EFFECT OF METHODS OF APPLICATION AND RESIDUAL EFFECT OF MOLYBDENUM ON THE MOLYBDENUM CONCENTRATION AND YIELD OF FORAGES ON PODZOL SOILS

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Abstract
Alfalfa (Medicago sativa L. ’Saranac’), red clover (Trifolium pratense L. ’Lakeland’), and timothy (Phleum pratense L. ’Climax’) were grown at two locations on Charlottetown fine sandy loam soils in Prince Edward Island. The pH values of the soils were 5.6 and 5.7, respectively. The three levels of lime were 0, 2.24 and 4.48 metric tonnes/ha and the Mo treatments included no Mo, Mo added as foliar spray and Mo added to the soils. In the first sampling, applications of 0.44 kg Mo/ha as foliar spray to soil limed to pH 5.9 and 6.3 in the three crops resulted in tissue Mo concentrations of greater than 10 ppm which when fed to livestock could produce Mo toxicity. With soil applications of 0.88 kg Mo/ha, tissue Mo concentrations of greater than 10 ppm occurred only in alfalfa and red clover limed to soil pH 5.6, 5.9 and 6.3. The tissue Mo levels in the second sampling decreased sharply when compared to those in the first sampling. The differences in Mo concentrations in second, third and fourth samplings were very small. There was a significant interaction (Mo × lime) because the increases of Mo concentration in red clover due to liming were much greater at higher rates of Mo than at lower rates of Mo. In the case of a suspected Mo deficiency, addition of about 0.2 kg Mo/ha as foliar spray or of 0.4 kg Mo/ha applied to the soil should alleviate a Mo deficiency problem. Residual effects at these levels of Mo should last for 2–3 yr from the crop sufficiency point of view. Molybdenum applied as foliar spray increased timothy yields by 15–17% at one location.