METHANE EMISSION FROM RICE FIELDS AS INFLUENCED BY SOLAR RADIATION, TEMPERATURE, AND STRAW INCORPORATION

Since rice fields emit methane, an important contributor to the increasing greenhouse effect, one of our goals is to characterize factors that influence this emission. To create a range in plant and soil temperature, solar radiation, and microbial substrate, rice fields were planted on April 13, May 18 and June 18 of 1990 on silty clay soils near Beaumont, Texas. Immediately prior to planting, one half of each field was supplemented with 6000 kg ha(-1) of disc-incorporated grass straw (Paspalum spp.). Methane emission rates were measured throughout the cultivation period. Methane emission rates varied markedly with planting date and straw addition. The highest emission rate originated from the earliest planted straw supplemented field. In general, methane emission decreased with the later plantings that received less solar radiation. Annual emission rates of methane and rice grain yield from individual fields were positively correlated with accumulated solar radiation for both straw-incorporated and control plots. Straw incorporation resulted in decreased grain yield and increased methane emission in all three fields. Diel variation of methane emission strongly correlated with temperature. The activation energies for methane production, obtained from laboratory soil incubations, and methane emission, obtained from diel field measurements, were approximately the same: 88-98 kJ mol(-1) for production and 87 kJ mol(-1) for emission.