Abstract
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 high-grade 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.
Highlights
By 2050, the global human population is expected to rise to 10 billion, and yields of the world’s fourth largest food crop—potato (Solanum tuberosum L.)—need to be increased
We have shown that ureic amine stabilisation increases shoot biomass, leaf relative chlorophyll content and flower numbers in a range of horticultural species (Wilkinson et al 2019)
We investigate whether the proposed yield increase induced by stabilisation is merely a result of reducing degradation and prolonging nitrogen availability, or whether alterations in biomass partitioning and chlorophyll concentration induced by ureic amine N make a contribution
Summary
By 2050, the global human population is expected to rise to 10 billion, and yields of the world’s fourth largest food crop—potato (Solanum tuberosum L.)—need to be increased. It is important for the environment that nitrogen fertiliser production and use does not increase in parallel. Present-day methods of supplying plants with nitrogen (N), in the form of ammonium nitrate- or urea-based fertilisers, are inefficient: up to 70% of this N is degraded before plants can acquire it, forming harmful greenhouse gases and leaching polluting nitrate into water systems (Liu et al 2013); and governments are legislating to control their use (Cantarella et al 2018). Technologies that stabilise ureic nitrogen in fertiliser, such that it is less degraded, can reduce pollution whilst prolonging nitrogen availability to plants This means that lower fertiliser application rates are viable for attaining the required increases in the production of many crops (Prasad et al 2016). We propose that urea and ureic amine are nitrogen forms that have unique properties that improve plant form and function, such that their stabilisation increases yield by mechanisms unrelated to prolonging the availability of nitrogen per se
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