Showing papers on "Humic acid published in 2019"

Humic Acid Fertilizer Improved Soil Properties and Soil Microbial Diversity of Continuous Cropping Peanut: A Three-Year Experiment

Abstract: Although humic acid has been demonstrated to improve the quality of some soil types, the long-term effects of humic acid on soil under continuous cropping peanut are not fully understood. This study aimed to investigate the continuous effects of humic acid on the physicochemical properties, microbial diversity, and enzyme activities of soil under continuous cropping peanut. In this study, a three-year consecutive experiment of cropping peanut was conducted in the North China Plain. In addition to the equal nitrogen, phosphorus, and potassium inputs, humic acid treatment was applied with inorganic fertilizers. Compared with control experiments, humic acid increased the yield and quality of continuous cropping peanut. To elucidate the mechanism of humic acid affecting the soil quality, various soil quality indicators were evaluated and compared in this study. It was found that humic acid increased soil nutrient contents, including the total soil nitrogen, total phosphorus, total potassium, available nitrogen, available phosphorus, available potassium, and organic matter contents, which exhibited the maximum effect in the third year. Meanwhile, the urease, sucrase, and phosphatase activities in the soil significantly increased after treated with humic acid, of which the maturity period increased most significantly. The same results were observed for three consecutive years. Microbial diversity varied considerably according to the high throughput sequencing analysis. Specifically, the number of bacteria decreased while that of fungi increased after humic acid treatment. The abundance of Firmicutes in bacteria, Basidiomycota, and Mortierellomycota in fungi all increased, which have been reported as being beneficial to plant growth. In contrast, the abundance of Ascomycota in fungi was reduced, and most of the related genera identified are pathogenic to plants. In conclusion, humic acid improved the yield and quality of continuous cropping peanut because of improved physicochemical properties, enzymatic activities, and microbial diversity of soil, which is beneficial for alleviating the obstacles of continuous cropping peanut.

Environmental and Agricultural Relevance of Humic Fractions Extracted by Alkali from Soils and Natural Waters

Abstract: To study the structure and function of soil organic matter, soil scientists have performed alkali extractions for soil humic acid (HA) and fulvic acid (FA) fractions for more than 200 years. Over the last few decades aquatic scientists have used similar fractions of dissolved organic matter, extracted by resin adsorption followed by alkali desorption. Critics have claimed that alkali-extractable fractions are laboratory artifacts, hence unsuitable for studying natural organic matter structure and function in field conditions. In response, this review first addresses specific conceptual concerns about humic fractions. Then we discuss several case studies in which HA and FA were extracted from soils, waters, and organic materials to address meaningful problems across diverse research settings. Specifically, one case study demonstrated the importance of humic substances for understanding transport and bioavailability of persistent organic pollutants. An understanding of metal binding sites in FA and HA proved essential to accurately model metal ion behavior in soil and water. In landscape-based studies, pesticides were preferentially bound to HA, reducing their mobility. Compost maturity and acceptability of other organic waste for land application were well evaluated by properties of HA extracted from these materials. A young humic fraction helped understand N cycling in paddy rice ( L.) soils, leading to improved rice management. The HA and FA fractions accurately represent natural organic matter across multiple environments, source materials, and research objectives. Studying them can help resolve important scientific and practical issues.

The influence of the quantity and quality of sediment organic matter on the potential mobility and toxicity of trace elements in bottom sediment.

Abstract: Knowledge on the fraction of trace elements in the bottom sediments is a key to understand their mobility and ecotoxicological impact. The purpose of this study was to assess the influence of the content of organic matter fractions on the mobility and ecotoxicity of trace elements in sediments from the Rybnik reservoir. The most refractory fraction of organic matter—Cnh (non-hydrolysing carbon)—dominated in the sediments. The content of organic matter fractions are arranged in the following order: Cnh (non-hydrolysing carbon) > Cfa (fulvic acid) > Cha (humic acid) > DOC (dissolved organic carbon). On the other hand, the highest value of correlation coefficients was found for different fractions of trace elements and DOC content in the bottom sediments. A higher content of TOC in the sediments significantly increased the share of elements in the potential mobile fraction and, at the same time, decreased the binding of elements in the mobile fractions. Moreover, in sediments that contain more than 100 g/kg d.m. TOC, no and medium risk of trace element release from sediments was observed. The Cu, Cd and Ni were potentially the most toxic elements for biota in the Rybnik reservoir. However, the correlation between the content of trace elements and the response of bacteria was insignificant. These results suggested that the complexation of trace elements with organic matter makes them less toxic for Vibrio fischeri. The transformation and sources of organic matter play an important role in the behaviour of trace elements in the bottom sediments of the Rybnik reservoir.

Kinetic study of the biodegradation of glyphosate by indigenous soil bacterial isolates in presence of humic acid, Fe(III) and Cu(II) ions

Abstract: The present study was executed to investigate the kinetics of the biodegradation of glyphosate in an aqueous medium. Three bacterial strains (Streptomyces sp., Bacillus subtilis, and Rhizobium leguminosarum) with excellent glyphosate-degrading capabilities were isolated from the agricultural soils and characterized on the basis of 16S ribosomal RNA (rRNA) gene sequencing methods. Biodegradation of glyphosate was performed with and without applications of metal ions [Fe(III) and Cu(II)] and humic acid (HA). In thirty days experiment, three strains were utilized 85-90% (with half life periods from 8.36 to 9.12 days) of glyphosate. Applications of Fe(III) and Cu(II) have inhibited the biodegradation to 70-80% (with half life periods from 10.03 to 11.15 days). In the presence of HA, biodegradation was inhibited significantly (57-70%) with half life periods from 12.54 to 13.09 days. Overall, glyphosate’s biodegradation inhibition order under different conditions was as HA > Cu(II) > Fe (III). UV-visible and mass spectrometric results indicated two concurrent pathways of degradation of glyphosate with major metabolites included glycine, aminomethylphosphonic acid (AMPA), sarcosine, glyoxylate, metaphosphoric acid and phosphate. Glyphosate breakdown by these three strains was achieved by the C-P lyase and the glyphosate oxidoreductase activity. Hence, these strains could be used as potential biological agents in the effective biodegradation campaign for other pesticide-contaminated sites.

Magnetic zirconium-based metal-organic frameworks for selective phosphate adsorption from water.

Abstract: Although adsorbents can effectively remove phosphate from water, most are difficult to separate from water and their phosphate removal efficiencies are adversely affected by coexisting anions or humic acid. Here, a magnetic core–shell composite with Fe3O4 as the core and carbon as the shell (denoted as MFC) was functionalized with a metal–organic framework, UiO-66, and its phosphate adsorption ability was studied. The composite (denoted as MFC@UiO-66) was effectively separated from water within 1 min under an external magnetic field. The kinetics of phosphate adsorption onto MFC@UiO-66 was controlled by the intraparticle diffusion process, suggesting that the Zr in UiO-66 played an important role in phosphate adsorption. The isotherm for phosphate adsorption onto MFC@UiO-66 was well described by the Freundlich model. The adsorbent exhibited higher affinity toward phosphate than toward coexisting anions (e.g., Cl−, NO3−, and SO42−), reflecting high phosphate adsorption selectivity. The adsorption affinity of MFC@UiO-66 to phosphate increased with the increasing temperature, but decreased with increasing pH. The presence of dissolved humic acid negligibly affected phosphate adsorption onto MFC@UiO-66 because of its size-exclusion effects. The used adsorbent was easily regenerated with NaOH solution, and the sorbent displayed stable phosphate adsorption behavior after five regeneration cycles.