DISTRIBUTION OF NITROGEN AND RADIATION USE EFFICIENCY IN PEANUT CANOPIES

The allocation pattern of leaf nitrogen throughout a crop canopy can theoretically affect crop photosynthetic performance and radiation use efficiency (RUE). No information is available on the existence of leaf nitrogen gradients in peanut (Arachis hypogaea L.) canopies, nor on how these gradients might impact on RUE. Peanut crops (cv. Tifton-8) were grown in warm and cool environments, and the canopy profiles of leaf area index, light interception, specific leaf weight (SLW), leaf nitrogen concentration (LNC) and specific leaf nitrogen (SLN) were examined at 73 and 112 days after planting. Crop RUE was also measured during this period. There was a marked decline in SLN from the top to the base of the canopy in both environments. The gradient in SLN occurred due to changes in SLW and LNC in the warm environment, but only due to changes in SLW in the cool environment. The gradient appeared to be largely controlled by the light environment within the canopy, as evidenced by the commonality (across environments) of the relationship between SLN and cumulative light interception throughout the canopy. Radiation use efficiency was 33% higher in the crop grown in the warm compared to the cool environment, suggesting that cool temperatures can limit RUE in peanut. For the crop at the warm site, RUE was 32% higher than the theoretical RUE assuming a uniform SLN distribution in the canopy. It is suggested that the existence of non-uniform SLN distribution in the canopy may allow enhanced RUE compared to canopies with uniform SLN distribution.