Abstract
Abstract. Tea plantations are rapidly expanding in China and other countries in the tropical and subtropical zones, but so far there are very few studies including direct measurements of nitrogenous gas fluxes from tea plantations. On the basis of 2-year field measurements from 2012 to 2014, we provided an insight into the assessment of annual nitrous oxide (N2O) and nitric oxide (NO) fluxes from Chinese subtropical tea plantations under three practices of conventional urea application, alternative oilcake incorporation and no nitrogen fertilization. Clearly, the N2O and NO fluxes exhibited large intra- and inter-annual variations, and furthermore, their temporal variability could be well described by a combination of soil environmental factors including soil mineral N, water-filled pore space and temperature, based on a revised "hole-in-the-pipe" model. Averaged over a 2-year study, annual background N2O and NO emissions were approximately 4.0 and 1.6 kg N ha−1 yr−1, respectively. Compared to no nitrogen fertilization, both urea and oilcake application significantly stimulated annual N2O and NO emissions, amounting to 14.4–32.7 kg N2O–N ha−1 yr−1 and at least 12.3–19.4 kg NO–N ha−1 yr−1, respectively. In comparison with conventional urea treatment, on average, the application of organic fertilizer significantly increased N2O emission by 71 % but decreased NO emission by 22 %. Although the magnitude of N2O and NO fluxes was substantially influenced by the source of N, the annual direct emission factors of N fertilizer were estimated to be 2.8–5.9, 2.7–4.0 and 6.8–9.1 % for N2O, NO and N2O+NO, respectively, which are significantly higher than those defaults for global upland croplands. This indicated that the rarely determined N2O and NO formation appeared to be a significant pathway in the nitrogen cycle of tea plantations, which are a potential source of national nitrogenous gases inventory.
Highlights
Nitrous oxide (N2O) and nitric oxide (NO) are two of the most important anthropogenic nitrogen compounds emitted to the atmosphere, which are directly or indirectly involved in global warming and atmospheric chemistry (Williams et al, 1992; IPCC, 2013)
One should admit that a dearth of direct measurements of nitrogenous gas fluxes in some agricultural areas makes these estimates highly uncertain, and it results in the projection and mitigation of agricultural N2O and NO emissions posing considerable challenges (Davidson and Kingerlee, 1997; Reay et al, 2012), the measurements of these emissions have been made for many decades
Based on 2-year field measurements, this study provided an integrated evaluation on N2O and NO emissions in response to no nitrogen fertilization, conventional urea, and alternative oilcake application in Chinese subtropical tea plantations
Summary
Nitrous oxide (N2O) and nitric oxide (NO) are two of the most important anthropogenic nitrogen compounds emitted to the atmosphere, which are directly or indirectly involved in global warming and atmospheric chemistry (Williams et al, 1992; IPCC, 2013). Soil acidity appears to be an important factor in affecting biotic and abiotic processes and promoting nitrogen losses, such as enhancing N2O production ratios from nitrification and depressing the conversion of N2O to N2 in denitrification (Zhu et al, 2011) as well as inducing chemodenitrification for NO production (Venterea et al, 2003; Medinets et al, 2015) It should, be noted that with limited data available from tea plantations of the world and the high uncertainties of metaanalytic results, caution should be exercised in the interpretation of the differences in background emissions of N2O and NO between the current and previous studies
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