1. How shallow water table conditions affect N2O emissions and associated microbial abundances under different nitrogen fertilisations.
- Author
-
Cocco, E., Bertora, C., Squartini, A., Delle Vedove, G., Berti, A., Grignani, C., Lazzaro, B., and Morari, F.
- Subjects
- *
WATER depth , *NITROUS oxide , *NITROGEN fertilizers , *GROUNDWATER , *MICROORGANISM populations , *POLYMERASE chain reaction - Abstract
Globally, agriculture is the largest source of nitrous oxide (N 2 O), a potent greenhouse gas (GHG). A recognised tool to prevent its loss from agricultural soils is the presence of a shallow water table. A four-year lysimeter experiment (2011–2014) was conducted in northeast Italy to investigate how water table levels affect N 2 O emissions after different N fertilisation techniques. Soil surface flux and groundwater-dissolved N 2 O were studied under free drainage and at two shallow water table levels (60 cm and 120 cm) and at two levels of N input (250 and 368 kg N ha −1 y −1 ), using dry manure in 2011 and 2012 and fresh manure in 2013 and 2014. DNA was extracted from soils and quantitative PCR (qPCR) was used to assess the size of nitrifying, denitrifying and N 2 -fixing bacterial communities. at three soil depths. The day after pre-seeding fertiliser incorporation, N 2 O emission started to be detected and continued for two-three weeks; brief measurable emissions also followed top–dressing fertilisation events. Cumulative N 2 O emission measured between 0.97 and 2.33 kg N 2 O-N ha −1 y −1 , corresponding to emission factors from 0.4% to 1.1%. Manure fertilisation significantly affected the N dose only when applied as fresh manure. Water-filled pore space (WFPS) affected daily N 2 O emissions with a significant interaction with fertilisation level. The two N input levels showed differences only when WFPS was >40%, which revealed N availability as key to increased N 2 O emissions at high water content, supposedly by fostering anaerobic denitrification. No significant relationships were observed between peak N 2 O emissions and the values of the temperature or irrigation variables recorded during the experimental observation period. Groundwater dissolved N 2 O-N concentrations measured about 1.7 μg L −1 with some peak variability from nitrate leaching. Quantitative PCR assays demonstrated that shifts in microbial population that can be involved in oxidation processes and heterotrophic denitrification occurred in the soil, even though the contributions of the different N pathways on N 2 O emissions were indistinguishable. Indeed, both nitrifying and denitrifying genes were simultaneously promoted by the high fertilisation input and hindered by the high water table level. Shallow groundwater conditions appeared to reduce N 2 O emissions probably by favouring complete denitrification. These results suggest that in the Po Plain, regulated by the Nitrate Directive, shallow groundwater conditions, with a balanced N input, may mitigate air and water pollution. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF