Coupling atmospheric ammonia exchange process over a rice paddy field with a multi-layer atmosphere-soil-vegetation model

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• 作者：Genki Katata ; Kentaro Hayashi ; Kensuke Ono ; Haruyasu Nagai ; Akira Miyata ; Masayoshi Mano
• 关键词：Ammonia ; Rice paddy field ; A multi-layer land surface model ; Dry deposition ; Emission ; Recapture by foliage
• 刊名：Agricultural and Forest Meteorology
• 出版年：2013
• 出版时间：15 October, 2013
• 年：2013
• 卷：180
• 期：Complete
• 页码：1-21
• 全文大小：3800 K

文摘

To understand the process of atmospheric ammonia (NH₃) exchange over a paddy field, an existing multi-layer atmosphere-SOiL-VEGetation model (SOLVEG) was modified. Heat transfer at the paddy water layer and dry deposition of water-soluble gases such as NH₃ and sulfur dioxide (SO₂) onto the wet canopy, as well as the emission potentials of NH₃ from the rice foliage and floodwater or soil surface, were newly modeled. The performance of the modified model was tested using flux data derived using the eddy covariance and gradient methods used for single rice crops in central Japan. The modified model reproduced the observed fluxes of momentum, heat, and CO₂, as well as the observed net radiation, Bowen ratio, paddy water temperature, and soil temperature and moisture during both the fallow (bare soil incorporating rice residues) and cropping (flooded) seasons. By adjusting the NH₃ emission potentials of the sub-stomatal cavity, the observed upward and near-zero downward fluxes of NH₃ were simulated. The calculated deposition velocity of NH₃ was 0.4-0.8 and 0.2-1.0 cm s^?1 in the fallow and cropping seasons, respectively. Numerical experiments were conducted using the modified model to investigate the effects of canopy structure on stomatal uptake or emissions of NH₃ for various rice growth stages. The NH₃ exchange (uptake and emissions) rate within a canopy decreased with an increase in the leaf area index (LAI) and became constant at LAI > 1 because of decoupling between in-canopy flow and above-canopy turbulence. Since much of the volatilized NH₃ is absorbed within a dense canopy with no stomatal emission potentials, the recapture process is important in reducing NH₃ vaporization loss of fertilizer broadcast to the growing rice.