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-nodulating genotype and three nodulating cultivars were grown at two locations contrasting primarily in night temperature to derive critical levels of leaf N necessary for maintenance of dry matter (DM) accumulation rates. Nonnodulating plants were grown in field plots with four N treatments ranging from 0 g N m-2 (with 1.0 kg m-2 finely chopped cereal straw) 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 the 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 (early-warm), but crop duration in SD1 was 31 d longer. Crop development and DM accumulation were restricted in the second sowing in the cool environment (late-cool) due to a frost. Slower DM accumulation in early-cool was related to both reduced interception of incident photosynthetically active radiation, due to slow leaf area development, and to a 20% lower conversion efficiency of intercepted radiation to DM (RUE). The 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 had similar SLN and RUE values as the non-nodulating genotype grown under the high N treatment.