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Purpose: This study aims to evaluate the effects of chitosan and D-fructose 1,6-bisphosphate (F16BP) trisodium salt on the acidity of selected Ultisols (Ultisol-QY1, Ultisol-QY2, Ultisol-LX, and Ultisol-YT) and their resistance to soil acidification. Materials and methods: The effect of adsorbed chitosan and F16BP on soil acidity was evaluated by interacting different concentrations of the organic substrates with 4.0 g soil under different agitation times (2 to 264 h, 200 rpm, 25 °C). Also, the soils were amended with the organic substrate and incubated for 14 days to determine their effects on soil physicochemical properties. Afterwards, the soil solid phases from the adsorption studies and incubated soil were acidified with different concentrations of nitric acid to simulate soil acidification and activate soil aluminum (Al). Results and discussion: The adsorption interactions of chitosan and F16BP with Ultisols demonstrated different potentials in their ability to displace mineral-bound hydroxyl groups and ameliorate soil acidity. The R-PO43− group of F16BP was more effective in displacing the hydroxyl groups through a ligand exchange mechanism and thus showed greater ameliorating effect on soil acidity than chitosan. Compared to lime and F16BP, chitosan-treated soils exhibited the least decrease in pH during soil acidification due to the significant improvement in soil pH buffering capacity (pHBC). Specifically, when amended with chitosan, the pHBC of Ultisol-QY1, Ultisol-QY2, Ultisol-LX, and Ultisol-YT was increased by 262.2%, 88.9%, 337.7%, and 320.6% as opposed to 22.1%, 18.4%, 27.4%, and 83.0% for these Ultisols by F16BP, respectively. Thus, F16BP is a better material to improve soil pH, while chitosan is a better option to improve soil pHBC, inhibit soil acidification, and retard the activation of phytotoxic Al3+. By the nature of their functional groups, we deduced that F16BP ameliorated soil acidity by displacing the hydroxyl groups on soils due to adsorption of R-PO43− group through ligand exchange mechanism, while chitosan directly improved pHBC by providing abundant R-NH2 groups to accommodate excess exogenous H+. Conclusions: Chitosan is a promising soil amendment material for use in the management of acidic soils due to its high N content and potential to inhibit soil acidification. Given the readily available raw materials and ease of producing chitosan, long-term incubation studies should be carried out to assess the effect of chitosan on soil pH variations, carbon, and N mineralization. [ABSTRACT FROM AUTHOR]

Biochar research has experienced a significant increase in the recent two decades. It is growing quickly, with hundreds of reviews, including meta-analyses, that have been published reporting diverse effects of biochar on soil properties and plant performance. However, an in-depth synthesis of biochar–soil interactions at the molecular level is not available. For instance, in many meta-analyses, the effects of biochar on soil properties and functions were summarized without focusing on the specificity of the biochar and soil properties. When applied to soils, biochar interacts with different soil components including minerals, organic matter, gases, liquids, and nutrients, while it also changes soil microbial community structure and their occurrence. These different interactions modify soil physicochemical properties with consequences for dynamic changes in nutrient availability and, thus, plant performance. This review systematically analyzed biochar effects on soil properties and functions: (a) soil physical properties; (b) chemical properties; (c) biological properties; and (d) functions (plant performance, nutrient cycling, etc.). Our synthesis revealed that the surface properties of biochar (specific surface area and charge) and its associated nutrient content determine its role in the soil. At the same time, the extent of changes depends on soil properties, suggesting that both biochar and soil properties need to be considered for harvesting benefits of biochar application. Altogether, we believe our synthesis will provide a guide for researchers and practitioners for future research as well as large-scale field applications. [ABSTRACT FROM AUTHOR]

