MANGANESE SOIL TESTS FOR BOTH DEFICIENT AND TOXIC LEVELS IN APPLE ORCHARDS

Soil pH and Mn extracted by 1.0 M NH4OAc (pH 7.0), 0.02 M CaCl2, 0.25 M MgCl2, 0.03 M H3PO4, DTPA and HF/HC1 (total Mn) from two soil depths (0–15 cm, 15–30 cm) were compared to leaf Mn concentrations of Delicious apple trees (Malus domestica Borkh) from 34 Okanagan Valley orchards. Leaf Mn concentrations ranged from deficient (below 25 μg g−1) to toxic (above 60 μg g−1). For all orchards (pH 3.5–8.4), leaf Mn concentration varied directly with soil Mn extracted from 15–30 cm depth by all extractants except HF/HCl (total Mn) and 0.03 M H3PO4, and inversely with pH at both depths. For soils with pH > 6.5, DTPA and 0.25 M MgCl2 extractable soil Mn (15–30 cm depth) was most closely related to leaf Mn concentration, whereas for soils with pH < 6.5, pH (15–30 cm depth) was the best indicator of Mn availability. Thus soil tests for Mn availability to apple trees may not perform equally well in toxic and deficient situations. Key words: Manganese, soil test, apple trees, Malus domestica Borkh