Response of wheat seedlings to Mn‐lignosulfonate adhered to granular NPK

Manganese (Mn) deficiency is a widespread crop micronutrient disorder. The aim of this work was to evaluate two NPK fertilizers coated with Mn that eliminate the specific labor cost for applying Mn and that allow the correction of Mn deficiency in wheat (Triticum aestivum L.). Two Mn sources MnSO₄ and Mn‐lignosulfonate (MnLS)] were compared as NPK coatings at doses of 0.1, 0.3, and 1.0% (w/w) in hydroponic, perlite, and soil pot cultures under growth chamber and greenhouse conditions with wheat to evaluate the effects on dry matter production and Mn concentrations. For the NPK+MnLS product, 52–63% of the total Mn remained in solution at calcareous conditions. However, the NPK+MnSO₄ product was able to maintain only 14–25% of the total Mn added in solution. As expected, the MnLS product resulted in higher Mn concentrations in shoots than the MnSO₄ product due to the Mn complexation by lignosulfonate which preserved Mn from precipitation and maintained it available for plants. In the experiment with perlite as growth substrate, at low Mn dose (0.1% Mn) a similar Mn concentration in wheat shoots was found (57 mg kg^?1 DW for the MnSO₄ coating versus 72 mg kg^?1 DW for MnLS coating), but at the highest dose (1.0% Mn) the NPK+MnLS showed a significant increase in shoot Mn concentration (167 versus 132 mg kg^?1 DW). Soil application of coated NPK products showed similar Mn concentrations in shoots with both Mn sources (29–37 mg kg^?1 DW), except for the NPK+MnSO₄ (0.1%) treatment (only 18 mg kg^?1 DW). Based on the recommended Fe/Mn values (Fe : Mn ratio = 1.5–2.5) given in the literature for plants with a correct nutrition, only the NPK+MnLS (0.3%) fulfilled this ratio (Fe : Mn = 2.5).