Diffuse Fertilization Effect in Maize and Soybean Is Driven by Improved Light Use Efficiency Rather Than by Light Absorption

Abstract Diffuse radiation can improve the efficiency of terrestrial carbon uptake. Both light absorption and canopy light use efficiency (LUE) are affected by the fraction of diffuse radiation (DF). However, the relative contribution of these two factors to the diffuse fertilization effect (DFE) in the short term is not well understood. To investigate the mechanism of DFE in cropland, we collected gross primary productivity, fraction of absorbed photosynthetically active radiation (FAPAR), and other meteorological parameters from June to August in three crop sites. Our results indicated that the short‐term DFE in soybean and maize was primarily driven by the improvement of LUE rather than light absorption. The LUE increased significantly with DF, while the FAPAR changed a little with DF. The increased DF is typically associated with reduced photosynthetically active radiation (PAR). Our results showed that the potential gain in light absorption and canopy LUE from DF could not fully offset the reduced PAR in soybean and maize. The findings in this study contribute to our understanding of the mechanisms underlying the DFE.