Methane emission patterns from rice fields planted to several rice cultivars for nine seasons

The presented data set comprises a series of field experiments conducted in the period from 1993 to 1999 at the International Rice Research Institute, Philippines. Methane emissions from different rice cultivars were compared during nine seasons using an automated measuring system. The list of cultivars in this experiment consists of high yielding semi-dwarf cultivars (IR72, IR52, PSBRc20, PSBRc14), traditional tall cultivars (Dular, Intan), hybrid (Magat) as well as plant types with high yield potential that are currently under development (IR65597, IR65600). Seasonal averages in emission rates ranged from 20 to 89 mg CH4 m(-2) d(-1) under inorganic fertilization and from 129 to 413 mg CH4 m(-2) d(-1) following organic amendments. However, differences were generally small within a given season and stayed below significance level for the bulk of the inter-cultivar comparisons. Each experiment included IR72 to allow computation of cultivar-specific emission indices in relation to this reference. These indices ranged from 0.57 (PSBRc14) to 1.8 (Magat), but did not reveal consistent ranking for rice genotypes. The similarity in methane emissions was corroborated in a field screening of 19 cultivars using dissolved CH4 in soil solution as a proxy for relative emission rates. Irrespective of cultivars, higher plant density (10*20 cm spacing vs. 20*20 cm spacing of plant hills) stimulated methane production in the soil, but did not result in higher emission rates. This finding was attributed to higher oxygen influx into the soil and subsequent stimulation of methane oxidation when plants hills were more abundant. Over multi-seasonal periods, differences observed between cultivars were inconsistent indicating complex interactions with the environment. These results stress the need for more mechanistic understanding on cultivar effects to exploit the mitigation potential of cultivar selection in rice systems.