Understanding the chemistry of manganese fertilizers and glyphosate mixtures by using synchrotron X-ray spectrometry
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Understanding the chemistry of manganese fertilizers and glyphosate mixtures by using synchrotron X‑ray spectrometry Bianca de Almeida Machado1 · Marcos Henrique Feresin Gomes1 · Eduardo de Almeida1 · Rafael Otto2 · Marcos Yassuo Kamogawa3 · Hudson Wallace Pereira de Carvalho1 Received: 27 May 2020 / Accepted: 5 October 2020 © Springer Nature Switzerland AG 2020
Abstract The spraying of tank mixtures with manganese (Mn) and glyphosate is a practical alternative to alleviate nutritional deficiency while controlling weeds. Thereby, this study investigates the chemical interactions between glyphosate and commercial sources of Mn, such as MnSO4, Mn–phosphite, Mn–EDTA, Mn–glycine, and MnCO3. Nearly 30% of the Mn supplied as M nSO4 and Mn–glycine precipitated with glyphosate, yielding a Mn:glyphosate solid complex with molar ratio of nearly 2:1, both presenting similar chemical environment. XANES analysis of the supernatants indicate no formation of Mn–glyphosate soluble complexes. The use of Mn–EDTA as well as the maintenance of the mixture pH below 2.5 prevented precipitation, while pH above 7 caused the formation of MnO(OH). In conclusion, the Mn source and the pH of the mixtures matter. The absence of Mn–glyphosate soluble complexes suggests that dissolved Mn and glyphosate are still able to accomplish their functions, however, the precipitation significantly decreases their active availability. Keywords Tank mixture · Mn–glyphosate complex · Soybean · Weed control · XAS
1 Introduction In the 2019/2020 crop season, Brazil cultivated 36 million of hectares of soybean (Glycine max L.), harvesting more than 125 million tons of grains. Such achievement made Brazil the world’s largest soybean producer, a title previously belonged to the USA [1]. The increasing cultivation under no-tillage systems has caused the widespread use of lime applications in Brazil. This practice raise the topsoil pH, decreasing availability and consequent root uptake of transition metal micronutrients, such as manganese (Mn) [2]. Manganese is required by many plant enzymes, and plays an important role in photosynthesis, nitrogen
metabolism, nodulation, and respiration. It is also a component of aromatic amino acids, auxins, phenols and lignin [3]. The importance of Mn for plant nutrition and the current evidence of Mn deficiency in soybean trials increased the usage of Mn by soybean growers all over Brazil. Meanwhile, the transgenic glyphosate-resistant soybean was introduce and rapidly adopted in Brazil, since it highly facilitates the weed management. Indeed, glyphosate ([N-(phosphonomethyl)glycine]) is a non-selective herbicide which mechanism of action consists of competitive inhibition of the enzyme 5-enolpyruvylshikimate3-phosphate synthase, essential for the biosynthesis of the aromatic amino acids phenylalanine, tyrosine and
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s42452-020-03632-y) contains supplementary material, which is available to authorized users. * Hud
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