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Estimation of plant available manganese in acidic subsoil horizons

Wright, R.J., Baligar, V.C., Wright, S.F.
Communications in soil science and plant analysis 1988 v.19 no.6 pp. 643
Trifolium subterraneum, Panicum virgatum, manganese, aluminum, calcium, phytotoxicity, acid soils, subsoil, soil solution, liming, soil toxicity, physicochemical properties, chemical constituents of plants
General agreement does not exist as to the most appropriate method to estimate plant available Mn in soils. In the current investigation soil and soil solution Mn were measured in limed and unlimed treatments of 11 acidic subsoil horizons and related to plant Mn concentrations, Mn uptake and growth of subterranean clover (Trifolium subterraneum L. cv. Mt. Barker) and switchgrass (Panicum virgatum cv. Cave-in-Rock). Manganese measurements were taken at planting and harvest and included: Mn extracted by 1M NH4OAc (pH 7), 0.01M. CaCl2, 0.05M CaCl2, 0.033M H3PO4, 0.005M DTPA, 0.2% hydroquinone in 1M NH4OAc (pH 7), 0.01M NH2OH .cntdot.HCl in 0.01M HNO3, total soil solution Mn and concentrations and activities of Mn2+ calculated from the GEOCHEM program. Measured and calculated values of soil solution Mn generally gave the best correlations with subterranean clover and switchgrass Mn concentrations and Mn uptake. Root Mn concentrations were highly correlated with soil solution Mn measurements taken at harvest with r=0.97 and r=0.95 (p < 0.01) for subterranean clover and switchgrass respectively. The Mn extracted by 0.01M CaCl2 was also significantly correlated (p < 0.01) with plant Mn concentrations and Mn uptake and proved to be better than the other extractants in estimating plant available Mn. Although Mn concentrations as high as 1769 mg/kg (shoots) and 8489 mg/kg (roots) were found in subterranean clover. Mn did not appear to be the major factor limiting growth. Measurements of soil and soil solution Mn were not strongly correlated with yield. Both Al toxicities and Ca deficiencies seemed to be more important than Mn toxicities in limiting growth of subterranean clover and switchgrass in these horizons.