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Measurement of Instantaneous Nitrogen Use Efficiency among Pearl Millet Genotypes

ICRISAT, Patancheru, India 502324
North Dakota State Univ. Carrington Res. Ext. Ctr., Carrington, ND 58421
Dep. of Agronomy Univ. of Nebraska, Lincoln, NE 68583
Dep. of Agronomy and USDA-ARS, Univ. of Nebraska, Lincoln, NE 68583

^* Corresponding author.

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 CO₂ 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 (cm² g^–1) was calculated from an accompanying growth analysis. Leaf CO₂ 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 cm² g^–1) and were generally less responsive in terms of leaf N concentrations and leaf CO₂ 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.

Key Words: Pennisetum glaucum (L.) R. Br. • Nitrogen response • Photosynthesis • Leaf nitrogen content • Leaf area

Received for publication June 22, 1987.

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