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The properties of biochar determine its ability to alleviate soil acidity and improve plant growth; however, its key properties remain unclear. Therefore, the purpose of this study was to screen the key characteristics of biochar that strongly influence soil acidity and plant growth to obtain a better estimation of biochar characteristics that is suitable for acid soil amelioration. Pak choi was selected as the experimental plant in this pot trial. Soil acidity and pak choi biomass were used to estimate the effect of biochar derived from different organic wastes on acid soil amelioration. Pearson’s correlation combined with a random forest model analysis was applied to investigate the relationship between the characteristics of biochar and soil acidity or plant growth. The results showed that the presence of biochar altered the soil pH by − 0.2 to 1.7 unit and pak choi biomass yield by − 6% to 314%. The Ca, Mg, and P contents (importance = 34.6%), basic surface functional groups, and BET surface area significantly affected the soil acidity. The properties of biochar, including the Fe content, dissolved organic carbon (DOC), electrical conductivity (EC), and micropores, played pivotal roles in promoting pak choi growth, and the importance of the above properties reached to 53.9% according to random forest model analysis. In addition, all biochars used in this study improved soil fertility by 48.26–113.04%, and the comprehensive benefits of pak choi improved by 34.14–180.11%, especially for sheep dung biochar and bone powder biochar. Biochars with rich pores, abundant Ca, Mg, P, and Fe, high DOC and EC, and basic surface functional groups are favorable for acid soil improvement and pak choi growth. Applying biochar to acid soils may be a promising way to improve the comprehensive benefits of soil fertility and vegetable production.

Cadmium (Cd) and lead (Pb) contaminated soils that are used for food production can lead to metal bioaccumulation in the food chain and eventually affect human health. In these agroecosystems, means by which Cd and Pb bioavailability can be reduced are desperately required, with biochar as a proxy for bioavailability reductions. Molecular Cd and Pb sorption mechanisms within short- (0–2 years) or long-term (8–10 years) time periods following biochar application to a contaminated rice paddy soil were investigated. A combination of Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and soft X-ray imaging was utilized to discern potential metal sorption mechanisms. Following both short- and long-term biochar applications, soil Cd and Pb bioavailable fractions shifted partially towards metal (hydr)oxide and carbonate precipitates, and partially towards biochar-organic function group associations; oxygen-containing groups, such as C=O and O–H, appeared to bind Cd and Pb. Soft X-ray imaging results suggested that heavy metals were primarily sorbed on biochar exterior surfaces, yet given time and particle disintegration, metals sorbed onto biochar interior pore walls. Findings suggest that biochar may play a pivotal role in reducing long-term bioavailable Cd and Pb in contaminated soils. Observations also support previous findings that suggest biochar use can lead to reduced heavy metal transfer to plants and potentially to reduced heavy metal consumption by humans.

The production of ginseng, an important Chinese medicine crop, has been increasingly challenged by soil degradation and pathogenic disease under continuous cropping in Northeast China. In a field experiment, an Alfisol garden continuously cropped with Chinese ginseng (Panax ginsengC. A. Meyer) was treated with soil amendment at 20 t ha−1with maize (MB) and wood (WB) biochar, respectively, compared to conventional manure compost (MC). Two years after the amendment, the rooted topsoil and ginseng plants were sampled. The changes in soil fertility and health, particularly in the soil microbial community and root disease incidence, and in ginseng growth and quality were portrayed using soil physico-chemical assays, biochemical assays of extracellular enzyme activities and gene sequencing assays as well as ginsenoside assays. Topsoil fertility was improved by 23% and 39%, ginseng root biomass increased by 25% and 27%, and root quality improved by 6% and 18% with WB and MB, respectively, compared to MC. In the ginseng rhizosphere, fungal abundance increased by 96% and 384%, with a significant and insignificant increase in bacterial abundance, respectively, under WB and MB. Specifically, the abundance of Fusariumspp. was significantly reduced by 19–35%, while that of Burkholderiaspp. increased by folds under biochar amendments over MC. Relevantly, there was a significant decrease in the abundance proportion of pathotrophic fungi but a great increase in that of arbuscular mycorrhizal fungi, along with an enhanced microbial community network complexity, especially fungal community complexity, under biochar amendments. Thus, biochar, particularly from maize residue, could promote ginseng quality production while enhancing soil health and ecological services, including carbon sequestration, in continuously cropped fields.Graphical Abstract