Physiological Responses of Rice Cultivars to Various Nitrogen Levels

This paper is an attempt to assess the physiological responses (photosynthetic rate, Nitrate Reductase (NR) activity, leaf chlorophyll, flag leaf angle and yield traits) of rice cultivars to various nitrogen levels. Field investigations were therefore, carried out on four rice cultivars namely Vasumati, Kasturi, Tulsi and Krishna Hamsa treated with four nitrogen levels (0, 50, 100 and 200 kg ha⁻¹) for two years at G.B.P.U. A. & T. Pantnagar (India). Genotypic variability was apparent with cv. Vasumati displaying the highest mean photosynthetic rate during flowering stage (8.1 ìmol CO₂ m⁻² s⁻¹) whereas the mean NR activities were at the peak during active tillering (0.164 ìmol NO₂ g⁻¹ fresh wt.h⁻¹) and flowering stages (0.125 ìmol NO₂ g⁻¹ fresh wt.h⁻¹). The cv. Tulsi recorded the lowest values for these traits in that order (7.34 ìmol ìmol CO₂ m⁻² s⁻¹, 0.102 ìmol NO₂⁻g⁻¹ fresh wt.h⁻¹ and 0.088 ìmol NO₂⁻g⁻¹ fresh wt.h⁻¹). Leaf chlorophyll content (SPAD value) enhanced in response to increasing nitrogen doses with cv. Kasturi accumulating more of it (24.42). Flag leaf angle widened due to increased nitrogen applications reflecting large genotypic variations such that the cv. Krishna Hamsa exhibited the highest value of leaf angle (29.5⁰) and cv. Tulsi, the least (20.58⁰). Longest panicle and flag leaf was expressed by cv. Kasturi and Vasumati respectively. Yield related traits viz. number of panicle/m² and grains/panicle was utmost decided for cv. Vasumati and Tulsi whereas least for cv. Kasturi and Vasumati respectively. The values of each trait are shown in terms of mean of two years. It is recorded that the application of excess quantity of nitrogen fertilizer might be enhanced functional traits or physiological responses. It is also suggested that this study may be used to screen nitrogen efficient rice cultivars in future to address environmental problems, energy issues and cost of production of nitrogen fertilizers, needed in huge quantities for rice cultivation.

Rate of physiological traits enhanced due to increased nitrogen applications reflecting large genotypic variations.

Rice cultivar Tulsi exhibited the highest response with respect to grain yield followed by Kasturi, Krishna Hamsa and Vasumati.