https://horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_7/b_fdi_57-58/010025232.pdf

Production, oxidation, emission and consumption of methane by soils: A review

▪ Abstract Agriculture is a resource-intensive enterprise. The manner in which food production systems utilize resources has a large influence on environmental quality. To evaluate prospects for conserving natural resources while meeting increased demand for cereals, we interpret recent trends and future trajectories in crop yields, land and nitrogen fertilizer use, carbon sequestration, and greenhouse gas emissions to identify key issues and challenges. Based on this assessment, we conclude that avoiding expansion of cultivation into natural ecosystems, increased nitrogen use efficiency, and improved soil quality are pivotal components of a sustainable agriculture that meets human needs and protects natural resources. To achieve this outcome will depend on raising the yield potential and closing existing yield gaps of the major cereal crops to avoid yield stagnation in some of the world's most productive systems. Recent trends suggest, however, that increasing crop yield potential is a formidable scienti...

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Meeting Cereal Demand While Protecting Natural Resources and Improving Environmental Quality

A critical assessment of the system of rice intensification (SRI)

Rice plants play a pivotal role in different levels of the methane (CH4) budget of rice fields. CH4 production in rice fields largely depends on plant-borne material that can be either decaying tissue or root exudates. The quantity and quality of root exudates is affected by mechanical impedance, presence of toxic elements, nutrient deficiencies, water status of growing medium, and nitrogenase activity in the rhizosphere. CH4 oxidation in rice fields is localized in the rhizosphere where the concentration gradients of CH4 and oxygen overlap. CH4 oxidation capacity is a function of the downward transport of oxygen through the aerenchyma, which, in turn, also acts as a conduit for CH4 from the soil to the atmosphere. The decisive step in the passage of CH4 through rice plant is the transition from root to stem. However, rice plants show an enormous variety of morphological and physiological properties, including differences in root exudation and gas transfer capacity. Comparative studies on different cultivars are deemed crucial for accomplishing a better understanding of the mechanisms of CH4 consumption in the rhizosphere and CH4 transport through the rice plant as well as the interaction of these processes. The results of such studies are considered tools for devising mitigation options.

The role of rice plants in regulating mechanisms of methane missions

Methane (CH4) is a particularly potent greenhouse gas with a radiative forcing 23 times that of CO2 on a per mass basis. Flooded rice paddies are a major source of CH4 emissions to the Earth's atmosphere. A free-air CO2 enrichment (FACE) experiment was conducted to evaluate changes in crop productivity and the crop ecosystem under enriched CO2 conditions during three rice growth seasons from 1998 to 2000 in a rice paddy at Shizukuishi, Iwate, Japan. To understand the influence of elevated atmospheric CO2 concentrations on CH4 emission, we measured methane flux from FACE rice fields and rice fields with ambient levels of CO2 during the 1999 and 2000 growing seasons. Methane production and oxidation potentials of soil samples collected when the rice was at the tillering and flowering stages in 2000 were measured in the laboratory by the anaerobic incubation and alternative propylene substrates methods, respectively. The average tiller number and root dry biomass were clearly larger in the plots with elevated CO2 during all rice growth stages. No difference in methane oxidation potential between FACE and ambient treatments was found, but the methane production potential of soils during the flowering stage was significantly greater under FACE than under ambient conditions. When free-air CO2 was enriched to 550 ppmv, the CH4 emissions from the rice paddy field increased significantly, by 38% in 1999 and 51% in 2000. The increased CH4 emissions were attributed to accelerated CH4 production potential as a result of more root exudates and root autolysis products and to increased plant-mediated CH4 emissions because of the larger rice tiller numbers under FACE conditions.

Effects of free‐air CO2 enrichment (FACE) on CH4 emission from a rice paddy field

Measurements of methane emission rates and concentrations in the soil were made during four growing seasons at the International Rice Research Institute in the Philippines, on plots receiving different levels of organic input. Fluxes were measured using the automated closed chambers system (total emission) and small chambers installed between plants (water surface flux). Concentrations of methane in the soil were measured by collecting soil cores including the gas phase (soil-entrapped methane) and by sampling soil solution in situ (dissolved methane). There was much variability between seasons, but total fluxes from plots receiving high organic inputs (16-24 g CH4 m(-2)) always exceeded those from the low input plots (3-9 g CH4 m(-2)). The fraction of the total emission emerging from the surface water (presumably dominated by ebullition) was greater during the first part of the season, and greater from the high organic input plots (35-62%) than from the low input plots (15-23%). Concentrations of dissolved and entrapped methane in the low organic input plots increased gradually throughout the season; in the high input plots there was an early-season peak which was also seen in emissions. On both treatments, periods of high methane concentrations in the soil coincided with high rates of water surface flux whereas low concentrations of methane were generally associated with low flux rates.

D. Llenaresas

Papers

Fluxes and pools of methane in wetland rice soils with varying organic inputs