Comparison of sources with different solubilities for Mn supply and retranslocation along with soybean development

Abstract

Foliar sprays with micronutrients are widely employed in agricultural production as an alternative to improve soil fertilization and plant nutritional status. We hypothesized that less water-soluble sources of manganese (Mn; MnCO3) could serve as a slow-release source compared to a water-soluble source (MnSO4.H2O). Our goal here was to evaluate Mn-sources (MnSO4.H2O and MnCO3) and rates (150; 250; 350; and 450 g ha−1) sprayed in the 3rd and 4th trifoliate leaflets of soybean growing in clayey and sandy soil under controled conditions. In phenological stages V7 (vegetative period) and R1 (reproductive period), dry matter, height, the diameter of the stem, and Mn-content in the shoot, stem, and in the trifoliate leaflets were determined. Results showed that the application of Mn resulted in an augmented Mn-content in the 3rd and 4th trifoliate leaflets (sandy) and the 3rd and 5th trifoliate (clayey). The MnSO4.H2O promoted Mn-retranslocation from the 3rd/4th trifoliate to the stem and the 5th/6th trifoliate. However, MnCO3 was accumulated in the 3rd/4th trifoliate. The Mn-rates presented a linear response in sandy soil and quadratic response in clayey soil. Clayey soil was characterized by the higher Mn-contents in the stem, while sandy soil presented the higher Mn-contents in the 3rd, 4th, 5th, and 6th trifoliate. Our results suggest that MnSO4.H2O is more effective in increasing Mn-content in soybean leaves during plant development due to the Mn-retranslocation to sink organs (5th/6th trifoliate leaflets and shoot).