Charactistics Of Nitric Oxide Fluxes From A Tea Plantation

Nitric oxide (NO) is one of the major components of air pollutants as well as an important part of nitrogen (N) biogeochemical cycle. The fertilized croplands are a major source of anthropogenic NO emission. China is the largest tea planting country in the world and its tea plantation is characterized by high nitrogen fertilizer inputs, which is considered to be important source of NO production. So far, however, there has been no investigation on NO flux from the typical tea plantation. To characterize and quantify annual NO fluxes and to clarify the underlying mechanisms and factors controlling NO fluxes from tea fields, we performed in situ measurements of NO flux for a full year from a Chinese subtropical tea field under different fertilization managements (i.e., the conventional farmers’practice with urea application, an alternative practice with organic fertilizer application, and no nitrogen application as a control), using a method of static opaque chamber and chemiluminescent analysis. Through this study, the results showed that:1. The majority of NO fluxes occurred during the tea tree-growing period from March to September (i.e., in the spring and summer seasons), accounting for approximately 58%-73% of annual cumulative NO emissions from the fertilized tea fields;2. Across the annual tea plantation, the cumulative NO emissions were about 2.85,19.42 and 17.04 kg N·ha-1 for the control, urea and organic fertilizer treatments, respectively, with fertilization significantly increasing NO emissions;3. Over the year measurements, the direct emission factors of NO for treatments of urea and organic fertilizer amendments were estimated to be 3.68% and 3.15%, respectively;4. For the fertilized treatments, the application of organic fertilizer significantly reduced annual NO emission by 12% as compared to the conventional farmers’urea application;5. During this period, soil ammonium content was the key environmental factor regulating the temporal variations of NO flux。Based on a continuous field observations the results showed that, comparing with other farmland ecosystems, subtropical tea plantations in China may be an inevitable source of NO, but, to consolidate these results, future studies are needed to conduct multi-site and long term measurements.