Radiation Interception, Radiation Use Efficiency and Crop Productivity

Abstract

Photosynthesis is the set of processes whereby radiant energy is converted and stored as chemical energy in most plants, algae and cyanobacteria. This process depends on radiation, temperature and CO₂ concentration. The maximum efficiency of the process is 6 % but it is usually well below. The leaf-level photosynthesis can be described mathematically, and this analysis can be extended to the calculation of crop photosynthesis, as a function of its leaf area index, the coefficient of extinction as a shortcut to represent canopy architecture, and leaf photosynthetic parameters.

The respiration of the crop can be decomposed into a maintenance component that is dependent on biomass and temperature, and a growth component which is proportional to gross photosynthesis.

Crop yield can be expressed as the product of three factors, the amount of intercepted radiation, radiation use efficiency (RUE) and harvest index (HI). RUE is smaller for C3 than C4 crops, and is smaller in crops with oil- and protein-rich seed in comparison to cereals. Radiation interception depends on incident radiation, leaf area index and the extinction coefficient accounting for canopy architecture. The HI depends on the species and its use. The main cause of genetic yield improvements in the past has been the increase in HI, which has been a remarkable success in the case of cereals; maize is the main expectation to this trend. In some cases, such as high-yielding wheat in northern Europe, HI is reaching a biophysical limit, hence further improvements in yield would require increasing RUE and biomass.