The application of manganese fertilizer is a common practice to correct Mn deficiencies for soybean, although the agronomic efficiency of different sources is not well known. Thus the direct and residual effect of two Mn sources, applied at different rates, were evaluated for soybean in a pot experiment conducted in Campinas, State of Sao Paulo, Brazil, from November 1992 until April 1993. Pots were filled with 2 dm 3 soil of a Red Yellow Latosol with pH of 6.9, 88% base saturation and 1.0 mg dm -3 of DTPA-extractable Mn. Mn was applied at 0, 5, 10, 20 and 40 mg dm -3 , using manganese sulfate and manganese oxide as fertilizers. Two consecutive plantings of soybean were made, with harvests at 58 and 48 days after seeding. In both cases, the above-ground dry matter yield and manganese content of plants were determined. Manganese sulfate provided higher Mn contents in plants for both plantings. Manganese oxide also increased Mn in plants, but the amount of nutrient necessary to correct the deficiency was higher as compared to manganese sulphate. Soil Mn contents determined by Mehlich-1 were similar, independent of Mn source, whereas DTPA-extractable Mn was lower for the oxide, as well as plant Mn contents. Overall, the correlation between Mn uptake by soybean and soil Mn was higher for DTPA (R 2 = 0.76 ** ) than for Mehlich-1 (R 2 = 0.67 ** ). It was concluded that both Mn sources corrected manganese deficiency for soybean; that higher manganese contents in plants were observed for manganese sulphate; and that the residual effect was higher for manganese sulphate and that DTPA was the best extractant to determine Mn availability in the soil that received Mn fertilizations.
C. A. Abreu, B. Raij, R. T. Tanaka
Revista Brasileira De Ciencia Do Solo