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Methods and Rates of Applied Manganese for Soybeans¹

Soybeans [Glycine max (L.) Merr.] have responded to supplemental Mn fertilizer on high water table soils when limed to soil pH levels near neutrality, but the effect of method and rate of Mn application under these conditions is not well understood. In a 3-year study (1975–1977) on an Olustee-Leefield sand (Ultic Haplaquod-Arenic Plinthaquic Paleudult), four application methods (broadcast preplant, row at planting, sidedress, and broadcast preplant plus foliar spray), at four rates (0, 5.6, 11.2, and 22.4 kg/ha) of Mn were employed to evaluate their effects on yield, leaf blade concentrations, seed Mn levels, and extractable soil Mn levels. A 239% yield increase was obtained in 1977 with 11.2 kg Mn/ha compared to no applied Mn. Yield increases due to applied Mn were not obtained in 1975 and 1976, although visual deficiencies were evident early in the growing season every year. Yield increases were related to seed weight for the various Mn rates. Methods of Mn application did not influence yields in any given year. However, the row at planting application may have produced toxic effects since there were visual toxicity symptoms and trends of decreased yields each year. Leaf tissue sampled at the R-2 growth stage indicated the Mn level should be greater than 15 ppm for maximum yields with broadcast application and the critical Mn level in the seed is 16 ppm. In this study, correlation and regression analyses indicated the seed Mn levels were better related to yield than leaf blade Mn levels. Double acid extractable soil Ma increased from 1975 through 1977 while DTPA extractable Mn showed a slight decrease. Both methods were well related to applied Mn rates. These data indicate that applied Mn rates influence soybean yields, soil Mn, tissue Mn, and seed Mn concentrations more than methods of Mn application.

Key Words: Tissue Mn • Seed Mn • Glycine max (L.) Merr. • Soil Mn • Double acid • DTPA extractable Mn

² Professors and associate professors of agronomy, respectively, Univ. of Georgia, Georgia Station, Experiment, GA 30212.

³ Assistant professor of agronomy, Univ. of Georgia, Coastal Plain Station, Tifton, GA 31793.

Received for publication March 17, 1980.