The effect of organic and inorganic amendments on methane emission in a riverine alluvial soil

A. Xaviar, J. Samy, M. Zulkefli and J. Ramalah

Abstract

A field determination of methane emission from direct-seeded rice plots treated with amendments of organic and inorganic sources was conducted. The ‘closed chamber’ method was used in the measurement of methane flux at several phenological growth stages for the various management practices. Gas chromatography was used to determine methane concentration. The increase in methane concentration of the air within the chamber measured over two time intervals was used to calculate the methane fluxes. The decline in oxidation-reduction potential was rapid with organic matter incorporation. After 6 days of incorporation, plots with organic matter additions had an oxidation-reduction potential in the range of –132 mV to –165 mV. Plots without organic matter additions had an oxidation-reduction potential of –104mV. Oxidation-reduction potential fluctuated with the growth of the rice crop. Fertilizer application caused a decline in oxidation-reduction potential. There were only slight differences in pH between treatments and variations in pH within a treatment during the crop growth period were within 0.5 unit. The decrease in pH following application of organic matter was more sudden for plots with sesbania and/or Bioferti. Among the treatments evaluated, straw incorporation caused the least fluctuation. Methane emission varied with treatments and with crop growth stages. POMES generally caused a large methane emission. In contrast, methane emission from plots treated with Complehumus and Bioferti was relatively smaller. Peak emissions of methane occurred either at the panicle initiation stage or at the reduction division stage of rice growth. Plots with POMES had an emission flux of 195 mg/m² per hour at the panicle initiation stage, five times the amount emitted from Complehumus plots. Peak emission of methane from straw and POMES + straw treated plots occurred at the reduction division stage with an emission flux of 924 and 898 mg/m² per hour, respectively. In contrast, NPK treated plots or Bioferti + NPK had an emission of 58 mg/m² per hour. Methane emission declined substantially subsequent to flowering stage and methane emission was not detected at the time of harvest.

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