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Denitrification is the main source of the greenhouse gas N2O emitted from agricultural soils. While N2O emissions and influencing factors have been very well studied in field experiments, there are hardly any reliable data for N2 emissions on the field scale. However, these are essential to understand under which conditions complete denitrification occurs leading to N2 formation and when N2O is the main end product. Whether NO3- is reduced to N2O or N2 depends on several factors: the availability of NO3- and available organic C, as well as pH, oxygen availability, soil moisture, denitrifier community structure, and temperature. All of these parameters are highly dependent on crop development, as growing plants take up NO3- and water while increasing organic C availability via root exudates and dying roots, and alter soil pH as well as microbial communities by rhizosphere dynamics.The objective of this field trial was to collect reliable measurement data on N2 and N2O emissions in typical German crops. Two crops were chosen that differ greatly in their temporal development: Winter wheat (Triticum aestivum L.) and sugar beet (Beta vulgaris subsp. vulgaris). Both crops were grown site-typically according to the rules of good agricultural practice. To measure N2O and N2 emissions, the improved 15N gas flux method including high enrichment 15N-labeled fertilizer was applied. Prior to gas sampling, chambers were purged with a mixture of helium and oxygen (80:20) to reduce the atmospheric N2 background to < 2%. Soil samples were taken at regular intervals and analyzed for mineral N (NO3- and NH4+) and water-soluble Corg content. In addition, we monitored crop development, plant N uptake, N transformation processes in soil, and N translocation to deeper soil layers. |
