Measurement of Instantaneous Nitrogen Use Efficiency among Pearl Millet Genotypes

Abstract

Nitrogen is often a limiting factor in pearl millet [ Pennisetum glaucum (L.) R. Br.] production. Genotypes are known that differ their response to N. In this study four pearl millet genotypes, which were previously identified as extremes in N use efficiency (total above ground biomass/unit of N absorbed) in the field, were compared in nutrient solution culture for their response to N supply and the instantaneous measurement of photosynthetic N efficiency (μmol CO 2 g −1 N s −1 ). The latter component possibly contributes to N use efficiency. N‐efficient genotypes, ‘Souna B’ and 700112, and N‐inefficient genotypes, ‘BK560’ and ‘BJ104’, were grown at four N levels containing 60, 120, 180, and 240 mg N plant −1 . Specific leaf area (cm 2 g −1 ) was calculated from an accompanying growth analysis. Leaf CO 2 exchange rate was measured on several leaves as they became fully expanded. Photosynthetic N efficiency was derived using values of leaf N concentration. Nitrogen‐efficient genotypes maintained thicker leaves (316.1 vs. 332.5 cm 2 g −1 ) and were generally less responsive in terms of leaf N concentrations and leaf CO 2 exchanger ate (CER) to the N available in solution as compared to the N‐inefficient genotypes. Souna B, the most efficient genotype, maintained a stable CER across all N levels. Photosynthetic N efficiency was similar for all genotypes except BK560, which was 10 to 15% less efficient. The small difference in photosynthetic N efficiency among genotypes coupled with relatively high photosynthetic N efficiency values of BJ104 (N‐inefficient genotype) suggests that differences in instantaneous measures of N use efficiency occurring during photosynthesis offer little explanation for overall differences in N use efficiency among these genotypes in a previous field study. Nitrogen use efficiency was more related to the partitioning of N resources available into additional leaf area.