METHANE EMISSION FROM INDONESIAN RICE FIELDS WITH SPECIAL REFERENCES TO THE EFFECTS OF YEARLY AND SEASONAL-VARIATIONS, RICE VARIETY, SOIL TYPE AND WATER MANAGEMENT

Total amounts of CH4 emission from a Sumatra rice field were in the ra nges 29.5-48.2 and 43.0-64.6 g CH4 m(-2) season(-1) for the plots with chemical fertilizer (CF-plot) and those with rice straw application ( RS-plot), respectively. Nearly the same amounts of CH, were emitted in the first and second half of the growth period, irrespective of rice straw application. The increase in the amounts of CH4 emission by rice straw application were from 1.3 to 1.6 times. There was no significan t difference in the mean CH, emission rates between rainy and dry seas ons. Rain-fed conditions decreased the CH4 emission by 27-37% compared with continuously flooded conditions. Total amounts of CH4 emission f rom a rice held growing eight popular modern rice varieties in Indones ia were in the ranges 32.6-41.7 and 51.3-64.6 g CH4 m(-2) season(-1) f or CF-and RS-plots, respectively. Total amounts of CH4 emission from f our Sumatra rice fields with different soil types (a Typic Paleudult, a Typic Sulfaquent, a Typic Tropohumult and a Typic Tropopsament) were in the range 22.1 (a Typic Sulfaquent) to 53.4 (a Typic Tropohumult) g CH4 m(-2) season(-1) for CF-plots and from 26.7 (a Typic Sulfaquent) to 72.2 (a Typic Tropohumuit)g CH4 m(-2) season(-1) for RS-plots. CH4 emission rates from Ball rice fields with soils of volcanic ash origi n were very low; 3.5-7.7 and 5.3-14.3 g CH4 m(-2) season(-1) for CF- a nd RS-plots, respectively. Respective rice fields showed the specific productivity of grain production, and CH4 emission rates for 1 kg grai n production were scattered widely from 8-11 and 11.24 g CH4 kg(-1) gr ain for rice fields of volcanic ash origin to 83 and 121 g CH4 kg(-1) grain for a Sumatra rice field for CF- and RS-plots, respectively. Wat er management was also an important factor in decreasing the CH4 emiss ion rate. (C) 1998 John Wiley & Sons, Ltd.