Release of entrapped methane from wetland rice fields upon soil drying.

Methane emissions from Philippine rice paddies, fertilized with either urea or green manure, were monitored for several weeks after harvesting the dry and the wet season crops of 1992. The fields were still flooded during harvest but irrigation was stopped after harvest and the fields were allowed to evaporatively dry while CH4 emissions were monitored with a closed chamber technique. In all plots we observed a sudden, strong increase of CH4 emissions to the atmosphere for 2 to 4 days just after the soil fell dry. As soil drying continued, the soils began to crack and CH4 emissions decreased to nil. The release of CH4 during soil drying was observed for fields on three different soil types and both for urea or organically manured rice fields in both seasons. The absolute amounts of CH4 emitted during soil drying differed greatly depending on fertilizer treatment. However, the ratio between the amount of CH4 released upon soil drying and CH4 emitted during die growing season was quite c onstant (0.10 ¤ 0.04). This suggests that about 10 per cent of the CH4 emitted during a full rice crop cycle is released during drying of the fields and thus needs to be included in estimates of the total CH4 emission from rice agriculture

Effect of water and straw management practices on methane emissions from rice fields: A review through a meta-analysis

[EN] Rice fields contribute substantially to global warming of the atmosphere through emission of methane (CH4). This article reviews the state of the art of factors affecting CH4 emissions in rice fields, focusing on soil organic matter content and water management practices. A quantitative relationship between these factors was established through a meta-analysis based on a literature survey. This relationship can be useful to update emission factors used to estimate CH4 in the National Emission Inventories. Methane emissions in rice fields can be as much as 90% higher in continuously flooded rice fields compared with other water management practices, independent from straw addition. Water management systems that involve absence of flooding in total or for part of the growing period such as midseason drainages, intermittent flooding, and percolation control, can reduce CH4 emissions substantially. Moreover, CH4 emissions increase with the amount of straw added up to 7.7 t/ha for continuously flooded soils and up to 5.1 t/ha for other water regimes. Above these levels, no further increase is produced with further addition of straw. With regard to rice straw management mitigation strategies, recommended practices are composting rice straw, straw burning under controlled conditions, recollecting rice straw for biochar production, generation of energy, to be used as a substrate, or to obtain other byproducts with added value. This review improves the understanding of the relationship between straw application rate, water regimes, and CH4 emissions from rice fields to date. This relationship can help to select the most appropriate management practices to improve current mitigation strategies to reduce atmospheric CH4. © 2012 Mary Ann Liebert, Inc.This study was financially supported by Fundacio´n Agroalimed from the Consellerı´a de Agricultura of Valencia, Spain and the Vicerrectorado de Investigacio´n of the UPV (Programa de Apoyo a la Investigacio´n y Desarrollo, PAID06-11 Program, Project No. 1950).Sanchís Jiménez, EM.; Ferrer Roglán, M.; Torres, AG.; Cambra López, M.; Calvet Sanz, S. (2012). Effect of water and straw management practices on methane emissions from rice fields: A review through a meta-analysis. Environmental Engineering Science. 29(12):1053-1062. https://doi.org/10.1089/ees.2012.0006S10531062291

Characterization of methane emissions from rice fields in Asia. I. Comparison among field sites in five countries

The Interregional Research Program on Methane Emissions from Rice Fields established a network of eight measuring stations in five Asian countries. These stations covered different environments and encompassed varying practices in crop management. All stations were equipped with a closed chamber system designed for frequent sampling and long-term measurements of emission rates. Even under identical treatment - e. g., continuous flooding and no organic fertilizers - average emission rates varied from 15 to 200 kg CH sub 4 ha high -1 season high -1. Low temperatures limited CH sub 4 emissions in temperate and subtropical stations such as northern China and northern India. Differences observed under given climates, (e. g., within the tropics) indicated the importance of soil properties in regulating the CH sub 4 emission potential. However, local variations in crop management superseded the impact o soil- and climate-related factors. This resulted in uniformly high emission rates of about 300 kg CH sub 4 ha high -1 season high -1 for the irrigated rice stations in the Philippines (Maligaya) and China (Beijing and Hangzhou). The station in northern India (Delhi) was characterized by exceptionally low emission rates of less than 20 kg CH sub 4 ha high -1 season high -1 under local practice. These findings also suggest opportunities for reducing CH sub 4 emission through a deliberate modification of cultural practice for most irrigated rice fields