SOYBEAN RADIATION-USE EFFICIENCY AS INFLUENCED BY NONUNIFORM SPECIFICLEAF NITROGEN DISTRIBUTION AND DIFFUSE-RADIATION

Radiation-use efficiency (RUE) has proven to be an effective expressio n of the biomass accumulation capacity of crop canopies. Two factors t hat may influence RUE, however, are the N distribution among leaves in the canopy and the fraction of the diffuse component in the incident radiation. Radiation-use efficiency was measured for soybean [Glycine max (L.) Merr.] grown at Gainesville, FL, and Shiga, Japan, to examine the potential influence of these two factors on RUE. Radiation-use ef ficiency was found to be substantially greater for soybean grown in Ja pan as compared with Florida. It was hypothesized that a greater fract ion of incident diffuse radiation in Japan could explain much of the d ifference in RUE between the locations. In addition, a nonuniform spec ific leaf N distribution (SLN, g N m-2) was shown theoretically to enh ance RUE. A comparison is presented between the experimental observati ons of RUE, and the RU E obtained by accounting for the nonuniform SLN distribution in soybean canopies and for hypothetical differences bet ween locations in the diffuse radiation component.