## 5 Challenges and Opportunities
### Application of Biochar Return to Field  
With a growing global population and limited arable land, restoring soil quality to nonproductive soils is critical to future food production, food security, and energy supply. Biochar may help in this attempt [138]. Biochar has qualities comparable to those of activated carbons but is far less expensive. Biochar has the potential to be utilized as a renewable and sustainable sorbent to remove contaminants from the soil due to its high surface-to-volume ratio and large surface area (as shown in Figure 1). However, the processes governing the fate and behavior of organic pollutants in the environment, particularly pesticides in biochar-amended soil, are poorly known [139]. To optimize the advantages of biochar in soil settings, the methods by which biochar interacts with soil components should be further investigated [140]. This will provide insight into the effect of biochar on soil ecology and biogeochemical processes. The specific processes of contaminant-biochar retention and release over time, as well as the environmental impact of biochar additions on soil organisms, remain unknown [141]. How and to what degree biochar can alter pollutant transit and fate in the environment is uncertain. Soil pollutants, herbicides, and minerals must be stabilized and bioavailable using charcoal. This will enable the construction of biochar with specified physicochemical features and help manage the released pollutants. Biochar is not without its environmental dangers, such as pollutant release, biota toxicity, and impact on global carbon fluxes and contaminant movement [140].  
While these are valid concerns, physical, chemical, and biological treatments can affect the effectiveness of biochar [142].  
Biochar offers several advantages in forest soils, especially in low-fertility plantation soils [143; 144]. Due to its unusual structure and remarkable physicochemical qualities, biochar has shown promise as a compost ingredient. It improves physicochemical and nutritional characteristics, reduces bioavailability, and removes resistance genes from compost. Biochar increases fertilizer utilization efficiency and water retention capacity in soil. Straw is a readily available biomass with a global production surpassing 3.97 billion tons per year [102; 145]. Among all biochar types, straw biochar was shown to be the best compost supplement [102]. Crop straw direct burning in the field which will cause serious air pollution is prohibited in China. Returning crop straw without direct burning to the field may aggravate the occurrence of various crop diseases. The direct straw return to the field will be transformed into a technical chain of \"collection and storage-carbonization-productization-return to the field\". Based on carbonization technology, through the industrialization and large-scale application of carbon-based agricultural inputs, farmland soil carbon sequestration will be realized, greenhouse gas emission will be reduced, and full quantitative utilization of straw and the improvement of farmland quality will be promoted. Straw-derived biochar returning to the field for emission reduction and sequestration of carbon technology, as one of ten major technical projects of the Ministry of Agriculture and Rural Affairs, China in 2021, will provide a great opportunity for biochar application for remediation of pesticide-contaminated soils. With the continuous application of pesticides, the contamination of soil by pesticides will continue to occur. However, whether repeated biochar return to pesticide-contaminated fields will cause long-term adverse effects on the soil ecosystem is still unknown.