Mitigation of nitrous oxide emission by nitrification inhibitors : Efficacy under irrigated-induced moisture and soil pH
The objective of this PhD dissertation was to investigate how the factors of soil drying and rewetting, texture, temporary waterlogging, soil pH, drip irrigation method, and N rate regulate the effectiveness of the NIs Dicyandiamide (DCD), 3,4-Dimethylpyrazole phosphate (DMPP), and 3-Methylpyrazol combined with Triazol (MP+TZ). Firstly, in Chapter 2, it was indicated that DMPP and MP+TZ might trigger high N2O-N release from fine-textured soil with constant high moisture after a short-term inhibitory effect. In addition, DMPP and MP+TZ effectively reduce the relative abundance of nitrifying bacteria and N2O-N emissions under soil drying and rewetting, irrespective of soil texture. Secondly, in Chapter 3, it was demonstrated that subsurface drip irrigation (SBD) decreases N2O-N emissions relative to surface drip irrigation. Moreover, among the investigated NIs, DMPP has the highest effectiveness in retarding nitrification and mitigating N2O-N release under the investigated soil textures and drip irrigation methods. Finally, in coarse-textured soils, solely using NIs can be sufficient to abate N2O-N emissions. However, using NIs and SBD has additive effects in lowering N2O-N release from fine-texture soils. Thirdly, in Chapter 4, it was confirmed that DMPP suppressed nitrification irrespective of soil pH by reducing the relative abundance of nitrifying bacteria. Likewise, DMPP has been demonstrated to be an excellent mitigation measure for N2O release from unlimed soils subjected to waterlogging. Furthermore, our study showed that low N rates can lead to insignificant effects of DMPP on N2O release in limed soils subjected to temporary waterlogging.
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