Foliar N application at anthesis alters grain protein composition and enhances baking quality in winter wheat only under a low N fertiliser regimen

Wheat is the second biggest staple crop worldwide and is mainly consumed in the form of baked goods, requiring a specific flour quality. Grain protein concentration (GPC) is an underpinning parameter for baking quality and therefore strongly influences the value of wheat. It is a common strategy to increase GPC by combining high protein varieties with the application of a late dose of nitrogen. However, the late use of N fertilisers can cause environmental problems, such as nitrate leaching and gaseous losses. Furthermore, recent studies show, that there is only a weak relationship between GPC and bread volume. The aim of this study was to re-evaluate the merits of a late N application by investigating the effects of a late foliar N application, not only on GPC, but also on the gluten protein composition and on bread volume. In this study, an increasing GPC did not necessarily lead to improved baking quality. Baking performance rather depended on the grain protein composition. Only at a low N fertiliser level (100 kg N ha⁻¹), the foliar N application decreased the HMW-GS/LMW-GS ratio and increased the gliadin/HMW-GS ratio, which led to an improved bread volume. These results imply that a late foliar N application can be used to effectively improve baking quality when the total N uptake was low due to low fertilisation or unfavourable weather conditions. The results also show that quality cannot be evaluated by measuring GPC alone but also needs information of storage protein composition as well as bread volume.