Effect of rice cultivar on diel and seasonal methane emission

Date

11-1995

Abstract

Methane emission from rice fields has been receiving increasing attention in recent years. Methane is an important greenhouse gas and rice fields are identified as the largest agricultural source id global methane emission. Information on the effects of rice plants on diel and seasonal methane emission patterns is a key to a process-based understanding of methane emission from rice fields. Greenhouse, phytotron, or laboratory experiments were conducted to provide knowledge on how rice plants affect methane emissions with emphasis on the effect of rice cultivars on diel and seasonal methane emission patterns. Three (3) rice cultivars were used to study the differences in methane emissions among rice cultivars. Cultivar IR 72 was used to examine methane emission sites in rice organs.

Variation of diel methane emission rates followed a normal pattern. The methane emission rate increased in the morning, reached highest in the early afternoon, decreased rapidly thereafter and leveled off at night. This pattern was found in all the three rice cultivars and three growth stages irrespective of the methane emission amplitude. The amplitudes of methane emission rate differed among growth stages but not among cultivars. The amplitude (maximum rate/minimum rate) is positively correlated to diel methane emission rate and dissolved methane concentration in soil solution without discrimination of rice cultivars and growth stages.

Significant correlation between diel methane emission rates and air temperature as well as soil temperature was found. Using Arrhenius equation to simulate the temperature dependence of methane emission variations indicated that soil temperature had closer correlation to methane emission variation than air temperature. Artificial diurnal and diel soil temperature regimes changed methane emission patterns. This confirmed the significant correlation between diel methane emission variation and soil temperature under ambient soil temperature regime, indicating that soil temperature was the major factor driving diel methane emission variation. Using diffusion model to simulate the integrated effect of both soil temperature and dissolved methane concentration in soil solutions increased the correlation coefficient between diel methane variation and soil temperature, indicating that methane source strength was another major factor controlling diel methane emission variation.

Humidity had no effect on methane emission rate. Light intensity had an effect on methane emission rate under phytotron condition, but it could not change diel methane emission patterns under ambient air temperature in the greenhouse. The light intensity possibly affected methane emission rate through its effect on air temperature in the phytotron. There was no direct correlation between diel soil Eh and pH variations and diel methane emission patterns.

Diel methane emission rates differed significantly among rice cultivars. Traditional rice variety Dular had highest methane emission rate. This was followed by improved variety IR 72 while the new plant type IR 65598 had the lowest methane emission rate. Significant correlation between methane emission rates and dissolved methane in soil solution indicated that the differences in methane emission rates were determined by differences in methane strength. Differences in dry matter production and related root exudates as well as root oxidation powers among rice cultivars were the main factors causing the difference in methane source strength. Higher dry matter production resulted in higher root exudates. Methane emission capacity the cultivars was not a limiting factor of methane emission although there were differences in root air space. Root oxidation power differed among rice cultivars. IR 65598 had higher oxidation power at later growth stage. Oxidation power may be a factor depressing methane source strength in soil solutions.

Methane emission in different parts of rice plant and methane emission process were examined in IR 72. Methane emissions through different parts of rice plant indicated that methane emission sites were located in leaves, panicles, and nodes. Gradient of methane concentration existed in rice stems, indicating methane emission through rice plant is a diffusion process. Leaves are very important in methane emission when rice plants are young. Emission from leaves decreased when plants grew older. Generally, panicles were not important in methane emission because most methane was emitted through leaves and nodes. Nodes were the most important methane releasing sites.

Increasing water depth temporarily reduced methane emission rates but did not affect emission rates generally.

Three rice cultivars showed two distinct seasonal methane emission patterns. All the 3 rice cultivars caused one methane emission maxima at early growth stage. The easily decomposable soil carbon source increased methane concentration in soil solution. Rice plants mediated methane emissions. IR 72 and Dular caused a second methane emission maxima at heading stage and filling stage. The methane emission rate of IR 65598 remained at lower level after the first maximum without showing a second maximum like IR 72 and Dular. Dular showed high root exudation, high root porosity and low root oxidation power resulting in highest emission rate. IR 72 had high root exudates, lower root porosity and low root oxidation power resulting in lower emission rate. The lowest emission rate of the new plant type (IR 65598) is due to low root exudation, intermediate root porosity and high root oxidation power.

Document Type

Dissertation

Degree

Doctor of Philosophy in Soil Science

College

Graduate School (GS)

Adviser/Committee Chair

Henry P. Samonte

Co-adviser

Heinz-Ulrich Neue

Committee Member

Santiago M. Alviar, Restituta P. Robles, Ireneo J. Manguiat

Language

English

LC Subject

Rice, Methane

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

LG 996 1995 S72 B85

Notes

Doctor of Philosophy ( Soil Science)

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