Boron toxicity in South Australian barley crops

Abstract

Boron toxicity was identified in barley crops grown on a range of soils at 16 widespread locations in South Australia, and also at one site in western Victoria. The soils on which boron toxicity occurred included red-brown earths (Calcic Natrixeralf), calcareous earths (Xerollic Calciorthid and Calcic Paleorthid), and calcareous sands ('Petrocalcixerollic' Xerochrept). At one site the soil was a grey clay (Palexerollic Chromoxerert). The properties of some examples of normal and high-boron soils which were sampled in close proximity are discussed. For individual high-boron soil profiles it was possible to demonstrate statistically significant relationships between extractable boron and ESP, CEC and clay content. However, these relationships did not hold generally for comparisons between normal and high-boron soils. Boron concentrations in affected barley ranged from 56 mg/kg in mature straw to 323 mg/kg in whole tops at Feekes stage 10.1. In control samples the mean boron concentration was 22.8 mg/kg. The concentrations of other nutrient elements (P, K, S, Mg, Cu, Zn, Mn, Mo) were within normal ranges, and did not differ between control samples and plants with toxicity symptoms. Barley plants affected by the toxicity had increased concentrations of Na and Cl, and decreased concentrations of Ca compared with control plants. These effects were small, but statistically significant, and were consistent with the notion that the toxicity was associated with sodic soils. The findings extend our earlier work on boron toxicity at a single site, and demonstrate that the toxicity is widespread in South Australia.