Influence of Nitrogen Levels on Physiological Response, Nitrogen Use Efficiency and Yield of Rice (Oryza sativa L.) Genotypes

A field experiment was conducted during 2011-12 to evaluate the efficiency of varying nitrogen fertilizer rates on growth and yield parameters, along with nitrogen use efficiency with two nitrogen levels 60 and 120 kg N ha-1 as main treatments and twenty six rice genotypes as sub treatments. Application of appropriate level of nitrogen fertilization is a major objective to increase nitrogen use efficiency 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 (Nitrogen Use Efficiency) 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 nitrogen application and higher nitrogen levels showed significantly lower NUE values. 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.