Revamping highly weathered soils in the tropics with biochar application: What we know and what is needed.

Fast weathering of parent materials and rapid mineralization of organic matter because of prevalent climatic conditions, and subsequent development of acidity and loss/exhaustion of nutrient elements due to intensive agricultural practices have resulted in the degradation of soil fertility and productivity in the vast tropical areas of the world. There is an urgent need for rejuvenation of weathered tropical soils to improve crop productivity and sustainability. For this purpose, biochar has been found to be more effective than other organic soil amendments due to biochar's stability in soil, and thus can extend the benefits over long duration. This review synthesizes information concerning the present status of biochar application in highly weathered tropical soils highlighting promising application strategies for improving resource use efficiency in terms of economic feasibility. In this respect, biochar has been found to improve crop productivity and soil quality consistently through liming and fertilization effects in low pH and infertile soils under low-input conditions typical of weathered tropical soils. This paper identifies several advance strategies that can maximize the effectiveness of biochar application in weathered tropical soils. However, strategies for the reduction of costs of biochar production and application to increase the material's use efficiency need future development. At the same time, policy decision by linking economic benefits with social and environmental issues is necessary for successful implementation of biochar technology in weathered tropical soils. This review recommends that advanced biochar strategies hold potential for sustaining soil quality and agricultural productivity in tropical soils.