# Agricultural Waste-Based Biochar for Agronomic Applications
## 7 Limitations  
Although the majority of research studies reported beneficial aspects of biochar use as a soil amendment, others reported insignificant or sometimes negative results, giving rise to some apprehension regarding its large-scale and long-term application. The availability of biochar could be a limitation to its application; biochar may not be sufficiently available to reach significant positive results. Furthermore, the positive impact of biochar has been reported to be soil-specific; its application may not be beneficial for all types of soil [256, 257]. Other problems related to biochar application were also reported. [PERSON] et al. [258] recorded an increase in weed growth by 200% during lentil culture after biochar application at a rate of 15 t/ha. The effect of biochar on crop productivity varies depending on the plant species and the target part of the plant. [PERSON] et al. [259] observed no fruit yield of tomato plants after the addition of biochar at 14 t/ha, while an increase in vegetative growth was recorded. A delay in flowering for plants was also observed because of biochar addition to the soil [260]. Biochar may also be selective, and in some cases its addition does not import any immobilization effect towards some contaminants in soil [261]. The higher ash content of biochars produced at high temperatures may also induce detrimental effects on plants growth [262]. Another limitation of biochar amendment is its ability to adsorb essential nutrients for plant growth and then act as a competitor, which can be counterproductive to crop productivity [263; 264]. For instance, the addition of biochar and phosphorous fertilizer in saline sodic soil promotes the precipitation/sorption reactions of phosphate and thus reduce the availability of phosphorous for plants [149]. Addition of biochar in soils may also cause a disturbance in organic matter decomposition, which may decrease the abundance of fungi species such as Ascomycota and Basidiomycota [265]. Other inconsistent effects may also occur depending on the biochar starting feedstock. In the study performed by [PERSON] et al. [266], soils treated by coconut husk biochar at 30 t/ha allowed for an improvement of the Zea mays biomass by about 90%, while no significant effect was observed with orange bagasse biochar applied at the same rate. The application of biochar derived from some nutrient-poor biomasses may also limit their efficiency in improving crop productivity, which may require its combined application with compost or some chemical or organic fertilizers. Additionally, some feedstock used for biochar preparation may contain contaminant substances, which in turn affect plant growth [267]. Unless a good number of studies prove that these limitations can be overcome, the future of biochar for agricultural applications may be uncertain [154]. Crucial examination of all factors should be performed to prevent any potential detrimental effects of biochar that can limit its large-scale application. More research is after all needed to explore all mechanisms and to assess the long-term risk of biochar agronomic applications.