Selective Modifier-Assisted Humic Acid Extraction: Implications for Soil Quality Enhancement.

Efficient use of humic acid (HA) for eco-friendly farming and environmental remediation requires further understanding of how targeted modification of HA affects the chemical structure of HA and thereby its effectiveness in enhancing soil quality. We developed novel selective modifiers (SMs) for extracting HA by codoping sodium and copper elements into the birnessite lattice. The structure of SMs was thoroughly examined, and the HAs extracted using SMs, referred to as SMHs, were subjected to a detailed evaluation of their functional groups, molecular weight, carbon composition, flocculation limits, and effectiveness in saline soil remediation. The results showed that replacing manganese with sodium and copper in SMs alters the valence state and reactive oxygen species. In contrast, SMHs exhibited increased acidic functional groups, a lower molecular weight, and transformed aliphatic carbon. Furthermore, the saline soil was improved through increased salt leaching and an optimized soil aggregate structure by SMHs. This research highlights the importance of targeted modification of HA and demonstrates the potential of these modifiers in improving soil quality for eco-friendly farming and environmental remediation.

Effect of microplastics on soil greenhouse gas emissions in agroecosystems: Does it depend upon microplastic shape and soil type?

Microplastics have emerged as a significant pollutant in terrestrial ecosystems, with their accumulation in agricultural fields influencing soil greenhouse gas emissions. Nevertheless, the specific impact of microplastics, particularly in relation to their varying shapes, and how this effect manifests across diverse soil types, remains largely unexplored. In this study, a 56-day incubation experiment was conducted to assess the influence of microplastic shapes (fibers, films, and spheres) on CO2 and N2O emissions in three types of soils (Chernozems, Luvisols, and Ferralsols), while also investigating potential associations with the compositional and functional characteristics of soil bacterial communities. When compared to the control group, the introduction of microplastic fibers resulted in an increase of 21.7 % in cumulative CO2 emissions and a 31.4 % rise in cumulative N2O emissions in Ferralsols. This increase was closely linked to the proliferation of the Actinobacteria and Bacilli classes and the orders of Catenulisporales, Bacillales, Streptomycetales, Micrococcales, and Burkholderiales within the bacterial communities of Ferralsols, alongside an observed elevation in N-acetyl-glucosaminidase enzyme activity. The inclusion of microplastic fibers did not result in significant alterations in greenhouse gas emissions within Chernozems and Luvisols. This is likely attributed to the inherent buffering capacity of these soils, which helps stabilize substrate and nutrient availability for microbial communities. These findings highlight that the response of greenhouse gas emissions to microplastic additions is contingent upon the shape of the microplastics and the specific soil types.

Effects of microbial diversity loss on the stability of CO2 production and N2O emission in agricultural soils.

The relationship between biodiversity and ecosystem stability is a hot topic in ecology. However, current studies focus mainly on aboveground system with plants, little attention has been paid to belowground system with soils. In this study, we constructed three soil suspensions with varying microbial diversity (100, 10-2, 10-6) by the dilution method and inoculated separately into agricultural Mollisols and Oxisols to examine the stability (indicated by resistance and resilience) of soil CO2 production and N2O emission to copper pollution and heat stress. Results showed that the stability of CO2 production in Mollisols was not influenced by microbial diversity loss, while the resistance and resilience of N2O emission in Mollisols were significantly decreased at the 10-6 diversity. In the Oxisols, the resistance and resilience of N2O emission to copper pollution and heat stress started to decrease even at the 10-2 diversity, and the stability of CO2 production decreased at the 10-6 diversity. These results suggested that both soil types and the identity of soil functions influenced the relationship between microbial diversity and the stability of function. It was concluded that soils with ample nutrients and resistant microbial communities tend to have higher functional stability, and that the fundamental soil functions (e.g., CO2 production) are more resistant and resilient than the specific soil functions (e.g., N2O emission) in response to environmental stress.

Effects of microplastic type on growth and physiology of soil crops: Implications for farmland yield and food quality.

