Effects Of Mg On C And N Metabolism Of Soybean At Different N Levels

A pot experiment was conducted to study the effects of Mg on the carbon and nitrogen metabolism of soybean at N50/ha and N75/ha levels. Contents of soluble protein, sucrose, soluble sugar and starch, ureide content in leaves, stems and pods, nodule dry weight, N, P, K, accumulation amount of plant were investigated. Besides, effects of dry matter accumulation amount of plant, transferation amount of carbon and amount of photosynthetic assimilation of carbon on soybean yield and quality were analyzed.The results showed that application of Mg at N50 and N75 levels promoted the absorption and assimilation of nitrogen effectively as well as the synthesis of photosynthesis enzyme, raised the soluble protein content, ureide content and SPAD values at all growth stages. The effects of application of Mg at N75 level was better. The soluble protein content, N content and chororphyll content are three indexes to judge whether the leaves are senescing or not, the results showed that the three indexes of N75 and N75+Mg all increased compared with that of N50 at V4, R2 and R4 stages, N75+Mg was much higher than that of N75. There was no difference between the soluble protein content and SPAD values of N50 and N75 at R5 stage. What's more, the N content of N75 decreased compared with that of N50 at R5 stage, but the three indexes of N75+Mg all increased in contrast with that of N50, which indicated that application of more nitrogen fertilizer can't delay the senescing of leaves, but application of Mg at higher nitrogen level could prolong the life of leaves. The nodule dry weight and ureide accumulation amount of N75 decreased than that of N50 at productive stages, but application of Mg at N75 level alleviate the prohibition of nodule formation, the ureide accumulation amount of N75+Mg increased by 59.81% and 25.67% respectively at R2 and R5 stage than that of N50, significant at p=0.05. From the ample evidence mentioned above, we can arrive at the conclusion that, application of more nitrogen fertilizer enhanced the nitrogen metabolism, but the nodule growth and symbiotic nitrogen fixation were inhibited. However, application of Mg while increase the nitrogen fertilizer could not only enhance the nitrogen metabolism to a larger extent, but also promote the nodule formation and symbiotic nitrogen fixation.Application of Mg at N50 and N75 levels promoted the synthesis of sucrose and soluble sugar at all growth stages, the effect was much better at N75 level. The effects of application of Mg on starch content were different at N50 and N75 level, the starch content of N50+Mg decreased gradually with growth stage in contrast with N50, while the starch content of N75+Mg increased at all growth stages in contrast with N75, increased by 59.34% and 99.02% at R4 and R5 stage, significant at p=0.01. The results indicated that application of Mg at N75 level could supply ample energy for plant growth and pod development, which is beneficial for high yield. Compared with...