ALFALFA RESPONSES TO FOLIAR AND SOIL APPLICATIONS OF MANGANESE

Manganese (Mn) deficiency often occurs in crops grown on well-limed sandy soils of the Atlantic Coastal Plain region of the United States. This study was conducted to compare the responses of established alfalfa (Medicago sativa S.) to various application methods of manganese sulfate (MnSO4) fertilizer. Experiments conducted in farmers' fields at three New Jersey locations determined the effects of applied Mn on forage yield, tissue Mn concentration, and leaf chlorophyll meter readings. An untreated control was compared to the following treatments: foliar Mn applied once before each harvest, foliar Mn applied twice before each harvest, and a one-time broadcast Mn application in April or May at 22.4 kg Mn/ha to the soil surface. The rate of foliar Mn used in 1990 was 1.12 kg Mn/ha and in 1991 was 0.56 kg Mn/ha at each treatment time. Forage yield increases were greater with foliar than soil-applied Mn but there were no differences between foliar-applied Mn treatments. Total seasonal forage yields were increased (P<0.05) at all three locations with foliar-applied Mn but at only one location with soil-applied Mn. When averaged across all locations, forage yields were 6.4% higher than the control for the foliar-applied Mn treatments compared to 2.9% higher for the soil-applied Mn treatment. A Mn concentration of 21 mg/kg was determined as the critical level in the upper 15 cm of alfalfa tissue at the early bloom growth stage. Foliar Mn applied twice between harvests most effectively increased tissue Mn concentrations. Soil-applied Mn initially increased tissue Mn concentration, but there was little long-term benefit from this treatment. Applied Mn was observed to improve leaf color and chlorophyll meter readings of Mn-deficient alfalfa. Results indicate that foliar Mn applied before each harvest was a more effective treatment for correction of Mn deficiency of alfalfa than a one-time soil application of Mn.