Abstract:

Sulphur (S) deficiency has become a marked problem in agricultural system in many regions in the last two decades, and sulphur application in S-deficiency soils may increase crop yield and improve the grain quality. In plants, there is a close relationship between sulphur and nitrogen. Crop response to S fertilizer often depends on the amount of N supply. Deficiency of S may be induced by a high nitrogen amount, and responses to S application are usually greater when abundant nitrogen fertilizer applied. Although wheat has a relatively low requirement for S, deficiency of S in wheat growth has been observed in many regions in China. Previous studies have focused on effects of single S fertilizer on growth and yield of wheat. We took a strong-gluten wheat (Triticum aestivum L.) cultivar Yumai 34 as experimental material to explore the activities of key enzymes for nitrogen and sulphur assimilation and the response of grain yield to different fertilizer applications of sulphur and nitrogen. The experiment was conducted in the soil with available sulphur content of 22.78 mg kg^-1 in 2003/2004 and 2004/2005 growing seasons by split plot design. The main plot was two nitrogen levels with 330 (N330) and 240 (N240) kg ha^-1, respectively, and the subplot was three sulphur levels with 0 (S0), 60 (S60), and 100 (S100) kg ha^-1, respectivly. The results indicated that sulphur fertilizer could improve the activities of nitrate reductase (NR), glutamine synthetase (GS), and glutamic-pyruvic transaminase (GPT), which are the key enzymes of nitrogen assimilation, and may be speculated to improve the nitrogen assimilation ability. But, under different nitrogen application levels, the amount of sulphur needed was different. In N330 treatment, sulphur application could reduce NR activity and improve GS and GPT activities. In N240 treatment, 0 sulphur application could improve NR and GS activities. The activity of o-acetylserine thiollyase (OASS), a key enzyme of sulphur assimilation, reduced with inreasing of sulphur application rate. Furthermore, OASS activity enhanced under high N-supply and S-deficiency conditions. The effects of N and its interaction with S on grain yield were significant (P<5%) , and those of S were highly significant (P<1%). Under the both nitrogen levels of N330 and N240, dry matter accumulation of S application treatments increased significantly as compared with that of control (S0), and the grain yield of N330S100, N330S60, N240S100, and N240S60 treatments rose by 28.6% (P＜0.01), 12.6% (P＜0.05), 25.7% (P＜0.01), and 25.3% (P＜0.01) respectively. The 1000-grain weight of sulphur treatments significantly increased at both nitrogen levels, but the spike number and grains per spike had no significant difference among the treatments.

Key words: Wheat, Nitrogen, Surphur, Assimilation enzyme, Yield