Relationships between diffuse radiation fraction and light use efficiency and gross primary productivity of winter wheat

© 2018 Editorial Board of Chinese Journal of Agrometeorology. All rights reserved. The quantitative relationships between the diffuse radiation fraction (DF) and light use efficiency (LUE) and gross primary productivity (GPP) from jointing to milky maturity of winter wheat (from April 1, 2004 to May 20 and from April 10, 2005 to May 31) were analyzed in this research on the basis of field CO2 flux observation. The research results can improve the simulation accuracy of LUE model and crop model. The results indicated that the relationship between DF and LUE was significantly positive linear (P＜0.001), and the relationship between DF and GPP was significantly parabolic curve (P＜0.001). LUE increased linearly with the increasing of DF, while GPP increased first and then decreased. Observational experiments on 2004 and 2005 showed that the GPP of winter wheat reached the highest under the condition of moderate solar radiation, with the average values of DF and photosynthetic active radiation (PAR) were 0.57, 27.7molm−2d−1, respectively. The quantitative equations between DF and LUE and GPP in two years were different. The differences were mainly attributed to the different PAR level and the distribution frequency of DF from jointing to milky maturity of winter wheat during the two years