LEAF NITROGEN-CONTENT AND MINIMUM TEMPERATURE INTERACTIONS AFFECT RADIATION-USE EFFICIENCY IN PEANUT

Reproductive development in peanut (Arachis hypogaea L.) is generally characterized by progressively declining leaf N content. A non-nodulat ing genotype and three nodulating cultivars were grown at two location s contrasting primarily in night temperature to derive critical levels of leaf N necessary for maintenance of dry matter (DM) accumulation r ates. Nonnodulating plants were grown in field plots with four N treat ments ranging from 0 g N m-2 (with 1.0 kg m-2 finely chopped cereal st raw) to 26.0 g N m-2. The accumulation of DM and N were monitored for two sowing dates in the cooler environment and at a single sowing in t he warm environment. Early sowing in the cool environment (early-cool) resulted in the nonnodulating genotype accumulating similar levels of DM at high N to the comparable treatment in the warm environment (ear ly-warm), but crop duration in SD1 was 31 d longer. Crop development a nd DM accumulation were restricted in the second sowing in the cool en vironment (late-cool) due to a frost. Slower DM accumulation in early- cool was related to both reduced interception of incident photosynthet ically active radiation, due to slow leaf area development, and to a 2 0% lower conversion efficiency of intercepted radiation to DM (RUE). T he lower RUE in the two cool environments may have been caused by the low minimum temperature. Responsiveness of RUE to the total amount of N per unit leaf area (SLN) was negligible in the two cool environments . Nodulating cultivars grown at the same locations and sowing dates ha d similar SLN and RUE values as the non-nodulating genotype grown unde r the high N treatment.