COMPARATIVE RESPONSES OF PEANUTS, ALFALFA, AND SOYBEANS TO VARYING RATES OF BORON AND MANGANESE ON TWO CALCAREOUS ONTARIO SOILS

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Abstract
This study evaluated the relative responses of alfalfa (Medicago sativa L.), peanuts (Arachis hypogaea L.), and soybeans [Glycine max (Merr.)] on two calcareous Ontario soils. The B-horizon of a Pontypool sand (Typic Psammentic Hapludalf) and the Ap-horizon of a Plainfield Fine Sand (Typic Udipsamment) were each cropped to all three species in the greenhouse. Thirty-six treatments comprised factorial combinations of three rates (0, 0.25 and 1.00 μg/g) of B, two rates (0 and 25 μg/g) of Mn, the two soils, and the three crops with three replications. Plants were clipped at soil level at flowering stage, oven-dried to constant weight, and analyzed for nutrient content. Boron and Mn additions significantly increased concentrations of these elements in plant tissue. Boron uptake was significantly higher on the coarser-textured Pontypool soil and toxicity significantly reduced soybean yields on this soil, but alfalfa and peanut yields were unaffected. Peanuts appeared least sensitive to B toxicity and Mn deficiency. Soybeans were most sensitive to B toxicity and alfalfa most sensitive to Mn deficiency. The differences in tolerance to B seem attributable to the relative abilities of the three species to withstand high B concentrations in plant tissue rather than to differences in uptake. Differential susceptibility to Mn deficiency on the other hand seems attributable to relative efficiencies of the crops to extract Mn from Mn-deficient soils. Soil organic matter may have had some ameliorative effect on B toxicity. Yield and nutrient uptake were not significantly affected by B × Mn interactions.