ffects of nitrogen fertilizer rate and post-anthesis soil water content on characteristics of nitrogen metabolism and grain protein content in wheat

With the ultimate goal of maximising productivity and quality of wheat, effects of soil water content (SRWC) and N fertilization rate on nitrogen metabolism and grain protein content in wheat was tested under proof-rainfall pool culture condition. The results indicated that the activities of nitrate reductase (NR) and glutamine synthase (GS) were the highest in flag leaves and grains of wheat at the same level of nitrogen fertilizer rate with suitable SRWC (60%70%) after anthesis. High (80%90%) and low (40%50%) SRWC suppressed the activities of nitrate reductase (NR) and glutamine synthase (GS). Protease activities decreased with the increase of SRWC after anthesis. Low SRWC after anthesis was unfavorable for the increase of free amino acid content in wheat leaves, while high SRWC resulted in low synthesis rate at early stages. Consequently, its transferring into grains was not complete at late stage. Moreover, free amino acid content and protein content decreased with the increase of SRWC in wheat grains after anthesis. Protein accumulation in grains was the highest under SRWC (60%70%) after anthesis, whereas high (80%90%) and low (40%50%) SRWC made against the protein accumulation in grains after anthesis. Under the same level of SRWC, the increase of nitrogen fertilizer rate resulted in an increase of the activities of nitrate reductase (NR) and glutamine synthase (GS) in flag leaves and grains whereas it lead to a decrease of protease activities. Free amino acid content, protein content and accumulation increased with the increase of nitrogen fertilizer rate in wheat leaves and grains after anthesis. Excessive nitrogen fertilizer rate reduced the magnitude of increased protein accumulation. It is considered that nitrogen metabolism might be regulated to maximizing grain protein content in wheat production by controlling nitrogen application rate and soil water content after anthesis.