Much of the nitrogen in crop fertiliser is degraded before acquisition. Technologies that stabilise urea-nitrogen minimise this. Degradation also specifically reduces the amount of ureic amine that many fertilisers initially contain, which is important because this nitrogen form has unique beneficial effects on plants. To investigate mechanisms whereby urea stabilisation increases potato tuber yield, we compare effects of foliar applications of chemically stabilised and non-stabilised urea against industry-standard fertiliser, on the physiology, form and yield of greenhouse-grown Casablanca under identical nitrogen supply. Stabilised urea is tested on Rooster and Shelford yields in Irish and British field trials. Stabilised amine nitrogen (SAN) increases Casablanca leaf relative chlorophyll content and initially reduces shoot growth rate. When harvested shortly after tuber initiation, SAN-treated plants have increased root to shoot weight ratios and we find tight negative correlations between shoot growth rate and root weight: large roots and slow shoot extension occur predominantly in SAN-treated plants. SAN increases ratios between initiation-stage tuber weight and (a) shoot length and (b) shoot growth rate. At a second harvest at mid-bulking, SAN increases highgrade Casablanca tuber yielding. At this later stage, yield correlates positively with shoot weight. In the field, SAN increases Rooster canopy greenness and marketable yields of both Rooster and Shelford. Yield improvements specific to this N form when stabilised are suggested to occur through increased photosynthesis and early-stage increases in root to shoot weight ratio. This phenotype then supports increased bulking-stage shoot growth and shoot-sourced resource for tuber growth. Stabilising urea amine induces high-yielding phenotypes with improved internal nitrogen utilisation efficiencies.

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Nitrogen is the main nutrient required by plants for growth. The production of onions (Allium cepa) results in low nitrogen use efficiency (NUE) as nitrogen is applied when it is not required by the plant; resulting in loss to the environment. This work assessed the ability of stabilised amine nitrogen (SAN) to increase the NUE and yield of onion. In a glasshouse, two onion cultivars (F1 Hybound (pelleted) and Ramrod) were grown and fertilised with 150 kg N ha−1 as urea applied to the soil or 2.7 kg N ha−1 as SAN applied foliarly at the three, four and five leaf stages. The survival percentage, number of leaves, height, weight, bulb diameter and stem diameter were recorded. For both cultivars, the survival percentage was increased with the SAN, with the increase being significant for Ramrod. While for all other parameters, SAN resulted in significant increases for both cultivars. In field plot trails, applications of 150 kg N ha−1 were compared to applications of 7.56 kg N ha−1 as SAN, which gave statistically similar yields and increased the NUE. This work shows that considerably reduced N as SAN was a significant improvement over the traditional 150 kg N ha−1 for onion production. Commercial application of this work would significantly improve the profitability of onion production due to reduced purchase of N and increased yield.