Non-cropping period accounting for over a half of annual nitric oxide releases from cultivated calcareous-soil alpine ecosystems with marginally low emission factors

<p>Nitric oxide (NO) emissions from alpine ecosystems conventionally being long-term cultivated with feed crops are not well quantified. The authors attempted to address this knowledge gap by performing a year-round experimental campaign in the northeastern Tibetan Plateau. Fertilized (F) and unfertilized (UF) treatments were established within a flat calcareous-soil site for the long-term cultivation of feed oats. NO fluxes and five soil variables were simultaneously measured. A single plow tillage accounted for approximately 54%–73% of the NO releases during the cropping period (CP); and the non-cropping period (NCP) contributed to 51%–58% of the annual emissions. The direct NO emissions factor (EF<sub>d</sub>) was 0.021% ± 0.021%. Significantly lower <i>Q</i><sub>10</sub> values (<i>p</i> < 0.01) occurred in the F treatment during the CP (approximately 3.6) compared to those during the other period or in the other treatment (approximately 4.9−5.1), indicating a fertilizer-induced reduction in the temperature sensitivity. The selected soil variables jointly accounted for up to 72% (<i>p</i> < 0.01) of the variance for all the fluxes across both treatments. This finding suggests that temporally and/or spatially distributed fluxes from alpine calcareous-soil ecosystems for feed crop production may be easily predicted if data on these soil variables are available. Further studies are needed to test the hypothesis that the EF<sub>d</sub> is larger in alpine feed-oat fields than those in this study if the soil moisture content is higher during the period following the basal application of ammonium- or urea-based fertilizer.</p>