Since the development of effective N2O mitigation options is a key challenge for future agricultural practice, we studied the interactive effect of tillage systems on fertilizer-derived N2O emissions and the abundance of microbial communities involved in N2O production and reduction. Soil samples from 0–10 cm and 10–20 cm depth of reduced tillage and ploughed plots were incubated with dairy slurry (SL) and manure compost (MC) in comparison with calcium ammonium nitrate (CAN) and an unfertilized control (ZERO) for 42 days. N2O and CO2 fluxes, ammonium, nitrate, dissolved organic C, and functional gene abundances (16S rRNA gene, nirK, nirS, nosZ, bacterial and archaeal amoA) were regularly monitored. Averaged across all soil samples, N2O emissions decreased in the order CAN and SL (CAN = 748.8 ± 206.3, SL = 489.4 ± 107.2 μg kg−1) followed by MC (284.2 ± 67.3 μg kg−1) and ZERO (29.1 ± 5.9 μg kg−1). Highest cumulative N2O emissions were found in 10–20 cm of the reduced tilled soil in CAN and SL. N2O fluxes were assigned to ammonium as source in CAN and SL and correlated positively to bacterial amoA abundances. Additionally, nosZ abundances correlated negatively to N2O fluxes in the organic fertilizer treatments. Soils showed a gradient in soil organic C, 16S rRNA, nirK, and nosZ with greater amounts in the 0–10 than 10–20 cm layer. Abundances of bacterial and archaeal amoA were higher in reduced tilled soil compared to ploughed soils. The study highlights that tillage system induced biophysicochemical stratification impacts net N2O emissions within the soil profile according to N and C species added during fertilization.
Bibliographical noteFunding Information:
We kindly thank our laboratory technicians Anton Kuhn and Adolphe Munyangabe for assistance. For external laboratory analysis, we acknowledge Hans Ruedi Oberholzer and his co-workers from Agroscope Reckenholz. We gratefully acknowledge the financial support for this project provided by the COOP Sustainability Fund and the CORE Organic II funding bodies, being partners of the FP7 ERA-Net project TILMAN-ORG (www.coreorganic2.org ). We also thank??for the financial support of the Swiss National Science Foundation in frame of the National Research Program "Soil as a Resource" (NRP 68). We thank the Swiss Federal Office for the Environment for financing the gas chromatograph and the Software AG-Stiftung, Stiftung zur Pflege von Mensch, Mitwelt und Erde and Swiss Federal Office for Agriculture for financing the Frick tillage trial. We thank Simon Moakes for his help with English editing.
- Nitrous oxide
- Reduced tillage
- Soil organic carbon