| Abstract: | Boron (B) toxicity has been found to be a common nutritional disorder in dry areas, where excessive B tends to accumulate in the subsoil. However, in many of the pot experiments on B toxicity, excess B was mixed uniformly in soil or added from the soil surface, a method that does not detect the subsoil B effect. The objective of this plastic‐house experiment was to study the effects of different patterns and timings of B application on the development of B toxicity (BT) symptoms, tissue B concentrations, and growth and yield of barley. A three‐factor factorial design with three patterns of B application, three timings of B application, and two barley lines was used. A moderately BT‐tolerant barley line from the cross ‘Arar/Arabic Aswad’ (abbreviated as AA) and the moderately BT‐susceptible variety ‘Harmal’ were compared. Each pot consisted of two sections of 20‐cm‐tall PVC pipe. The second section was watered to field capacity and joined to the bottom of the top section on 25 January (tillering; roots reached the bottom of top section), 15 February (stem elongation), and 20 March (flag leaf emerged for ‘Harmal’; booting stage for AA). The three patterns of B application were (1) no B added (?/?), (2) B added to the bottom section only (?/+), and (3) B added to both sections (+/+). The addition of 50 mg B/kg soil increased the hot‐water‐soluble B level from 0.7 to 21 mg kg?1. Interaction between pattern of B application and timing of B application had significant effects on BT symptom scores and straw B concentrations but not on grain yield. Grain yield of the +/+ treatment was much less than that of ?/+, which in turn was less than ?/?, but different timings of joining of the pot sections did not have a significant effect on grain yield. Relative to ?/?, the percentage of grain yield reduction (8%) sustained by AA when grown in ?/+ was less than half of the reduction (18%) suffered by ‘Harmal.’ In conclusion, subjecting plants to high‐B soils from germination to maturity exaggerates the effects of B on rainfed crops in the field. High subsoil B levels can cause significant yield reduction even when roots reach it as late as the boot stage, suggesting the need to screen/breed and grow BT‐tolerant cultivars. The use of subsectioned pots introduced in this study is an effective way to simulate BT in the field. |
