Epsilon Archive for Student Projects

Abstract

Agriculture is responsible for approximately 80% of anthropogenic emissions of
the potent and long-lived greenhouse gas nitrous oxide (N2O). N2O emissions from
agricultural soils are characterized by high temporal and spatial variability and
often peak in short bursts related to events such as precipitation, fertilization and
soil thawing. Frost-sensitive cover crops (CCs) could potentially enhance N2O
emissions during winter. This thesis work investigated the thaw-related N2O fluxes
induced by three different cover crops (oilseed radish, (Raphanus sativus), phacelia
(Phacelia tanacetifolia) and oats (Avena sativa)) by field measurements during a
six-week winter period when the CCs were successively terminated by low
temperatures. It was hypothesized that the magnitude of the emissions would be
related to the content of nitrogen (N) and soluble carbon (C) components in the CC
aboveground biomass, as these are substrates for denitrifying soil bacteria. Results
showed that oilseed radish plots had the highest cumulative emissions of N2O
during the study period, at 3.3 kg ha-1, whereas phacelia and oat plots each emitted
1.4 kg ha-1, all significantly higher compared to control plots without CCs. The
content of N and soluble C components in aboveground biomass could not fully
explain the emissions of N2O. However, it is possible that belowground biomass
was important, or that other qualities of the biomass were influential in governing
thaw-related N2O flux.