Genotypic Variability in Nitrogen Utilization Efficiency in Wetland Rice.
KV Rao, Kavitha B, Rama Prasad AS, Surekha K, and Gandhi G. Directorate of Rice Research, Rajendranagar, Andhra Pradesh, Hyderabad, 500030, India
Rice, the premier food crop of India, is cultivated in nearly 45 M.ha. and account for 42% of total food grain production and about 40% of total fertilizer consumption. Considering the future demands of rice and fertilizer use, relatively low use efficiency of nutrients in wetland rice, and growing costs on rice production, fertilizer subsidies and environmental sustainability, it is important to develop non-monitory input technologies to optimize nutrient use and improve its use efficiency. Identifying superior genotypes for different environments based on their differential responses and efficiency of utilizing soil and applied nutrients is one such area which is less explored. The efficiency of a genotype to utilize nutrients arises from a balance of several processes associated with acquisition and usage. Recognizing this gap of information, field studies were conducted in dry (December to April) and wet seasons (July to November) on N deficient clay soil (vertisol) to study genotype variability in wet land rice of utilizing nitrogen, the most limiting plant nutrient. Sixteen and 18 early to mid duration rice genotypes were gown, respectively, in dry and wet seasons with graded levels (0, 60, 120 and 180 kg /ha) of N out of which 14 genotypes were common in both the seasons. All other nutrients (26 kg P, 50 kg K and 5 kg Zn /ha) and crop management were uniformly maintained. In addition to recording grain and straw yields and N accumulation in dry matter during crop growth and harvest, N utilization efficiency attributes such as productivity rate, N uptake rate, agronomic efficiency, nitrogen recovery efficiency, internal efficiency (kg grain/ kg n uptake), soil and applied N uptake and nitrogen harvest index were used for identifying promising genotypes the influence of genotypes on soil N mineralization and its uptake was also studied separately in green house in support of the findings. Considerable genotype differences were recorded with regard to dry matter and N accumulation, yield response, crop productivity and N uptake rates and efficiency of soil and applied N utilization. Higher N uptake rates were recorded in early maturing varieties upto panicle initiation (PI) stage and between PI to maturity in mid early and mid duration genotypes. Response to N application was significant upto 120 and /or 180 kg N /ha for yield and N uptake. Mid early duration varieties viz., IET 11768, 11771 were promising in terms of grain yield, soil and applied N uptake and its utilization. With regard to response to N application genotypes such as IET 12884, IET 9979, IET 11768 and IET 11771 of mid early duration group were found promising followed by early duration culture Rasi. In general efficient genotypes for N utilization positively influenced soil N mineralization and its utilization indicating likely support for nitrogen fixation activity in the rhizosphere and reduction in de-nitrification loss.