EFFECT OF UREA FERTILIZER AND ENVIRONMENTAL-FACTORS ON CH4 EMISSIONS FROM A LOUISIANA, USA RICE FIELD

Methane emissions from a flooded Louisiana, USA, rice field were measured over the first crop-growing season. Microplots contained the semidwarf Lemont rice cultivar drill seeded into a Crowley silt loam soil (Typic Albaqualfs). Urea fertilizer was applied preflood at rates of 0, 100, 200 and 300 kg N ha-1. Emissions of CH4 from the plots to the atmosphere were measured over a 86-d sampling period until harvest. Methane samples were collected in the morning hours (07:30-09:30) using a closed-chamber technique. Emissions of CH4 Were highly variable over the first cropping season and a significant urea fertilizer effect was observed. Two peak CH4 emission periods were observed and occurred about 11 d after panicle differentiation and during the ripening stages. Maximum CH4 emissions from the 0, 100, 200 and 300 urea-N treatments were 6.0, 8.9, 9.8 and 11.2 kg CH4 ha-1 d-1, respectively. These flux measurements corresponded to approximately 210, 300, 310 and 370 kg CH4 evolved ha-1 over the 86-d sampling period for the 4 treatments.