Biochar has been widely used in the fields of environment and energy, and green preparation can make biochar-based materials more environmentally friendly. Particularly, in the low-temperature pyrolysis of biochar, labile C with low biological toxicity is the main influencing factor of bacteria in soil. Therefore, it is worth studying to develop the fabrication technology of low-temperature pyrolysis biochar with rich pore structure. The mechanical effect of ultrasonic cavitation is considered to be an effective strategy for the preparation of biochar. However, the sonochemical effects on biochar remain to be studied. In this review, ultrasonic modification and ultrasonic-chemical modification on biochar has been reviewed. Metal oxide/biochar composites can also be obtained by an ultrasonic-chemical method. It is worth mentioning that there have been some reports on the regeneration of biochar by ultrasound. In addition to ultrasonic preparation of biochar, ultrasound can also trigger the sonocatalytic performance and promote the adsorption ability of biochar for the removal of harmful substances. The catalytic mechanism of ultrasound/biochar needs to be further investigated. For application, biochar prepared by ultrasound has been used for the removal of heavy metals in water, the adsorption of carbon dioxide, and soil remediation.

Proper greenhouse fertilization is crucial for establishing high-quality yields, particularly as food demand grows. In this review, the effect of fertilizers, specifically nitrogen, on greenhouses and degradation caused by nitrogen interactions are critically evaluated based on a literature analysis. Nitrogen (N) fertilizers, which represent reactive or biologically accessible nitrogen in soil, are currently used in agricultural systems. Soil, water, and air are endangered by reactive nitrogen pollution. Increasing food demand causes a rise in N fertilizer use, which harms the environment and living organisms. In developing countries, more N is used per capita than in underdeveloped countries. Greenhouse agriculture accounts for 3.6% of total agricultural production. It was revealed that greenhouses in China often get 13–17 times as much nitrogen fertilizer as traditional farming. N was overused abundantly throughout the year, which led to soil acidity, nutritional imbalance, and secondary salinization. Studies on soil salinization and secondary salinization in China date back 70 years. This review attempts to draw attention to the soil damage in greenhouses caused by excessive nitrogen. Nitrate leaching and soil acidity received special attention in this review. Numerous eco-friendly techniques for avoiding soil degradation brought on by the execessive use of fertilizer are also discussed.

Iron is a vital element for plant and microbial growth; yet, the major portion of iron in soils is in the form of (oxi-)hydroxides with limited bioavailability, resulting in decreased crop yield quality. In response to iron deficiency, soil microorganisms produce siderophores that transform insoluble iron into a soluble form that plants and microorganisms can use. The abundance and activity of siderophore-producing bacteria (SPB) might be used as a biological assessment index for the fertility status of cultivated land. In order to achieve this goal, it is critical to investigate the influences of SPB on plant growth and soil quality. In this study, we performed a mixed-effect model meta-analysis on 342 research studies that compared plant growth with and without SPB. The findings revealed that SPB increased plant growth significantly (up to 30%). The stimulating effects on plants followed the sequences of pant weight, plant height, and germination rate.

Incorporation of crop straw into the soil along with inorganic fertilization is a widespread agricultural practice and is essential in nutrient-scarce soils, such as iron-rich (ferruginous) paddy soils. The responses of soil bacterial communities to straw incorporation under different nitrogen inputs in iron-rich soils remain unclear. Therefore, 6000 kg ha⁻¹ dry wheat (Triticum aestivum L. cv. Zhengmai 12) straw was applied to a rice paddy with and without nitrogen amendment (0, 80, 300, and 450 kg ha⁻¹ N as urea), to investigate its effects on soil fertility and bacterial community structure. Organic matter, total nitrogen, and water contents tended to decrease in straw-incorporated soils with different nitrogen inputs. Proteobacteria was the dominant bacterial phylum across all treatments (26.3–32.5% of total sequences), followed by Chloroflexi, Acidobacteria, and Nitrospirae. Up to 18.0% of all the taxa in the bacterial communities were associated with iron cycling. Straw incorporation with nitrogen amendment increased the relative abundance of iron oxidizers, Gallionellaceae, while decreasing the relative abundance of iron reducers, Geobacteraceae. Bacterial community composition shifted in different treatments, with total nitrogen, water, and Fe(III) contents being the key drivers. Straw incorporation supplemented by 300 kg ha⁻¹ N increased bacterial richness and enhanced all the predicted bacterial functions, so that it is recommended as the optimal nitrogen dosage in practice.

The release of endogenous phosphorus (P) from sediments is the main cause of lake eutrophication, even after the successful control of exogenous P. Among others, the release of iron-bound P is a major source of endogenous P, and it is necessary to reduce the P concentration by enhancing iron–phosphorus binding. Iron (Fe)-modified biochar adsorption is an effective and widely used method for fixing P in sediments. In this paper, the modification method, mechanism, and application effect of Fe-modified biochar are reviewed. It is found that most of the modification methods are realized through a physicochemical pathway. Therefore, the prospect of biochar modification through a biological pathway is presented. In particular, the possible application of iron-oxidizing bacteria (IOB) for promoting iron–phosphorus binding and biochar modifications is discussed. The potential effects of biochar additions on microbial communities in water and sediments are also discussed. In the future research, emphasis should be placed on the adsorption mechanism and effect analysis in simulated polluted environments before large-scale use, to ensure the economic practicability and sustainability of Fe-modified biochar applications.