PROBLEMS ASSOCIATED WITH THE USE OF FOLIAR ANALYSIS FOR DIAGNOSING BORON TOXICITY IN BARLEY

The effects of evapotranspiration conditions on the distribution of B in leaves and critical values for B toxicity measured in shoots were examined in solution culture experiments with barley. Increased water use resulted in increased B accumulation by plants and B was concentrated in the leaf tips. The relationship between shoot DM production and shoot B concentrations was markedly affected by evapotranspiration conditions, but the effect could be removed by not analysing leaf tips. Excluding the leaf tips also decreased the shoot B concentration at which shoot DM production was depressed. Regularly spraying plants with water removed considerable B from leaves without affecting DM production. The present results indicate a number of problems in the establishment of critical values and the use of foliar analysis for diagnosing B toxicity. These problems may account for conflicting reports of critical values and discrepencies between results from glasshouse- and field-cultured plants.