Neglecting the fallow season can significantly underestimate annual methane emissions in Mediterranean rice fields.

Maite Martínez-Eixarch,Joan Noguerol,Carles Alcaraz,Carles Ibáñez,Francesc Xavier Prenafeta-Boldú,Maria Del Mar Català,Jesús Antonio Saldaña-De La Vega,Marc Viñas,Xavier Aranda,Jorge Paz-Ferreiro

doi:10.1371/journal.pone.0198081

Maite Martínez-Eixarch, Joan Noguerol + Show 8 more

Open Access

https://doi.org/10.1371/journal.pone.0198081

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Abstract

Paddy rice fields are one of the most important sources of anthropogenic methane. Improving the accuracy in the CH4 budget is fundamental to identify strategies to mitigate climate change. Such improvement requires a mechanistic understanding of the complex interactions between environmental and agronomic factors determining CH4 emissions, and also the characterization of the annual temporal CH4 emissions pattern in the whole crop cycle. Hence, both the growing and fallow seasons must be included. However, most of the previous research has been based on single-factor analyses that are focused on the growing season. In order to fill this gap, a study was conducted in a Mediterranean rice agrosystem (Ebre Delta, Catalonia) following a farm-to-farm approach with the purpose of 1) evaluating the cumulative and temporal pattern of CH4 emission, and 2) conducting a multi-variate analyses to assess the associative pattern, relative contribution and temporal variation of the main explanatory variables concerning the observed CH4 emissions. Measurements of CH4 emissions and agronomic and environmental parameters in 15 commercial rice fields were monitored monthly, during a whole crop field cycle. The temporal pattern of CH4 emission followed a bi-modal distribution peaking in August and October. The cumulative annual CH4 emissions from rice fields amounted 314 kg CH4 kg ha-1, of which ca. 70% were emitted during the fallow season. The main controlling factors of the CH4 emission rate in the growing season were positive related to water level and plant cover, while soil redox was negatively related. The main controlling factors in the fallow season were water level (negatively related, conversely to the growing season), as well as straw incorporation and soil temperature (positively related). The results of this study highlight the importance of the often neglected fallow season in the accurate estimation of CH4 emissions and, thus, the necessity of measurement programs that cover the whole crop field cycle. This information is the first step for setting effective mitigation strategies based on straw and water management.

Highlights

Rice fields provide food for a half of the world population, in developing countries subjected to intense demographic growth [1]
The 15 studied rice fields in the Ebre Delta were largely variable in soil properties (Table 1)
The estimated annual cumulative CH4 emissions in the Ebre Delta rice fields were 314.1 kg CH4 ha-1 of ca. 70% were emitted in the fallow season

Summary

Introduction

Rice fields provide food for a half of the world population, in developing countries subjected to intense demographic growth [1]. Methane (CH4) emissions from wetland rice cultivation contributes to a 9% of the anthropogenic emissions of this greenhouse-effect gas [2]. The determination of effective mitigation options in wetland rice cultivation must be based on a deep understanding of the processes involved in CH4 production and emission dynamics: from the underlying rhizosphere and plant physiology aspects to relevant environmental and agronomic factors that affect the temporal pattern of emissions. Improving the accuracy in the CH4 budget is fundamental to manage realistic and effective strategies to mitigate climate change. For this purpose, a more intense monitoring of CH4 emission at local scale is needed to provide accurate inventories [2]

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