Morpho-Physiological Evaluation of Indica Rice Genotypes with Contrasting Crop Duration for Nitrogen Use Efficiency Under Graded Urea Doses

Low crop Nitrogen Use Efficiency (NUE) is an economic and environmental burden. Rice is an attractive target for NUE improvement in India, due to its highest N-fertilizer consumption and the availability of a vast germplasm. We screened 12 Indica rice genotypes (Oryza sativa ssp. Indica) on modified Arnon-Hoagland (AH) media containing graded urea doses from 0 to 7.5 mM (U₀, U₁₀, U₅₀, or U₁₀₀). We identified six genotypes with contrasting crop duration and germination rate for their life-long evaluation of 46 morpho-physiological parameters, including NUE, using at least 30 potted plants per genotype/treatment grown on nutrient-free soil supplemented with AH media containing urea as the sole N-source (U₁₀, U₅₀, or U₁₀₀). We found significant genotype and N-dose-dependent effects of urea that correlated positively for 28 of the phenotypic parameters including five for NUE, whereas three parameters showed a negative correlation for urea dose. We also found a significant positive correlation with genotype and urea dose–response for eight physiological parameters, including one for NUE, while seven parameters showed a negative correlation, including two for NUE. A ranking of all 6 genotypes by N-responsive yield and NUE revealed that the late-germinating, long-duration genotypes had better yield and NUE than the early germinating, short-duration genotypes. The only exception was Dhala Heera from the latter group, which had the preferred combination of early (short) duration and high NUE across all urea doses. This makes it a promising donor genotype for further field evaluation and crop improvement toward higher NUE.