Influence of nitrogen and sulphur form on manganese acquisition by barley (Hordeum vulgare)

The influence of various nitrogen (N) and sulphur (S) forms on the uptake of manganese (Mn) in young spring barley (Hordeum vulgare L cv Golf) plants was examined in both a hydroponic system and in a soil-based system. The soil was a typical Danish Mn-deficient soil viz. a sandy loam soil developed on old marine sediments. Plants growing in solution culture with $\mathrm{N}{\mathrm{O}}_{3}^{-}$ as the only N source had a higher Mn uptake than plants receiving mixtures of $\mathrm{N}{\mathrm{O}}_{3}^{-}$ and $\mathrm{N}{\mathrm{H}}_{4}^{+}$. These findings were opposite to the results obtained in the soil-based experiments, where plants fertilized with $\mathrm{N}{\mathrm{O}}_{3}^{-}$ as the only N source accumulated much less Mn than plants fertilized with $\mathrm{N}{\mathrm{H}}_{4}^{+}$. Combining the results of these experiments confirmed that $\mathrm{N}{\mathrm{H}}_{4}^{+}$ acted as a powerful antagonist to Mn2+ during uptake but that this antagonistic effect was more than compensated for by the influence of $\mathrm{N}{\mathrm{H}}_{4}^{+}$ in reducing plant-unavailable Mn(IV) to plant-available Mn(II) in the soil. Furthermore the soil experiments showed that fertilizers containing sulphur in the form of reduced S (thiosulphate) had a strong mobilizing effect on Mn, and enabled the plants to accumulate large amounts of Mn in the biomass compared with oxidized S (sulphate). Thus, fertilization with thiosulphate may be very effective in alleviating Mn-deficiency in soils developed on old marine sediments where Mn availability is limiting plant growth.