Abstract:

Many studies have indicated that irrigation and nitrogen fertilizer are the major factors influencing wheat quality. Protein content, protein composition and size distribution of glutenin in wheat grain are significantly modified by the rate and timing of nitrogen fertilizer. It is also found that irrigation has diluting effect on grain quality and this effect is lessened by more nitrogen application. Although the respective effect of irrigation and nitrogen fertilizer on wheat quality has been extensively studied, especially in arid area and under low yield condition, it is little known about the coupling effects of irrigation and nitrogen on wheat quality under high yield condition. In this experiment, with a new method of protein fraction extraction, the effect of different irrigation and nitrogen application regimes on grain yield, protein content, protein composition and grain quality of Jimai 20 (a winter wheat cultivar with strong gluten) was investigated on high fertility soil in order to find the optimal regime of irrigation and nitrogen with high grain yield and excellent quality. The result indicated that irrigation was a crucial factor influencing grain quality. The contents of grain protein and monomeric protein in irrigation treatments were significantly lower than these in non-irrigation treatment, but there were no significant differences among irrigation treatments. Soluble glutenin (low molecular weight glutenin) content was increased while insoluble glutenin (high molecular weight glutenin) content and polymerization index (insoluble glutenin/total glutenin) were reduced as irrigation frequency added. In addition, both dough development time and stability time had the same tendency as insoluble glutenin and polymerization index, which suggested retarded formation and accumulation of insoluble glutenin was the major reason of worsen grain quality with added irrigation frequency. Compared with N split application (50% of total N fertilizer was applied at preplanting and the remainder at jointing), N fertilizer totally top-dressed at jointing led to significantly improved grain quality and similar grain yield. Therefore, it is proposed that N fertilizer can be totally top-dressed at jointing under high yield condition for the sake of high grain yield and excellent quality.

Key words: Winter wheat, Coupling of irrigation and N fertilizer, Protein composition, Grain quality