Phosphorus (P) is essential for basic natural processes and can limit the productivity of entire ecosystems. However, agricultural lands worldwide currently suffer from P deficiency. The application of P fertilizers is not only poorly utilized, but also results in the gradual accumulation of P. Biochar, a substance produced by the pyrolysis of biomass under low oxygen levels, is frequently used as a soil amendment. It provides P in a form that is readily available for plant uptake, and thus addresses both short- and long-term soil P deficiencies. In this paper, we systematically reviewed relevant studies on “biochar and soil” or “biochar and soil P” published in the past decade (2013–2023). A synthesis of the reported results revealed that analyzing the effect of biochar on soil P through changes in soil physicochemical properties and microbial communities has gradually emerged as a prominent area of research in recent years. The purpose of this study was to analyze the differential effects of biochar addition on soil P availability, including the clarification of the underlying mechanisms. The results showed that although biochar application generally exerts a positive effect on soil P availability, there are differences in the extent of effects based on application conditions. Shifting to mechanisms, biochar application not only directly increases the available phosphorus (AP) content of soil, but also indirectly influences soil P availability via changes in soil physical, chemical, and biological properties. To summarize, biochar application can affect soil P availability to different degrees through direct or indirect pathways. Graphical Abstract

Soil ecosystems are under serious threat from microplastics (MPs), and this is causing worldwide concern. The relationship between soil and MPs has become a popular research topic, and the vertical migration of soil MPs is of increasing interest. This Review summarizes the current status of research into the factors affecting the vertical migration of soil MPs. Published research shows that the characteristics of MPs and the physicochemical properties of the soil affect the infiltration process. Soil organisms play a key role in the vertical migration by acting as vectors or as a result of adsorption. Dissolved organic matter and metal oxides transfer MPs by adsorption-desorption. In addition, rainfall and dry-wet cycles alter the mobility of soil MPs, leading to changes in migration processes. Agricultural activities such as tillage and irrigation may distribute MPs throughout the topsoil. Vertical migration of soil MPs is a process influenced by a combination of factors, and the role of these factors in MP deposition needs to be explored further.