Effect of Nitrogen Management on Growth and Yield of Diverse Nitrogen-efficient Genotypes of Rice (Oryza sativa L.) in the Southern Laterites of Kerala, India

A field experiment was conducted at the Department of Agronomy, College of Agriculture, Vellayani, Kerala, to evaluate the field performance of four nitrogen-efficient rice varieties (two short duration varieties and two medium duration rice varieties) selected based on a previous screening study involving 14 rice genotypes for nitrogen use efficiency (NUE). The selected varieties were evaluated under graded levels of the recommended dose of nitrogen (RDN). The experiment was laid out in a split plot design with four replications. The treatment consisted of four main plots comprising levels of recommended dose of nitrogen (RDN) [n1- 100 % RDN, n2 - 75 % RDN, n3 - 50 % RDN and n4- absolute control] and four sub plot treatments nitrogen-efficient varieties [v1- Harsha (PTB 55), v2- Varsha (PTB 56), v3- Sreyas (MO 22) and v4- Aiswarya (PTB 52)]. The study revealed that levels of RDN and varieties had significant influence on growth attributes and yield of rice. Notably, varieties that sustained stable yields under reduced nitrogen application exhibited superior adaptability and nitrogen use efficiency (NUE). The present study confirmed that genetic variability exists in nitrogen response, and the interaction between variety and nitrogen levels significantly influenced yield. Hence, identifying nitrogen-efficient genotypes represents a promising strategy for optimizing nitrogen management, ensuring sustainable rice production and preserving soil health. Based on the findings of the study, among the two short duration varieties (Harsha and Varsha), the RDN for the variety Varsha (PTB 56) could be reduced by 25% without significant yield reduction. Similarly, the RDN for both the medium duration varieties (Sreyas and Aiswarya) could be reduced by 25% (75% RDN) since the two varieties proved to be equally N efficient in terms of productivity.