Seasonal Changes in Distribution of Intercepted Photosynthetically Active Radiation for Layer and Dry Matter Production in Spring Wheat Canopy.

In order to understand the relationship between solar radiation and biomass production within crop canopies, penetration, reflection, and interception of photosynthetically active radiation (PAR) were measured in the canopy of a spring wheat variety called Haruyrutaka. The relationship was evaluated by looking at the plant and canopy architecture, the amount of intercepted PAR, the crop growth rate (CGR), and the conversion of PAR into dry matter (EPAR). The interception (%) of PAR increased rapidly from seedling emergence to flag leaf emergence. It was more than 90% from flag leaf emergence to maturity. Within the canopy, the interception of PAR by the ear was more than 30% after anthesis. The interception of the flag leaf increased from anthesis to milk ripe stage as the flag leaf reclined from an erect to a horizontal position. Interception decreased from the milk ripe stage to maturity as the flag leaf further drooped. Two regression lines fit the relationship between the amount of intercepted PAR by the living plant and the CGR for canopy. The slope of the line after heading was higher than the one before heading. This is because the ear covered the upper layer of the canopy so that assimilation increased under high PAR conditions and consumption increased under low PAR conditions. EPAR changed throughout the growing season as the plant and canopy configuration changed.