Impact of late-season N fertilisation strategies on the gluten content and composition of high protein wheat grown under humid Mediterranean conditions

The rise in high protein common wheat in humid Mediterranean areas has determined a need to compare specific and effective nitrogen (N) fertilisation protocols in order to increase their end-use value. The aim of the work was to assess the impact of late-season N fertilisation strategies on grain yield and protein content (GPC), gluten fraction composition, and rheological traits. Different applications and types of fertiliser (soil applied ammonium nitrate, soil applied urea, foliar applied urea and a foliar applied commercial fertiliser) were distributed at the same rate (30 kg N ha−1) in a field experiment in NW Italy, during three growing seasons. A control without any late-season N fertilisation was also considered. All the treatments received 130 kg N ha−1 as ammonium nitrate (AN), which was split between tillering and the beginning of the stem elongation growth stages. None of the compared late-season N fertilisations significantly affected canopy greenness and stay green duration during the grain filling period, or the grain yield, test weight, and thousand kernel weight, although the foliar application significantly increased foliage burning (+9.8%). The late application of N consistently increased GPC (+1.1%) and dough strength (W, +21%) in the different growing seasons. The type of fertilisation strategies clearly affected the gluten content and rheological parameters: AN was more effective than urea as a soil top-dressed applied fertiliser in increasing W (+10%), as a result of a higher rise in the GPC content (+0.5%) and extensibility (L, +11%). The foliar application at anthesis, at the same N rate, led to a comparable GPC and W with those of the soil top-dressed granular fertiliser. Only a weak effect of granular urea on y/x type HMW was observed for the gluten composition. Conversely, a notable influence of year was observed (i.e. GS/Glia and y/x type HMW), which in turn resulted in a significant impact on W and P and on the aggregation time and aggregation energy. This study offers a further contribution to the improvement of specific N fertilisation strategies in order to enhance the wheat quality according to its end-use value.