Microplastic residues pose one of the most serious environmental problems in areas where plastic mulch is used extensively. Microplastic pollution has potentially serious consequences for ecosystems and human health. Several studies have analyzed microplastics in greenhouses or laboratory climate-controlled chambers; however, field studies evaluating the effects of different microplastics on different crops in extensive farming are limited. Therefore, we selected three major crops, Zea mays (ZM, monocotyledon), Glycine max (GM, dicotyledon, aboveground-bearing), and Arachis hypogaea (AH, dicotyledon, belowground-bearing) and investigated the effect of adding polyester microplastics (PES-MPs) and polypropylene microplastics (PP-MPs). Our results demonstrate that PP-MPs and PES-MPs decreased the soil bulk density of ZM, GM, and AH. Regarding soil pH, PES-MPs increased the soil pH of AH and ZM, whereas PP-MPs decreased the soil pH of ZM, GM, and AH compared to controls. Intriguingly, different coordinated trait responses to PP-MPs and PES-MPs were observed in all crops. In general, commonly measured parameters of AH, such as plant height, culm diameter, total biomass, root biomass, PSII maximum photochemical quantum yield (Fv/Fm), hundred-gain weight, and soluble sugar tended to decrease under PP-MPs exposure; however, some indicators of ZM and GM increased under PP-MPs exposure. PES-MPs had no obviously adverse influence on the three crops, except for the biomass of GM, and even significantly increased the chlorophyll content of AH, specific leaf area, and soluble sugar of GM. Compared with PES-MPs, PP-MPs have serious negative effects on crop growth and quality, especially AH. The findings of the present study provides evidence for evaluating the impact of soil microplastic pollution on crop yield and quality in farmland and lay a foundation for future investigations on the exploration of MP toxicity mechanisms and adaptability of different crops to microplastics.

Soil Microbial Co-Occurrence Patterns under Controlled-Release Urea and Fulvic Acid Applications.

The increasing amount of agricultural applications of controlled-release urea (CRU) and fulvic acids (FA) demands a better understanding of FA's effects on microbially mediated nitrogen (N) nutrient cycling. Herein, a 0-60 day laboratory experiment and a consecutive pot experiment (2016-2018) were carried out to reveal the effects of using CRU on soil microbial N-cycling processes and soil fertility, with and without the application of FA. Compared to the CRU treatment, the CRU+FA treatment boosted wheat yield by 22.1%. To reveal the mechanism of CRU+FA affecting the soil fertility, soil nutrient supply and microbial community were assessed and contrasted in this research. From 0-60 days, compared with the CRU treatment, leaching NO3--N content of CRU+FA was dramatically decreased by 12.7-84.2% in the 20 cm depth of soil column. Different fertilizers and the day of fertilization both have an impact on the soil microbiota. The most dominant bacterial phyla Actinobacteria and Proteobacteria were increased with CRU+FA treatment during 0-60 days. Network analysis revealed that microbial co-occurrence grew more intensive during the CRU+FA treatment, and the environmental change enhanced the microbial community. The CRU+FA treatment, in particular, significantly decreased the relative abundance of Sphingomonas, Lysobacter and Nitrospira associated with nitrification reactions, Nocardioides and Gaiella related to denitrification reactions. Meanwhile, the CRU+FA treatment grew the relative abundance of Ensifer, Blastococcus, and Pseudolabrys that function in N fixation, and then could reduce NH4+-N and NO3--N leaching and improve the soil nutrient supply. In conclusion, the synergistic effects of slow nutrition release of CRU and growth promoting of FA could improve the soil microbial community of N cycle, reduce the loss of nutrients, and increase the wheat yield.

Coated Diammonium Phosphate Combined With Humic Acid Improves Soil Phosphorus Availability and Photosynthesis and the Yield of Maize.

