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

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 (EFd) was 0.021% ± 0.021%. Significantly lower Q10 values (p < 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% (p < 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 EFd 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.