Mineral nitrogen dynamics after flooding in lowland soils of Rio Grande do Sul

Abstract

The present work aims at assessing the releasing of N mineral in the forms of NH₄⁺ e NO₃^- in a due time after the beginning of the flooding in different lowland soils of RS and correlate the forms of N mineral to the soil characteristics. Samples of 15 lowland soils of RS were collected in 13 cities of flooded rice producing regions. The samples were put into leaching tubes and incubated for 24 weeks. During this period, leaching was carried out and the N-mineral content was determined. The N-NO₃^- contents decreased after the beginning of the incubation process and nearly disappeared after 8 weeks of incubation. However, the N-NH₄⁺ content increased with the flooding, reaching peaks around 4 to 5 weeks of incubation, showing a decline until the 18^th week. The soils present differences concerning the content of cumulated N-NH₄⁺ and it presented a correlation, among others, with the organic C content. The N-NO₃^- content did not presented a correlation with the evaluated parameters, except with total N content and, the highest peak of N-NH₄⁺ presented a correlation with the organic C content and the cumulated N-NH₄⁺. The lowland soils in RS may present different amounts of N-NO₃^- before the flooding and if it is not absorbed by the plants, it might be lost. The cumulated N-NH₄⁺ content in lowland soils presented variations related to the soils characteristics, mainly organic C content.