Controlled release phosphorus (P) fertilizers and humic acid (HA) applications are two effective and significant techniques or measures for preventing P loss and enhancing maize development. However, the underlying physiological mechanism of how the controlled release P fertilizers combined with HA affect the maize production and P-use efficiency (PUE) remains unknown. The effects of applying coated diammonium phosphate (CDAP) and HA together on soil nutrient supply intensity, soil phosphatase activity, photosynthesis, endogenous hormone contents, and yield of maize, as well as PUE, were examined in this study. In a pot experiment, two types of P fertilizers-CDAP and diammonium phosphate (DAP)- as well as two HA application rates (0 and 45 kg ha-1) and two P levels (60 and 75 kg P2O5 ha-1) were utilized. Results showed that the key elements that influence the growth and yield of the maize were the availability of P content in soil, plant photosynthesis, and hormone levels. The combination of CDAP and HA had a greater impact on yield and PUE over the course of 2 years than either DAP alone or DAP combined with HA. Besides, using CDAP in combination with HA increased the yield and PUE by 4.2 and 8.4%, respectively, as compared to the application of CDAP alone at 75 kg P2O5 ha-1. From the twelve-leaf to milk stages, the available P content in the soil was increased by an average of 38.6% with the combination of CDAP and HA compared to the application of CDAP alone at 75 kg P2O5 ha-1. In addition, the application of CDAP combined with HA boosted the activities of ATP synthase, as well as the content of cytokinin (CTK), and hence improved the maize photosynthetic rate (Pn). When compared to the application of CDAP alone or DAP combined with HA, the Pn of CDAP + HA treatments was enhanced by 17.9-35.1% at the same P rate. In conclusion, as an environmentally friendly fertilizer, the combined application of CDAP and HA improved the intensity of the soil nutrient supply, regulated photosynthetic capabilities, and increased the yield and PUE, which is important for agricultural production, P resource conservation, and environmental protection.

Effects of boric acid on urea-N transformation and 3,4-dimethylpyrazole phosphate efficiency.

BACKGROUND: 3,4-Dimethylpyrazole phosphate (DMPP) is a nitrification inhibitor which can restrict nitrate (NO3 - ) production. Boric acid is a substance which inhibits urease activity. However, few studies have focused on the inhibitory effect of boric acid on urea hydrolysis and the possible synergistic effect with DMPP. Thus, an incubation trial was conducted to determine the impact of boric acid and DMPP addition on urea-N transformation, and their synergistic effects, in chernozem soil (Che) and red soil (RS). Four treatments were set up in each soil: urea only (U); urea combined with DMPP (UD); urea combined with boric acid (UB); and urea combined with both DMPP and boric acid (UDB). RESULTS: Compared to U, adding DMPP (UD) increased NH3 emissions by 11% and 13% and decreased soil NO3 - -N concentration by 38% and 13% in Che and RS, respectively. Boric acid addition (UB) effectively prolonged the half-life time of urea by 0.8 and 0.4 days, reduced NH3 volatilizations by 11% and 16% and delayed the occurrence of NH3 emission peaks for 3 and 4 days in contrast to U treatment in Che and RS, respectively. UDB treatment mitigated the NH3 volatilizations caused by the addition of DMPP (UD) by 16% and 29% in Che and RS, respectively. Additionally, a better nitrification inhibition rate was found in the UDB treatment compared to other treatments in both soils. CONCLUSIONS: There is potential to develop a new N transformation inhibition strategy with the use of a combination of boric acid and DMPP. © 2020 Society of Chemical Industry.

Effects of poly-γ-glutamic acid (γ-PGA) on plant growth and its distribution in a controlled plant-soil system.

To demonstrate the responses of plant (Pakchoi) and soil to poly-γ-glutamic acid (γ-PGA) is essential to better understand the pathways of the promotional effect of γ-PGA on plant growth. In this study, the effects of γ-PGA on soil nutrient availability, plant nutrient uptake ability, plant metabolism and its distribution in a plant-soil system were tested using labeled γ-PGA synthesized from 13C1-15N-L-glutamic acid (L-Glu). γ-PGA significantly improved plant uptake of nitrogen (N), phosphorus (P), and potassium (K) and hence increased plant biomass. γ-PGA greatly strengthened the plant nutrient uptake capacity through enhancing both root biomass and activity. γ-PGA affected carbon (C) and N metabolism in plant which was evidenced with increased soluble sugar contents and decreased nitrate and free amino acids contents. About 26.5% of the γ-PGA-N uptake during the first 24 h, after γ-PGA application, was in the form of intact organic molecular. At plant harvest, 29.7% and 59.4% of γ-PGA-15N was recovered in plant and soil, respectively, with a 5.64% of plant N nutrition being derived from γ-PGA-N. The improved plant nutrient uptake capacity and soil nutrient availability by γ-PGA may partly explain the promotional effect of γ-PGA, however, the underlying reason may be closely related to L-Glu.