RESUMO
Rice (Oryza sativa L.) intermittent irrigation is a potential strategy to mitigate methane (CH4) and nitrous oxide (N2O) emissions, but the effects of dry-wetting intervals on soil electrochemical changes and plant characteristics should be considered. This study was conducted in a greenhouse evaluating CH4 and N2O fluxes in rice under five different irrigation management practices (continuous irrigation (CI), intermittent irrigation with flooding resumption in saturated soil condition (SSI) and soil moisture at field capacity (FCI), saturated soil and irrigation resumption with soil moisture bellow field capacity (FCS), and soil at field capacity (FCD)) and its relation to plant development and global warming potential (GWP). Soil electrochemical conditions and CH4 and N2O emissions were expressively affected by irrigation management. The CI system presented the greatest CH4 flux (20.14 g m-2) and GWP (462.7 g m-2 eq. CO2), whereas intermittent irrigation expressively reduced CH4 emissions. Overall, the N2O flux was low (bellow 20 µg m-2 h-1) even with N application, with greater emissions occurring at the FCD treatment at the beginning of the rice season. Soil moisture at field capacity had no CH4 flux but presented greater GWP (271 g m-2 eq. CO2) than intermittent irrigation systems due to N2O flux while compromising rice plant development. The best soil moisture condition to initiate a flooding cycle during intermittent irrigation is at saturated soil conditions.
Assuntos
Óxido Nitroso/análise , Oryza , Agricultura , China , Aquecimento Global , Metano/análise , SoloRESUMO
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 18th 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 con
O objetivo deste trabalho foi avaliar a liberação de N mineral nas formas de NH4+ e NO3- em função do tempo após o início do alagamento, em diferentes solos de várzea do RS, e correlacionar as formas de N mineral com características dos solos. Amostras de 15 solos de várzea do RS foram coletadas em 13 municípios de regiões produtoras de arroz irrigado, as quais foram acondicionadas em tubos de lixiviação e incubadas durante 24 semanas. Durante esse período, foram realizadas lixiviações e determinado o teor de N-mineral. Os teores de N-NO3- decresceram após o início da incubação e praticamente desapareceram após oito semanas de incubação enquanto o teor de N-NH4+ aumentou com o alagamento, atingindo picos ao redor de quatro a cinco semanas de incubação, com posterior declínio até a 18º semana. Os solos apresentaram diferenças quanto ao teor de N-NH4+ acumulado e este apresentou correlação, entre outros, com o teor de C orgânico. O teor de N-NO3- não apresentou correlação com os parâmetros avaliados, exceto com o teor de N total do solo, e o pico máximo de N-NH4+ apresentou correlação com o teor de C orgânico e com o N-NH4+ acumulado. Os solos de várzea do RS podem apresentar diferentes quantidades de N-NO3- antes do alagamento e se este não for absorvido pelas plantas, poderá ser perdido. O teor de N-NH4+ acumulado nos solos de várzea apresentou variações relacionadas às caract