This study reports the mitigating strategy against salinity by exploring the potential effects of biochar (5%), Arbuscular mycorrhizal fungi (20 g/pot, AMF), and biochar + AMF on maize (Zea mays L.) plants grown under saline stress in a greenhouse. The maize was grown on alkaline soil and subjected to four different saline levels; 0, 50, 100, and 150 mM NaCl. After 90 d for 100 mM NaCl treatment, the plant's height and fresh weight were reduced by 17.84% and 39.28%, respectively, compared to the control. When the saline-treated soil (100 mM NaCl) was amended with AMF, biochar, and biochar + AMF, the growth parameters were increased by 22.04%, 26.97%, 30.92% (height) and 24.79%, 62.36%, and 107.7% (fresh weight), respectively. Compared to the control and single AMF/biochar treatments, the combined application of biochar and AMF showed the most significant effect in improving maize growth under saline stress. The superior mitigating effect of biochar + AMF was attributed to its effective ability in (i) improving soil nutrient content, (ii) enhancing plant nutrient uptake, (iii) increasing the activities of antioxidant enzymes, and (iv improving the contents of palmitoleic acid (C16:1), oleic acid (C18:1), linoleic acid (C18:2), and linolenic acid (C18:3). Thus, our study shows that amending alkaline and saline soils with a combination of biochar-AMF can effectively mitigate abiotic stress and improve plant growth. Therefore, it can serve as a reference for managing salinity stress in agricultural soils. [ABSTRACT FROM AUTHOR]

The dual role of biochar for inhibiting soil acidification induced by nitrification was determined through two-step incubation experiments in this study. Ca(OH) 2 or biochar was added respectively to adjust soil pH to the same values (pH 5.15 and 5.85), and then the amended soils were incubated in the presence of urea for 70 days. The results showed that compared with Ca(OH) 2 treatment, both rice straw biochar and peanut straw biochar inhibited the decrease in soil pH and the increase in exchangeable acidity during the incubation. The application of biochars suppressed soil nitrification during the incubation, and thus reduced 7.5 mmol kg−1 and 1.4 mmol kg−1 protons released from nitrification compared to Ca(OH) 2 treatments. Compared with Ca(OH) 2 treatment, the ammonia-oxidizing bacteria population size was decreased by 8% and 12% in rice straw biochar and peanut straw biochar treatments respectively, which was the main responsibility for the inhibited nitrification after biochar application. In addition, the application of rice straw biochar and peanut straw biochar increased soil pH buffering capacity (pHBC) respectively by 22% and 32%. The increased pHBC played the main role (75%) in inhibiting the acidification of the soil amended with peanut straw biochar, while the rice straw biochar inhibited soil acidification mainly through suppressing nitrification during the incubation. Overall, compared with lime application, biochars can inhibit soil acidification caused by urea application through suppressing the nitrification process and improving the resistance of soils to acidification. The crop residue biochars presented a longer-lasting effect on ameliorating acidic soils than mineral lime. Image 1 • Biochar played a dual role in inhibiting soil acidification from nitrification. • Biochar decreased proton release through suppressing soil nitrification. • Biochar increased soil pH buffering capacity and the resistance to acidification. • Biochar would be a better option to ameliorate acidic soils than liming. [ABSTRACT FROM AUTHOR]

Biochar can effectively alleviate the Al phytotoxicity in acidic soils due to its alkaline nature. However, the longevity of this alleviation effect of biochar under re-acidification conditions is still unclear. In the present study, the maize root growth responding to the simulated re-acidification of two acidic soils amended by peanut straw biochar or Ca(OH) 2 was investigated to evaluate the long-term effect of biochar on alleviating Al toxicity in acidic soils. Compared with Ca(OH) 2 amendment, the application of biochar significantly retarded Al toxicity to plant during soil re-acidification. When 4.0 mM HNO 3 was added, the maize seedling root elongation in an Oxisol with biochar was 99% higher than that in the Oxisol with Ca(OH) 2. Also, the Evans blue uptake and Al content in the root tip in the biochar treatment were 60% and 51% lower than those in the Ca(OH) 2 treatment. The retarding effect was mainly attributed to the slow decrease in soil pH during acidification and the release of dissolved organic carbon (DOC) in the soils amended by biochar. The slower decrease in soil pH resulting from the increased pH buffering capacity after biochar application inhibited the increase of soluble and exchangeable Al during re-acidification. The increased DOC after biochar application decreased the toxic soluble Al speciation at the same pH value and total Al concentration in soil solution. Therefore, given the re-acidification of soils, biochar presented a longer-term effect on alleviating Al toxicity of acidic soil than liming. Unlabelled Image • Biochar retarded the Al toxicity to plant during soil re-acidification. • Biochar decreased the concentration of soil active Al during soil re-acidification. • Biochar altered the distribution of Al speciation in soil solution. • Biochar presented a long lasting effect on alleviating Al toxicity in acidic soils. [ABSTRACT FROM AUTHOR]