Denitrification and emission of N_2O from different soils and ~(15)N labelled fertilizers under anaerobic rice culture

摘要

To quantify the denitrification and evolution of N_2O from soils under anaerobic rice crop a green house study was conducted using three soils (viz. acid, normal, and sodic) and three ~(15)N labelled fertilizers (viz. (NH4)_2SO_4, urea and KNO_3 using gas chamber on the 50-cm soil column to tap the emanating N_2O and N_2 from soil. Evolution of N_2 and N_2O was masure up to 32 days after application of N at 100 mg kg~(-1) at transplanting of rice. After 32 days, plant and soil samples were taken and analysed for total N and ~(15)N contents for mass balance studies. The results have showed much of the denitrification, in the first 7 days after fertilizer application. Among the N sources, KNO_3 showed maximum denitrification in acid soil, in the first 7 days followed by sodic and normal soils. Whereas, urea and ammonium sulphate showed almost similar fluxes in normal soil followed by sodic and acid soils. From 27 days onwards there were almost similar fluxes of N_2+N_2O and N_2O among the N sources or soil types. On the basis of ~(15)N balance it has been revealed that unaccounted for fertilizer N loss was maximum due to use of KNO_3, being 54, 49, and 55% in acid, normal and sodic soils, respectively. With urea such losses was 35, 33, and 47% in the same order of soils. The (NH4)_2SO_4 has been found most effective source of N in submerged rice because of minimum emission and unaccounted for N losses from the soil-plant systems.