The effect of chamber placement site on N2O emission under different fertilizer regimes from maize field

Static chamber method has been used to monitor greenhouse gas (GHG) emission from agricultural soils. When monitoring GHG emission in rice or wheat systems, all the plant stems can be covered in the top chamber. Under this situation, both nitrous oxide (N2O) emission from the root free soils and the root area soils can be estimated. However, in maize field, most of the studies placed the chamber within the maize row due to the difficulty to cover the whole maize stalk. N2O emission from the root area was not estimated since the majority of maize roots were excluded in the chamber. This may lead to a under estimation of global N2O emission from maize cultivation. To evaluate the spatial variability of N2O emission from maize field, a two-year field experiment was conducted. N2O emissions from three sampling sites including inter-rows, within-rows and root area were monitored under five different fertilization regimes. Results showed that chamber placement site had a significant effect on the N2O emission during the maize growing season. Placing the chamber in inter-rows either overestimated or underestimated N2O emission. In 2018, N2O emission rate in the inter-rows was 69 % higher than the root area on average of the five treatments; whereas, in 2020, N2O emission rate in the inter-rows was 2.5 times lower than the root area. N fertilization regimes had a significant effect on N2O emission. On average of chamber sites, N2O emission under N fertilizer broadcasting was around 2 times lower compared to nest-applied. The highest N2O emission rate was observed when both basal and dressing N fertilizer were applied in a nest, which was 1.1–3.2 times higher than the other N fertilizer placement regimes. The N2O emission rate from the within-rows was close to the average value of the three sampling sites. Our results suggested that placing chamber in the center of two neighboring maize plants could represent the average area-scaled N2O emission in maize field.