Effects of Fe-Mn-Ce oxide-modified biochar on As accumulation, morphology, and quality of rice (Oryza sativa L.)

Microplastic Has No Effect on Rice Yield and Gaseous N Emission from an Infertile Soil with High Inorganic N Inputs

Microplastic might affect the crop yield, nitrogen (N) use efficiency and reactive N losses from agricultural soil systems. However, evaluation of these effects in infertile soil planted with different rice cultivars is lacking. We conducted a soil column experiment to determine the influence of a typical microplastic polyethylene (PE) input into an infertile soil with 270 kg N ha-1 and planted with two rice cultivars, i.e., a common rice Nangeng 5055 (NG) and a hybrid rice Jiafengyou 6 (JFY). The results showed that JFY produced a significantly (p < 0.05) greater grain yield than NG (61.6-66.2 vs. 48.2-52.5 g pot-1) but was not influenced by PE. Overall, PE hardly changed the N use efficiency of NG and JFY. Unexpectedly, PE significantly (p < 0.05) increased the total amino acid content of NG. Compared with JFY, NG volatilized significantly (p < 0.05) more ammonia (NH3) (0.84-0.92 vs. 0.64-0.67 g N pot-1) but emitted equal nitrous oxide (N2O). PE exerted no effect on either NH3 volatilization or the N2O emission flux pattern and cumulative losses of the rice growth cycle, whether with NG or JFY. Some properties of tested soils changed after planting with different rice cultivars and incorporating with microplastic. In conclusion, the rice production, N use efficiency, NH3 volatilization and N2O emission from the N-fertilized infertile soil were pronouncedly influenced by the rice cultivar, but not the PE. However, PE influenced the grain quality of common rice and some properties of tested soils with both rice cultivars.

Tuning active sites on biochars for remediation of mercury-contaminated soil: A comprehensive review

Mercury (Hg) contamination is acknowledged as a global issue and has generated concerns globally due to its toxicity and persistence. Tunable surface-active sites (SASs) are one of the key features of efficient BCs for Hg remediation, and detailed documentation of their interactions with metal ions in soil medium is essential to support the applications of functionalized BC for Hg remediation. Although a specific active site exhibits identical behavior during the adsorption process, a systematic documentation of their syntheses and interactions with various metal ions in soil medium is crucial to promote the applications of functionalized biochars in Hg remediation. Hence, we summarized the BC's impact on Hg mobility in soils and discussed the potential mechanisms and role of various SASs of BC for Hg remediation, including oxygen-, nitrogen-, sulfur-, and X (chlorine, bromine, iodine)- functional groups (FGs), surface area, pores and pH. The review also categorized synthesis routes to introduce oxygen, nitrogen, and sulfur to BC surfaces to enhance their Hg adsorptive properties. Last but not the least, the direct mechanisms (e.g., Hg- BC binding) and indirect mechanisms (i.e., BC has a significant impact on the cycling of sulfur and thus the Hg-soil binding) that can be used to explain the adverse effects of BC on plants and microorganisms, as well as other related consequences and risk reduction strategies were highlighted. The future perspective will focus on functional BC for multiple heavy metal remediation and other potential applications; hence, future work should focus on designing intelligent/artificial BC for multiple purposes.

The preparation of paddy soil amendment using granite and marble waste: Performance and mechanisms

The wastes generated from the mining and processing of granite and marble stone are generally regarded as useless. However, these waste materials were used as the soil amendments for the first time. The functional groups, crystalline structure and micro-morphology of granite and marble wastes amendments (GMWA) were different from the original wastes demonstrated by X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR) and Scanning electron microscope-energy dispersive spectrometer (SEM-EDS) analyses. With the addition of the amendments, the cation exchange capacity, electrical conductivity and nutrient availability of the soil increased, and the extractable heavy metals of the soil reduced significantly. Under the condition of the addition of 3% amendments, 7.0%, 99.9%, 99.7% and 70.5% of Cu, Pb, Zn and Cd in exchangeable fractions in soil were transformed to the more stable Fe-Mn oxides- or carbonates-bounded fractions. Tessier method and correlation analysis showed that the reduction of extractable metals in the acidic paddy soil can be attributed to the adsorption of available SiO₂, the co-precipitation induced by the elevated pH value, the complexation induced by Fe-Mn oxides and the cation exchange induced by mineral nutrients. This study provides a new strategy for resource recovery of waste stones and remediation of heavy metal-contaminated soil.

