Abstract
In a study on the emissions of nitrous oxide (N2O) from maize production in South-West Germany, N2O emissions where measured with an automated chamber system over two consecutive cropping seasons, including an intermediate fallow period. Urea-based fertilizer treatments included a fertilizer only control (U), as well as the use of pyraclostrobin, which showed inhibitory effects on denitrification in a laboratory experiment. Pyraclostrobin was used alone (U + P) and in combination with a NBPT/NPPT urease inhibitor (UI + P) and a reduced fertilizer rate (70% UI + P). The U control emitted 1.03 ± 0.22 and 1.94 ± 0.61 kg N2O-N ha−1 in the cropping seasons of 2012 and 2013, respectively. Fallow emissions mainly occurred after a soil freeze-thaw period and were 0.24 ± 0.08, 0.23 ± 0.09, 0.22 ± 0.06, 0.32 ± 0.21 kg N2O-N ha-1 for U, 70% UI + P, U + P and UI + P, respectively. In the cropping season 2012, no effects of the UI + P and U + P treatments could be observed. In 2013, UI + P increased N2O emissions by 13% when compared to the U control, while a significant reduction of 24% was observed for the U + P treatment. The 70% UI + P treatment resulted in significantly lower (∼30%) N2O emissions and only slight reductions (7–10%) of grain yields in both years. Climate conditions varied strongly between seasons (416 and 704 mm total rainfall in 2012 and 2013, respectively) which most likely also influenced the performance of the inhibitors. Direct emission factors (EFd%) also increased strongly in 2013 (0.28 ± 0.12 in 2012 vs. 0.94 ± 0.41 in 2013 for U) but were generally lower than the 1% IPCC default value. Values for nitrogen recovery efficiency and yield-scaled N2O emissions were most preferable for the 70% UI + P treatment and indicate that reduced fertilizer rates in combination with inhibitors could represent a viable means for N2O mitigation without significant yield penalties in agricultural systems.
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