Abstract:

Application of nitrogen fertilizer (N) is one of the most important measures to increase grain yield and improve the end-use quality of wheat. It is generally accepted that the protein content and nutrition quality of wheat grain could be improved by reasonably N application. But the effect of N rate on protein component and processing quality of wheat grain varied with cultivars and cultivation conditions. The strong-gluten wheat cultivars of wheat are obviously different from the weak-gluten cultivars in many quality parameters of grain, such as grain protein content, protein component, grain starch content, starch component. In the present study, a strong-gluten wheat (Triticum aestivum L.) cultivar GC8901 and a weak-gluten wheat cultivar SN1391 were used to investigate the effect of N rate on the grain quality. The experiment was conducted in a pool culture on the Experimental Farm of Shandong Agriculture University from 2002 to 2004 with three nitrogen application rates, 12(N₁₂), 24(N₂₄) and 36(N₃₆) g m^-2. The results showed that properties of starch and protein, and processing quality in both wheat cultivars could be markedly influenced by N application. As compared with the N₁₂ treatment, the N₂₄ treatment significantly increased amylopectin contents, decreased amylose contents and the ratio of amylose to amylopectin, promoted the starch accumulation and improved the paste properties. When the N application rate reached 36 g m^-2, amylopectin contents and starch accumulation decreased, however, the amylose content increased. The albumin, globulin, glutenin and protein content of GC8901 enhanced, but the gliadin content reduced with the increase of N application. The gliadin, gluten and protein content of SN1391 were much lower in the N24 treatment than those in the other two N treatments. The albumin content of SN1391 decreased and globulin increased with the increase of N rate. An appropriate N rate was beneficial to increased grain hardness, but excessive N application had an adverse effect. The volume weight of wheat grain declined with the increase of N application. The dough whiteness of GC8901 rose with increasing nitrogen, but that in N₂₄ treatment was lower than that in the other two treatments of SN1391. As for GC8901, with the increase of nitrogen application rate, the content and quality of wheat gluten, the development time, stability time, extension area and extensibility of the dough were all enhanced, leading to the improvement of food processing quality of strong-gluten wheat cultivars, but those for SN1391 were low resulting in the better processing quality of weak-gluten wheat cultivars. When the N application was 36 g m^-2, the quality of two cultivars went inferior. The results reveal that the N application rate affects protein, starch, and their component contents in grain, resulting in the changes of the processing quality of wheat.

Key words: Winter wheat (Triticum aestivum L.), Nitrogen rate, Starch, Protein, Grain quality