| This research was conducted at Hailun Agro-ecological experiment station of the Science Research Institute of China from 2003 to 2004. Three cultivars, Dongnong46 (high-oil), Heinong35 (high-protein) and Bei9395 (high-yield), were tested in this research by means of pots and fields experiments with four sulfur application levels (0kg/hm2, 30 kg/hm2, 60 kg/hm2, 90 kg/hm2) to study the effects of sulfur on photosynthesis, N-metabolism, accumulation and distribution of S, quality and yield of soybean. The results showed that:On the base of the soil fertility of this research, properly sulfur application could increase green leaf area, but when surpassed certain level (60 kg/hm2) , the expansion rate of leaf from seedling stage to florescence was restrained apparently, and this effect was dying out with the development of the plants. The content of chlorophyll in foliage, especially from florescence to pod-filling stage, increased greatly with the increase of sulfur application. The reaction of dry matter accumulation to sulfur is different according to cultivars. Dry matter weight of Heinong35 was enhanced with the increase of sulfur between 0-60kg/hm 2, and decreased under 90kg/hm2. While, for Dongnong46 and Bei9395, 60kg/hm2 application seemed to be an over dressing. Dry matter weight in the shoots and roots showed a significantly or most significantly positive correlationship. For high-oil variety, increasing sulfur application could stimulate the growth of shoots and roots jointly, while, for high-yielding variety, sulfur promoted the growth of roots chiefly.Carbon, soluble sugar, sucrose and starch contents in each organ were all influenced by sulfur application. Carbon concentration in the leaves changed obviously, but C% in other organs changed little. The most important influence of sulfur on concentration of soluble sugar showed at the same time as peak point, and different varieties reacted differently. In Heinong35, it showed in the periods from seedling stage to initial-flowering stage and from pod-filling stage to physiological mature stage. In Dongnong46, it showed in the periods from seedling stage to bloom-flowering stage. In Bei9395, it showed in the periods from initial-flowering stage to bloom-flowering stage. At seedling stage, soluble sugar concentrations in the stems and leaves decreased with the increase of sulfur, while at other stages, it increased within some certain levels, and the reactions of different varieties were not the same. Effects of sulfur on the sucrose concentrations in stems and leaves exhibited differently at some special stage, i.e., after flowering stage, the sucrose concentration in stems was lowered with the increase of sulfur, but that in leaves was increased to some extent. Starch concentration in the leaves and stems could be enhanced at pod-setting and pod-filling stages, but more higher sulfur application tends to reduce the starch concentration in leaves.Sulfur had an important effect on N-metabolism. It increased the NR activity significantly and made it keep high level for long time, thus promoted plant to absorb and accumulate more nitrogen, raised the quantity and efficiency of translocation as well as the harvest index of nitrogen. It alsochanged the distribution of nitrogen, which could be demonstrated by the fact that the nitrogen contents in stems were higher at the higher sulfur level, while, the nitrogen contents in leaves were higher at the lower sulfur level. Sulfur application promoted nitrogen-fixation ability of nodules, which could be illustrated by the increase of ureide concentrations in the stems and leaves from seedling stage to flowering stage.Sulfur absorbing ability of roots could be enhanced by high concentration of sulfur in rhizosphere. The distribution center was changing with the development of plants. Before pod-setting stage, sulfur was mainly allocated in the roots and leaves, then transferred to the seeds gradually, but the accumulation of sulfur in roots remained higher from the very beginning. The strongest absorption of sulfur was occurred at bloom-flowering stage and pod-filling stage. Sulfur concentration in the roots, stems, leaves and pods showed a declining tendency during the growth period, while that in the seeds increased. In each vegetative organ, sulfur content was affected significantly by different external sulfur concentrations. In generally, it increased in the treatments with sulfur application. Sulfur Concentration in the seeds of Heiong35 with sulfur application was lower than that of which with no application, while in Dongnong46 and Bei9395, it did the reverse.N/S in each organ was much influenced by sulfur. In a gross way, N/S was decreased with sulfur application except that in the leaves, it remained relatively stable within certain sulfur levels. When the sulfur level was too high, it decreased significantly, thus it was advisable to use N/S in the leaves as an indicator to sulfur nutritional diagnosis for soybean. The main reason for the decline of N/S when treated with sulfur application was due to the promotion of sulfur absorption ability stimulated by the high concentration of sulfur in rhizosphere.For high-protein and high-yield cultivars, sulfur increased not only the content of protein, but also the content of amino acid, especially S-containing amino acid. For high-oil cultivar, sulfur was favor for increasing protein content. On the contrary, the contents of most of the amino acids as well as total amino acid descended except His and Arg. There existed an interactive effect between nitrogen and sulfur on the content of amino acids. Sulfur promoted plant to absorb more nitrogen, but high nitrogen application level would restrict the exercise of sulfur's coordinative effects on the amino acids.Sulfur had different effects on oil content according to varieties. In Bei9395, sulfur application decreased oil content in both pot and field experiments. In Dongnong46 and Heinong35, oil contents of S30 treatment were higher in the pot experiment, and that of S60 treatment in the field experiment showed the best. The relative abundance of fatty acid was mainly determined by heredity, the sequence among varieties could-not be changed by sulfur application, but proper sulfur application could modify the balance of fatty acid in some extent. Sulfur application had a little effect on the contents of saturated fatty acids (palmitic acid and stearic acid), but exercised a great influence on the contents of unsaturated fatty acids (oleic acid, linoleic acid, linolenic acid). This effects showed most obvious in high oil cultivars, then in high-protein cultivars, the least in high-yield cultivars. Nitrogen and sulfur nutrient had interactive effect on the content of fatty acids.Only oleic acid increased at the higher nitrogen level, others decreased, namely, high nitrogen level was disadvantage for sulfur to balance the contents of fatty acid in the seeds.Effects of sulfur on yields were also different according to cultivars. In pot experiments, the S30 treatment of Heinong35 showed a little increase in yields, while S60 and S90 treatments' yields decreased, and with the increase of sulfur application, the spans of reduction were enlarged. Yield of Bei9395 was increased with the increase of sulfur application level. Sulfur Yield of Dongnong46 increased in some extent, S60 treatment showed the best. In fields experiment, only the yields of Dongnong46S30 treatment increased, the yields of other treatments all decreased.
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