ارزیابی کارایی فعالیت Sinorhizobium meliloti و خصوصیات کیفی یونجه تحت تأثیر کاربرد مولیبدن

Abstract

Introduction Agriculture depends heavily on nitrogen which is biologically fixed through the symbiotic association between rhizobia and legume plants in nodules located on plant roots. Alfalfa is a legume that should fix most of its own N requirement if it is sufficiently nodulated by viable Rhizobium meliloti inoculums. The process of nitrogen fixation is done by the help of an enzyme called nitrogenase and molybdenum which is an important element in the formation of this compound. Molybdenum is required by plants for protein synthesis and is especially important for legumes as it is needed for nitrogen fixation by rhizobia. Therefore the following research was done aimed on studying the effect of different amount of molybdenum and S. rhizobium bacteria on alfalfa’s yield. Material and Methods Alfalfa (Medicago sativa) were grown in a field. The experiment was conducted at Karaj in 2013 in split plot arrangement based on completely randomized block design (RCBD), including 2 caring S. rhizobium inoculated seed and non-inoculated) as the main plot factor)and 3 levels of Molybdenum (0,5,10 kg ha-1) from ammonium molybdate (as the sub plot factor) in three replications. Sinorhizobium meliloti bacteria were cultured on plates. Then half of the seeds were inoculated by Sinorhizobium meliloti. Nitrogen fertilizer was added only in one stage before planting up to 50 kg per hectare. Plants were grown until flowering. The data were analyzed by the SAS (9.1) software and mean comparisons were done by Duncan's MRT at the 1% and 5% probability level. Results and Discussion The results showed the effect of different levels of molybdenum and S. Rhizobium bacteria on dry matter yield, molybdenum concentrations in shoots and roots and the number of root nodules was significant. This treatment was significant in comparison to the control treatment with the14.27 ton per hectare. Increasing of molybdenum application, led to increasing of root nodules and showed a meaningful difference from non-inoculated. Concentration of molybdenum in shoot and root increased, this increase in S. Rhizobium inoculated case was more than non-inoculated cases. Conclusions The use of molybdenum and Rhizobium bacteria increase the production yield and also nitrogen-fixing nodules. The increase in the use of treatments with molybdenum, resulting biological nitrogen fixation leading to conversion of molecular nitrogen (N2) in the atmosphere into ammonium (NH3) in nodules on the roots of plants. Studies have showed that molybdenum important role in nitrogen fixation in legume family of plants, and adding this element increased growth by increasing the efficiency of nitrogen fixation and nitrogenase enzyme in the node structure, which ultimately will lead to increased yield and higher quality in alfalfa. Thus, molybdenum increased the number of branches of the fertile and increase the number of stem and leaf. Molybdenum is essential to plant growth as a component of the enzymes nitrogenase. Legumes need more molybdenum than other crops, such as grass or corn, because the symbiotic bacteria living in the root nodules of legumes require molybdenum for the fixation of atmospheric nitrogen. If sufficient molybdenum is not available, nodulation will be retarded and the amount of nitrogen fixed by the plant will be limited. If other factors are not limiting, the amount of molybdenum will determine the amount of nitrogen fixed by the plant. Increasingly vigorous plant growth, higher protein contents and greater buildup of nitrogen in the plant and soil accompany nodulation and symbiotic microbial activity. Therefore, due to less absorption of molybdenum in the shoot and the highest yield obtained from treated seeds inoculated with the first level of molybdenum, the amount kg ha-1. Molybdenum is suitable for growing of alfalfa. It is important to obtain maximum yield in just one stage (before the first two weeks of growth) for the supply of nitrogen for growth, nitrogen from urea at the rate of 50 kg ha-1added to soil, excessive consumption of nitrogen fertilizers can impair the activity of the nitrogen-fixing bacteria in nodules, and plant dependence to nitrate chemical, then the yield will not increase.