A Review of the Negative Effects of Biochar on Soil in Green Infrastructure with Consideration of Soil Properties

Biochar, valued for its high carbon content, nutrient supplement and porosity, has gained extensive usage as a soil enhancer. While many studies highlight its benefits like improving soil water retention and nutrient availability, some studies reveal unintended negative impacts on soil properties such as reducing soil strength and water-holding capacity. These findings raise concerns regarding biochar’s effectiveness in green infrastructure. This study comprehensively reviews the side effects of biochar on soil properties including soil strength, pH balance, cation exchange capacity, nutrient availability, and water retention within the context of green infrastructure. Biochar application affects soil properties, with optimal rates enhancing soil strength but excessive rates diminishing it, especially in silt and sandy soils. Notably, over-application of biochar can also elevate soil pH beyond the ideal range for crops, impacting nutrient availability and potentially reducing soil fertility and crop yields. Biochar’s hydrophobicity, dictated by its feedstock and pyrolysis temperature, can increase soil water repellency and reduce water retention ability. Additionally, excessive biochar can clog soil pores and absorb vital nutrients like phosphorus, manganese and calcium, hindering water and nutrient exchange and thereby restricting growth of vegetation. Moreover, while excessive biochar negatively impacts soil cation exchange capacity (CEC) by capturing key cations, biochar from pretreated biomass can improve CEC without causing alkalization. This study emphasizes the necessity for a thorough understanding of biochar’s impact on soil properties to provide a holistic perspective on its role within green infrastructure systems.