Greater nitrous and nitric oxide emissions from the soil between rows than under the canopy in subtropical tea plantations

Abstract

Subtropical agricultural soils are hotspots of nitrogen(N)-oxide emissions, whereas the spatiotemporal variability and driving factors of their emissions in different cultivation systems are poorly understood. Here, to assess the magnitude and pattern of soil N-oxide emissions, we conducted measurements of nitrous oxide (N2O) and nitric oxide (NO) fluxes from the soil between rows and under the canopy of tea plants in two subtropical tea plantations over a one-year period. Results showed that N2O and NO emissions from the soil between rows were 32.6 and 9.1 kg N ha−1 for the Yixing (YX) site and 33.9 and 9.9 kg N ha−1 for the Jurong (JR) site, respectively. Across both sites, N2O and NO emissions from the soil between rows were 2.8–5.2 and 1.4–4.0 times, respectively, larger than those from the soil under the canopy. We attributed greater N-oxide emissions from the soil between rows mainly to increased soil mineral N and water contents as compared to the soil under the canopy. On average, N2O and NO emissions from the soil under the canopy accounted for 36% and 44% of the total losses from the entire field, respectively. For the entire tea field, N2O emissions were 12.6 and 15.7 kg N ha−1 for the YX and JR sites, respectively, but the difference was not statistically different. In contrast, NO emissions from the YX and JR sites were 3.8 and 5.7 kg N ha−1 and differed significantly between the two sites, which was due to higher NO emissions from the soil under the canopy in the JR site. The greatest N-oxide fluxes occurred in the spring and summer seasons after topdressing when soil conditions were conducive to microbial N-oxide production. The structural equation modeling analyses suggested that the variables explaining the variances of soil N-oxide emissions were different between the two tea plantations. Our results indicated that microbial nitrification and abiotic chemodenitrification processes were likely the major pathways leading to N-oxide emissions in the soil under the canopy. Our findings highlight the importance of N-oxide fluxes simultaneously taken from the soil between rows and under the canopy and implementing mitigation practices in subtropical tea plantations.