Modification directions of agricultural waste biochars to improve their effectiveness as amendments for degraded soils

With over 140 billion tons of agricultural waste generated yearly, its management has become a critical issue posing economic and environmental concerns. The waste conversion into biochar (BC) provides a sustainable solution, that is, a promising material for various applications such as carbon sequestration, pollution remediation, and soil regeneration. The latest research has contributed significantly to the development of innovative techniques of biochar (BC) modification that go beyond conventional pyrolytic processing of biomass. These treatments usually increase textural parameters and surface chemistry of BC, thereby enhancing its ability to bind various species. High adsorption capacity makes it an effective carrier for nutrients essential for crops or an efficient immobilizer limiting availability of toxic compounds. So far, it was noted that modified BC has a satisfied impact on soil aeration, water retention, and growth of soil microorganisms, stimulating overall agroecosystem functionality. However, its effectiveness depending on soil type is not fully understood and difficult to predict, which is why modified BC use by farmers is limited and troublesome. Taking this into account, the review indicates the effects of BC modification on particular soil types, highlighting the most beneficial ones. The authors identified poor features of pristine BC and showed the most effective treatment increasing its performance as a soil conditioner. A roadmap was also presented to optimize the use of modified BC in addressing the issues of soil degradation, climate change, and agricultural waste management, along with suggestions for new research directions and ways to integrate modified BC with sustainable practices.