Incidence of Boron Toxicity in Spring Barley in Southwestern Australia

Abstract

One hundred and four crops of spring barley (Hordeum vulgare L. cv. Stirling) grown throughout southwestern Australia (WA) were surveyed for symptoms of boron (B) toxicity. Symptoms were identified as B toxicity and not spot-type net blotch, a foliar disease, caused by the fungus Pyrenohora teres f. spp. maculata that produces similar leaf symptoms. Symptoms of B toxicity occurred in 43 crops (about 40% of the surveyed crops) that were widely distributed in the <350 to 450 mm annual average rainfall zones of WA, on duplex soils with alkaline and fine-textured subsoils that were non-saline but sodic. Concentrations of mannitol-extractable B in sub-soils varied widely between 0.7 and 130 mg B/kg soil. Soil B concentrations measured in either mannitol or hot CaCl2 increased with soil depth and were highest where soil pH values were >8 (1:5 soil:0.01 M CaCl2, w/v). Concentrations of B in whole shoots (WS) were positively correlated with concentrations of hot CaCl2-extractable and mannitol-extractable soil B. The positive linear relationship between B concentration in WS and extractable-B in either mannitol or hot CaCl2 improved (R 2 value increased) with increasing soil depth, particularly in the 50 to 80 cm layer. Concentrations of B in the WS of barley plants with symptoms of B toxicity were found to vary between 4 and 76 mg B/kg dried WS. An additional study showed that symptoms of B toxicity developed in the later stages of Stirling barley growth [boot stage (GS 40) to maturity (GS 70)] grown on duplex soils with high concentrations of mannitol-extractable B in the sub-soils >30 cm from the soil surface. As toxic concentration of B occurred at late stages of Stirling barley development, reductions in grain yield resulting from B toxicity were small (up to 10%).