Boron deficiency and toxicity in potato cv. Sebago on an oxisol of the Atherton Tablelands, North Queensland

Abstract

A field experiment was established to determine whether excess boron (B) in a new, blended commercial fertiliser reduced growth of Sebago potatoes. Five rates of B as sodium borate (0, 2, 4, 8, and 12 kg B/ha) were mixed with superphosphate, potassium chloride, and ammonium sulfate and applied in bands, at planting, to an oxisol with a hot CaCl2-extractable B concentration of 0.7 mg/kg. At the common commercial rate of 1500 kg blended fertiliserba, 8 kg B/ha would be applied in the new blended fertiliser. Yield of grade 1 tubers was significantly (P<0.05) higher at 2 kg B/ha (27.2 t/ha) than without applied B (19.7 t/ha). Grade 1 tuber yield decreased with increasing B rate above 2 kg/ha, and the yields at 8 and 12 kg B/ha were significantly lower than the maximum yield. Plant height was not increased by low rates of B but was significantly (P<0.05) reduced by 8 and 12 kg B/ha, compared with nil B. Boron concentrations increased with increasing application rate. At 12 kg B/ha, whole shoots had 50 mg B/kg and youngest fully expanded leaves (YFEL) 31 mg/kg. Maximum tuber yield was obtained with 33 mg B/kg in whole shoots and 24 mg/kg in the YFEL. Tuber yield was significantly (P<0.05) reduced at >39 and 26 mg B/kg for whole shoots and YFEL, respectively. The sufficiency range for B in Sebago potatoes was 33-39 mg/kg for whole shoots and 24-26 mg/kg in YFEL. The threshold B concentrations for yield reduction in potatoes due to toxicity recorded in this study are much lower than those previously reported for other cultivars.