Magnesium (Mg) is part of the chlorophyll molecule and has an important physiological role as an enzyme activator of rubisco. It is known as a forgotten element due to scarcity of research in relation to the nutritional and physiological role of Mg in plants, in addition, it is found in low amounts in the soil, possibly due to anthropogenic activities, such as the inadequate supply of potassium fertilizers, causing antagonism of Mg absorption and resulting in low productivity. Since there is no nitrogen fertilization in the soybean culture due to symbiosis with bacteria of the genus Rhizobium, the present work has the hypothesis that plants well nourished with Mg have a higher concentration of chlorophyll, rubisco activity and, therefore, higher rate of photoassimilates like total sugar and sucrose that are translocated via phloem to nourish the bacteria present in the nodules. With a greater amount of sugar in the nodule, nitrogenase activity could be increased by converting a greater amount of atmospheric nitrogen into ureids (allantoin and allantoic acid), which are the main organic forms of nitrogen in soy. The present study aims to evaluate the application of doses and sources of Mg to elucidate the role of Mg in the process of FBN and soybean filling. The role of Mg in biological nitrogen fixation and relationships with soybean productivity are not yet understood and there is no literature on the subject. This study will provide relevant information regarding the role of Mg in biological nitrogen fixation, which can lead to increases in productivity.
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