and purifying water.

Fast On-Site Speciation and High Spatial Resolution Imaging of Labile Arsenic in Freshwater and Sediment Using the DGT-SERS Sensor.

Diffusive gradients in thin films (DGT) technique is renowned for in situ passive sampling but not for rapid on-site analysis, whereas surface-enhanced Raman spectroscopy (SERS) excels in ultrasensitive on-site detection but is limited by substrate contamination from complex matrices. Here, a hierarchical nanostructure of silver (Ag) mirror-supported large Ag nanoparticles (∼120 nm) was grown in situ in polyacrylamide hydrogel with a restricted pore size (PAM/Ag mirror/AgNPs) to serve as both the DGT binding phase and the SERS substrate. The substrate exhibited a maximum electric field enhancement factor of 9.9 × 108 and a signal relative standard error of 4.8%. Using the DGT-SERS sensor, As(III) and As(V) in freshwater were simultaneously detected at limits of 0.9 and 0.8 μg L-1, respectively, applicable across a wide range of environmental conditions. The DGT-SERS effectively mitigated the interfacial reduction of As(V) caused by humic acid by excluding it from plasmonic hotspots through size exclusion of the diffusive layer. The Raman analysis of a DGT sample in the field requires only 2 s using a portable spectrometer without DGT device disassembly. More importantly, the DGT-SERS captured the first two-dimensional image of As(III) and As(V) in one DGT at the micron scale resolution, revealing their spatially supplementary distribution patterns at the sediment-water interface. This study paves the way for next-generation speciation imaging DGT and the application of SERS in complex environments.

Weak magnetic field for enhanced degradation of sulfamethoxazole by the CoFe2O4/PAA system: Insights into performance and mechanism

In this work, a novel approach coupling a heterogeneous weak magnetic field (WMF) with the CoFe2O4/peroxyacetic acid (PAA) system was employed to enhance the degradation of sulfamethoxazole (SMX). Under the optimized conditions of 50 mT WMF, 0.1 g/L CoFe2O4, 0.2 mM PAA, and initial pH 6.0, a complete degradation of 10 μM SMX was achieved in 25 min, exhibiting a high synergistic coefficient of 1.61. This result indicates a significant synergistic effect among WMF, CoFe2O4, and PAA in effectively degrading SMX. The introduction of WMF did not alter the pH application range of the CoFe2O4/PAA system. Furthermore, the degradation efficiency of SMX by the CoFe2O4/PAA/WMF system was significantly reduced in the presence of humic acid (HA) and bicarbonate ions (HCO3−), while chloride ions (Cl−) exhibited a minor inhibitory effect. Quenching experiments and electron paramagnetic resonance (EPR) analysis reveal that WMF did not alter the types of reactive oxygen species (ROS) generated in the CoFe2O4/PAA system. The degradation of SMX in the CoFe2O4/PAA/WMF system involved both radical (CH3C(O)O∙ and CH3C(O)OO∙) and non-radical (1O2) oxidation pathways, driven by the redox cycling between ≡Co2+/≡Co3+ and PAA, as well as the rapid adsorption and transformation of oxygen (O2) at oxygen vacancies (OV), respectively. The presence of WMF enhanced the utilization of PAA by CoFe2O4 by improving the convection and mass transport in the solution, facilitating the formation of superoxide anion (O2∙−) and supplemented lattice oxygen (O2−) through the directional migration of paramagnetic O2 towards the CoFe2O4 surface, thus significantly promoting ROS formation. Additionally, the degradation pathways of SMX in the CoFe2O4/PAA/WMF system were proposed based on density functional theory (DFT) calculations and the detected transformation products (TPs). The toxicity of SMX was effectively reduced, as verified by predictions from the Ecological Structure-Activity Relationship Model (ECOSAR) procedure. The excellent catalytic performance, reusability, and effective degradation of various organic pollutants demonstrated by the CoFe2O4/PAA/WMF system suggest its potential as a promising strategy for water treatment.

Characteristics and Influencing Factors of Soil and Crops Selenium Content in Eastern Sanjiang Plain

Too identify seleniut（Se） content characteristics and influencing factors in soil and crops of Shengli Farm in eastern Sanjiang Plain, statistical analysis and correlation analysis were comprehensively used to analyze the test results of 83 groups of surface soil samples and 34 groups of crop seed samples. The results showed that the Se content in the study area ranged from 0.12 to 0.95 mg·kg-1, with an average value of 0.37 mg·kg-1, and the enrichment degree was stronger with an enrichment coefficient of 3.18. Oxidizable Se was the main Se fraction, accounting for 81%, 79%, 79%, and 80% of T-Se in marsh soil, white soil, dry land, and paddy field, respectively. The content of reducible Se was the lowest, accounting for less than 5%. The effects of soil physicochemical indexes on Se content differences mainly showed that Se was negatively correlated with pH and total potassium （TK） and significantly positively correlated with cation exchange capacity （CEC）, soil organic matter （SOM）, humus （HS）, total nitrogen （TN）, and total phosphorus （TP）. The average content of Se in different land use types was as follows： dryland > irrigated land > grassland > forest land, as the dryland soil with low pH and high SOM was more likely to enrich Se. Among different soil types, the average Se content in gleysols was the highest at 0.45 mg·kg-1, which was higher than the average value in the study area. The average content of Se in the quaternary alluvial layer was the highest at 0.43 mg·kg-1, and its parent material mainly consisted of lacustrine sediments rich in organic matter, which was one of the important factors in forming Se rich soil. The Se content in crops and root soil showed a negative correlation. Se in low pH or high SOM soil was not easily absorbed by crops, and its Se content was also controlled by the form of soil Se, which was positively correlated with available Se content and negatively correlated with oxidizable Se content. Therefore, it is suggested to reduce the amount of artificial fertilizer used in cultivated land as a means of increasing Se bioavailability to change the current situation of crop Se levels in this area.

Stand-alone and combined effects of protein hydrolysate and humic-like substances derived from waste materials on the growth, physiology and mineral nutrition of tea nursery plants

Stand-alone and combined effects of protein hydrolysate and humic-like substances derived from waste materials on the growth, physiology and mineral nutrition of tea nursery plants