70003 Methane Emissions During the Flooded Rice Growing Season As Affected by Different Straw Managements in Southern Brazil.

See more from this Division: Virtual Posters
See more from this Session: Virtual Posters

Leonardo M. Bastos Sr., Sandro Josť Giacomini, Eduardo Lorensi, Enio Marchesan, Alex Skolaude, Luana Freitas, Guilherme Dietrich and Bruno Chaves, Federal University of Santa Maria, Santa Maria, Brazil
Methane (CH4) is a key anthropogenic greenhouse gas in the atmosphere. Flooded rice soils have been recognized as an important source of atmospheric CH4. In Southern Brazil is cultivated annually approximately 1.2 million hectares of rice under flooded regime. The flooded rice fields in Southern Brazil were responsible for the emission of 350 Gg CH4 in 2005, 82% of the Brazilian emissions from that source. In these fields, rice is cultivated from October to March, and on the fallow period different straw managements are performed by the farmers. Therefore is essential to select straw managements applied after the rice harvest, which promote the reduction of CH4 emissions in rice fields. The aim of this study was to evaluate the CH4 emissions during the rice growing season as affected by different straw managements applied during the fallow period. Eight treatments were tested: non-straw management, cage roller after harvest, disk harrow after harvest, rice straw removal, non-straw management + ryegrass cropping, late disk harrow, disk harrow after harvest + late disk harrow and cage roller after harvest + late disk harrow. During the fallow period all plots remained drained. Methane flux was determined weekly by the static chamber technique. Gas samples were analyzed for CH4 concentration with a gas chromatograph (Shimadzu GC-2014 Greenhouse) equipped with a flame ionization detector. The treatments that leaded to a higher CH4 evolution during the rice growing season were non-straw management (585 kg CH4 ha-1) and ryegrass cropping (530 kg CH4 ha-1), the ones that had more rice straw on the soil surface available for CH4 production by methanogenic bacteria. The disk harrow after harvest treatment was the one with the least CH4 emissions (334 kg CH4 ha-1), probably due to the lack of available straw-C for the methanogenic bacteria, since it had already been degraded by the moment of its incorporation to the soil prior to the rice cultivation. Managements that stimulate the decomposition of the rice straw before its cultivation lead to a decrease of CH4 production after the soil flooding during rice growing season.
See more from this Division: Virtual Posters
See more from this Session: Virtual Posters