Recent advances in biochar amendments for immobilization of heavy metals in an agricultural ecosystem: A systematic review

Over the last several decades, extensive and inefficient use of contemporary technologies has resulted in substantial environmental pollution, predominantly caused by potentially hazardous elements (PTEs), like heavy metals that severely harm living species. To combat the presence of heavy metals (HMs) in the agrarian system, biochar becomes an attractive approach for stabilizing and limiting availability of HMs in soils due to its high surface area, porosity, pH, aromatic structure as well as several functional groups, which mostly rely on the feedstock and pyrolysis temperature. Additionally, agricultural waste-derived biochar is an effective management option to ensure carbon neutrality and circular economy while also addressing social and environmental concerns. Given these diverse parameters, the present systematic evaluation seeks to (i) ascertain the effectiveness of heavy metal immobilization by agro waste-derived biochar; (ii) examine the presence of biochar on soil physico-chemical, and thermal properties, along with microbial diversity; (iii) explore the underlying mechanisms responsible for the reduction in heavy metal concentration; and (iv) possibility of biochar implications to advance circular economy approach. The collection of more than 200 papers catalogues the immobilization efficiency of biochar in agricultural soil and its impacts on soil from multi-angle perspectives. The data gathered suggests that pristine biochar effectively reduced cationic heavy metals (Pb, Cd, Cu, Ni) and Cr mobilization and uptake by plants, whereas modified biochar effectively reduced As in soil and plant systems. However, the exact mechanism underlying is a complex biochar-soil interaction. In addition to successfully immobilizing heavy metals in the soil, the application of biochar improved soil fertility and increased agricultural productivity. However, the lack of knowledge on unfavorable impacts on the agricultural systems, along with discrepancies between the use of biochar and experimental conditions, impeded a thorough understanding on a deeper level.

The toxicity of heavy metals and plant signaling facilitated by biochar application: Implications for stress mitigation and crop production

Heavy metals (HMs) accumulation in soil poses a severe threat worldwide for soil, plants, and humans. The accumulation of HMs in soil and uptake by plants leads to disrupt physiological and biochemical metabolisms. As a potential and sustainable soil amendment, biochar has attained huge attention to reduce HMs toxicity in soil and improve plant growth influenced by HMs stress. Despite an array of research studies, there is a lack of knowledge on how biochar interacts with HMs, moderate plant defence system, induce HMs stress signals pathways and promote plant growth. At first, the review highlights the possible effects of HMs on soil and plant and their consequences on plant signaling network. Secondly, the biochar's impact on soil physiochemical properties and the sorption of HMs on biochar surface through direct and indirect mechanisms are reviewed. Finally, the review shows the key roles of biochar in soil improvement to enhance plant growth and signaling response to HMs by enhancing the activities of antioxidants and reducing chlorophyll injury, reactive oxygen species (ROS) accumulation, and cell membrane degradation under HMs stress. However, future studies are needed to evaluate the role of biochar in diverse climatic conditions as well as the long-term effects of biochar on HMs persistency in soil and crop productivity. This review will provide new avenues for future studies to address and quantify the advancement in biochar's role in alleviating plant's HMs stress on a sustainable basis.

Recent developments in modification of biochar and its application in soil pollution control and ecoregulation

Soil pollution has become a real threat to mankind in the 21st century. On the one hand, soil pollution has reduced the world's arable land area, resulting in the contradiction between the world's population expansion and the shortage of arable land. On the other hand, soil pollution has seriously disrupted the soil ecological balance and significantly affected the biodiversity in the soil. Soil pollutants may further affect the survival, reproduction and health of humans and other organisms through the food chain. Several studies have suggested that biochar has the potential to act as a soil conditioner and to promote crop growth, and is widely used to remove environmental pollutants. Biochar modified by physical, chemical, and biological methods will affect the treatment efficiency of soil pollution, soil quality, soil ecology and interaction with organisms, especially with microorganisms. Therefore, in this review, we summarized several main biochar modification methods and the mechanisms of the modification and introduced the effects of the application of modified biochar to soil pollutant control, soil ecological regulation and soil nutrient regulation. We also introduced some case studies for the development of modified biochars suitable for different soil conditions, which plays a guiding role in the future development and application of modified biochar. In general, this review provides a reference for the green treatment of different soil pollutants by modified biochar and provides data support for the sustainable development of agriculture.

Applications of Biochar and Modified Biochar in Heavy Metal Contaminated Soil: A Descriptive Review

Given that the problem of contaminated soil continues to grow, the development of effective control and remediation measures has become imperative, especially for heavy-metal-contaminated soil. Biochar and modified biochar are eco-friendly and cost-effective remediation materials that are widely used in the remediation of contaminated soil. This review provides an overview of the different raw materials used in the preparation of biochar as well as the modification of biochar using various synthesis methods, highlighting their differences and providing recommendations for biochar and modified biochar as applied toward ameliorating pollution in soil contaminated by heavy metals. We also explore the effects of the physicochemical properties of raw materials, pyrolysis temperature, additives, and modification methods on the properties of the resulting biochar and modified biochar, and systematically present the types of soil and operating factors for repair. Moreover, the mechanisms involved in remediation of heavy-metal-contaminated soil by biochar and modified biochar are outlined in detail, and include adsorption, complexation, precipitation, ion exchange, and electrostatic attractions. Finally, the corresponding monitoring technologies after remediation are illustrated. Future directions for studies on biochar and modified biochar in the remediation of contaminated soil are also proposed to support the development of green environmental protection materials, simple preparation methods, and effective follow-up monitoring techniques.

