STRAW APPLICATION EFFECTS ON METHANE AND OXYGEN-EXCHANGE AND GROWTH IN RICE

Currently, there is a paucity of information on plant-soil interactive effects and plant-related factors that control CH4 production and its emission from rice (Oryza sativa L.) paddies. Laboratory studies were conducted to evaluate the effects of rice straw application rates on growth, root porosity (POR), and gas (O-2 and CH4) exchange in rice un der continuously hooded conditions. Three rice cultivars were grown in Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualf) a mended with two levels (11 and 22 t ha(-1)) of rice straw. Plants were harvested for growth, POR, and radial oxygen loss (ROL) estimates at 40 d after transplanting. Methane measurements were made at 20, 30, an d 40 d after transplanting. Plant growth and straw application rates w ere negatively correlated. Variations existed among cultivars in param eters studied. Although POR was enhanced by the higher application rat e (22 t ha(-1)), reductions in shoot and root growth consequently resu lted in reduced ROL. Two of the cultivars exhibited significant POR-RO L correlations. Highest CH4 emissions occurred at the 11 t ha(-1) appl ication rate. At the 22 t ha(-1) application rate, CH4 emissions were significantly reduced in all vegetated treatments, although emissions from unvegetated treatments were enhanced. Results indicated that redu ctions in CH4 emissions at the higher straw application rate resulted from reduction in the total diffusive pathway of the gas and were not due to the mitigation of methanogenesis.