Effect of sulfur and potassium foliar applications on wheat grain protein quality

Context: The effects of sulfur and potassium fertilizers on wheat yield and quality have been well studied, but most of them are used as basal fertilizers. However, the root system is senescent at the later stages of wheat growth and cannot absorb sufficient sulfur and potassium fertilizers plant needed. It is still unclear whether sulfur and potassium foliar applications at the later stages can affect wheat yield and quality. Objective: This experiment was conducted to investigate the changes of sulfur and potassium accumulation and transport, protein synthesis and flour processing quality after foliar application of sulfur and potassium fertilizers, transport and the relating physiological mechanisms. Methods: In 2020-2021 and 2021-2022, a three-factor split plot experiment was carried out in the middle and lower reaches of Yangtze River, with wheat variety, concentration of sulfur fertilizer and potassium fertilizer served as main factor, subfactor and sub-subfactor respectively. Results: In the study from 2020 to 2022, the albumin protein content of both varieties decreased in the nutrient spraying treatment, particularly in the high potassium level. However, there was no significant effect on the globulin content. Moreover, the gliadin protein content decreased in the sulfur spraying treatment alone, but significantly increased the wheat gluten content, and thereby the total protein content. We also found significant genotypic differences in the composition and content of high molecular weight wheat glutenin subunits (HMWGS) between the two varieties. The foliar spraying of sulfur and potassium fertilizers significantly increased the content of subunits 1 and 8 in Yangmai (YM15) and subunits 7 and 12 in Yangmai (YM16), and the effect of mixed spraying was better than single-nutrient spraying, especially the amount of 0.2 % sulfur and 0.3 % potassium fertilizer treatment. Conclusions: The superimposed effect of sulfur and potassium effectively increased the total protein content by promoting the accumulation of sulfur in transit to the seeds, increasing the substrate supply level, and enhancing enzyme activity. Although sulfur and potassium combination can improve the grain protein quality and flour processing quality, too high spraying concentrations can decrease the flour processing quality. Implications: Spraying the appropriate amount of 0.2 % sulfur and 0.3 % potassium fertilizer can serve as an optimization measure for high-quality and efficient production of different types of wheat varieties.