[Nitrous oxide emission, nitrification, denitrification and nitrogen mineralization during rice growing season in 2...

Microbial processes such as mineralization, nitrification and denitrification regulate nitrogen dynamics in the soil. The last two processes may produce nitrous oxide (N₂O). In this work N₂O fluxes were quantified at four moments of the rice cycle, sowing, tillering, panicle initiation and maturity, in two sites that differed mainly in their soil organic matter (OM) content, Salto (higher OM) and Treinta y Tres. Potential net N mineralization, ammonium oxidation and denitrification as well as the most probable numbers (MPN) of ammonia oxidizers and denitrifiers were determined. Potential N mineralization did not vary with the soil type and increased at rice maturity. Neither ammonia oxidation potential nor MPN were different among the soils. However, the soil with higher OM exhibited higher activity and MPN of denitrifiers, irrespective of the rice stage. In turn, at the latest phases of the crop, the MPN of denitrifiers increased coinciding with the highest mineralization potential and mineral N content of the soil. Significant differences in N₂O flux were observed in Salto, where the highest emissions were detected at rice maturity, after the soil was drained (44.2 vs 20.8g N-N₂O/ha d in Treinta y Tres). This work shows the importance of considering the soil type and end-of-season drainage of the rice field to elaborate GHGs (greenhouse gases) inventories.