Abstract

Canopy cooling in dry heat-stressed areas is regarded as one of the most physiologically efficient way to attain high grain yields in wheat. Twelve wheat genotypes were grown with four N levels in a 2-year field trial to investigate their efficiency to utilize addition of nitrogen for canopy cooling and high chlorophyll accumulation under a dry but irrigated hot environment in Sudan. Both canopy temperature depression (CTD) and chlorophyll content (CC) increased significantly with addition of 43 (N₄₃), 86 (N₈₆) and 129 (N₁₂₉) kg N/ha compared to zero N (N₀) treatment. The two-season average increases in CTD were 33, 59 and 67% at N₄₃, N₈₆ and N₁₂₉, respectively, relative to N₀. The average increases in CC were 15, 22 and 23% at N₄₃, N₈₆ and N₁₂₉, respectively. However, genotypes showed a wide range of responses to addition of N especially for CTD. The combined genotypic ranges in percent increase of CTD and CC were 19 to 63% and 4 to 22% at N₄₃, 38 to 88% and 13 to 36% at N_86, and 34 to 113% and 15 to 28% At N₁₂₉, respectively. Strong association was found between CTD and CC, which in-turn, was highly and significantly associated with biomass and grain yield. On the other hand, CTD showed significant negative association with harvest index. The results indicate that application of N fertilizer was reflected in a cooler canopy under the dry heat stress conditions of this study. However, genotypic variation in utilizing N fertilizer in canopy cooling necessitate that this should be done in accordance with the response and efficiency of each cultivar.

Key words: Nitrogen fertilizer, canopy temperature depression, chlorophyll content, heat stress, wheat.