Intensive application of nitrogen-based (N-based) fertilisers has become a common practise to achieve high crop yields to feed the growing global population. However, a substantial fraction of the applied N is lost from the plant-soil system to the surrounding environment, via ammonia volatilisation, nitrate leaching, and denitrification. These N losses negatively impact the environment and lead to unwanted groundwater contamination, eutrophication of waterways, biodiversity loss, greenhouse gas emission and stratospheric ozone depletion. Addition of nitrification inhibitors (NIs) to fertilisers is an effective strategy to minimise N losses and improve overall N-use efficiency in agricultural soils. 3,4-Dimethylpyrazole phosphate (DMPP) is the most successful NI to date but has a highly variable efficacy. New compounds with reliable performance under different agricultural and environmental settings that will assist in better synchronising the fertiliser N supply and crop demand are needed. Therefore, this thesis uses a systematic approach to explore the stability of current and newly developed NIs through degradation studies, to gain a better understanding of how degradation impacts the inhibitory activity, which should assist in the development of more efficient NIs with reliable performance.