CRITICAL TOXIC CONCENTRATIONS OF BORON ARE VARIABLE IN BARLEY

The use of leaf symptoms and plant analysis in diagnosing and predicti ng yield depressions associated with boron (B) toxicity in barley was examined. Barley (Hordeum vulgare L., cv. Stirling) was grown in pots of a sandy soil to which six levels of B were added. With increasing a dditions to the soil, B accumulated in the older leaves, increasing le af injury and senescence. Leaf injury symptoms at high levels of B sup ply appeared in time well before dry mailer was depressed. Root weight was decreased more than shoot weight. Grain filling was affected only at severe levels of B toxicity. Critical toxic concentrations (CTC) o f B in shoots were found to vary between approximately 40 and 150 mu g , depending on the stage of plant growth at the lime of B analysis and the yield parameter chosen. A distinction is made between CTC values of B that are diagnostic or prognostic.