METHANE EMISSIONS FROM LOUISIANA 1ST AND RATOON CROP RICE

Field experiments were conducted to measure CH4 fluxes over the first and ratoon cropping seasons from a flooded Louisiana rice field. Treat ment plots contained the semidwarf, early, long-grain rice cultivar Te xmont, drill-seeded into a Crowley silt loam soil (Typic Albaqualfs). Main crop treatments were (i) urea (100 kg N ha-1) with rice plants, ( ii) urea without plants and (iii) unfertilized plants; ratoon crop tre atments consisted of (i) urea (84 kg N ha-1) with plants (ii) urea wit h plants plus rice straw (10 tons ha-1) and (iii) unfertilized plants. Methane emissions from the microplots were measured over the 77-day f irst crop and 73-day ratoon crop growing seasons. A closed-chamber tec hnique was used to collect CH4 gas samples in the morning and afternoo n hours. Significant urea fertilizer and rice straw effects were obser ved, and CH4 fluxes were highly variable over the two rice-cropping se asons. Over the main crop-growing season (77 days) approximately 50, 2 40, and 340 kg of CH4 ha-1 were released to the atmosphere from the ur ea without plants, unfertilized plants, and urea with plants treatment s, respectively. Methane emissions from the ratoon crop (73 days) were 220, 520, and 1,490 kg ha-1 for the unfertilized plants, urea with pl ants, and urea with plants plus rice straw treatments, respectively. A pproximately 1,830 kg of CH4 ha-1 were emitted from the urea-treated p lanted plots over the 150-day collection period provided the first cro p straw was left in the field after harvest.