Arsenic contamination, impact and mitigation strategies in rice agro-environment: An inclusive insight

Arsenic (As) contamination and its adverse consequences on rice agroecosystem are well known. Rice has the credit to feed more than 50% of the world population but concurrently, rice accumulates a substantial amount of As, thereby compromising food security. The gravity of the situation lays in the fact that the population in theAs uncontaminated areas may be accidentally exposed to toxic levels of As from rice consumption. In this review, we are trying to summarize the documents on the impact of As contamination and phytotoxicity in past two decades. The unique feature of this attempt is wide spectrum coverages of topics, and that makes it truly an interdisciplinary review. Aprat from the behaviour of As in rice field soil, we have documented the cellular and molecular response of rice plant upon exposure to As. The potential of various mitigation strategies with particular emphasis on using biochar, seed priming technology, irrigation management, transgenic variety development and other agronomic methods have been critically explored. The review attempts to give a comprehensive and multidiciplinary insight into the behaviour of As in Paddy -Water - Soil - Plate prospective from molecular to post-harvest phase. From the comprehensive literature review, we may conclude that considerable emphasis on rice grain, nutritional and anti-nutritional components, and grain quality traits under arsenic stress condition is yet to be given. Besides these, some emerging mitigation options like seed priming technology, adoption of nanotechnological strategies, applications of biochar should be fortified in large scale without interfering with the proper use of biodiversity.

Enhanced arsenate removal by Fe-impregnated canola straw: assessment of XANES solid-phase speciation, impacts of solution properties, sorption mechanisms, and evolutionary polynomial regression (EPR) models

The impact of arsenic (As) contamination of water is an ongoing concern worldwide with As released from anthropogenic activities including mining and agriculture. Biosorption is a promising As treatment methodology used currently for arsenate (As(V)) sorption from water. The biosorbent was developed by a simple and inexpensive treatment of coating of canola straw particles with iron hydroxides. The modification procedure was optimized with consideration of the concentration of iron solution, pH of modification process, and sonication time. A higher concentration of iron and lower pH led to an improved sorption capacity of the iron-loaded canola straw (ICS), while impacts of sonication time were not conclusive. Pareto analyses indicated that the magnitude of the effect of the pH was higher than that of the iron concentration. Overall, the maximum As(V) sorption capacity of the ICS was 5.5 mg/g for an 0.25 M FeCl₃ solution concentration at pH 3. Analysis of kinetic data showed that the sorption processes of As(V) followed pseudo-second order and Elovich mechanisms, while sorption isotherm data were best represented by Freundlich and Temkin isotherm models. Studying the effect of ionic strength using NaCl suggested that the inner-sphere complex was the probable sorption mechanism. The thermodynamic parameters including ΔS°, ΔH°, and ΔG° showed that the As(V) sorption was thermodynamically favorable and spontaneous. Arsenic K-edge X-ray absorption near edge structure (XANES) spectroscopy indicated that no reaction to As(III) occurred during the sorption of As(V) using the optimum ICS biosorbent. The evolutionary polynomial regression (EPR) approach was able to closely match predicted vs. experimental sorption capacities (R² = 0.95). Overall, the improved understanding of the biosorbent's capability for removal of As(V) will be beneficial for assessment of its use for treatment of various water and wastewater matrices. In addition, knowledge gained from this research can assist in the understanding of sorption capacities of a variety of other biosorbents.

Effects of Fe-Mn oxide-modified biochar composite applications on phthalate esters (PAEs) accumulation in wheat grains and grain quality under PAEs-polluted brown soil

Phthalate esters (PAEs), such as dibutyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP), are used extensively as additives and plasticizers, and have become ubiquitous in the environment. PAEs in the soil could have adverse effects on crop plants as well as humans via accumulations in food chain. Thus, it is important to explore strategies to reduce the bioavailability of phthalate esters. We investigated the effects of Fe-Mn oxide-modified biochar composite (FMBC) applications on the quality of wheat grown in DBP- and DEHP-polluted brown soil. The application of FMBC and biochar (BC) increased the wheat grain biomass by 9.71-223.01% and 5.40-120.15% in the DBP-polluted soil, and 10.52-186.21% and 4.50-99.53% in the DEHP-spiked soil in comparison to the controls. All FMBC treatments were better than the BC treatments, in terms of decreasing DBP and DEHP bioavailability for the wheat grains. The activities of the glutamine synthetase and glutamic-pyruvic transaminase in the flag leaves at the filling stage and of granule-bound starch synthase, soluble starch synthase, and adenosine diphosphate-glucose pyrophosphorylase in the grains at maturity increased significantly with increases in either the BC or FMBC applications. This, in turn, increased the starch, protein, and amino acid content in the wheat grains. Compared with the BC treatment, the FMBC amendment induced only slight increases in the aforementioned factors. This study offers novel insights into potential strategies for decreasing PAEs bioavailability in soil, with potential positive implications for crop quality and environmental health improvements.