ALFALFA RESPONSES TO FOLIAR AND SOIL APPLICATIONS OF MANGANESE

Manganese (Mn) deficiency often occurs in crops grown on well-limed sa ndy soils of the Atlantic Coastal Plain region of the United States. T his study was conducted to compare the responses of established alfalf a (Medicago sativa S.) to various application methods of manganese sul fate (MnSO4) fertilizer. Experiments conducted in farmers' fields at t hree New Jersey locations determined the effects of applied Mn on fora ge yield, tissue Mn concentration, and leaf chlorophyll meter readings . An untreated control was compared to the following treatments: folia r 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 19 90 was 1.12 kg Mn/ha and in 1991 was 0.56 kg Mn/ha at each treatment t ime. 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 lo cations with foliar-applied Mn but at only one location with soil-appl ied Mn. When averaged across all locations, forage yields were 6.4% hi gher 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 al falfa 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 obse rved to improve leaf color and chlorophyll meter readings of Mn-defici ent alfalfa. Results indicate that foliar Mn applied before each harve st was a more effective treatment for correction of Mn deficiency of a lfalfa than a one-time soil application of Mn.