Response of surface albedo and soil carbon dioxide fluxes to biochar amendment in farmland

Abstract

Understanding the effect of biochar on surface albedo and soil CO2 fluxes is a crucial issue in evaluating the impact of biochar on carbon sequestration and greenhouse gas mitigation. In this study, we consider the following research questions: (1) Under bare soil and crop coverage conditions, do different dosages of biochar decrease the surface albedo? (2) How does the application of biochar affect soil CO2 fluxes? (3) What are the influencing factors of surface albedo and soil CO2 fluxes after biochar is applied? We examined the influence of biochar applications on farmland on the surface albedo, soil CO2 flux, soil temperature, soil moisture, and soil organic carbon fractions over a period of 15 months. There are six treatments (CK+, CK−, BC5+, BC5−, BC45+, and BC45−) in this study, and three biochar application rates, which are as follows: 0 t ha−1 year−1 (CK), 5 t ha−1 year−1 (BC5), and 45 t ha−1 year−1 (BC45) of biochar, and each application is rated with two crop coverage conditions, a wheat-maize crop rotation (+) and bare soil (−). We found that in the early stage of crop growth, the surface albedo of BC45+ and BC5+ were decreased significantly compared with the control treatment (P < 0.05). As the crop canopy structures developed, the surface albedo reduction weakened or even disappeared. Under the bare soil condition, the surface albedos of BC45− and BC5− was decreased significantly in most of the measurements (P < 0.05). The soil CO2 fluxes of the biochar treatments were increased significantly (P < 0.05). However, the growth rates of the soil CO2 fluxes of BC45+, BC5+, BC45−, and BC5− gradually decreased with time. The increase in the CO2 emissions of biochar treatments may be due to mineralization of the readily oxidizable organic carbon (e.g., water-soluble organic carbon) in the biochar-soil system. Adding biochar to the soil reduced the sensitivity of the soil respiration to temperature changes. The leaf area index is one of the factors that affects the surface albedo. The surface albedo did not decrease proportionally with the increase in biochar application. Readily oxidizable organic carbon played an important role in the soil CO2 emissions. The reduction of surface albedo caused by the biochar has no direct effect on soil CO2 fluxes. The findings were helpful in evaluating the effects of adding biochar to soil and its consequences for C sequestration in agricultural soils.