What are the impacts of grazing and cutting events on the N₂O dynamics in humid temperate grassland?

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• 作者：Rashad Rafique^a ; ^b ; ^{rashidbao@gmail.com} ; Robert Anex^a ; Deirdre Hennessy^c ; Gerard Kiely^b
• 关键词：Nitrous oxide ; Grassland ; NH4&ndash ; N ; NO3&ndash ; N ; Grass cutting ; Animal grazing
• 刊名：Geoderma
• 出版年：2012
• 期刊代码：28_00167061
• 类别：ear
• 出版时间：July, 2012
• 卷：181-182
• 期：Complete
• 页码：36-44
• 文件大小：725 K

摘要

Atmospheric concentrations of nitrous oxide (N₂O) have been increasing over the last century with much of this increase from agricultural soils, fertilized with nitrogen. To understand the N₂O emissions from terrestrial ecosystems (e.g. grassland soils) it is necessary to understand the processes leading to N₂O production. From February to August in 2010, we conducted a field study to measure the N₂O fluxes using the chamber technique, at a grazed and cut grassland site in South West Ireland. The objectives of the study were: 1) to understand the temporal variation of the N₂O fluxes during the spring and summer periods; 2) to examine the separate effects of grazing and cutting events on N₂O fluxes; and 3) to examine the relationship of soil ammonium (NH₄ + 鈭?#xA0;N) and soil nitrate (NO₃--N) with N₂O fluxes. We found the highest peak of daily N₂O flux occurred at the start of spring; however the total of summer fluxes (June, July and August) of 1.81 卤 0.7 kg N₂O-N ha^鈭?#xA0;1 were higher than those of the spring (March, April and May) fluxes of 1.51 卤 0.6 kg N₂O-N ha^鈭?#xA0;1. The soil NH₄ + 鈭?#xA0;N concentration was higher than the soil NO₃-N concentration over the study period and elevated N₂O fluxes coincided with elevated soil NH₄-N concentrations. There were two short (2 day duration) cattle grazing events; one on April 26/27 and the second on June 27/28. There were two grass cutting (for silage) events: on May 30 and on August 4. After the two grazing and two cutting events, the N₂O fluxes increased markedly. After both grazing events, there was an immediate step increase of ~ 200 渭g N₂O-Nm^鈭?#xA0;2 h^鈭?#xA0;1, after which the fluxes decreased over the next few weeks. After both cutting events, there was a gradual increase in N₂O fluxes over the next several weeks. We found that the N₂O flux increases post grazing, were due to grazing only, since the other variables (soil temperature, WFPS, N application) did not change. However, the flux increases post cutting could not ascribed to cutting only, as other flux favouring variables of: changes in soil temperature and WFPS also occurred at this time. The N₂O fluxes correlated better with soil NH₄-N concentration (r² = 0.73 (p = < 0.05)) than with NO₃--N (r² = 0.25 (p = not significant)). The occurrence of elevated NH₄-N in conjunction with elevated WFPS, frequently in the range of 50-60%suggests that nitrification rather than denitrification was likely the dominant process involved in the production of N₂O at this site.