EFFECT OF MOLYBDENUM, LIME AND CROPPING ON YIELD AND MOLYBDENUM CONCENTRATION OF GRASS-LEGUME MIXTURES AND CABBAGE

Abstract

A greenhouse study was conducted to determine the effects of Mo applied as seed treatment and to the soil, and of lime (soil pH range 5.1–6.7) on yield and Mo content of crops. The crops grown were: alfalfa (Medicago sativa L. ’Iroquois’)–timothy (Phleum pratense L. ’Climax’) mixture; summer cabbage (Brassica oleracea var. capitata L. ’Bergkabis’); and a red clover (Trifolium pratense L. ’Lakeland’)–timothy mixture. These were grown in the sequence listed above. The second and third sequence crops were grown in pots of the treatments where first sequence crops were grown to deplete the soil of its Mo reserves. Liming significantly increased the yield of all crops studied with the largest increases occurring between pH 5.1 and 5.6. In the forage mixtures, percent timothy yield was much higher at soil pH 5.1 than at pH values of 5.6–6.7. Applied Mo increased cabbage yield while forage yields were generally not affected. The tissue Mo levels of 0.17 ppm in cabbage were associated with Mo deficiency. In the check (0 Mo) treatments of the third sequence crops, the Mo concentrations of grass–legume mixture were as low as 0.11 ppm but there was no evidence of Mo deficiency. Soil-applied Mo resulted in tissue Mo concentrations of 1.26–3.03 ppm in the mixtures. The tissue Mo concentrations of greater than 10 ppm were found in the treatments where germinating seeds were treated with a Mo preparation. Liming the soil increased the average tissue Mo concentration from 0.42 ppm at soil pH 5.1 to 1.84 ppm at pH 6.7 in the grass–legume mixtures.