N2O Emissions From a Tea Field In Southern Subtropical China.

Nitrous oxide (N₂O) is one of the potent greenhouse gases, and accurate estimation of N₂O emissions from fertilized soils is vital for the national greenhouse gas inventory and the development of emission mitigation strategies. Given the recent boom and intensification of tea industries in southern subtropical China, we therefore observe in situ N₂O emissions continuously from a tea field using a static closed chamber method for three field treatments: the conventional (CON, 450 kg N ha^-1 yr^-1 with three even splits: two in March-May using urea and one in October using oilseed trashes), the rice straw mulching (SM, the N fertilizer application rate refers to the CON treatment), and the non-fertilized (CK). We have made observations of N₂O emissions from the soil for one year since January 20 2010. The results show that the fertilization significantly enhances N₂O emissions from the tea field soil. Compared with CK (emitting 9.8 kg N ha^-1 yr^-1 of N₂O), CON and SM both emit more N₂O (18.3 and 14.8 kg N ha^-1 yr^-1, respectively). The fact that SM emits slightly less N₂O than CON may imply that the rice straw mulching, widely used to transfer organic materials from lowland to upland in southern subtropical China, has a potential to reduce N₂O emissions in tea fields. Other environmental variables may also play an important role in controlling N₂O emissions, such as topography, temperature and rainfall. It is observed that lower fluxes respond well to colder seasons and higher positions, and higher fluxes to continuous raining seasons and lower positions. We also study the spatial variability of N₂O emissions in a 4.8-ha tea field, and find that N₂O emissions exhibit strong spatial autocorrelation, characterised by a Matérn-type semivariogram model and an effective range of 16.1 m, and mainly controlled by the elevation.