Physiological Response of Nitrogen Use Efficiency and Yield Attributes in Rice (Oryza sativa L.) Genotypes under Different Nitrogen Levels

This chapter is useful to screen most N efficient genotypes which can be strongly suggested to rice growers to enhance crop yield irrespective of use of high dose of N fertilizers. The conventional farming greatly depending on chemical fertilizer input has been double-sided; yield increase but environmental concerns such as soil degradation, biological diversity. A Field experiment was conducted at PJTSAU, Hyderabad, Telanagana, India during 2011-12 to evaluate the efficiency of varying nitrogen (N) fertilizer rates on growth and yield parameters, along with NUE (Nitrogen Use Efficiency) with two N levels 60 and 120 kg N ha-1 as main treatments and twenty six rice genotypes as sub treatments. N nutrition influences the content of photosynthetic pigments, synthesis of the enzymes taking part in the carbon reduction, formation of the membrane system of chloroplasts, etc. Photosynthetic rate increased from maximum tillering (18.41 m mol CO2 m-2 s-1) to flowering stage (22.24 m mol CO2 m-2 s-1) and recorded a decrease thereafter towards maturity stage (13.23 m mol CO2 m-2 s-1). Application of appropriate level of N fertilization is a major objective to increase NUE by rice varieties. Among the genotypes, MTU-1001 recorded the maximum grain yield of 5021 kg ha-1 even under application of 60 kg N ha-1 with maximum NUE in 60 kg N ha-1 (83.68) and minimum in 120 kg N ha-1 (45.53). NUE did not increase linearly with the amount of N application and higher N levels showed significantly lower NUE values. N contributes to carbohydrate accumulation in culms and leaf sheaths during the pre-heading stage and in the grain during the ripening stage of rice. Maximum yield can be attributed to maximum SCMR (SPAD Chlorophyll meter reading) values, more photosynthetic rate, more tillers and panicles, more number of grains hill-1, maximum filled grain percentage and minimum spikelet sterility.