METHANE EMISSIONS FROM LOUISIANA FIRST 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. Treatment plots contained the semidwarf, early, long-grain rice cultivar Texmont, 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 treatments consisted of (i) urea (84 kg N ha-1) with plants (ii) urea with plants plus rice straw (10 tons ha-1) and (iii) unfertilized plants. Methane emissions from the microplots were measured over the 77-day first crop and 73-day ratoon crop growing seasons. A closed-chamber technique was used to collect CH4 gas samples in the morning and afternoon hours. Significant urea fertilizer and rice straw effects were observed, and CH4 fluxes were highly variable over the two rice-cropping seasons. Over the main crop-growing season (77 days) approximately 50, 240, and 340 kg of CH4 ha-1 were released to the atmosphere from the urea without plants, unfertilized plants, and urea with plants treatments, respectively. Methane emissions from the ratoon crop (73 days) were 220, 520, and 1,490 kg ha-1 for the unfertilized plants, urea with plants, and urea with plants plus rice straw treatments, respectively. Approximately 1,830 kg of CH4 ha-1 were emitted from the urea-treated planted plots over the 150-day collection period provided the first crop straw was left in the field after harvest.