Radiation Use Efficiency: Evaluation of Cropping and Management Systems

Capture of solar radiation by plant canopies and conversion of this energy into biomass or grain has been described as radiation use efficiency. Radiation use efficiency (RUE) has been developed as a function of biomass accumulation and intercepted photosynthetically active radiation (IPAR) by the canopy and evaluated under conditions not limiting to plant growth. This study was designed to evaluate RUE across a number of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] experiments in central Iowa with various tillage and management inputs to determine how RUE changed as a function of agronomic management. In these studies, IPAR was derived through the use of a normalized difference vegetation index, which is a surrogate for the photosynthetically active radiation canopy interception term, and total canopy biomass was measured at five times during the growing season from the early vegetative stage through maturity. Grain yields were obtained from each plot with both hand-harvested and combine samples. Values for RUE showed a linear relationship between biomass and IPAR for the entire growing season, with the better fit when the relationship was confined to the vegetative development period. There were differences among years, with management and tillage systems affecting RUE values through the differences in biomass or grain yield. Grain yield relationships to IPAR showed more variation than total biomass, with yearly differences evident in the amount of IPAR during the grain-filling period suggesting that the length of the grain-filling period is a dominant factor in grain yield. Application of RUE to field-scale observations will provide a method of assessing where crop productivity is limited.