Variation in Crop Radiation‐Use Efficiency with Increased Diffuse Radiation

Abstract

Radiation‐use efficiency (RUE; grams of biomass accumulated, divided by total solar radiation intercepted) has proven to be a useful variable for quantifying biomass accumulation by crops. Experimental results and theoretical analysis indicate that differences in RUE exist among species, but that RUE for unstressed conditions is relatively stable within a species. A departure from the general conclusion is that high values of RUE have been reported for conditions where the diffuse proportion of the total radiation is commonly large (e.g., glasshouse‐grown plants). In this paper, a simple theoretical derivation of RUE was examined to quantify potential responses in RUE to variation in the fraction of diffuse radiation. To simulate natural conditions, the absolute amount of incident diffuse radiation was held constant and the amount of the direct radiation component was varied so that both the fraction of diffuse radiation and total radiation were varied. The estimates of RUE for soybean [ Glycine max (L.) Merr.] and maize ( Zea mays L.) increased as the fraction of diffuse radiation increased and the total radiation decreased. These results indicate that plants grown in glasshouses or in other locations with large fractions of diffuse radiation are likely to have greater radiation‐use efficiency than observed under primarily direct radiation.