Maximizing crop yield and water productivity through biochar application: A global synthesis of field experiments

Abstract

Thus far, a series of field experiments have been conducted across the globe to investigate the effects of biochar on crop productivity. However, a comprehensive evaluation of the improvement potential of crop yield, water use, and relevant underlying drivers after adding biochar remains lacking. A synthesis based on global field experiments was conducted herein to investigate the efficacy of biochar in crop-yield and water-use improvement, taking a range of potential impacting factors into account. The results showed that biochar significantly increased crop yield and crop water productivity (WP_c), by 11.2 % and 14.8 %, respectively, but caused a significant decline (1.8 %) in crop evapotranspiration (ET_c). The highest crop-yield improvement was reached at an application rate of > 20 t ha⁻¹ in the initial year after adding biochar. Low C/N, high pyrolysis temperature, low pH, and wood-based raw materials were found to be beneficial biochar properties for increasing crop production. Biochar generally performed better in soils of low pH and low fertility, especially in hot and humid climates. There was a higher increase in crop yield for corn compared with those for wheat and rice. In addition, changes in WP_c were generally commensurate with those of crop yield in most scenarios. Conditions beneficial for crop-yield improvement tend to result in a higher increase in WP_c through their effects on ET_c. Overall, this study illustrates that crop yield improvement is closely related to improvements in both soil fertility and water use. The latter represents an important factor related to crop growth and productivity through the regulation of evaporation and transpiration after biochar amendment. Despite the promising performance of biochar in promoting crop yield and WP_c, a further challenge involves ways to maximize the effects of biochar across global croplands by properly considering the impacting factors during the process of policy design and implementation.