Beware of comparing RUE values calculated from PAR vs solar radiation or absorbed vs intercepted radiation

The concept of radiation-use efficiency (RUE: biomass produced/energy intercepted by a crop) is commonly used for analysis and modelling of crop growth. The various values found in the literature have not, however, been calculated in the same way. This paper focuses on two aspects that account for differences in the published values. First, the differential effect of canopy development on radiation interception and hence on RUE calculated from photosynthetically active radiation (PAR) and overall solar radiation, respectively. Second, the differences in RUE values calculated from absorbed as compared with intercepted radiation. The analyses reveal why it is difficult to make precise comparisons of published values of RUE and why the biggest differences are found for crops with small LAI or with long LAI establishment phase. (C) 2000 Elsevier Science B.V. All rights reserved.