Manganese Toxicity in Flax Growing on Certain Calcareous Soils Low in Available Iron

Abstract

Manganese toxicity and high levels of plant Mn are normally found in plants growing on acid soils with high levels of watersoluble or salt-extractable Mn. However flax (Linum usitatissimum L.) accumulates excessive Mn and develops Mn-toxicity symptoms, which are eliminated by application of FeEDDHA, when grown on some calcareous soils. Flax was grown in the greenhouse on seven soils, varying in pH and extractable Mn and Fe, in the presence and absence of 2 ppm FeEDDHA-Fe. Plants on three of the soils, which were calcareous and had the highest pH values, developed Mn-toxicity symptoms and accumulated approximately 500 ppm Mn in above-soil parts in the absence of the chelate and less than 50 ppm Mn when the chelate was applied. Plant-Mn concentration was poorly related to Mn extracted from soils with DTPA (0.005M diethylenetriamine pentaacetic acid, 0.005M CaCl₂, 0.01M triethanolamine, pH=7.3), 0.01M CaCl₂, 1N NH₄OAc (pH=7), or 1N NH₄OAc + 0.2% hydroquinone (pH=7), but was significantly inversely related to DTPA-extractable Fe. It is hypothesized that plant-Fe status influenced the ability of flax roots to utilize soil Mn, possibly through changes in pH or redox potential at or adjacent to roots. The influence of P fertilizer, Ca(H₂PO₄)₂, on Mn toxicity in one of the three problem soils, with 3.5 ppm NaHCO₃-extractable P, was also studied. Addition of P greatly increased yields, due presumably to a P response, but also increased plant-Mn concentration. Manganese-toxicity symptoms were observed both in the presence and absence of the added P.