Comparison of the requirements and utilization of nitrogen by genotypes of sorghum (Sorghum bicolor (L.) Moench), and nodulating and non-nodulating groundnut (Arachis hypogaea L.)
1986
Nambiar, P T C | Rego, T J | Rao, B S
Nitrogen requirements and utilization of mineral nitrogen (N) by sorghum and groundnut were compared. At the maximum N use level, sorghum genotypes showed greater N use efficiency (120 kg biomass/kg N harvested) than groundnut genotypes (36 kg biomass/kg N harvested). Using a non-nodulating groundnut genotype (Non-nod) or sorghum as controls for soil N uptake, the amounts of N2 fixed by the nodulated groundnut genotypes were estimated to be 183–190 kg N/ha. Nitrogen fertilization increased harvest index and percentage N translocated to seeds in sorghum genotypes, but decreased harvest index and had variable effects on percentage N translocated to seed in groundnut genotypes. Leaf nitrate reductase activity (NRA) and nitrate content in the leaves of two sorghum genotypes, one nodulating, and ‘Non-nod’ groundnut genotypes were also compared. The concentration of nitrate was lower in sorghum than in groundnut leaves, but NRA was higher in sorghum. It is suggested that either NRA in the groundnut leaves has relatively lower affinity for the substrate (higher Km, the Michaelis-Menton constant) or higher nitrate is required for the induction of nitrate reductase in groundnut than in sorghum. This implies that groundnut is a poor utilizer of fertilizer nitrogen.
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